One of questions frequently asked by those who have built my Z90
panadapter kit and use it with a K2 is "what is that blip that I see
even with the antenna disconnected?"
It is the BFO leaking backwards through the IF chain back to the
post-mixer amplifier output. From what I've learned from my customers,
it's present in all K2s, and seems to vary from K2 to K2 about 10 dB or
so in level. With the receiver input connected to a dummy load or the
antenna disconnected, it's visible with a Z90 connected to my K2 at
about 25 dB above the noise level, and this level seems to be typical
of my customers observations.
With an antenna connected, particularly on the lower bands, enough noise
is received to mostly hide the BFO leakage signal on the Z90 panadapter.
You can see my measured BFO leakage data at
http://www.cliftonlaboratories.com/k2_interface.htm. This page also
discusses the probably leakage path and estimates the expected leakage
level, based on the reverse isolation of the amplifiers in question.
Jack K8ZOA
www.cliftonlaboratories.com
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