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Old October 24th 05, 11:03 PM
TRABEM
 
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Default HIGH Q CAPS FOR VLF LOOP ANTENNA?



Therefore the size of his loop is a square of sides = 5 metres. Total
length of wire = 20 metres. Or somehing similar.

Assume the wire diameter is a conservative thick 2mm.


Assume nothing Reg.

The loop is indeed 5M per side.

But, it is however made out or 2/0 copper cable used for arc welding.

I got a good deal on it. It has many many fine strands, never bothered
to count them or to measure the diameter of the individual strands.

But, suffice it to say that it is much larger than 2 mm.

I'm hoping for a Q of 600 at 60 Khz.

I looked at 3 inch copper pipe, couldn't estimate which had the better
ac resistance, so I went with the welding cable rather than the large
copper pipe.



And getting down to practicalities, this means that the 0.2 uF tuning
capacitor has to be adjusted to an accuracy of about 0.3 percent, or
within a few hundred pF.

That is why I suggested a 2000 pF variable capacitor be included in
the bunch. A 2000 pF variable capacitor consists of an old fashioned
4-gang, 500 pF, receiving-type capacitor with all sections connected
in parallel.

As the loop is to be installed outdoors (with 5 metre sides it HAS to
be) the variable 2000 pF component might be useful to re-tuning it
between summer and winter temperature variations.


I have some 365 pF air variables I planned to use one for fine tuning
the loop.

There will be no ssb reception. Generally I'm interested in 6 to 10 Hz
wide channels at 185.3 Khz and in the 137 KHz ham band.

Fortunately, I have a DDS with a tcxo, so I can spot the frequencies I
want to listen on and then tweek the loop with the variable cap.

Regards,

T
 
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