On 11/5/2014 8:29 PM, Jeff Liebermann wrote:
Incidentally, I don't believe using a high impedance loop and amp are
good ideas. While there are benefits, my experiences from the marine
radio biz convinced me that high voltage is an invitation to problems
from condensation, salt fog, and PCB leakage. In other words, it
works on the bench, but craps out in the field. I'll probably end up
with a large high Q loop, and a separate low-Z coupling loop (i.e. a
step down xformer).

Not sure why you can't discuss this in the right thread of this group.
I've posted my reply to your post in the loop antenna thread.

First, I'm not sure what you are talking about connecting high impedance
antennas to condensation and salt fog. If you are transmitting, then
maybe you could get such high voltages as to attract microscopic
objects, but this is a receiver design.

Also, the antenna is not high impedance, just the input to the receiver.
The transformer I am looking at is a high turns ratio current sensor.
It spans the right frequency range and is a nice compact package easy
to mount on a PCB.

My main concern is lowering the Q because of the loading from the
receiver input, especially with the change in impedance as reflected
through the transformer. I think when I simulated it, I found the max
signal strength came with a 25 or 33:1 turns ratio because with higher
turns ratios the Q was spoiled enough to bring the voltage down at the
receiver input.

This simulation didn't include the effect of the radiation resistance,
so I will need to add that in. I expect this will lower the Q as a
starting point which means the affect from the receiver input loading
will not be as significant, possibly making a higher turns ratio in the
transformer more useful.

--

Rick