[600MRG] re. Loop Antennas

[david vanhorn]

Re varactor tuning: Problematic, large value varactors are becoming scarce,
and if you're looking to run the loop in transmit other problems come up.
The voltage even on a ferrite rod antenna can easily be 400-500Vpp.  I've
done this, but with switched caps using FETs.


On Mon, Sep 9, 2024 at 3:35 AM david vanhorn <kc6ete at gmail.com> wrote:

> What sort of Q values were you able to achieve with the loop loaded to 50
> ohms?
>
> On Sun, Sep 8, 2024 at 5:01 PM Edward Larsen <ki6rcm98 at gmail.com> wrote:
>
>>    Thanks Dave for the posting regarding loop antennas for VLF.  I like
>> your approach and if your loop is out-performing a good active whip it is
>> certainly working.
>>    I did some loop tests a few years ago.  What I built was:
>> 13 turns of silver plated AWG 22 stranded/teflon, 79" diameter, wires
>> spaced 1/2" and crossed-over at the bottom (mobius wound).
>>    About 725 uH inductance resonated to VLF with 80-1250pF varactor
>> tuning capacitance.  Loop self resonance was about 3.02 MHz.  I used a one
>> turn coupling loop inside which I adjusted for 50 Ohm match.  I've found
>> that a high-Q tunable loop eliminates any overload or intermodulation
>> problems in a receiver.
>>    I left this loop with KI6MTV when I moved to Arizona.  I need to build
>> another.  It would tune about 140 kHz to 650 kHz via vari-cap diode tuning.
>>    I have designed/built a pretty good active amplified ferrite rod
>> antenna for 17.2 kHz.  I can email you the schematic if you like.  It too
>> parallel resonates the high-Q loop for sharp narrow-band tuning.  The
>> circuit could be modified for higher frequencies if desired.
>>    There has been a lot of excellent VLF loop design work in the past by
>> several low frequency Gurus who published in the Lowdown magazine.
>> Unfortunately this data is not available anywhere.  I have most of the old
>> Lowdowns going back to the 1980s.
>>    Keep on experimenting!
>> 73
>> Ed, KI6R
>> SaddleBrooke, Az
>>
>>
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>
>
> --
> K1FZY (WA4TPW) SK  9/29/37-4/13/15
>


-- 
K1FZY (WA4TPW) SK  9/29/37-4/13/15
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