I've also tried a MFJ TNC switch. Both for digital mode and microphone
switching. When I use these devices I get interference when in mic
mode from
rf pickup. With the mic alone., no problem.
In addition to Don's advice, I'll add this. Most electronic boxes have
Pin One Problems, and that very likely includes all that you're trying
to interconnect. I suggest dumping the TNC switch and instead make a
cable that goes from your Rigblaster to the K2 mic input, with shields
connected to the CHASSIS of the K2. Build a simple 10:1 (-20dB) voltage
divider as described in the link that Don gave you. It's often possible
to put that inside the connectors -- it's a series R and a parallel R. I
often put the series R in the connector for the driving box, and the
parallel R in the mic connector.
If the bonding described in the link doesn't solve your problems, add a
multi-turn ferrite choke to both of the cables between the K2 and the
computer, and also to the cable connecting the Rigblaster to the
computer. 5 turns through a typical #31 or #43 clamp-on is about right
for 40M - 10M.
We have these problems because the guys who design ham gear and consumer
gear and computer gear know nothing about RFI, and they ignore the
advice of the audio engineers who discovered "The Pin One Problem" more
than 20 years ago. The logic appears to be "audio is only 20-20,000 Hz,
those guys can't possibly know as much about EE as we do -- our stuff
goes to GHz!"
FWIW, I have no use for the dedicated ham interface boxes no matter
whose name is on them -- the wiring interface for the ones I've seen are
an invitation to RFI and hum/buzz problems, and most have Pin One
Problems. A very good USB sound card can be bought for $70 (see the ASUS
U5 Zonar), You can build a WinKey for about $75, or the Yankee Clipper
SO2R box for about twice that cost. A serial to serial cable is two
connectors and some CAT5. Serial to USB adapters are inexpensive.
There are several tutorials on The Pin One Problem on my website.
73, Jim K9YC
Vice-Chair AES Standards Committee Working Group on EMC
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