[Lowfer] Isolation Transformers

[Peter Barick]

>>> lyle@mlecmn.net 08/19/02 09:11AM >>>
>I'm not sure if isolation transformers alone will do a lot of good
when you
still have a DC path to the antenna via the power and tuning lines.
With a
good ground system at the antenna site, it's likely that a combination
of
isolation transformers on the coax, and chokes in both the power and
ground
lines would be effective in reducing the conducted noise from the
shack.
>
Yes, in an 10-84 dated article I have, by A.J. Cawthorne, for a
remotely tuned receiving loop, it uses two 33 mH chokes per balanced
feed in a common signals/control lines configuration. These are signal
bypassed for loop reception, however.

>The
chokes could be something like 1 mH on MF; larger on LF if you can
tolerate
the DC resistance. It's important to stay below the self-resonant
frequency.
There should also be isolation in the tuning line. Since the tuning
circuit
is usually high impedance, you can put a big resistor like 100k in
series.

>Lyle, K0LR

Cawthorne's power source for the varactor, in this instance, was a 9V
bat. in the shack.

He also employed loop feeders of coax grounded at the rx end. I think
John Andrews and possibly others on the LowFER net described this
technique.

So then the question: If using Lyle's balanced rx-loop approach which
allows loop-located grounding at the center, should the coax feeder/s be
ground connected at the loop, the rx, or both [I think not the latter,
but... .] ?

The URL was carcanada.net/dx/rtl.html.

Peter