Hi Reg,

Didn't know you monitored here!



The normal 5 or 10 percent tolerance means that you will have to
measure and select values from a larger batch of inexpensive
capacitors.

Don't forget you will have to select from a small number of standard
values such as 0.22, 0.1, 0.047, 0.033, etc.


I've ordered a good supply of polystyrene caps in the standard values.
I also have an RCL meter, which is cheap and not accurate, but I can
measure the actual value of the caps I get from Mouser and assemble
them to hit the target frequency pretty easily. So, I'm actually
hoping the values they send are somewhat dispersed from the marked
values.


Specially manufactured close tolerance capacitors will cost the Earth.

Temperature coefficients don't matter very much but if you have a
choice then select those with the lowest coefficient. But TC is seldom
specified by manufacturers. You would need a very good capacitance
bridge to measure the small TCs involved although it is easy to make
TC measurements.

I learned about TC in the WB4VVF Accukeyer days when I was much
younger and foolish. I built one, it worked great. But, I used a disc
ceramic cap for the clock speed generator. I could actually detect the
keyer changing speed as I sent cw, which I assumed was due to the TC
of the disc ceramic. Touching a soldering iron to the outside of the
cap drove the keyer speed wild. Anyway, I learned my lesson about
disk ceramic caps the hard way and didn't want to repeat the error 25
years later by using a cap that didn't have a good temco.


To reduce size of the capacitor just increase the number of coil
turns. You will notice little or no difference in operation.

The most efficient loop has a single turn of very thick wire.

Which is exactly what I intend to do! I had a choice between large
copper welding cable and 3 inch copper pipe. I chose the welding cable
because it was actually cheaper although I'm not sure which would have
the best Q.

The ONLY reason for multiple coil turns at VLF is to avoid impractical
values of capacitance. Receiving sensitivity does not depend on the
number of turns, only on the area enclosed by the loop.

A change in the number of coil turns involves only a change in how the
loop is Z-matched to the receiver. With a single-turn coupling loop
no changes are needed.


Actually, I have a receiver with a 2 ohm input impedance Reg. So, it
can be fed directly from the series tuned loop. My only selectivity in
the front end of the receiver will be the loop tuning, so Q is
important.

The receiver is small and draws low power, so I am going to locate the
receiver at the antenna and feed the audio to teh house with common
mode audio transformers...thus avoiding the chance to conduct
household noise from the house to the receiver through the connecting
cable.

You may find program RJELOOP3 useful. It covers multi-turn square
loops and other regular shapes of the same enclosed area.

Download program from website below in a few seconds and run
immediately.

Already got RJELOOP3 and love it Reg. It has helped immensely and
saved me so much time because it allows me to evaluate how good
antennas will work without having to assemble them! Thanks for making
the software available.

GL.

T

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