In a message dated 24/01/05 02:07:20 GMT Standard Time, [EMAIL PROTECTED] writes:
Problem found. I added a fixed audio out port to the K2. Disconnecting the wire to the sound card stopped the modulation. An audio transformer in line also eliminated the problem. -------------------------------------------------------------- A similar solution was of value in clearing up my problems in using Spectrogram. I was getting spikes on the Spectrogram display at 50Hz (our power freq) and every 100Hz from 150Hz upwards. This was believed to be due to my PC having a power line filter installed to clear hash from the PC switch mode PSU and this left the PC case floating above ground at RF. Series capacitors had no effect, where a transformer placed in the audio path completely cured the problem. Used a miniature audio transistor interstage transformer for the purpose with the higher impedance side to the PC sound card. Would guess a transistor output transformer with the usual 1.2K to 4 ohms windings may have been even more suitable, but did not have one in the junk box. The only proviso in going down this path is to use a transformer that has a response well below 300Hz and 50 Hz if possible to ensure correct placement point of the BFO is seen. A totally different problem, though in the end with the same solution. Bob, G3VVT _______________________________________________ Elecraft mailing list Post to: [email protected] 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
