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Old August 21st 03, 12:58 PM
Stephan Grossklass
 
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Bob D schrieb:

Have not tried a small AM/MW loop antenna.

What I'm puzzeled by is that my Panasonic RF-B65 and GE Superadio do not
experience this same problem. Is there and explanation for that?


Yup, rather poor image rejection... one of the few non-minor flaws of
the design. As suspected, the 7600G/GR uses a 2nd IF of 455 kHz, and the
images of that are not rejected as much as would be desirable (my
guesstimate for the 7600G: ~40 dB, probably a few dBs higher since I was
comparing the audio S/N by hearing and fiddling the the attenuator, but
that's still not much). Probably the filtering on 1st IF level (55.845
MHz) isn't great. Images have mainly been annoying me on 60 and 20
meters. To confirm the image theory, tune away 1 kHz or so from the
nominal frequency - you should get a noticeable het. This is because
images behave differently from real stations: If you tune 1 kHz upwards,
a real station will be 1 kHz lower (of course), while an image will be 1
kHz higher. A selective tuneable MW loop would probably help here.

Stephan
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