a P.S. on my previous post and a reply to Kevin


sloshatron <wa1gwh@...>
 

I forgot to mention a few things on my previous post. They bubbled
up later as I was doing yard work!

My basket weave coil is about 4.1" diameter and 1.2" in length. So
it is "loop-like". I think that a longer and narrower solenoidal
coil will work more poorly as an antenna. Thought I should mention
this in case anyone throws something together to fool around with.

I was thinking of the spider web type coil because the turns count
could be easily manipulated for alignment purposes. I think it would
be easier to unwind a portion of a turn off the broad flat spokes of
a plastic form than from a solenoidal type loop. I wonder if the
wire unwound could be left intact (if short) for an iteration or two
until the "ballpark" is found. Then wire cutting could happen. Off
the coil its inductance would be fairly low at 600 kHz.

I think it was John who furnished the nice one-pager on the SRF stock
ferrite bar coil complete with measurements of inductance (+/- 580
uH). Does anyone know how much it is possible to vary the inductance
by sliding the smaller winding across the customary range that is
used in alignment? That would give an indication of how much an air
core loop would have to be varied during alignment.

Kevin;

Interesting situation on the MW vs LW windings used with the same
variable. I know that more turns and less C create a higher voltage
at the loop terminals. This is handy with crystal set loops because
the higher performance diodes will work more efficiently with higher
voltage. But I think this should not make any difference with a
magnetically coupled arrangement like you describe. In fact, if the
wire sizes for both windings are the same and the windings are the
same size I would think that the shorter winding would be superior
because the total copper losses would be lower in the shorter length
of wire. And, the capacitor would be used at a higher value to
resonate the pair at the same frequency. Unless the capacitor is a
high quality one (ceramic insulators, no corrosion at joints) it will
have a higher Q at higher capacity settings. This idea is (once
again!) from a Ben Tongue paper where he documented that a small
receiver type phenolic insulated variable had lower losses at higher
settings of C.

I suspect that having two loops on one frame might be the answer to
this situation. I believe that unused windings and tapped windings
are usually avoided in constructing high performance loops. Guess it
depends on convenience and what is desired for efficiency.

How big is your box loop? My current crystal set is a 3' x 3' box
loop of #14 bare solid wire. In the last listening contest in
January I logged about 90 stations with it in a week or so. I don't
use a spotter radio -- I like to do it all with the crystal set.
Just nuts I guess. Ought to fit in well here!

Garry
near Syracuse, NY


dhsatyadhana <satya@...>
 

Hey Garry:

Interesting! I don't know enough ferrite-core antennae, although in
a way the idea of less turns the better makes sense, in that large
ferrite rods with smaller lengths of wire have more gain than the
tiny ferrites, which must put on more turns to get enough
inductance. In your scenario, might there there still be more gain
by laying on a few more turns of wire, in that the additional turns
would more than make up for their copper losses?

I have a 28" x 42" box loop (essentially a slightly-squashed three
footer), with 10 turns of 16 gauge for 540-1700+ khz and an
additional 17 turns for 150-700 khz. I use two DPDT switches to make
it work, along with a 3-gang (15-450 pf per section w/ceramic posts)
cap. Putting my Quantum Loop in the middle of it makes for some
incredible gain or passive phasing, depending on the circumstances.
I have noticed that, on MW, I have to short out the LW coil in order
to prevent it from de-Qing the MW coil and adding unwanted
inductance.



Kevin


--- In ultralightdx@yahoogroups.com, "sloshatron" <wa1gwh@...> wrote:
Kevin;

Interesting situation on the MW vs LW windings used with the same
variable. I know that more turns and less C create a higher
voltage
at the loop terminals. This is handy with crystal set loops
because
the higher performance diodes will work more efficiently with
higher
voltage. But I think this should not make any difference with a
magnetically coupled arrangement like you describe. In fact, if
the
wire sizes for both windings are the same and the windings are the
same size I would think that the shorter winding would be superior
because the total copper losses would be lower in the shorter
length
of wire. And, the capacitor would be used at a higher value to
resonate the pair at the same frequency. Unless the capacitor is a
high quality one (ceramic insulators, no corrosion at joints) it
will
have a higher Q at higher capacity settings. This idea is (once
again!) from a Ben Tongue paper where he documented that a small
receiver type phenolic insulated variable had lower losses at
higher
settings of C.

I suspect that having two loops on one frame might be the answer to
this situation. I believe that unused windings and tapped windings
are usually avoided in constructing high performance loops. Guess
it
depends on convenience and what is desired for efficiency.

How big is your box loop? My current crystal set is a 3' x 3' box
loop of #14 bare solid wire. In the last listening contest in
January I logged about 90 stations with it in a week or so. I
don't
use a spotter radio -- I like to do it all with the crystal set.
Just nuts I guess. Ought to fit in well here!

Garry
near Syracuse, NY


Peter Tankard <peter.tankard@...>
 

AVERY big hi from peter tankard in sheffield south yorkshire in the UK. I have just jound the Ultralight dx gruop.I find MW LW dexing very xsiting I have head meny local radio stations on mw am from the US on my 1970 grundig yacht boy model 210 and I have been a mw lw dexer sins 1976.I am at the momont trying to find some half inch ferrite rods that are half inch 12.7mm in diameter and or six inches long or more with hi Q for the mw lw band I have got meny ads in the radio magaseens in the uk for the half inch ferrite rods but I do not seem to have eny look in finding eny at all and when I do get some thay are awase the rong permability for the mw lw band back in the 198s I had some half inch ferrite that had very hi Q on the mw lw band I put two six inch long half inch ferrite rods toghter and made one 12 inch long rod and it was as good as using a mw fram aril But the shop were I bout the half inch rods from is no more The rod that I had worked in eny mw lw radio with the radios oun mw lw cails I did not have to change the mw lw cails at all in eny of the radios that I put it in. in some radios that I put the half inch rod in the Q was so HI the it overloded the frunt end of the radio on strong local stations and made very week distant stations sound very good and clear.I have tryed amedon in the us I even sent them a sampul of the half inch rod I was looking for but thay said that thay could not help me but thay did send back my sampul of half inch rod to me.I will pay very good money for some half inch ferrite rods that have got a very HI Q for the mw lw band.Very Best regards from peter tankard my user name is (ferriterodman)