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Old March 3rd 04, 07:05 AM
Mark Keith
 
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Telamon wrote in message

The shield is electrostatic and would only help against local noise
(example - in the room computer) being the pickup loop.


Yes, And I could tell no real difference from it to a unshielded loop.
This assumes the unshielded loop is fairly well balanced though.

If you had an un-tuned broadband amplified single turn shielded loop
compared to one that was not shielded then you would expect to see a
difference.


I would think so. But so far I don't really see a drastic difference.

Loop antenna is a broad term.
Here are some features:
1. Small or large compared to the received wavelength.


A small loop is directional inline with the windings. A large loop,
broadside to the windings.

2. Shielded or not.


Again, this is debatable as to the effectiveness...I consider it an
option.

3. Single or multi turn and shape type example - pancake or solinoid.


A pancake coil is directional broadside to the loop. A solenoid,
inline with the loop. Or so I've read...So far, almost all of my small
loops are solenoid type. I have thought about planting a big pancake
coil on a door though...

4. Tuned or un-tuned.


All small passive loops should be tuned. At the least, using the self
resonant freq. With the cap, lower in freq...

5. Several ways to couple them to the receiver.


I use normal coupling loops, both shielded, and unshielded as a test.
I see no difference in results..I don't use preamps. Don't need em...

Now you can mix and match the 5 above into many possibilities all with
different tradeoffs.


Thats what I'm doing here, but with not always the results I want...
IE: I made a 45 turn LW loop that I hang up against my usual 16 turn
MW loop. I used the same cap for each loop, by using a switch. It
worked great on both "bands". Didn't mess up the MW loop. So then, I
decided to wind a LW loop on the same frame hoping for the same
results. The LW worked fine, but the MW was detuned. So I just now
ripped all the LW turns back off and will go back to the previous
method with a bit more separation between the windings. I'm rigging
mine up to cover from about 150hz to 2000 hz in two steps. "coils".
This lets me use the same cap for both, and I don't have to tack on
extra fixed caps for LW. But I still want to build some type of
unidirectional rotatable small loop. In messing with the LW loops, I
have discovered something about my radio I hadn't noticed.
"IC-706mk2g". Although it tunes down to 30 cycles, the radio goes
pretty dead below about 150 cycles. Not the greatest LW radio in the
world for real low freq's... It's ok from about 175 hz, up.. MK