On 8/9/2022 8:48 PM, Steve Dyer via RFI wrote:
The IC-7610 group on groups.io is a good place to search for this very
issue. The 7610 does appear to be ultra sensitive to any RF present at
the USB port from some of the posts I've seen.
Probably the classic "Pin One Problem" -- the connector shell is not
bonded to the chassis at the point of entry, which is a VERY well known
cause of hum, buzz, and RFI. The mechanism is that interconnecting
cables act as receiving antennas, the current on the cable shield
wanders around the circuit board until it finally gets to the chassis,
creating voltage drops along the way that couple to the input of a
nearby gain stage or logic input.
This was first documented by a ham working in pro audio, Neil Muncy,
W3WJE (SK). It got its name because Pin One in the XLR connectors used
for shielded twisted pair in pro audio is the designated shield contact.
He was elected a Fellow of the Audio Engineering Society partly on the
basis of this work (but he did a LOT more important things).
When Neil published his paper exposing Pin One, nearly every piece of
equipment in hundreds of booths on a very large convention floor was
built with Pin One Problems. Ten years later, few pieces of pro audio
gear had Pin One Problem. In 2003, I published an AES Paper documenting
the Pin One Problem in very expensive condenser microphones from a major
German microphone company that caused RFI from the TV and FM
transmitters in downtown Chicago.
At ham conventions, I visit all the booths checking for Pin One
Problems. EVERY radio I have checked (ALL the major brands) had a Pin
One Problem at most if not all of their accessory connectors.
There are several good solutions, and they can be used in combination.
1) Chassis-to-chassis bonding between every piece of equipment that's
part of your station. This is good engineering practice anyway, both for
electrical shock and lightning protection. Bonding should follow the
direct route of the interconnections. The chassis of laptops can USUALLY
be accessed at the shell of a D-connector.
2) Use a serious transmitting choke at the feedpoint of every antenna,
including end-fed wires that end in the shack. This prevents the
antenna's return current from flowing on the cable shield. Also, be sure
to provide an effective counterpoise or radials to carry the return
current.
3) Bond all coax shields to ground where they enter the shack, and
extend that ground to the shack. Again, this is all part of proper
bonding for safety.
4) Wind five turns of every cable connected to the victim equipment
through a 1-in long #31 Fair-Rite clamp-on. Any one with i.d. sufficient
to hold the winding will work. Wind the turns in order around the core
(that is, NOT "scramble wound"). Turns that cross-over each other
cancel. With ferrite chokes, the number of turns is the number of times
the cable passes THROUGH the connector. Alternatively, use my 2018
Transmitting Choke Cookbook as a starting point for winding on #31
2.4-in i.d. toroids. k9yc.com/publish.htm
73, Jim K9YC
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