I've recently gotten Writelog / Soundblaster
working with an FT1000MP on SSB. Here's what I did to get it
working well:
1) The microphone input sensitivity on the
Soundblaster is not very good. It's a lot less sensitive
than the microphone input on an FT1000MP (and likely the
same on the Kenwood).
2) The microphone and phone-patch inputs to the
radio are very sensitive to hum and digital noise in the
computer. I built an isolation transformer for the radio,
it did get rid of some very low-level digital noise, but
did not improve the hum and noise at all. I took great care
to properly shield the transformer, avoid ground loops, etc.
3) Setting of the soundblaster input and output levels
required lots of gain so that the microphone would modulate the
radio. Then I had to set the gain of the WAVE files from the
computer way down to avoid overloading the radio when the
computer "speaks". With a WAV editor, I can see that the mic
doesn't generate very much audio as recorded in the WAV file.
Using a WAV editor, the level can be easily adjusted, however.
The solution to the problem was to build a 30 dB
microphone amplifier. I power this with a 9V battery, and put
RFI fltering on the inputs and outputs. This allows the
microphone to properly drive the soundblaster mic input. This
gets all the levels in the SB card about equal. Then, the SB
levels can be setup properly - with the SB output level set
rather high, and the mic gain on the radio set very low. Now
the noise, hum, etc. that get into the radio are hardly
amplified at all, and the much higher levels from the soundcard
sound quite good. I got excellent audio quality reports all
through the last two contests. The RFI shielding is quite
effective as a 1.5 KW amplifier is about 1 foot away and has
no effect on the mic-amplifier.
Ultimately did not use the isolation transformer, just
ran the SB output to the mic input of the radio, and the
headset microphone through the mic-amp to the SB mic input.
Writelog does all the audio switching auto-magically.
-- Tom, N5EG
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