"Richard Clark" wrote -

Try googling the archives to see he does more than monitor.

Richard,

I'm a little surprised you have time to spy on my activities. I trust
you are not a spare-time member of the CIA which appears to take an
interest in most things which go on on this planet. By the way, your
use of the English Language has recently improved. I have been able to
understand better what you are talking about.

But your concern about Effective Series Resistance (ESR) of the tuning
capacitors in connection with VLF tuned loops is a bit overdone.
Remembering Lord Kelvin, let's crudely quantify things.

All we have to go on is Trabem's value of the tuning capacitor of 0.2
uF.

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.

Therefore we have L = 31 microHenrys, Reactance at 60 KHz = 12 ohms,
and RF resistance 0.23 ohms.

From which the intrinsic Q of the loop inductance = 50.

Assume the tuning capacitor is comprised of ten 0.02 uF capacitors in
parallel. The resistance of 10 capacitor leads in parallel is
negligible in comparison with the loop's single-turn conductor RF
resistance of 0.23 ohms.

He, Trabem, will be obliged to use a bundle of capacitors to make an
EXACT value for the tuning capacitor because of the impossibiltity of
obtaining a single capacitor of exactly the correct value, at a
particular temerature, and of sufficient long-term stability. He
can't afford it!

Immediately, the ESR of a 0.02 uF capacitor, whatever it is, is
divided by 10. Yes, I know that the ESR of a capacitor at 60 KHz
involves a little more than lead resistance. But it's too small for an
American General Radio bridge to accurately measure it.

But to return to Earth, the working Q of the 5-metre-per-side loop is
a function of the sum of the conductor resistance, plus the small ESR,
plus the radiation resistance (which is also negligible), PLUS the
loss resistance due interaction of the loop with its environment.

Unless the loop is removed from ground and other foreign structures by
at least 1/3 of its diameter the losses due to its environment will
greatly exeed all other losses.

If the environmental loss is equal only to conductor resistance loss,
the working Q of the loop will be reduced to 25.

With a Q of 25 the bandwidth will be of the order of 60/25 = 2.4 KHz,
or enough to accommodate an audio SSB transmission.

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.

It's surprising what can be gleaned from a knowledge only of the value
of the proposed tuning capacitor.

Its all guesswork of course.

Incidentally, if Trabem obtains batchea of nominally identical value
capacitors, he will probably find they are all on the same side of the
tolerance. They probably all came from the same production line and
machine settings. Production values are not distributed at random.
This can seriously handicap his choice of particalar values to make up
the total of 0.2 uF.
----
Regards, Reg, G4FGQ.