[600MRG] re. Loop Antennas

[Tom W8JI]

What are you using for a receiver? What is overloading the receiver?

I haven't used a tuned loop for a  receive-only system since around 
1970.  As a matter of fact I avoid them! I either resistor load my loops 
or directly drive a low noise broadband amplifier with impedances set to 
make the system broad band.

73 Tom

On 9/9/2024 12:10 PM, Dave Riley via 600MRG wrote:
> All the time improvements, yea...
> Now  I think of a loop just made from old corroded silver plated 
> copper tubing..
> Is it really acting like a broadbander or what, silver polish?? Must 
> measure -3db points..
> Having fun anyhow...
>>
>> On 9/9/2024 9:12:13 AM, Edward Larsen <ki6rcm98 at gmail.com> wrote:
>>
>> Measured -3dB bandwidth at 201 khz using a frequency selective level 
>> meter was about 3.22 kHz, thus the Q was about 62.  I used 
>> quantity-10, 1SV149 diodes in a series/parallel arrangement to 
>> achieve a broad tuning range.  If there is a problem with 
>> over-voltage on the diodes during transmit, one might add a T/R relay 
>> to short-out the loop.
>> When you use a high-Q loop like this it is most interesting tuning 
>> the bands since the loop also has to be tuned.  It would be fun to 
>> try to automate loop tuning to match receiver tuning.
>> 73
>> Ed
>>
>> On Mon, Sep 9, 2024 at 2:35 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
>>
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