[Yaesu] FT-900 with 'motorboat' audio on SSB

[David Willmore]

> Hello, all.  Long time reader, infrequent poster. :)
> 
> I have an FT-900 which I bought from my elmer a long time back with the
> intention of using it as a general coverage receiver--I was a no-code
> tech at the time and had no HF TX privledges.  So, it's served that role
> just fine for a long time.  Now, I've upgraded and I'm trying to use it
> as an actual tranceiver.  But, I've got a problem.  When I put a receiver
> next to it, and transmit in SSB, I have an odd modulation on top of my
> voice.  It sounds like a 5-10Hz or so AM modulation--sort of a wavering.
> I'm going to run the RX into a spectrum plot so I can better see what
> the issue is, but I'm stumped as to what may cause this problem.
> 
> I tried FM and AM modulations and they work fine.  That may help to
> eliminate possible causes.
> 
> Does anyone have an idea what may be the issue and/or what I should
> do to further diagnose the problem?

More info.  I got a chance to see the TX spectrum.  Hooked the receiver
to the computer and ran 'baudline' on the computer.  Here's what I saw:
http://www.w2zq.com/n0ymv-full.png

So, that's a CW note that's supposed to be a nice pure tone at or about
700Hz.  As you can see, it brought company.  Looks like 12Hz spacking.
The waterfall and the instantanious spectra are from 0 to 3KHz, so you
can interpolate as necessary.

Further playing shows that the modulation *does happen in all modes*,
including FM and AM--earlier tests were in err.

Time to crack it open and start poking around.

Cheers,
David n0ymv