Jims point is well taken. This is one and the precice reason that I stress
one must connect a ground wire from the radio ground terminal to the power
supply ground terminal. DO NOT rely on the power supply negative lead and
associated connectors to be of adequale of low resistance to keep the radio
at zero volt potential.
So to summarize, to connect the radio to the power supply requires three
wires: Positive, Negative, and Ground.
73
Bob, K4TAX
Bonding -12VDC to the chassis causes a problem when powering a SSB rig
that SOUNDS like RFI, but is NOT RFI. W8JI pointed out this problem to me
several years ago. Ohm's Law causes IR drop in both V+ and V- conductors
that varies with SSB modulation. Nothing new. But when V- is bonded to
the chassis, and when audio accessories are running from that same supply,
the modulation of V- is added to the audio. That modulation SOUNDS like
SSB in an AM detector -- it SOUNDS like RFI. But it's not. You can hear
this modulation if you connect headphones between one end and the other of
the V- conductor of your power supply wiring.
I have long advocated bonding chassis to chassis for all equipment in our
ham shacks to minimize problems with hum, buzz, and RFI. This practice
also reduces the above problem to the point where it is not audible. .
73, Jim K9YC
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