Steve says:
"I have had good results with an ordinary (unbalanced) air-core loop of 10'
diameter. Nulls are approaching 50 db on groundwave signals. The loop uses
a
standard single-turn pickup loop out to the rx via 50 ohm coax. I agree
with
Jan that a preamp is of no value once your limiting noise floor is
background sky/atmospheric noise".
Jan says:
"As long as the background noise without pre-amplifier is 10-20dB above the
background band
noise it is totally vaste to use a pre-amplifier, it may only worsening the
result
I already agree to the balance, but using a balanced amplifier for a
balanced
antenna is only amateur nonsense."
I'm guessing that the only problem we have here is the terminology. Steve
says his loop is unbalanced. I would call it 'floating' since the connection
to the receiver is an isolated single-turn pickup coil. If he were to
connect one side of the main loop winding to the coax shield it would become
unbalanced and the performance would be degraded considerably.
If the loop is a single winding center-tapped design, a balanced amplifier
having three input connections, a +, -, and a common is needed. Call it a
differential amplifier if you would like.
At my base situation an amplifier is required because I do NOT have the
'10db above background' condition, identified above, for my weakest signals.
The problem is that there are large 60Hz plus harmonics (buzzz), currents in
the ground that my 200ft coax lead-in picks up. I'm thinking of trying a
balanced line (oops, here we go again <G>) per John Andrew's suggestion, in
order to eliminate this pickup ......so the need for the amplifier goes
away.
Bill A
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