The other day I was in a QSO when the other operator mentioned seeing what he called hum bars on my transmission. It seemed stranged at the time but I did back off on the Tx audio a bit and he said it was better.
A couple of days later I was trying to work to the North East and the FT-857 would not key. (I was running digital VOX.) Knowing that I had not changed the Tx Audio levels since the previous session, I started testing. The radio would key when I changed the PTT logic to the CAT but it was extremely insensitive when set to digital VOX. That seemed a bit strange so I pulled the Tx audio connector and plugged in my headset. What to my wondering ears did appear but a harsh low pitched growl when I started to transmit.
I switched DM780 to the internal soundcard to verify that it was a soundcard problem not a computer problem. It was the external soundcard so I am now off the air waiting for my new Signalink USB to arrive.Hopefully it will be here Thursday of Friday so I can get back on the air this weekend.
Late last summer when I was having computer and radio problems, a station in South Carolina mentioned that I was driving the Tx audio a bit hard because he could see distortion on the waterfall. There was a noticeable but faint set of tracks ... not nearly as bad as some of the Cuban stations but still noticeable. At that time I dialed back on the audio going to the TS-2000 and he said it cleared up - Mostly. At that time I did not recognize a sound card problem...I monitored the audio with my headset but did not notice any distortion. I my mind the external soundcard I have used for several years was degraded and continuing to fail but I did not notice it.
So now I wonder how is the best way to actually monitor the output signal of the soundcard - really, how to monitor the IMD of the radio/souncard combo. I am open to suggestions, not all Digital Mode software supports IMD measurement and in most instances it really is only a measure of the Rx audio path from the receiver to the waterfall and is subject to significant overdrive in the audio and DSP chain.
If anyone has a good recommendation - I am willing to try it.
73 de ND2E/Joe
