On Sat,12/20/2014 4:57 PM, Alan wrote:
Perhaps the problem is due to noise on the computer ground. The PX3
has differential amplifiers at the I/Q inputs.
Why? It's an unbalanced interface!
For the computer-based panadapter, it might help to connect the
grounds of the computer audio input connectors to the KX3 ground with
a short, large-diameter wire.
PLEASE study my tutorial on Bonding, previously linked. What should be
bonded are the CHASSIS of all the interconnected equipment.
Another possible solution would be to use audio isolation transformers
on the I and Q signals to isolate the grounds. That will cause a
notch in the panadapter response. The notch width will be twice the
transformers' low-frequency cutoff frequency.
This is smelling VERY much like Pin One Problems. The KX3 has Pin One
Problems at the connectors not screwed down to the chassis. The only
connectors screwed down to the chassis are mic connector and the BNC
antenna connector. On the PX3, two of the I/O connectors are not screwed
down to the chassis. THESE ARE PIN ONE PROBLEMS.
The ONLY proper connection point for a cable shield the is shielding
enclosure. When a cable shield is insulated from the shielding enclosure
and goes through an enclosure penetration to the circuit board, that
cable, and that equipment are UNSHIELDED, and the cable shield conducts
shield current into the equipment.
PLEASE study my material on The Pin One Problem. Many users would be
spared a lot of grief if gear was built without Pin One Problems.
k9yc.com/publish.htm
And please excuse my frustration about this. Thanks to the late Neil
Muncy, W3WJE, we discovered and fixed our Pin One Problems in the pro
audio world back in 1994. Ham gear is full of Pin One Problems, and I've
been trying to teach ham manufacturers about this issue for ten years. I
first discussed this with Wayne in Dayton in 2004 or 2005. It's almost
2015, and Elecraft products are still being built with Pin One Problems.
73, Jim K9YC
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