Dear Mal, LF group
A couple of suggestions to try with your loop:
...My loop parallel resonated on 136 khz gives about the same signal/noise
as the vertical, no discernable difference on RX...
This is not surprising in a quiet location, since the band noise will
define the SNR with any reasonable antenna - but the really interesting
experiment to try would be to compare efficiencies using the strength of
received signals, first with the loop, and second with the same antenna set
up as a vertical, ie. with one vertical leg and the bottom leg removed. The
vertical could be tuned with a small loading coil for receive only, wound
on a pot core for example. DCF39 could be used as a reference signal, and
your SPM12 would be ideal for comparing the sig levels.
...If I had a truck load of high grade components, megawatt rated
insulators, capacitors and toroids I would be tempted to try
-But you could try some QRP tests without going to all the trouble of the
full power version. If you really do not want to transmit at all, measuring
the impedance (particularly the resistive component) of the tuned loop with
a bridge would be a very interesting result, especially if it was done at
several different frequencies.
Cheers, Jim Moritz
73 de M0BMU