[Lowfer] New Loop NG

[Lyle Koehler]

With regard to my "universal" preamp: In the low-Z position, the input
circuit is essentially a 4.7 mH choke in series with a tuning capacitor. If
the choke Q is on the order of 100, it will have a series resistance of
about 50 ohms at resonance, and that will be the input impedance of the
preamp.

When used in combination with a series-tuned loop, the preamp and loop
behave as two tightly-coupled tuned circuits, so they are likely to exhibit
some strange tuning behavior. However, the combination works just fine, as
long as you're not concerned about the apparent broad tuning of the loop.
And as I understand it, Peter was not using the preamp with the loop when he
made his observations.

Several years ago I used a 4-foot series-tuned loop in the woodshed, with
the "universal" preamp in the shack, to copy BPSK signals from California
LowFER "HDO" at a distance of 1600 miles. There was a run of about 100 feet
of coax between the loop and the preamp.

I agree with John Andrews' observation that a preamp is necessary when using
a small loop for receiving, no matter what kind of coupling or tuning
network it has!

Lyle, K0LR