Hi All, Bernt mentioned about coupling between an RX loop and a wire aerial
loading coil. I believe it does not have to be the loading coil and an
inverted 'L' ,for instance, can act as a one turn coupling loop, coupling
signal into a small multiturn loop, even with the loading coil orthoganal to
the RX loop. I have not tried turning the loop at right angles to the plane
of the 'L' though. Disconnecting the wire from ground, or the Rx, returns
the normal response of the loop.
One question (am I being silly ??) but if you match a loop by tapping the
feeder into it, or using a coupling loop, are you not loosing 3dB of the
signal? I suppose this only matters if you don't have more aerial noise
than the front end in the RX. I use a similar preamp to Tony, but a single
ended one, that puts the FET gate directly across the tuned loop with no
bias resistors. Then the coax is fed from an emitter follower. Although the
gain on mine is too much I do get a useful advantage on very weak signals.
This is probably because the Q is relatively low ( around 50) because of the
thin multipath telephone cable used.
On the noise front, I find I can detect a 10nV (in normal band noise, but
with local QRM off) in the 0.3Hz bandwidth of Spectrogram. I do not have a
stable enough source to measure this in the bandwidths that John and Laurie
are using with Argo. I now have a DDS source to play with, so that may
change.
Cheers de Alan G3NYK
[email protected]
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