[Lowfer] How do I....

[Michael Sapp]

J.B.  Toying with an online LC calc, pairing up a 50,000 pf  (50 nf or 
.05uf) capacitor with a 1.8mH coil gets me to 16.77 kHz.

40,000 pf and 1.8mH  gets to 18.75 kHz and 30,000 pf with 1.8 mH gets to 
21.66 kHz.

For a quick experiment here I took 4 meters of 20 gauge speaker wire (close 
spaced zip cord type) and measured about 150pf with my LCR meter
with the wire stretched out on the floor.  Rolled that wire up on the 
plastic cap of a Right Guard can about 3 inches in diameter close wound, and 
the total capacitance
between the two wires of the zip cord increased to  about 190 pf..... an 
increase of 1.267.

    If you have 25 turns at 4 meters per turn my (swag) guess is you have 
something in the ball park range of 150pf x 25 turns x 1.3 to 1.5 for the 
close-wound windings, or

4,875 to 5,625 pf.  Let's call it 5,000 pf.  That seems too small of a 
capacitance value by an order of magnitude for your 25 turn loop to truely 
resonant below 20 kHz......

Just a guess on my part, but it would be interesting to see what adding two 
to four .01uf caps across the loop would accomplish.....with a handful of 
.01 and .005 caps

you may be able to infer where the (fundemental) self resonance is by 
substitution.....there is a chance you may be currently observing a harmonic 
resonance....

With that much capacitance I can see the LC ratio on the loop being rather 
temperature sensitive as well. I had that problem with a tuning network on 
short vertical on 160m ten or so years ago...it wandered all over the place 
with too much C, W1MK straightened me out on that issue.....


Thanks for the single-minded distraction, kinda fun to run through those 
numbers, your mileage could certainly vary tho.....73,  Mike wa3tts



----- Original Message ----- 
From: "John Bruce McCreath" <weazle at hurontel.on.ca>
To: "Discussion of the Lowfer (US, European, &amp; UK) and MedFer bands" 
<lowfer at mailman.qth.net>
Sent: Sunday, February 23, 2014 2:22 PM
Subject: Re: [Lowfer] How do I....


> Here are the results of my testing so far.  I installed SAQrx which 
> provided me a 0 to 22 kHz. spectrum analyser.
> The loop is connected to an 8 ohm to 600 ohm transformer (Hammond 119DA) 
> and on to the mic in jack of the
> laptop PC.  No attempt was made to tune the loop with parallel or series 
> capacitance.
>
> The noise floor seems to be in the -100 to -110 dB range.  Between 2 and 7 
> kHz. there was a "plateau" where
> the noise floor was -90 dB.   With the AF signal generator loosely coupled 
> to the loop, I swept it over the range
> from 2 to 20 kHz. and noted that the signal came up to -30 dB. across the 
> span of 2 to 7 kHz.
>
> I'm next going to try inputing that data into an on-line L-C-F calculator 
> and see if that gives my a rough idea of
> the loop's self capacitance value.  Again, thanks to Bob and Mike for 
> their suggestions.
>
> 73, J.B., VE3EAR
>
> LowFER Beacon "EAR"
> 188.830 kHz. QRSS30
> EN93dr
>
>
>
>
>
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