ferrite vs sensitivity


lrdheat
 

The sensitivity of my ICF-S5W and ICF-EX5 with their 6.375" bars is the equal of my PR-D5 with it's 8" bar. If constructed properly, should there be an expectation of greater daytime sensitivity with an 8" bar in a radio, or is it like a calculus problem where we are already approaching the limiting case with a 6.375" bar?
 
On another topic concerning EX5 vs S5W, I had assumed that the S5W had greater raw sensitivity. With experimentation just a few miles further away from the mw rf jungle in my area (largely related to the abundance of Nuevo Laredo mw's in addition to Laredo's stations), the two sets appear identical as far as usable sensitivity. If the S5W is more sensitive, the EX5 seems to counter with a lower noise floor. The rf jungle and relatedmixing products are so intense that (on all of my radio sets including the Grundig G3 with ssb and sync options, and the Tecsun 390 with it's 1 KHz filter) only mixing products are heard on 1230 KHz, yet 4 miles down the road, Corpus Christi is heard on that frequency in comfortably listenable fashion.
 
Heatwave


satya@sounddsl.com <satya@...>
 

Hi Richard:

My understanding is that there are more factors beside ferrite length, including the quality of
ferrite material, the diameter, the type of Litz wire, and probably others. MY guess is that the
S5W and EX5 have good-quality components, whereas Sangean may have given the PR-D5 lesser-quality
components? If you peek inside the units and see what the ferrite diameter and Litz wire looks
like, that would be good info.

I have a S5W, which also struggles here in my RF jungle near Seattle. A tuned loop is oftn needed
to keep the hets and mixing products at bay, even at night.

Kevin

------- Original Message -------
From : Richard Berler[mailto:lrdheat@...]
Sent : 10/20/2010 12:01:20 PM
To : ultralightdx@...
Cc :
Subject : RE: [ultralightdx] ferrite vs sensitivity












The sensitivity of my ICF-S5W and ICF-EX5 with their 6.375" bars is the equal of my PR-D5
with it's 8" bar. If constructed properly, should there be an expectation of greater daytime
sensitivity with an 8" bar in a radio, or is it like a calculus problem where we are already
approaching the limiting case with a 6.375" bar?

On another topic concerning EX5 vs S5W, I had assumed that the S5W had greater raw sensitivity.
With experimentation just a few miles further away from the mw rf jungle in my area (largely
related to the abundance of Nuevo Laredo mw's in addition to Laredo's stations), the two sets
appear identical as far as usable sensitivity. If the S5W is more sensitive, the EX5 seems to
counter with a lower noise floor. The rf jungle and relatedmixing products are so intense that (on
all of my radio sets including the Grundig G3 with ssb and sync options, and the Tecsun 390 with
it's 1 KHz filter) only mixing products are heard on 1230 KHz, yet 4 miles down the road, Corpus
Christi is heard on that frequency in comfortably listenable fashion.

Heatwave


ferrite61 <dxrx@...>
 

The answer is complex, but does use a non-calculus approach. For a given inductance, The selectivity and sensitivity are both optimzed when the following conditions are met:
1.) The coil is centered on the ferrite rod
2.) The coil occupies about 40% of the ferrite rod length.
3 .) The coil has each turned spaced to a distance equal to the wire (NOT wire + insulation and/or jacket) diameter.

Therefore there is a "correct" number of turns of wire, and gauge of wire that will make a coil of the needed inductance. Using litz is tricky because the woven wire is referred to as a "bundle diameter". This is the correct diameter to use. To figure out the diameter one has to convert "circular mils"... simply take the square root of the number shown, and divide by 1000. This answer is in inches. For example 400 circular mils = 20/1000 or 0.02" diameter.

IMHO most commercial receivers use too much wire poorly centered. As others have shown, doing "an alignment" upon several coils on ferrite rods almost always improves reception with just a little adjustment of the coil and the trimmer. In the case of moving the coil towards the center, this will increase the inductance, selectivity, and sensitivity. However, the coil has too many turns to accurately center the coil, and the trimmer runs out of adjustment. I have formulas that I refer to in order to get this "right", but this might not be the time or place to go into that. /IMHO

Paul S. in CT

--- In ultralightdx@..., Richard Berler <lrdheat@...> wrote:

The sensitivity of my ICF-S5W and ICF-EX5 with their 6.375" bars is the equal of my PR-D5 with it's 8" bar. If constructed properly, should there be an expectation of greater daytime sensitivity with an 8" bar in a radio, or is it like a calculus problem where we are already approaching the limiting case with a 6.375" bar?
�
On another topic concerning EX5 vs S5W, I had assumed that the S5W had greater raw sensitivity. With experimentation just a few miles further away from the mw rf jungle in my area (largely related to the abundance of Nuevo Laredo mw's in addition to Laredo's stations), the two sets appear identical as far as usable sensitivity. If the S5W is more sensitive, the EX5 seems to counter with a lower noise floor. The rf jungle and relatedmixing products are so intense that (on all of my radio sets including the Grundig G3 with ssb and sync options, and the Tecsun 390 with it's 1 KHz filter) only mixing products are heard on 1230 KHz, yet 4 miles down the road, Corpus Christi is heard on that frequency in comfortably listenable fashion.
�
Heatwave


Hugo
 

Paul S. in CT :

Would you care to further explain your previous answer or at least give some links or formulas where I could learn more about how to wind a coil in the ferrite for optimum performance ?

Huesby

--- In ultralightdx@..., "ferrite61" <dxrx@...> wrote:

The answer is complex, but does use a non-calculus approach. For a given inductance, The selectivity and sensitivity are both optimzed when the following conditions are met:
1.) The coil is centered on the ferrite rod
2.) The coil occupies about 40% of the ferrite rod length.
3 .) The coil has each turned spaced to a distance equal to the wire (NOT wire + insulation and/or jacket) diameter.

Therefore there is a "correct" number of turns of wire, and gauge of wire that will make a coil of the needed inductance. Using litz is tricky because the woven wire is referred to as a "bundle diameter". This is the correct diameter to use. To figure out the diameter one has to convert "circular mils"... simply take the square root of the number shown, and divide by 1000. This answer is in inches. For example 400 circular mils = 20/1000 or 0.02" diameter.

IMHO most commercial receivers use too much wire poorly centered. As others have shown, doing "an alignment" upon several coils on ferrite rods almost always improves reception with just a little adjustment of the coil and the trimmer. In the case of moving the coil towards the center, this will increase the inductance, selectivity, and sensitivity. However, the coil has too many turns to accurately center the coil, and the trimmer runs out of adjustment. I have formulas that I refer to in order to get this "right", but this might not be the time or place to go into that. /IMHO

Paul S. in CT


lrdheat
 

Also, I'm still curious as to if, given optimum winding, if we are approaching the limiting case of sensitivity with a 6.375" ferrite (i.e., with optimum winding, would we expect much more sensitivity with an 8" bar, a 12" bar, ect)?
 
Heatwave


--- On Thu, 10/21/10, Hugo wrote:

From: Hugo
Subject: [ultralightdx] Re: ferrite vs sensitivity
To: ultralightdx@...
Date: Thursday, October 21, 2010, 3:08 PM

 
Paul S. in CT :

Would you care to further explain your previous answer or at least give some links or formulas where I could learn more about how to wind a coil in the ferrite for optimum performance ?

Huesby

--- In ultralightdx@..., "ferrite61" wrote:
>
> The answer is complex, but does use a non-calculus approach. For a given inductance, The selectivity and sensitivity are both optimzed when the following conditions are met:
> 1.) The coil is centered on the ferrite rod
> 2.) The coil occupies about 40% of the ferrite rod length.
> 3 .) The coil has each turned spaced to a distance equal to the wire (NOT wire + insulation and/or jacket) diameter.
>
> Therefore there is a "correct" number of turns of wire, and gauge of wire that will make a coil of the needed inductance. Using litz is tricky because the woven wire is referred to as a "bundle diameter". This is the correct diameter to use. To figure out the diameter one has to convert "circular mils"... simply take the square root of the number shown, and divide by 1000. This answer is in inches. For example 400 circular mils = 20/1000 or 0.02" diameter.
>
> IMHO most commercial receivers use too much wire poorly centered. As others have shown, doing "an alignment" upon several coils on ferrite rods almost always improves reception with just a little adjustment of the coil and the trimmer. In the case of moving the coil towards the center, this will increase the inductance, selectivity, and sensitivity. However, the coil has too many turns to accurately center the coil, and the trimmer runs out of adjustment. I have formulas that I refer to in order to get this "right", but this might not be the time or place to go into that. /IMHO
>
> Paul S. in CT
>
>



ferrite61 <dxrx@...>
 

You can go here for a close approximation:
http://www.am3-radio.us/formulas.htm

Paul S. in CT

--- In ultralightdx@..., Richard Berler <lrdheat@...> wrote:

Also, I'm still curious as to if, given optimum winding, if we are approaching the limiting case of sensitivity with a 6.375" ferrite (i.e., with optimum winding, would we expect much more sensitivity with an 8" bar, a 12" bar, ect)?

Heatwave

--- On Thu, 10/21/10, Hugo <HCOB@...> wrote:


From: Hugo <HCOB@...>
Subject: [ultralightdx] Re: ferrite vs sensitivity
To: ultralightdx@...
Date: Thursday, October 21, 2010, 3:08 PM






Paul S. in CT :

Would you care to further explain your previous answer or at least give some links or formulas where I could learn more about how to wind a coil in the ferrite for optimum performance ?

Huesby

--- In ultralightdx@..., "ferrite61" <dxrx@> wrote:

The answer is complex, but does use a non-calculus approach. For a given inductance, The selectivity and sensitivity are both optimzed when the following conditions are met:
1.) The coil is centered on the ferrite rod
2.) The coil occupies about 40% of the ferrite rod length.
3 .) The coil has each turned spaced to a distance equal to the wire (NOT wire + insulation and/or jacket) diameter.

Therefore there is a "correct" number of turns of wire, and gauge of wire that will make a coil of the needed inductance. Using litz is tricky because the woven wire is referred to as a "bundle diameter". This is the correct diameter to use. To figure out the diameter one has to convert "circular mils"... simply take the square root of the number shown, and divide by 1000. This answer is in inches. For example 400 circular mils = 20/1000 or 0.02" diameter.

IMHO most commercial receivers use too much wire poorly centered. As others have shown, doing "an alignment" upon several coils on ferrite rods almost always improves reception with just a little adjustment of the coil and the trimmer. In the case of moving the coil towards the center, this will increase the inductance, selectivity, and sensitivity. However, the coil has too many turns to accurately center the coil, and the trimmer runs out of adjustment. I have formulas that I refer to in order to get this "right", but this might not be the time or place to go into that. /IMHO

Paul S. in CT


George Magiros
 

According to IRCA reprint A009 a matched condition exists when when the ratio of length of the ferrite rod to its diameter equals the square root of the rod's permeability.   

So for
a mu of 125 and a diameter of .5" the matched length is 5.6"
a mu of 800 and diameter of .5" the matched length is 14.1"
a mu of 2000 and diameter of 1" the matched length is 44.7"

The author says a matched condition occurs when the "Available Flux Field" (AFF) - that is, the flux flowing into an air loop of effectively the same size as the ferrite loop - is equally divided between the rod and the air surrounding the rod.

While trying to understand more how this works, I found out magnetism has more or less an ohm's law.   Instead of resistance you use reluctance.  The reluctance of a ferrite rod is 1/(mu*pi/4*D^2) while the reluctance of the air within the AFF but not in the rod is 1/(pi/4*(L^2-D^2).  The flux (which is analogous to current) flowing into the AFF is the flux density of air times pi/4*L^2.

Using this information and solving some equations, I calculated a few plots.  The first two plots below show the ratio of the magnetic power - I think this exists - flowing into the rod of given length (flux_into_rod^2 * reluctance_of_rod) to the magnetic power flowing into an air loop of effectively the same size as the rod (flux_into_aff^2 * reluctance_of_aff).   A matched condition in effect gives you the best magnetic power ratio.  Once past this length you hit a point of diminishing returns. 


http://img178.imageshack.us/img178/5495/screenshot1oe.png


http://img411.imageshack.us/img411/235/screenshot2djm.png

Flux however continues to increase and doesn't flatten out till later.  Another plot shows this.


http://img192.imageshack.us/img192/5138/screenshotaz.png

George



lrdheat
 

Neat!


--- On Fri, 10/22/10, george magiros wrote:

From: george magiros
Subject: Re: [ultralightdx] Re: ferrite vs sensitivity
To: ultralightdx@...
Date: Friday, October 22, 2010, 6:22 PM

 
According to IRCA reprint A009 a matched condition exists when when the ratio of length of the ferrite rod to its diameter equals the square root of the rod's permeability.   

So for
a mu of 125 and a diameter of .5" the matched length is 5.6"
a mu of 800 and diameter of .5" the matched length is 14.1"
a mu of 2000 and diameter of 1" the matched length is 44.7"

The author says a matched condition occurs when the "Available Flux Field" (AFF) - that is, the flux flowing into an air loop of effectively the same size as the ferrite loop - is equally divided between the rod and the air surrounding the rod.

While trying to understand more how this works, I found out magnetism has more or less an ohm's law.   Instead of resistance you use reluctance.  The reluctance of a ferrite rod is 1/(mu*pi/4*D^2) while the reluctance of the air within the AFF but not in the rod is 1/(pi/4*(L^2-D^2).  The flux (which is analogous to current) flowing into the AFF is the flux density of air times pi/4*L^2.

Using this information and solving some equations, I calculated a few plots.  The first two plots below show the ratio of the magnetic power - I think this exists - flowing into the rod of given length (flux_into_rod^2 * reluctance_of_rod) to the magnetic power flowing into an air loop of effectively the same size as the rod (flux_into_aff^2 * reluctance_of_aff).   A matched condition in effect gives you the best magnetic power ratio.  Once past this length you hit a point of diminishing returns. 


http://img178.imageshack.us/img178/5495/screenshot1oe.png


http://img411.imageshack.us/img411/235/screenshot2djm.png

Flux however continues to increase and doesn't flatten out till later.  Another plot shows this.


http://img192.imageshack.us/img192/5138/screenshotaz.png

George




Pollock,Raphael E <rpollock@...>
 

This is fascinating--how do these observations impact on optimal ferrite bar antenna design? For example, is the optimal length of a 125 mu ferrite bar antenna for use on MW frequencies 5.6 ", provided that a bar of 0.5" diameter is used?


On Oct 22, 2010, at 6:22 PM, "george magiros" <submodd@...> wrote:

 

According to IRCA reprint A009 a matched condition exists when when the ratio of length of the ferrite rod to its diameter equals the square root of the rod's permeability.   

So for
a mu of 125 and a diameter of .5" the matched length is 5.6"
a mu of 800 and diameter of .5" the matched length is 14.1"
a mu of 2000 and diameter of 1" the matched length is 44.7"

The author says a matched condition occurs when the "Available Flux Field" (AFF) - that is, the flux flowing into an air loop of effectively the same size as the ferrite loop - is equally divided between the rod and the air surrounding the rod.

While trying to understand more how this works, I found out magnetism has more or less an ohm's law.   Instead of resistance you use reluctance.  The reluctance of a ferrite rod is 1/(mu*pi/4*D^2) while the reluctance of the air within the AFF but not in the rod is 1/(pi/4*(L^2-D^2).  The flux (which is analogous to current) flowing into the AFF is the flux density of air times pi/4*L^2.

Using this information and solving some equations, I calculated a few plots.  The first two plots below show the ratio of the magnetic power - I think this exists - flowing into the rod of given length (flux_into_rod^2 * reluctance_of_rod) to the magnetic power flowing into an air loop of effectively the same size as the rod (flux_into_aff^2 * reluctance_of_aff).   A matched condition in effect gives you the best magnetic power ratio.  Once past this length you hit a point of diminishing returns. 


http://img178.imageshack.us/img178/5495/screenshot1oe.png


http://img411.imageshack.us/img411/235/screenshot2djm.png

Flux however continues to increase and doesn't flatten out till later.  Another plot shows this.


http://img192.imageshack.us/img192/5138/screenshotaz.png

George



George Magiros
 

It is fascinating! 

I replotted the graphs the other day after factoring in that permeability is itself dependent on the length to diameter ratio of the rod.  I forgot about this.  So a rod with a mu of 125 and a D of .5" doesn't exactly have a "effective" mu of 125 when it is 6" long, rather the effective mu is something like 50.   I'm away from home at the moment but I'll post the numbers and the plots soon.  But the matched condition appears to be less than what the article says.

I think the import of all this is that the longer is better but the smaller can be too small.  You can go too long however where you max out the flux concentration of the rod at flux_in_air*mu.  But within the realm of practicality the flux in the rod will linearly increase with rod length.

I wish I knew why a high ratio of potential energy stored in the rod to the potential energy stored in an air loop of effectively the same size is desired or even if this is what a matched condition represents.  Maybe it gives you an optimal signal to noise ratio or maybe it is just a minimum length.

George


On Sat, Oct 23, 2010 at 11:34 AM, Pollock,Raphael E <rpollock@...> wrote:
 

This is fascinating--how do these observations impact on optimal ferrite bar antenna design? For example, is the optimal length of a 125 mu ferrite bar antenna for use on MW frequencies 5.6 ", provided that a bar of 0.5" diameter is used?


On Oct 22, 2010, at 6:22 PM, "george magiros" <submodd@...> wrote:

 

According to IRCA reprint A009 a matched condition exists when when the ratio of length of the ferrite rod to its diameter equals the square root of the rod's permeability.   

So for
a mu of 125 and a diameter of .5" the matched length is 5.6"
a mu of 800 and diameter of .5" the matched length is 14.1"
a mu of 2000 and diameter of 1" the matched length is 44.7"

The author says a matched condition occurs when the "Available Flux Field" (AFF) - that is, the flux flowing into an air loop of effectively the same size as the ferrite loop - is equally divided between the rod and the air surrounding the rod.

While trying to understand more how this works, I found out magnetism has more or less an ohm's law.   Instead of resistance you use reluctance.  The reluctance of a ferrite rod is 1/(mu*pi/4*D^2) while the reluctance of the air within the AFF but not in the rod is 1/(pi/4*(L^2-D^2).  The flux (which is analogous to current) flowing into the AFF is the flux density of air times pi/4*L^2.

Using this information and solving some equations, I calculated a few plots.  The first two plots below show the ratio of the magnetic power - I think this exists - flowing into the rod of given length (flux_into_rod^2 * reluctance_of_rod) to the magnetic power flowing into an air loop of effectively the same size as the rod (flux_into_aff^2 * reluctance_of_aff).   A matched condition in effect gives you the best magnetic power ratio.  Once past this length you hit a point of diminishing returns. 


http://img178.imageshack.us/img178/5495/screenshot1oe.png


http://img411.imageshack.us/img411/235/screenshot2djm.png

Flux however continues to increase and doesn't flatten out till later.  Another plot shows this.


http://img192.imageshack.us/img192/5138/screenshotaz.png

George




ferrite61 <dxrx@...>
 

I kinda have a problem with this.

First the permeability of 125 is for an infinite-length ferrite bar. Since it is much smaller than infinite, Ue is a lot less than 125. When the length to diameter ratio is 10 to 1, the Ue of most "125" ferrites is about 35 +/- recipe.

To have an infinite length ferrite rod requires it to be bent into a circle and fused... we call that a toroid core. That has a Ue of 125. However, by making a doughnut shape the lines of force concentrate to the center, not the ends. It is a "closed" field, as opposed to an "open" field when using a cylinder-rod.

Second, the coil should not be as long as the rod due to "end effects". Simply, end effects occur at each pole of the cylinder-rod because of the right-angle of the edge. Most manufacturers bevel this edge, but the "end effects" remain. Imagine a ferrite rod inside a football from end to end. The "points" of the football has the magnetic lines of force (the "pigskin") very closely bunched up. Near the center of the rod where the laces are, the distance from rod to pigskin is large, and the lines of force are not squeezed together as much. This makes the center of the rod more susceptible to being affected by a resonant signal. At the ends, this signal has to overcome a dense field, and tightly packed lines of force, thus the center is more sensitive.

To keep the end-effects at bay, one has to wind a coil shorter than the rod. But keep in mind that a long coil with many turns has another problem called inter-winding capacitance or stray capacitance. Therefore the coil length must be short to keep the number of turns reduced, and to stay away from the ends. The best way to reduce inter-winding capacitance is to space the turns at a distance equal to the wire diameter. This will not remove the capacitance, just minimize it. The property of inductance with sensitivity requires that some signal jump from turn-to-turn so as to increase the inductance within the coil. The cost is a small (a few pf) increase in capacitance. this effect will make the inductor look like it has too many uH's at a radio frequency, but look identical to specs at say an audio frequency.

So even to our "35" ferrite, a factor has to be established due to the coil being shorter than the cylinder-rod. This is the "K" factor, and it multiplies Ue. In a previous post I mentioned that the coil should be about 40% of the rod-length to be near-ideal. Keeping the football picture in mind, winding the coil 20% away from the center in each direction (total 40%) keeps these windings in the fat part of the football, making the coil sensitive, and yet far from the ends of the football where there is a dense compaction of the lines of force needing more signal energy to overcome the dense field.

Buidding a radio-reciever inductor is much different than say a power inductor, or an energy transformation inductor (transformer). The requirements are sensitivity with proper spacing of the winding in proper place on the inductor. The other two types need as little spacing as possible over the complete rod to provide power or power-ratio changes. Radio recievers are supplied with the tiniest amount amount of power and need to preserve it as much as possible.

Paul S. in CT


Pollock,Raphael E <rpollock@...>
 

Dear George: Thank you for these additional thoughts. As a practical matter this could provide an explanation as to why my 19" and 27" 125 mu ferrite bar antennas, both with primary coils of 630/46 Litz wire (38 turns, tightly wound, centered on both ferrite bars) behave almost identically with near identical gain as assessed in the inductively coupled mode using either a Grundig Satellit 750 or a Sony 2010. An alternative explanation might be that maximum gain might have been achieved with an even shorter ferrite bar comparably wound and coupled, and that any additional length would be superfluous.

I will eagerly await your further thoughts!

Raph Pollock
 

From: george magiros [mailto:submodd@...]
Sent: Sunday, October 24, 2010 12:59 PM
To: ultralightdx@... <ultralightdx@...>
Subject: Re: [ultralightdx] Re: ferrite vs sensitivity
 
 

It is fascinating! 

I replotted the graphs the other day after factoring in that permeability is itself dependent on the length to diameter ratio of the rod.  I forgot about this.  So a rod with a mu of 125 and a D of .5" doesn't exactly have a "effective" mu of 125 when it is 6" long, rather the effective mu is something like 50.   I'm away from home at the moment but I'll post the numbers and the plots soon.  But the matched condition appears to be less than what the article says.

I think the import of all this is that the longer is better but the smaller can be too small.  You can go too long however where you max out the flux concentration of the rod at flux_in_air*mu.  But within the realm of practicality the flux in the rod will linearly increase with rod length.

I wish I knew why a high ratio of potential energy stored in the rod to the potential energy stored in an air loop of effectively the same size is desired or even if this is what a matched condition represents.  Maybe it gives you an optimal signal to noise ratio or maybe it is just a minimum length.

George

On Sat, Oct 23, 2010 at 11:34 AM, Pollock,Raphael E <rpollock@...> wrote:
 

This is fascinating--how do these observations impact on optimal ferrite bar antenna design? For example, is the optimal length of a 125 mu ferrite bar antenna for use on MW frequencies 5.6 ", provided that a bar of 0.5" diameter is used?


On Oct 22, 2010, at 6:22 PM, "george magiros" <submodd@...> wrote:

 

According to IRCA reprint A009 a matched condition exists when when the ratio of length of the ferrite rod to its diameter equals the square root of the rod's permeability.   

So for
a mu of 125 and a diameter of .5" the matched length is 5.6"
a mu of 800 and diameter of .5" the matched length is 14.1"
a mu of 2000 and diameter of 1" the matched length is 44.7"

The author says a matched condition occurs when the "Available Flux Field" (AFF) - that is, the flux flowing into an air loop of effectively the same size as the ferrite loop - is equally divided between the rod and the air surrounding the rod.

While trying to understand more how this works, I found out magnetism has more or less an ohm's law.   Instead of resistance you use reluctance.  The reluctance of a ferrite rod is 1/(mu*pi/4*D^2) while the reluctance of the air within the AFF but not in the rod is 1/(pi/4*(L^2-D^2).  The flux (which is analogous to current) flowing into the AFF is the flux density of air times pi/4*L^2.

Using this information and solving some equations, I calculated a few plots.  The first two plots below show the ratio of the magnetic power - I think this exists - flowing into the rod of given length (flux_into_rod^2 * reluctance_of_rod) to the magnetic power flowing into an air loop of effectively the same size as the rod (flux_into_aff^2 * reluctance_of_aff).   A matched condition in effect gives you the best magnetic power ratio.  Once past this length you hit a point of diminishing returns. 


http://img178.imageshack.us/img178/5495/screenshot1oe.png


http://img411.imageshack.us/img411/235/screenshot2djm.png

Flux however continues to increase and doesn't flatten out till later.  Another plot shows this.


http://img192.imageshack.us/img192/5138/screenshotaz.png

George




George Magiros
 

Thank you for the kind remarks.  I promised to post some more graphs
so here are my latest.

I stopped assuming in my calculations that the permeability of a
ferrite rod was fixed because this simply was not true.  I found an
approximation in Google Books which I use now to account for the fact
that permeability changes with rod length.

Looking at my updated graphs, the matched condition that I mentioned
before still exists but it occurs at lengths so small - like 2" for a
D=.5" rod and 4" for a D=1" rod - that it doesn't really matter.

From Faraday's law of induction, we know that flux flowing through a
loop causes a voltage to appear across it.  So the more flux the more
voltage we can get out of one turn.  Around the point where the rod is
long enough to reach its initial permeability lengthening it will only
ever so slowly increase the amount of flux in the rod, as you can see
in the following graphs.  In the graphs, B is the flux density, in
Tesla, E is the E-field, in V/m, and H is the H-field, in A/m.  H is
derived from E using H = E/377.  B = mu0*H where mu0 is the
permeability of free space.  B was then used to calculate the flux in
the rod.


http://img193.imageshack.us/img193/2166/flux40.png

I also plotted the voltage output at 1 Mhz for the various rods.  Each
rod is wound with the right number of turns over its full length to
reach 250 uH.  The formula used to calculate the voltage output of
the loop is Q*2*pi*f*N*flux_in_rod, where N is the number of turns.
Plots at other frequencies give similar results when tuned at the same
capacitance.


http://img844.imageshack.us/img844/6829/dbv40.png

I also tried the other formula I've seen, Q*2*pi*f*N*Area*mu0*mu_rod*H.
The results look the same except the voltage is about 10 dB more.
Reality is probably somewhere in between since B and H influence each
other.

George


Pollock,Raphael E <rpollock@...>
 

Dear George: These graphs are very interesting, especially the implications concerning length of ferrite as a function of inductance. I have worked with 125 mu bars, and it is apparent that extra length in 125 mu bars beyond somewhere around 16" doesn't really appear buy you an advantage; at that length of bar you are already on the shoulder of what appears to be a logarithmic plot--again, thank you for providing this information.
 
As a practical matter, I would be very interested to see how you would apply these findings in the design of an "optimal" ferrite booster bar type antenna to be inductively coupled to a radio with an internal ferrite bar antenna, seeking to come up with the best possible combination of parameters; i.e., bar length, bar diameter, bar inductance, coil position on bar, coil wire composition, "tightness" of coil wrap, etc.
 
Any insights would be deeply appreciated!
 
Raph Pollock
 


From: ultralightdx@... [ultralightdx@...] On Behalf Of george magiros [submodd@...]
Sent: Monday, November 01, 2010 10:56 PM
To: ultralightdx@...
Subject: Re: [ultralightdx] Re: ferrite vs sensitivity

 

Thank you for the kind remarks.  I promised to post some more graphs
so here are my latest.

I stopped assuming in my calculations that the permeability of a
ferrite rod was fixed because this simply was not true.  I found an
approximation in Google Books which I use now to account for the fact
that permeability changes with rod length.

Looking at my updated graphs, the matched condition that I mentioned
before still exists but it occurs at lengths so small - like 2" for a
D=.5" rod and 4" for a D=1" rod - that it doesn't really matter.

From Faraday's law of induction, we know that flux flowing through a
loop causes a voltage to appear across it.  So the more flux the more
voltage we can get out of one turn.  Around the point where the rod is
long enough to reach its initial permeability lengthening it will only
ever so slowly increase the amount of flux in the rod, as you can see
in the following graphs.  In the graphs, B is the flux density, in
Tesla, E is the E-field, in V/m, and H is the H-field, in A/m.  H is
derived from E using H = E/377.  B = mu0*H where mu0 is the
permeability of free space.  B was then used to calculate the flux in
the rod.


http://img193.imageshack.us/img193/2166/flux40.png

I also plotted the voltage output at 1 Mhz for the various rods.  Each
rod is wound with the right number of turns over its full length to
reach 250 uH.  The formula used to calculate the voltage output of
the loop is Q*2*pi*f*N*flux_in_rod, where N is the number of turns.
Plots at other frequencies give similar results when tuned at the same
capacitance.


http://img844.imageshack.us/img844/6829/dbv40.png

I also tried the other formula I've seen, Q*2*pi*f*N*Area*mu0*mu_rod*H.
The results look the same except the voltage is about 10 dB more.
Reality is probably somewhere in between since B and H influence each
other.

George


George Magiros
 

I'm still on my quest to simulate ferrite loop antennas, this time for their signal to noise ratios.  I hope I'm not proving that 17 swallows are as strong as a horse with all my graphs.  Experimentation and actual DXing comes next I promise.

Let me point out a few simple design observations that I gleamed from the graphs.

First, use as many turns as possible without making the Q too high.  My Sony ICF-S10MK2 apparently uses a small loopstick with an inductance of 650 uH.  That is more than enough turns I would think.  300 uH is probably sufficient too, maybe lower.  Having a good number of turns puts you into a kind of linear region where increasing the length of the rod improves the SNR the most.  While increasing the number of turns on the loop does improve the SNR, best results come from increasing the length of the rod. 

Second, increasing the diameter of rod does not improve the SNR that much, unless of course your rod has a very small diameter to begin with.  It appears to be better SNR-wise, and less costly, to simply increase the length of the rod rather than its diameter.  In addition there appears to be, for a given rod diameter, a maximum rod length beyond which no increase in the SNR occures. 

Now here are the graphs.  First for a ferrite loopstick antenna with an initial permeability of 125.  One graph plots rod length against turns and the other plots rod diameter against turns.  For a loopstick with a diameter of 12.7mm the best length seems to be between 200mm and 300mm FYI.


http://img225.imageshack.us/img225/2042/mu125len.png


http://img833.imageshack.us/img833/1018/mu125dia.png

Next, here are the graphs for a loopstick antenna with a mu of 800.  The best length for a rod with a 12.7mm diameter seems to be between 300mm to 450mm.


http://img585.imageshack.us/img585/3674/mu800len.png


http://img577.imageshack.us/img577/2258/mu800dia.png

George

Ps. Just to be sure I haven't made any glaring mistakes here is the Matlab/Octave function I used to calculate the signal to noise ratio.

% mui: initial relative permeability of the rod
% n: number of turns
% lr: length of rod in mm
% dw: diameter of wire in mm
% f: frequency in Hz
% E: E-field in V/m
function [ snr Rac Rdc ] = loopstick (mui, n, d, lr, f, dw, E)
  Kb = 1.38e-23;                  % boltzmann constant
  T = 293;                        % room temperature 20C (293K)
  muo = 4 * pi * 1e-7;            % permeability of free space
  sigma = 5.96e7;                 % conductivity of copper at 20C (293K)
  B = 3e3;                        % bandwidth (3 khz)

  lw = n .* pi .* d;                          % length of wire need
  delta = 1 ./ sqrt(pi * muo * sigma * f);    % skin depth of wire
  Rdc = lw * .001 ./ (pi / 4 .* (dw * .001).^2 * sigma);
  Rac = lw * .001 ./ (pi * sigma * delta .* dw * .001);
  en = sqrt(4 * Kb * T * B * Rac);            % noise voltage

  mu = 1./(1./mui+(d./lr).^2.*(log(lr./(d/2))-1)); % rod relative permeability
  a = pi / 4 * (d * .001).^2;                 % rod winding area
  es = 2 * pi * n .* a .* mu * E / (3e8 / f); % signal voltage
  snr = 20 * log10(es ./ en);          
end






Pollock,Raphael E <rpollock@...>
 

Dear George: Your 17 swallows analogy got me to really laughing! In any event, I will await your practical applications in that the vast majority of our fellow hobbyists, myself included, lack much in-depth knowledge about the underlying electronics, let alone the theoretical modeling that you are so generously providing to us. It will be a real service to the hobby to be able to come forth with an optimized and practical application, including step-by-step instructions as well as supply sources. It may very well be that a 7.5” ferrite bar, such as what is being used for so many of the boosted Tecsun ULRs, is the best option, end of discussion. I continue to be very pleased with the 19” ferrite bar booster that I built, “designed” by reading through sources from the various Yahoo clubs, the web, Gerry’s Q-stick + which is my original inspiration, etc. All that is well and good, but is it the best that can be done??? If I am to interpret the graphs below correctly then a 19”L x 1”D 125 mu ferrite bar wrapped with a primary coil of 38 turns should yield a SNR of about +6dB and a 27” L x 1” D would be about +8dB. As a practical matter both of these antennas generate just about the same amount of apparent gain when inductively coupled to any of several radios that I own that have S-meters—slightly more gain with the 27”er but not enough to have ever made a difference in being able to receive a weak signal, plus the nulls are sharper with the 19”er.

 

I am really enjoying your insights, and look forward to more. BTW, basic demographic info?  I’m about to turn 60, have been playing w/ radios since second grade, am a surgeon and work/live in the middle of Houston, TX.  If I had been better at calculus I might have gone into EE; instead, I stand on the sidelines and play around with ferrite bars and wires and PVC piping while being taught by smarter folks like yourself!

 

73s

 

Raph Pollock

 

From: ultralightdx@... [mailto:ultralightdx@...] On Behalf Of george magiros
Sent: Saturday, November 13, 2010 9:20 PM
To: ultralightdx@...
Subject: Re: [ultralightdx] Re: ferrite vs sensitivity

 

 

I'm still on my quest to simulate ferrite loop antennas, this time for their signal to noise ratios.  I hope I'm not proving that 17 swallows are as strong as a horse with all my graphs.  Experimentation and actual DXing comes next I promise.

Let me point out a few simple design observations that I gleamed from the graphs.

First, use as many turns as possible without making the Q too high.  My Sony ICF-S10MK2 apparently uses a small loopstick with an inductance of 650 uH.  That is more than enough turns I would think.  300 uH is probably sufficient too, maybe lower.  Having a good number of turns puts you into a kind of linear region where increasing the length of the rod improves the SNR the most.  While increasing the number of turns on the loop does improve the SNR, best results come from increasing the length of the rod. 

Second, increasing the diameter of rod does not improve the SNR that much, unless of course your rod has a very small diameter to begin with.  It appears to be better SNR-wise, and less costly, to simply increase the length of the rod rather than its diameter.  In addition there appears to be, for a given rod diameter, a maximum rod length beyond which no increase in the SNR occures. 

Now here are the graphs.  First for a ferrite loopstick antenna with an initial permeability of 125.  One graph plots rod length against turns and the other plots rod diameter against turns.  For a loopstick with a diameter of 12.7mm the best length seems to be between 200mm and 300mm FYI.


http://img225.imageshack.us/img225/2042/mu125len.png


http://img833.imageshack.us/img833/1018/mu125dia.png

Next, here are the graphs for a loopstick antenna with a mu of 800.  The best length for a rod with a 12.7mm diameter seems to be between 300mm to 450mm.


http://img585.imageshack.us/img585/3674/mu800len.png


http://img577.imageshack.us/img577/2258/mu800dia.png

George

Ps. Just to be sure I haven't made any glaring mistakes here is the Matlab/Octave function I used to calculate the signal to noise ratio.

% mui: initial relative permeability of the rod
% n: number of turns
% lr: length of rod in mm
% dw: diameter of wire in mm
% f: frequency in Hz
% E: E-field in V/m
function [ snr Rac Rdc ] = loopstick (mui, n, d, lr, f, dw, E)
  Kb = 1.38e-23;                  % boltzmann constant
  T = 293;                        % room temperature 20C (293K)
  muo = 4 * pi * 1e-7;            % permeability of free space
  sigma = 5.96e7;                 % conductivity of copper at 20C (293K)
  B = 3e3;                        % bandwidth (3 khz)

  lw = n .* pi .* d;                          % length of wire need
  delta = 1 ./ sqrt(pi * muo * sigma * f);    % skin depth of wire
  Rdc = lw * .001 ./ (pi / 4 .* (dw * .001).^2 * sigma);
  Rac = lw * .001 ./ (pi * sigma * delta .* dw * .001);
  en = sqrt(4 * Kb * T * B * Rac);            % noise voltage

  mu = 1./(1./mui+(d./lr).^2.*(log(lr./(d/2))-1)); % rod relative permeability
  a = pi / 4 * (d * .001).^2;                 % rod winding area
  es = 2 * pi * n .* a .* mu * E / (3e8 / f); % signal voltage
  snr = 20 * log10(es ./ en);          
end





Gary DeBock
 

Hi George and Ralph,
 
Thanks again to George for explaining many of the theoretical concepts behind loopstick design, which I have also found quite fascinating.
 
Ralph, the 7.5" loopstick ULR designs commonly used in the ULR group (Slider loopsticks, 7.5" loopstick PL-380's, etc.) were all developed through extensive live-signal A/B testing and tinkering, with the only standard of success being DXing performance. Although I was fortunate to receive Navy electronics training as a sonar repair technican, loopstick design theory was not part of the training curriculum. As such, George's ability to explain loopstick design science is appreciated.
 
Regarding the practical use of very long loopsticks, during the development of the variable-inductance E100 Slider loopstick (in the summer of 2008), John Bryant and Guy Atkins went in the direction of longer loopsticks, while I concentrated on refining the 7.5" Slider loopstick as a reasonable compromise of DXing performance and portability. The 20" and larger loopsticks did provide slightly more gain than the 7.5" Slider models, but not as much as we had hoped. On the other hand, Guy's 18" Stormwise ferrite-bar PL-380 loopstick design does provide significantly more DXing gain than the 7.5" loopstick PL-380, although there certainly is a tradeoff between portability and performance in such a case.
 
73, Gary DeBock
(in Puyallup, WA) 
 
          
 

In a message dated 11/15/2010 8:40:34 A.M. Pacific Standard Time, rpollock@... writes:
 

Dear George: Your 17 swallows analogy got me to really laughing! In any event, I will await your practical applications in that the vast majority of our fellow hobbyists, myself included, lack much in-depth knowledge about the underlying electronics, let alone the theoretical modeling that you are so generously providing to us. It will be a real service to the hobby to be able to come forth with an optimized and practical application, including step-by-step instructions as well as supply sources. It may very well be that a 7.5” ferrite bar, such as what is being used for so many of the boosted Tecsun ULRs, is the best option, end of discussion. I continue to be very pleased with the 19” ferrite bar booster that I built, “designed” by reading through sources from the various Yahoo clubs, the web, Gerry’s Q-stick + which is my original inspiration, etc. All that is well and good, but is it the best that can be done??? If I am to interpret the graphs below correctly then a 19”L x 1”D 125 mu ferrite bar wrapped with a primary coil of 38 turns should yield a SNR of about +6dB and a 27” L x 1” D would be about +8dB. As a practical matter both of these antennas generate just about the same amount of apparent gain when inductively coupled to any of several radios that I own that have S-meters—slightly more gain with the 27”er but not enough to have ever made a difference in being able to receive a weak signal, plus the nulls are sharper with the 19”er.

I am really enjoying your insights, and look forward to more. BTW, basic demographic info?  I’m about to turn 60, have been playing w/ radios since second grade, am a surgeon and work/live in the middle of Houston, TX.  If I had been better at calculus I might have gone into EE; instead, I stand on the sidelines and play around with ferrite bars and wires and PVC piping while being taught by smarter folks like yourself!

73s

Raph Pollock

From: ultralightdx@... [mailto:ultralightdx@...] On Behalf Of george magiros
Sent: Saturday, November 13, 2010 9:20 PM
To: ultralightdx@...
Subject: Re: [ultralightdx] Re: ferrite vs sensitivity

 

I'm still on my quest to simulate ferrite loop antennas, this time for their signal to noise ratios.  I hope I'm not proving that 17 swallows are as strong as a horse with all my graphs.  Experimentation and actual DXing comes next I promise.

Let me point out a few simple design observations that I gleamed from the graphs.

First, use as many turns as possible without making the Q too high.  My Sony ICF-S10MK2 apparently uses a small loopstick with an inductance of 650 uH.  That is more than enough turns I would think.  300 uH is probably sufficient too, maybe lower.  Having a good number of turns puts you into a kind of linear region where increasing the length of the rod improves the SNR the most.  While increasing the number of turns on the loop does improve the SNR, best results come from increasing the length of the rod. 

Second, increasing the diameter of rod does not improve the SNR that much, unless of course your rod has a very small diameter to begin with.  It appears to be better SNR-wise, and less costly, to simply increase the length of the rod rather than its diameter.  In addition there appears to be, for a given rod diameter, a maximum rod length beyond which no increase in the SNR occures. 

Now here are the graphs.  First for a ferrite loopstick antenna with an initial permeability of 125.  One graph plots rod length against turns and the other plots rod diameter against turns.  For a loopstick with a diameter of 12.7mm the best length seems to be between 200mm and 300mm FYI.


http://img225.imageshack.us/img225/2042/mu125len.png


http://img833.imageshack.us/img833/1018/mu125dia.png

Next, here are the graphs for a loopstick antenna with a mu of 800.  The best length for a rod with a 12.7mm diameter seems to be between 300mm to 450mm.


http://img585.imageshack.us/img585/3674/mu800len.png


http://img577.imageshack.us/img577/2258/mu800dia.png

George

Ps. Just to be sure I haven't made any glaring mistakes here is the Matlab/Octave function I used to calculate the signal to noise ratio.

% mui: initial relative permeability of the rod
% n: number of turns
% lr: length of rod in mm
% dw: diameter of wire in mm
% f: frequency in Hz
% E: E-field in V/m
function [ snr Rac Rdc ] = loopstick (mui, n, d, lr, f, dw, E)
  Kb = 1.38e-23;                  % boltzmann constant
  T = 293;                        % room temperature 20C (293K)
  muo = 4 * pi * 1e-7;            % permeability of free space
  sigma = 5.96e7;                 % conductivity of copper at 20C (293K)
  B = 3e3;                        % bandwidth (3 khz)

  lw = n .* pi .* d;                          % length of wire need
  delta = 1 ./ sqrt(pi * muo * sigma * f);    % skin depth of wire
  Rdc = lw * .001 ./ (pi / 4 .* (dw * .001).^2 * sigma);
  Rac = lw * .001 ./ (pi * sigma * delta .* dw * .001);
  en = sqrt(4 * Kb * T * B * Rac);            % noise voltage

  mu = 1./(1./mui+(d./lr).^2.*(log(lr./(d/2))-1)); % rod relative permeability
  a = pi / 4 * (d * .001).^2;                 % rod winding area
  es = 2 * pi * n .* a .* mu * E / (3e8 / f); % signal voltage
  snr = 20 * log10(es ./ en);          
end





Pollock,Raphael E <rpollock@...>
 

Thanks for this posting. I have found that the 19" ferrite bar fits nicely into a 2' long piece of PVC pipe 2" in diameter with enough internal room to also accomodate a 365 pfd variable capacitor and a vernier reduction drive mechanism. This sits nicely on an 18" lazy susan along with a 2010 or a Satellit 750. The entire package can be easily transported; maybe some day to the Pacific NW for some of that great TP/DU DX!!

73s

Raphael Pollock
 

From: D1028Gary@... [mailto:D1028Gary@...]
Sent: Monday, November 15, 2010 05:55 PM
To: ultralightdx@... <ultralightdx@...>
Subject: Re: [ultralightdx] Re: ferrite vs sensitivity
 
 

Hi George and Ralph,
 
Thanks again to George for explaining many of the theoretical concepts behind loopstick design, which I have also found quite fascinating.
 
Ralph, the 7.5" loopstick ULR designs commonly used in the ULR group (Slider loopsticks, 7.5" loopstick PL-380's, etc.) were all developed through extensive live-signal A/B testing and tinkering, with the only standard of success being DXing performance. Although I was fortunate to receive Navy electronics training as a sonar repair technican, loopstick design theory was not part of the training curriculum. As such, George's ability to explain loopstick design science is appreciated.
 
Regarding the practical use of very long loopsticks, during the development of the variable-inductance E100 Slider loopstick (in the summer of 2008), John Bryant and Guy Atkins went in the direction of longer loopsticks, while I concentrated on refining the 7.5" Slider loopstick as a reasonable compromise of DXing performance and portability. The 20" and larger loopsticks did provide slightly more gain than the 7.5" Slider models, but not as much as we had hoped. On the other hand, Guy's 18" Stormwise ferrite-bar PL-380 loopstick design does provide significantly more DXing gain than the 7.5" loopstick PL-380, although there certainly is a tradeoff between portability and performance in such a case.
 
73, Gary DeBock
(in Puyallup, WA) 
 
          
 
In a message dated 11/15/2010 8:40:34 A.M. Pacific Standard Time, rpollock@... writes:
 

Dear George: Your 17 swallows analogy got me to really laughing! In any event, I will await your practical applications in that the vast majority of our fellow hobbyists, myself included, lack much in-depth knowledge about the underlying electronics, let alone the theoretical modeling that you are so generously providing to us. It will be a real service to the hobby to be able to come forth with an optimized and practical application, including step-by-step instructions as well as supply sources. It may very well be that a 7.5” ferrite bar, such as what is being used for so many of the boosted Tecsun ULRs, is the best option, end of discussion. I continue to be very pleased with the 19” ferrite bar booster that I built, “designed” by reading through sources from the various Yahoo clubs, the web, Gerry’s Q-stick + which is my original inspiration, etc. All that is well and good, but is it the best that can be done??? If I am to interpret the graphs below correctly then a 19”L x 1”D 125 mu ferrite bar wrapped with a primary coil of 38 turns should yield a SNR of about +6dB and a 27” L x 1” D would be about +8dB. As a practical matter both of these antennas generate just about the same amount of apparent gain when inductively coupled to any of several radios that I own that have S-meters—slightly more gain with the 27”er but not enough to have ever made a difference in being able to receive a weak signal, plus the nulls are sharper with the 19”er.

I am really enjoying your insights, and look forward to more. BTW, basic demographic info?  I’m about to turn 60, have been playing w/ radios since second grade, am a surgeon and work/live in the middle of Houston, TX.  If I had been better at calculus I might have gone into EE; instead, I stand on the sidelines and play around with ferrite bars and wires and PVC piping while being taught by smarter folks like yourself!

73s

Raph Pollock

From: ultralightdx@... [mailto:ultralightdx@...] On Behalf Of george magiros
Sent: Saturday, November 13, 2010 9:20 PM
To: ultralightdx@...
Subject: Re: [ultralightdx] Re: ferrite vs sensitivity

 

I'm still on my quest to simulate ferrite loop antennas, this time for their signal to noise ratios.  I hope I'm not proving that 17 swallows are as strong as a horse with all my graphs.  Experimentation and actual DXing comes next I promise.

Let me point out a few simple design observations that I gleamed from the graphs.

First, use as many turns as possible without making the Q too high.  My Sony ICF-S10MK2 apparently uses a small loopstick with an inductance of 650 uH.  That is more than enough turns I would think.  300 uH is probably sufficient too, maybe lower.  Having a good number of turns puts you into a kind of linear region where increasing the length of the rod improves the SNR the most.  While increasing the number of turns on the loop does improve the SNR, best results come from increasing the length of the rod. 

Second, increasing the diameter of rod does not improve the SNR that much, unless of course your rod has a very small diameter to begin with.  It appears to be better SNR-wise, and less costly, to simply increase the length of the rod rather than its diameter.  In addition there appears to be, for a given rod diameter, a maximum rod length beyond which no increase in the SNR occures. 

Now here are the graphs.  First for a ferrite loopstick antenna with an initial permeability of 125.  One graph plots rod length against turns and the other plots rod diameter against turns.  For a loopstick with a diameter of 12.7mm the best length seems to be between 200mm and 300mm FYI.


http://img225.imageshack.us/img225/2042/mu125len.png


http://img833.imageshack.us/img833/1018/mu125dia.png

Next, here are the graphs for a loopstick antenna with a mu of 800.  The best length for a rod with a 12.7mm diameter seems to be between 300mm to 450mm.


http://img585.imageshack.us/img585/3674/mu800len.png


http://img577.imageshack.us/img577/2258/mu800dia.png

George

Ps. Just to be sure I haven't made any glaring mistakes here is the Matlab/Octave function I used to calculate the signal to noise ratio.

% mui: initial relative permeability of the rod
% n: number of turns
% lr: length of rod in mm
% dw: diameter of wire in mm
% f: frequency in Hz
% E: E-field in V/m
function [ snr Rac Rdc ] = loopstick (mui, n, d, lr, f, dw, E)
  Kb = 1.38e-23;                  % boltzmann constant
  T = 293;                        % room temperature 20C (293K)
  muo = 4 * pi * 1e-7;            % permeability of free space
  sigma = 5.96e7;                 % conductivity of copper at 20C (293K)
  B = 3e3;                        % bandwidth (3 khz)

  lw = n .* pi .* d;                          % length of wire need
  delta = 1 ./ sqrt(pi * muo * sigma * f);    % skin depth of wire
  Rdc = lw * .001 ./ (pi / 4 .* (dw * .001).^2 * sigma);
  Rac = lw * .001 ./ (pi * sigma * delta .* dw * .001);
  en = sqrt(4 * Kb * T * B * Rac);            % noise voltage

  mu = 1./(1./mui+(d./lr).^2.*(log(lr./(d/2))-1)); % rod relative permeability
  a = pi / 4 * (d * .001).^2;                 % rod winding area
  es = 2 * pi * n .* a .* mu * E / (3e8 / f); % signal voltage
  snr = 20 * log10(es ./ en);          
end





Pollock,Raphael E <rpollock@...>
 

Hi Gary!
 
Do you know if Guy wrote up his experiences with the 18" Stormwise ferrite bar, especially design considerations (i.e.; wire used--Litz vs AWG, pick up coil--# of turns, spacing between turns, position on bar, housing) as well as actual dx results? My 19" Stormwise-based antenna, which is the approximate size of a two-foot long baker's rolling pin (i.e.; pretty easily transported), just about pins the S-meter on every radio that I own that is capable of inductive coupling, with nice sharp nulls and very tight tuning (e.g.; pretty good Q although I don't have the knowledge or equipment to measure). I am happy with it, but would love to get some comparative performance information from similar set ups--always looking to improve on what I can hear. Do you think that the reason that the 20" and larger loop sticks didn't do as well as the 18" Stormwise, if I am reading your email below correctly, was due to the greater diameter of the Stormwise ferrite bar?
 
73s;
 
Raphael Pollock
 


From: ultralightdx@... [ultralightdx@...] On Behalf Of D1028Gary@... [D1028Gary@...]
Sent: Monday, November 15, 2010 5:55 PM
To: ultralightdx@...
Subject: Re: [ultralightdx] Re: ferrite vs sensitivity

 

Hi George and Ralph,
 
Thanks again to George for explaining many of the theoretical concepts behind loopstick design, which I have also found quite fascinating.
 
Ralph, the 7.5" loopstick ULR designs commonly used in the ULR group (Slider loopsticks, 7.5" loopstick PL-380's, etc.) were all developed through extensive live-signal A/B testing and tinkering, with the only standard of success being DXing performance. Although I was fortunate to receive Navy electronics training as a sonar repair technican, loopstick design theory was not part of the training curriculum. As such, George's ability to explain loopstick design science is appreciated.
 
Regarding the practical use of very long loopsticks, during the development of the variable-inductance E100 Slider loopstick (in the summer of 2008), John Bryant and Guy Atkins went in the direction of longer loopsticks, while I concentrated on refining the 7.5" Slider loopstick as a reasonable compromise of DXing performance and portability. The 20" and larger loopsticks did provide slightly more gain than the 7.5" Slider models, but not as much as we had hoped. On the other hand, Guy's 18" Stormwise ferrite-bar PL-380 loopstick design does provide significantly more DXing gain than the 7.5" loopstick PL-380, although there certainly is a tradeoff between portability and performance in such a case.
 
73, Gary DeBock
(in Puyallup, WA) 
 
          
 
In a message dated 11/15/2010 8:40:34 A.M. Pacific Standard Time, rpollock@... writes:
 

Dear George: Your 17 swallows analogy got me to really laughing! In any event, I will await your practical applications in that the vast majority of our fellow hobbyists, myself included, lack much in-depth knowledge about the underlying electronics, let alone the theoretical modeling that you are so generously providing to us. It will be a real service to the hobby to be able to come forth with an optimized and practical application, including step-by-step instructions as well as supply sources. It may very well be that a 7.5” ferrite bar, such as what is being used for so many of the boosted Tecsun ULRs, is the best option, end of discussion. I continue to be very pleased with the 19” ferrite bar booster that I built, “designed” by reading through sources from the various Yahoo clubs, the web, Gerry’s Q-stick + which is my original inspiration, etc. All that is well and good, but is it the best that can be done??? If I am to interpret the graphs below correctly then a 19”L x 1”D 125 mu ferrite bar wrapped with a primary coil of 38 turns should yield a SNR of about +6dB and a 27” L x 1” D would be about +8dB. As a practical matter both of these antennas generate just about the same amount of apparent gain when inductively coupled to any of several radios that I own that have S-meters—slightly more gain with the 27”er but not enough to have ever made a difference in being able to receive a weak signal, plus the nulls are sharper with the 19”er.

I am really enjoying your insights, and look forward to more. BTW, basic demographic info?  I’m about to turn 60, have been playing w/ radios since second grade, am a surgeon and work/live in the middle of Houston, TX.  If I had been better at calculus I might have gone into EE; instead, I stand on the sidelines and play around with ferrite bars and wires and PVC piping while being taught by smarter folks like yourself!

73s

Raph Pollock

From: ultralightdx@... [mailto:ultralightdx@...] On Behalf Of george magiros
Sent: Saturday, November 13, 2010 9:20 PM
To: ultralightdx@...
Subject: Re: [ultralightdx] Re: ferrite vs sensitivity

I'm still on my quest to simulate ferrite loop antennas, this time for their signal to noise ratios.  I hope I'm not proving that 17 swallows are as strong as a horse with all my graphs.  Experimentation and actual DXing comes next I promise.

Let me point out a few simple design observations that I gleamed from the graphs.

First, use as many turns as possible without making the Q too high.  My Sony ICF-S10MK2 apparently uses a small loopstick with an inductance of 650 uH.  That is more than enough turns I would think.  300 uH is probably sufficient too, maybe lower.  Having a good number of turns puts you into a kind of linear region where increasing the length of the rod improves the SNR the most.  While increasing the number of turns on the loop does improve the SNR, best results come from increasing the length of the rod. 

Second, increasing the diameter of rod does not improve the SNR that much, unless of course your rod has a very small diameter to begin with.  It appears to be better SNR-wise, and less costly, to simply increase the length of the rod rather than its diameter.  In addition there appears to be, for a given rod diameter, a maximum rod length beyond which no increase in the SNR occures. 

Now here are the graphs.  First for a ferrite loopstick antenna with an initial permeability of 125.  One graph plots rod length against turns and the other plots rod diameter against turns.  For a loopstick with a diameter of 12.7mm the best length seems to be between 200mm and 300mm FYI.


http://img225.imageshack.us/img225/2042/mu125len.png


http://img833.imageshack.us/img833/1018/mu125dia.png

Next, here are the graphs for a loopstick antenna with a mu of 800.  The best length for a rod with a 12.7mm diameter seems to be between 300mm to 450mm.


http://img585.imageshack.us/img585/3674/mu800len.png


http://img577.imageshack.us/img577/2258/mu800dia.png

George

Ps. Just to be sure I haven't made any glaring mistakes here is the Matlab/Octave function I used to calculate the signal to noise ratio.

% mui: initial relative permeability of the rod
% n: number of turns
% lr: length of rod in mm
% dw: diameter of wire in mm
% f: frequency in Hz
% E: E-field in V/m
function [ snr Rac Rdc ] = loopstick (mui, n, d, lr, f, dw, E)
  Kb = 1.38e-23;                  % boltzmann constant
  T = 293;                        % room temperature 20C (293K)
  muo = 4 * pi * 1e-7;            % permeability of free space
  sigma = 5.96e7;                 % conductivity of copper at 20C (293K)
  B = 3e3;                        % bandwidth (3 khz)

  lw = n .* pi .* d;                          % length of wire need
  delta = 1 ./ sqrt(pi * muo * sigma * f);    % skin depth of wire
  Rdc = lw * .001 ./ (pi / 4 .* (dw * .001).^2 * sigma);
  Rac = lw * .001 ./ (pi * sigma * delta .* dw * .001);
  en = sqrt(4 * Kb * T * B * Rac);            % noise voltage

  mu = 1./(1./mui+(d./lr).^2.*(log(lr./(d/2))-1)); % rod relative permeability
  a = pi / 4 * (d * .001).^2;                 % rod winding area
  es = 2 * pi * n .* a .* mu * E / (3e8 / f); % signal voltage
  snr = 20 * log10(es ./ en);          
end





Gary DeBock
 

Hi Ralph,
 
Thanks for your interest in Guy's 18" Stormwise loopstick PL-380 model, and I'm sure that he will be happy to explain the details to you. Guy is currently at Grayland, WA (a famous west coast DXpedition site), but I'll forward your email to him.
 
To my knowledge, Guy adapted my 7.5" loopstick PL-380 design (a 500 uh coil of 40/44 Litz wire on a 7.5" type 61 ferrite bar) to create his 18" loopstick model. He used a center-wound coil of similar inductance on the 18" ferrite bar, with Litz wire leads running through a slot at the top center of the cabinet. We ran a brief "shootout" at a local Puyallup park to test his mega-loopstick PL-380 against my 7.5" model, and understandably found that his 18" antenna had a significant gain advantage over my smaller PL-380 loopstick. During the "shootout" we also set up my 3' portable PVC loop, and found that this tuned passive loop provided a potent AM-DXing boost for both modified PL-380 models.
 
Some photos from the "Stormwise Shootout" are linked below, for those interested.
 
73 and Good DX,
Gary DeBock
 
Guy's 18" loopstick PL-380                           http://www.mediafire.com/i/?imykf4ndnnj
Guy holding the 18" loopstick PL-380            http://www.mediafire.com/i/?w0gjm1fzo4m
Me holding the 7.5" loopstick PL-380            http://www.mediafire.com/i/?mo0gjynwjzf  
Guy's 18" loopstick PL-380 + 3' PVC Loop    http://www.mediafire.com/i/?uy0mwyjjydi
   
 

In a message dated 11/16/2010 5:31:07 A.M. Pacific Standard Time, rpollock@... writes:
 

Hi Gary!
 
Do you know if Guy wrote up his experiences with the 18" Stormwise ferrite bar, especially design considerations (i.e.; wire used--Litz vs AWG, pick up coil--# of turns, spacing between turns, position on bar, housing) as well as actual dx results? My 19" Stormwise-based antenna, which is the approximate size of a two-foot long baker's rolling pin (i.e.; pretty easily transported), just about pins the S-meter on every radio that I own that is capable of inductive coupling, with nice sharp nulls and very tight tuning (e.g.; pretty good Q although I don't have the knowledge or equipment to measure). I am happy with it, but would love to get some comparative performance information from similar set ups--always looking to improve on what I can hear. Do you think that the reason that the 20" and larger loop sticks didn't do as well as the 18" Stormwise, if I am reading your email below correctly, was due to the greater diameter of the Stormwise ferrite bar?
 
73s;
 
Raphael Pollock
 

From: ultralightdx@... [ultralightdx@...] On Behalf Of D1028Gary@... [D1028Gary@...]
Sent: Monday, November 15, 2010 5:55 PM
To: ultralightdx@...
Subject: Re: [ultralightdx] Re: ferrite vs sensitivity

 

Hi George and Ralph,
 
Thanks again to George for explaining many of the theoretical concepts behind loopstick design, which I have also found quite fascinating.
 
Ralph, the 7.5" loopstick ULR designs commonly used in the ULR group (Slider loopsticks, 7.5" loopstick PL-380's, etc.) were all developed through extensive live-signal A/B testing and tinkering, with the only standard of success being DXing performance. Although I was fortunate to receive Navy electronics training as a sonar repair technican, loopstick design theory was not part of the training curriculum. As such, George's ability to explain loopstick design science is appreciated.
 
Regarding the practical use of very long loopsticks, during the development of the variable-inductance E100 Slider loopstick (in the summer of 2008), John Bryant and Guy Atkins went in the direction of longer loopsticks, while I concentrated on refining the 7.5" Slider loopstick as a reasonable compromise of DXing performance and portability. The 20" and larger loopsticks did provide slightly more gain than the 7.5" Slider models, but not as much as we had hoped. On the other hand, Guy's 18" Stormwise ferrite-bar PL-380 loopstick design does provide significantly more DXing gain than the 7.5" loopstick PL-380, although there certainly is a tradeoff between portability and performance in such a case.
 
73, Gary DeBock
(in Puyallup, WA) 
 
          
 
In a message dated 11/15/2010 8:40:34 A.M. Pacific Standard Time, rpollock@... writes:
 

Dear George: Your 17 swallows analogy got me to really laughing! In any event, I will await your practical applications in that the vast majority of our fellow hobbyists, myself included, lack much in-depth knowledge about the underlying electronics, let alone the theoretical modeling that you are so generously providing to us. It will be a real service to the hobby to be able to come forth with an optimized and practical application, including step-by-step instructions as well as supply sources. It may very well be that a 7.5” ferrite bar, such as what is being used for so many of the boosted Tecsun ULRs, is the best option, end of discussion. I continue to be very pleased with the 19” ferrite bar booster that I built, “designed” by reading through sources from the various Yahoo clubs, the web, Gerry’s Q-stick + which is my original inspiration, etc. All that is well and good, but is it the best that can be done??? If I am to interpret the graphs below correctly then a 19”L x 1”D 125 mu ferrite bar wrapped with a primary coil of 38 turns should yield a SNR of about +6dB and a 27” L x 1” D would be about +8dB. As a practical matter both of these antennas generate just about the same amount of apparent gain when inductively coupled to any of several radios that I own that have S-meters—slightly more gain with the 27”er but not enough to have ever made a difference in being able to receive a weak signal, plus the nulls are sharper with the 19”er.

I am really enjoying your insights, and look forward to more. BTW, basic demographic info?  I’m about to turn 60, have been playing w/ radios since second grade, am a surgeon and work/live in the middle of Houston, TX.  If I had been better at calculus I might have gone into EE; instead, I stand on the sidelines and play around with ferrite bars and wires and PVC piping while being taught by smarter folks like yourself!

73s

Raph Pollock

From: ultralightdx@... [mailto:ultralightdx@...] On Behalf Of george magiros
Sent: Saturday, November 13, 2010 9:20 PM
To: ultralightdx@...
Subject: Re: [ultralightdx] Re: ferrite vs sensitivity

I'm still on my quest to simulate ferrite loop antennas, this time for their signal to noise ratios.  I hope I'm not proving that 17 swallows are as strong as a horse with all my graphs.  Experimentation and actual DXing comes next I promise.

Let me point out a few simple design observations that I gleamed from the graphs.

First, use as many turns as possible without making the Q too high.  My Sony ICF-S10MK2 apparently uses a small loopstick with an inductance of 650 uH.  That is more than enough turns I would think.  300 uH is probably sufficient too, maybe lower.  Having a good number of turns puts you into a kind of linear region where increasing the length of the rod improves the SNR the most.  While increasing the number of turns on the loop does improve the SNR, best results come from increasing the length of the rod. 

Second, increasing the diameter of rod does not improve the SNR that much, unless of course your rod has a very small diameter to begin with.  It appears to be better SNR-wise, and less costly, to simply increase the length of the rod rather than its diameter.  In addition there appears to be, for a given rod diameter, a maximum rod length beyond which no increase in the SNR occures. 

Now here are the graphs.  First for a ferrite loopstick antenna with an initial permeability of 125.  One graph plots rod length against turns and the other plots rod diameter against turns.  For a loopstick with a diameter of 12.7mm the best length seems to be between 200mm and 300mm FYI.


http://img225.imageshack.us/img225/2042/mu125len.png


http://img833.imageshack.us/img833/1018/mu125dia.png

Next, here are the graphs for a loopstick antenna with a mu of 800.  The best length for a rod with a 12.7mm diameter seems to be between 300mm to 450mm.


http://img585.imageshack.us/img585/3674/mu800len.png


http://img577.imageshack.us/img577/2258/mu800dia.png

George

Ps. Just to be sure I haven't made any glaring mistakes here is the Matlab/Octave function I used to calculate the signal to noise ratio.

% mui: initial relative permeability of the rod
% n: number of turns
% lr: length of rod in mm
% dw: diameter of wire in mm
% f: frequency in Hz
% E: E-field in V/m
function [ snr Rac Rdc ] = loopstick (mui, n, d, lr, f, dw, E)
  Kb = 1.38e-23;                  % boltzmann constant
  T = 293;                        % room temperature 20C (293K)
  muo = 4 * pi * 1e-7;            % permeability of free space
  sigma = 5.96e7;                 % conductivity of copper at 20C (293K)
  B = 3e3;                        % bandwidth (3 khz)

  lw = n .* pi .* d;                          % length of wire need
  delta = 1 ./ sqrt(pi * muo * sigma * f);    % skin depth of wire
  Rdc = lw * .001 ./ (pi / 4 .* (dw * .001).^2 * sigma);
  Rac = lw * .001 ./ (pi * sigma * delta .* dw * .001);
  en = sqrt(4 * Kb * T * B * Rac);            % noise voltage

  mu = 1./(1./mui+(d./lr).^2.*(log(lr./(d/2))-1)); % rod relative permeability
  a = pi / 4 * (d * .001).^2;                 % rod winding area
  es = 2 * pi * n .* a .* mu * E / (3e8 / f); % signal voltage
  snr = 20 * log10(es ./ en);          
end