Air loop vs Ferrite loop


maxim_sdr
 

Hi, i have a question, what is the size that i should consider for a square air loop made with standard wire to give the same result of a ferrite antenna size 200x10mm?


Steve Ratzlaff
 

Purely my own opinion and not based on direct comparison tests, but I'd say a square loop of 8-10 inches might give equivalent results to a 200 mm long ferrite rod. I'm assuming both loops are tuned with a capacitor, not untuned loops. And if you could use Litz wire of maybe 175/46 or larger, that would help too. But if just standard wire then use the largest gauge you can find/afford, hopefully #18 gauge or larger (in AWG wire size, I don't know the metric equivalent size).

Good luck!

73,

Steve AA7U

On 1/4/2019 9:19 PM, max2006@... [ultralightdx] wrote:
 

Hi, i have a question, what is the size that i should consider for a square air loop made with standard wire to give the same result of a ferrite antenna size 200x10mm?


Michael <michael.setaazul@...>
 

Agreed, Steve.
A longer butt-glued tuned ferrite is better than a short one.
But extending it further makes it unwieldy and accident-prone -
and brings no further audible improvement.

A tuned frame aerial delivers vintage excellence, the bigger the better.

Of course, an FSL enables bitcoin-winners to wipe the floor with the rest of us!

Michael UK

On Samstag.05.01.19 05:04, STEVE ratzlaffsteve@gmail.com [ultralightdx] wrote:
Purely my own opinion and not based on direct comparison tests, but I'd say a square loop of 8-10 inches might give equivalent results to a 200 mm long ferrite rod. I'm assuming both loops are tuned with a capacitor, not untuned loops.
On 1/4/2019 9:19 PM, max2006@email.it [ultralightdx] wrote:

Hi, i have a question, what is the size that i should consider for a square air loop made with standard wire to give the same result of a ferrite antenna size 200x10mm?


maxim_sdr
 

Thank you for your replies, the bigger the better, i know, but i am insterested to find the equivalent size, i do not care about vintage or aesthtic look, i want to make a loop that can be folded, to use at home or bring with me for trips in the weekends but considered that it has to be used at home i cannot follow the rule the bigger the better nor i want to make it undersized so that a 200x10 ferrite is still better.
8-10 inch looks to me a bit too small, i don't think it will give any advantage over the stock ferrite antenna of my  Xhdata D-808; at the moment i am using a 16 inch loop made with ribbon cable using alternate wires to reduce parassite capacity between the loops and i have some improvement with weak signals but i don't know if compared to a 200x10 ferrite would still give some adavantage.
Also has to be considered that i use the air loop as a passive antenna with tuning capacitor but i may also insert a jack to the radio to disconnect the internal ferrite and plug it directy without capacitor, i don't know if doing so will improve the signal.

Anyone made a direct comparison?


Michael <michael.setaazul@...>
 

Max, it will indeed be a pragmatic compromise. The D808, with which
I am not familiar, will probably have an auto-tuned internal ferrite.
Coupling or hard-wiring between a tuned external ferrite or loop and
the D808 frontend can be determinant - and tricky if external
tuning has to "compete" with internal software tuning. Inductive
coupling to the internal ferrite might work better, resulting
in a double-tuned frontend, manual tracking automatic. Disconnecting
the internal ferrite and allowing the internal autotune to tune
the external ferrite or loop might work well if the inductance
of the external aerial is well matched. Time to experiment!

Michael UK

On Samstag.05.01.19 09:23, max2006@email.it [ultralightdx] wrote:
Thank you for your replies, the bigger the better, i know, but i am insterested to find the equivalent size, i do not care about vintage or aesthtic look, i want to make a loop that can be folded, to use at home or bring with me for trips in the weekends but considered that it has to be used at home i cannot follow the rule the bigger the better nor i want to make it undersized so that a 200x10 ferrite is still better.
8-10 inch looks to me a bit too small, i don't think it will give any advantage over the stock ferrite antenna of my  Xhdata D-808; at the moment i am using a 16 inch loop made with ribbon cable using alternate wires to reduce parassite capacity between the loops and i have some improvement with weak signals but i don't know if compared to a 200x10 ferrite would still give some adavantage.
Also has to be considered that i use the air loop as a passive antenna with tuning capacitor but i may also insert a jack to the radio to disconnect the i nternal ferrite and plug it directy without capacitor, i don't know if doing so will improve the signal.
Anyone made a direct comparison?


steven
 

Hi Max,
I have only made one FSL antenna, and it works great both indoors and out.
My FSL is a 4" one. (30 ferrite rods)
My findings were, in direct comparison checks/tests that my 4" FSL gave approx the same signal as my 2 foot box loop/air cored loop.
Inductively coupled or a coupling loop works fine both antennas.
I have added a link to a short youtube video of both my FSL and Box loop.
Regards,
Steven,
Scotland.







On Saturday, 5 January 2019, 10:40:33 GMT, Michael michael.setaazul@... [ultralightdx] wrote:


 

Max, it will indeed be a pragmatic compromise. The D808, with which
I am not familiar, will probably have an auto-tuned internal ferrite.
Coupling or hard-wiring between a tuned external ferrite or loop and
the D808 frontend can be determinant - and tricky if external
tuning has to "compete" with internal software tuning. Inductive
coupling to the internal ferrite might work better, resulting
in a double-tuned frontend, manual tracking automatic. Disconnecting
the internal ferrite and allowing the internal autotune to tune
the external ferrite or loop might work well if the inductance
of the external aerial is well matched. Time to experiment!

Michael UK

On Samstag.05.01.19 09:23, max2006@... [ultralightdx] wrote:
> Thank you for your replies, the bigger the better, i know, but i am
> insterested to find the equivalent size, i do not care about vintage or
> aesthtic look, i want to make a loop that can be folded, to use at home
> or bring with me for trips in the weekends but considered that it has to
> be used at home i cannot follow the rule the bigger the better nor i
> want to make it undersized so that a 200x10 ferrite is still better.
> 8-10 inch looks to me a bit too small, i don't think it will give any
> advantage over the stock ferrite antenna of my  Xhdata D-808; at the
> moment i am using a 16 inch loop made with ribbon cable using alternate
> wires to reduce parassite capacity between the loops and i have some
> improvement with weak signals but i don't know if compared to a 200x10
> ferrite would still give some adavantage.
> Also has to be considered that i use the air loop as a passive antenna
> with tuning capacitor but i may also insert a jack to the radio to
> disconnect the i nternal ferrite and plug it directy without capacitor,
> i don't know if doing so will improve the signal.
>
> Anyone made a direct comparison?
>
>


Virus-free. www.avg.com


maxim_sdr
 

Steven, nice receiver, thank you for the video and comparative infos that give me an idea of what to expect.
Michael, i agree with what you say, i did not think of using a coupling loop hard wired to the D-808, that will work for a standard receiver but not for last generation radios with Silicon Labs chip.
You give me the chance to make the poit on this: there are 3 possible ways to connect a air loop antenna:

1) Using a tuning capacitor in parallel and passively coupling to the internal ferrite antenna keeping the receiver closed to it.
this will work in any radio equipped with a ferrite antenna.

2) Winding a coupling loop on the air loop antenna and hard wiring this secondary loop to the input of the receiver. The air loop antenna is still tuned with its capacitor in parallel.
This will work on a classic receiver like Steven confirmed (and like many of us have done before for the HF). It will also work with a old generation portable receiver without auto tuning chip after having disconnected its internal ferrite antenna (not sure if some impedance transformer is needed in this case). It will not work on the D-808 or any other last generation DSP radio because the internal chip will try to tune the small coupling loop but its inducance will be out of range.

3) Connecting the air loop antenna directly to the input of the receiver without using a tuning capacitor.
It will work only on the last generation portable radios with DSP chip like the D-808, after having disconnected the internal ferrite antenna of course.
The characteristics of the external air loop are specified in the Silicon Labs Design Guidelines AN383 (inductange in the 180 to 450uH range).
That document also mentions a inductance transformer to be used only when the loop is just a small wrap of wire, to rise the inductance from 10–20 μH to the 180 to 450uH range needed from the receiver but this is not our case.

Methods number 1 and 3 are the ones that i will be using for my Xhdata D-808 and method number 2 is the one i would use for the SDR receiver.


Rik
 

Ferrite loops can provide much narrower pick up patterns than air core in my experience. I do not know what design factors control which are very narrow. I have a coil I use over a 16 inch long stack of ferrite which is extremely directional allowing me to choose a number of stations on AM frequencies at night from here in Connecticut USA. It will not hear very distant DX stations, it only chooses 2-4 stations on some  frequencies  within a couple hundred miles on the best evenings. On 1250 AM I have chosen between stations in MA, NY, PA and NJ from CT.

So it does depend on your goals for a better antenna.

Even if you do plan to build your own, you may as well look at commercially successful designs. I have four PK Loops from Australia, the W6LVP amplified single turn loops with two size elements. Besides the home made ferrite stack, Litz on single 9 and 12 inch ferrite cores, a much larger Stormwise ferrite , home made box loops in 2 and 4 foot square sizes etc. They are all different, and each is probably better for different uses. In general the large tuned  air core loops often  hear more than one station per frequency at a time at night, but not during the day.

-FARMERIK


mediumwavedx
 

Sorry if this blathers on, but I'll input my experiences on small loops.

I've built tons of loops here, both passive-tuned and hard wired for the DSP radios.

I will hazard a guess here and say the rough passive-tuned loop equivalent to a 200 mm ferrite is in the range of 8-9 inches square.

I have built smaller ones, on the order of 6 inches. They produce a signal strength about equivalent to the existing ferrite in a Tecsun PL-380. The problem I've had with the really small loops of that size is that the nulling is pretty poor. The figure-8 pattern is not well-defined.

I have a hacked Tecsun PL-380 with the ferrite removed, and also an Eton Traveler 3 with the ferrite removed. I soldered wire leads in place and brought them out the tops of the radios for testing hard wired loops. I use micro-clips for all connections here for testing.

I use two loops currently, an 8 inch and an 18 inch. Both are square loops, close-wound with insulated telephone wire, about 24 gauge solid. The 8 inch has 26 turns and the 18 inch has 12 turns. If you wind a 12 inch loop, use 16 turns.

Both the 8 inch and 18 inch give good hard-wired results. Of course the 18 inch blows the doors off the 8 inch, and is the better nuller. You don't need a 5:1 step up transformer for impedance matching. Use the fully-wound loop. Inductance for both these loops is ballpark around 240 uH. I've found that is a good value to shoot for.

I will say, be careful if hard-wiring directly to the input of the DSP radios. They are very sensitive to static. I haven't blown one out yet, but I've come close. Any static or spike on the line when clipping to the chip will send it into desense for a few minutes. It eventually recovers, at least mine have so far.

Both 8 inch and 18 inch loops can be made passive and tuned with a 365 uuF capacitor very nicely. The 18 inch ranges out nicely from 530-700 KHz without further attention. The 8 inch only tunes to about 1430 KHz, so I jumper a clip wire across a few turns to get to 1700 KHz.

At night, the PL-380 handles an 18 inch hard-wired loop pretty well without overloading. Not so much the Eton Traveler 3. It's sensitivity is a touch better than the PL-380, and otherwise will occasionally overload. A 12 inch loop might be a better bet for the Traveler 3. You shouldn't have any overload trouble with the 8 inch loop.

The advantage of the passive-tuned loops is that you can reduce the coupling by moving the loop a bit farther away from the radio, thus reducing the signal overload problem.

As others have stated, coupling a passive-tuned loop to a modern DSP chipped radio can be finicky because the radio gets de-tuned by the loop, then it re-tunes, then the loop is upset again.. I have best results by coupling the passive loop off the end of the radio's ferrite. The tuning interaction is less. As so:

|
|
L
O
O --RADIO FERRITE--
P
|
|

These DSP radios will start to overload much above 80 or 90 dBu on the RSSI meter. The Eton Traveler 3 measures to 99 dBu and the PL-380 only measures to 63 dBu.

Remember, an RSSI reading of 34 dBu is the equivalent of the old S-9 on vintage receivers us hams remember. 50 microvolts to the input = S-9. A respectable signal.

Also, consider that the induced voltage in a loop increases linearly with the number of turns, the area of the loop, and the frequency. An 8 inch loop has nearly twice the voltage output as a 6 inch loop. Area 64/36 = 1.77 times the output.

Here's a curious tuning tip that may not be apparent at first. It requires two DSP radios. Hard-wire the loop to the first DSP radio (ferrite removed). This DSP radio tunes the loop in place of a 365 uuF variable capacitor if you don't have a spare. Sort of a "digitally tuned passive loop". Couple this loop inductively to the second DSP radio like you normally would. Now you can accurately tune the passive loop by reading the frequency on the first DSP radio. Overkill, yes. But an interesting hack.

Bottom line on wanting a very small fold-able loop - 8 inch would be an ideal size if you can go that big.

Bill
SW Arizona


Rik
 

Excellent info!  I have had better results coupling modern portables with air core couplers than ferrite core ones to BOGs and amplified antennas.


Exact uH was not significant. Between 30 and 90 worked.  I never did try adding a tuned coil, just one  passive  coupler winding. It should work better still. - FARMERIK


Max Italy
 
Edited

I left this post in stand by during the move from the old Yahoo group and i have forgot it; in the meantime my user name was changed.
i am using at the moment a 16 inches square loop 233 uH so i understand that it is by far superior to a 200mm ferrite. I have to rebuild it because it is now wound on a carton box and i may keep the same size made with ribbon cable and collapsible frame.
I noticed the problem with overloading and jamming the adjacent frequencies but i adjust the distance of the radio in this case.
Thank you Bill for the warning about connecting the loop directly to the input of the DSP radio, i will remember it when i make the modification for external antenna and insert a ESD diode CM1213 as shown in the Silicon Labs application note 383.
And thank you to Famerik for the link to the air core coupler, that's usefull if i install the loop in the balcony and connect it to the radio with RG6 cable. In this case do you wire the cable directly to the coupling loop or are you using some transformer?


Rik
 

I believe the small winding I use as a coupler  becomes a sort of transformer when coupled to the coil on the ferrite inside the radio. I wanted a coil coupler to work with most any portable radio. If you had one particular set, you may want to try different numbers of turns. Without ferrite inside the coupler coil, they are very cheap to make, so you could make several slightly different numbers of turns, and see which works best on different radios. The air core couplers seem to have a larger and less critical ideal placement coupled to internal radio ferrite antennas, making them easier to use. In the link, I believe they are also using a tuned coil next to the coupler coil and an RF amp.  Coupling a relatively small  passive loop via co-ax to a small coupler coil at the radio, I don't believe will bring in strong signals. You may want an RF amp in between. I have not added a larger tuned second coil to the couplers I have made [yet].
I use my air core couplers with amplified loops or BOG antennas with strong  co-ax signal outputs, either of which could easily  over load a portable on MW. - FARMERIK


K7DWI Art
 
Edited

As you can see in the attached picture, I am partial to air loops.
They all perform well.
They are just a bit clumsy with certain radios.
I would say at least once a year I have to clean them and tightened the wiring.
I cuss each time I knock one over. I use a Rubbermaid Lazy Susan with a 1X4 screwed on, placed inside the lid of a 5 gallon bucket (Bird Seed) to rotate them.
My 1-Foot Box Loops are fabulous performers. At times, I take the Radio Shack Loop (TECSUN An-100 look a like) and mount it inside the 3 or 4 foot loops and really overdrive my collection.
I still hope to build a FSL in the future. I love comparing stuff and making the most in the hobby.

Art KA5DWI in Central Arizona


daiche
 

Hey Art! This is Dave Aichelman N7NZH formerly of 'The Villages' across from you in Dewey! We met just before moving up to Grants Pass, Oregon. Knew you liked MW DX from the AM DX group down there, but didn't know you experimented with assorted air loops and such. I will have to send you 2 pictures of my current FSL's, a 4" baby and larger 7" one (I think I still have your email). Both FSL's have heard a number of the ethnic LP Aussie stations in the 1611Khz to 1701Khz range. They are mostly 400 watts each. They are easier to hear on the coast, of course, but I have heard them here in Grants Pass about 55 miles inland too.     Dave Aichelman     N7NZH     Grants Pass, Oregon


K7DWI Art
 

Good to hear from you Dave.
For everyone's info..
The dark 1-foot loop ws my first in 1997 from a Monitoring Times article.
The 4-foot loop is a Shawn Axelrop (of Manitoba Canada) design.
The light 1-foot loop is for Longwave, the 3-foot PVC is a re-do of Shawn's design.
The Radio Shack (TECSUN look-a-like) was purchased on sale at RadioShack in 2001 and used on an Alaskan cruise in 2002.
All have served me well.
73 Art KA5DWI