James, Sometimes in addition to a noise generator and a PC with a soundcard running Spectrogram you may need to add a 600 ohm 1:1 isolation transformer between the LS output of the K2 and the PC sound card input. Perhaps I was unfortunate in that both my PC and a separate laptop had spikes on the display from harmonics of the AC power frequency. In the UK we use 50Hz AC power so that was present as a very large spike followed by 150Hz and every 100Hz after that through the audio spectrum. With your use of 60Hz AC power in the USA would possibly expect that plus multiples through the audio test range if afflicted. The use of an audio isolation transformer killed these spikes stone dead. Don, W3FPR suggested the audio transformers from scrap PC modem cards as a possible source of suitable 600 ohm transformers. The Spectrogram program turned out to have other uses for me beyond checking K2s. Having done a hurried rebuild on a 2m repeater for a semi local repeater group, when installed on site the through audio was poor and sounded muffled. With the aid of a VHF noise generator plus my laptop running Spectrogram was able to follow the audio through from the repeater RX audio output, through the logic and right up to the TX modulator. Apart from the normal RX de-emphasis and the blocking of the audio below 300Hz in the logic to remove the incoming CTCSS, the audio was correct right the way through the system. The problem in the end turned out to be the TX modulation pre-emphasis was not functioning. No doubt there are many other uses for the Spectrogram program, but on this occasion saved me a lot of time in fault finding on the repeater. Bob, G3VVT _______________________________________________ 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
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