[Moon-net] Ts-2000 fan chirp

[richard allen]

When testing my new ts-2000x on some 437 MHz cw satellite signals I
noticed some frequency variations that were abnormal. My concerns are
how well this radio would perform on various weak-signal modes where
good calibration and stability is important.  

I was tracking several satellites and correcting for Doppler shift.
When all is working correctly and the frequencies and Keplerian elements
are correct this will produce a  fairly straight line down my waterfall
display.  When I saw these abnormalities, I fired  up my z3801
oscillator and fed it into the ts-2000 first listening to the 128th
harmonic  of the 10 MHz output.  The radio was tuned in upper sideband
to 1279.999000 MHz which would yield a beat note of 1000 Hz.  I was glad
to see that the radio was only about 150 Hz off but over time I noticed
a cyclical frequency variation with about a 20 minute period.

The first thought was that the z3801 had not yet stablised but after
doing a new survey and waiting for all to settle down, the signal was
still varying.  After monitoring for several hours, I checked the local
channel two video carrier at 55.25000 MHz and could  see a small
variation on it also. As the channel two carrier shifted down by a few
Hertz, I noticed that the fan in the ts-2000 had just turned on.  

Sure enough, the cyclical pattern matched the fan cycling on and off.  I
posted an example waterfall on my website.  

You can view it at http://www.rcallen.com/ts2k-fan.gif ...

The plot starts at about 13:00 utc on April Fool's Day but,
unfortunately, it is not a joke.

>From 13:00 thru about 13:33 shows several fan cycles.  The ts-2000 was
tuned to 1279.999000 MHz and in upper sideband mode. As can be seen, the
frequency changes down to 800 Hz when the fan comes on and then peaks
back up to about 900 Hz at fan cutoff.  While this is well within the
+-0.5 ppm specification of the radio, it may be a problem for operating.
Offset I can handle but drift is another matter.

After 13:41, I switched to tracking the Argentinean ham satellite
LUSAT/LO-19.  It's cw beacon is nominally on 437.12545 MHz and with a M2
70 cm eggbeater antenna, peaks about 20-30 dB out of the noise.  The
apparent frequency smear is from the fact that I was only updating the
radio's frequency every 10 Hz.  The Doppler shift makes the apparent
frequency move more than the program can keep up with at 1 Hz
increments.

At marker 6, at about 13:47, the fan came on causing a drop in pitch.
The satellite peaked in elevation at 13:49:49 at 25 degrees.  The fan
then went off at about 13:53 shown by marker 7.  The satellite went on
to set at 13:57.

At marker 8 I switched the radio to 439.999000 MHz USB, the 44th
harmonic, and monitored another fan on/off cycle indicated approximately
by markers 9 and 10.

Any suggestions as to how I can stabilise the radio would be
appreciated.  I think I will first try to modify it so that the fan
stays on continuously.  The master oscillator is a  TCXO at 15.6 MHz and
it may be possible to replace it with an external oscillator slaved to
my z3801.  Some of the shift might also be a voltage drop when the fan
comes on.

Please feel free to forward this to any other interested vhf reflector.

Regards,

Richard W5SXD