Thanks Lee. What you've described is a classic example of a "pin 1 problem," and your solution was a good one. That is, you gave the cable shield a good RF path to the chassis and removed the path to the circuit board. The cap from the hot to ground MAY have mattered, but I'd guess a lot less than you think.
73, Jim K9YC On Mon, 18 Aug 2008 12:03:29 -0700, Lee Sawkins wrote: >Hi Bob. >I am not subscribed to the list, so I cannot post there. >I had exactly the same problem as you with my DX Doubler. Going through >the box, RF feedback. Going direct, no feedback. >The main difference between these two methods of connecting the mike was >that the DX Doubler had small capacitors to its circuit board from both >the mike hot and ground lines. I clipped one lead of each cap on the >top of the circuit board to remove them from these lines. I only >clipped one lead in case I wanted to re-install them. This cleared up >almost all of the problem. A small capacitor (.001) across the mike and >ground lines at the connector of the K3 completely elimated the problem, >even when running a TL922 amp with my K3. >The problem appears to be that the small bypass caps inside the DX >Doubler are coupling RF "into" the mike leads rather than getting it >out! >73 Lee VE7CC >>Unfortunately, I was not able to go full SO2R with my new microHAM MK2R SO2R >>box and N1MM DVK because of RF feedback getting into the audio lines. I had >>the same problem with my DXdoubler, so I know it is not the microHAM box, >>but something in my setup is causing a hollow echo distortion effect in my >>headphones even though it is not too bad on the air according to reports. >>When I plug the headset directly into the K3, no problems at all. I've >>got to figure this problem out so I can use all this fancy gear. ;-) >No virus found in this incoming message. >Checked by AVG - http://www.avg.com >Version: 8.0.138 / Virus Database: 270.6.5/1618 - Release Date: 8/18/2008 6:51 AM _______________________________________________ Elecraft mailing list Post to: Elecraft@mailman.qth.net You must be a subscriber to post to the list. Subscriber Info (Addr. Change, sub, unsub etc.): http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/subscribers.htm Elecraft web page: http://www.elecraft.com
