Since the problem occurs without an antenna connected, it is a version
of the "RF in the shack" problem, although the RF field is coming from
the nearby FM station rather than the classic situation where the
transmitted signal is the source of the RF.
Jim makes some very good suggestions for 'taming' that problem.
It would be very difficult to cure the K3 of the "pin 1" problems.
For those who are not familiar with the "pin 1" problem, that is a
situation where the shields of interconnecting cables are connected to
the circuit boards rather than directly to the outside of the
transceiver enclosure. That allows any pickup on attached cables to be
imposed into the boards of the transceivers. In days of old when we
mounted all connectors to the enclosure rather than to the circuit
boards, the enclosure itself provided a shield for whatever trash was
picked up by the external wiring - because those trash signals would
flow on the 'outside' of the enclosure and not affect the circuits
inside. With modern transceivers where cable jacks are connected to the
ground plane of the circuit boards rather than to the enclosure, the
external signals are coupled to the ground plane of the internal boards,
and will couple the offending signals into the transceiver.
In other words, "board ground plane" does not equal "ground" -
variations in the ground plane reference will cause "funny happenings"
within the interior circuits. In other words, the enclosure does not
offer a sufficient shielding effect for the circuits inside the enclosure.
The K3 is not alone in this problem, it is shared by any transceiver
that does not ground the connectors directly to the enclosure.
73,
Don W3FPR
73,
Don W3FPR
73,
Don W3FPR
On 2/10/2016 6:57 PM, Jim Brown wrote:
Yes, this hit me between the eyes as well. The K3 has Pin One Problems
at many (most?) connectors, so RF current flowing on shields of cables
plugged into those connectors will couple into the K3. I've been
preaching to Wayne about Pin One Problems since 2004, when we met in
Dayton.
If the problem is around 90 MHz, I'd use multiple one-turn and two
turn chokes with #43 material on every cable except the SO239 output,
which IS actually bonded to the chassis. Also choke the power cable.
73, Jim K9YC
On Wed,2/10/2016 2:53 PM, Fred Jensen wrote:
I easily could have misread the original emailed problem, but he
included the note that this RFI occurred with all antennas [and I
guess other cables] disconnected which is very strange indeed. If
that is so, then I doubt stubs/filters on the antenna circuits would
cure the problem.
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