[amsat-bb] Re: [Moon-net] LVB tracker noise

Guenter Koellner guenter.koellner at mixed-mode.de
Tue Dec 8 05:06:13 PST 2009


I had such a problem recently on my SDR part, the one that drives the
waterfall. Problem is divided into two distortions, some are narrowband
spurs, others a wideband noise that adds to the reception.

In order to find the causes I finally ran those components necessary from
a battery (23cm transverter, FT847 and PC) and removed power for the house
at all.

Then I found:
-> Ground loops: Transceiver and PC must be connected to the same mains
-> IQ mixer is now running from a 8V LiIon battery (R2Hobbies)
-> I removed the external oscillator that works as an LO for the IQ mixer
and use a simple 1.8432 computer oscillator there.

I also found that the 3-phase-inverters that I am using for the dish drive
have internal CPUs which unfortunately generate a strong spur on 144.016
and 144.020. I tried to pull them downwards but they are that awfully
accessible located in the inverters so I had to give up.

-> I put 5-turn-ferrit cores on each line that goes into the inverters

It really solved all problems despite the spurs of the inverter CPUs which
now are little bit weaker but maybe I have to mount these two units into a
screened box.

73, Günter (dl4mea)

> I am using and LVB tracker to control my GS5400B AZ/EL system.
> I mainly use it on EME and WSJT controlling it with NOVA. There has
> always been excessive noise
> shown on the waterfall when I am on certain 144mhz frequencies. I can cut
> power to the 5400 and it goes away so I am pretty sure it is either
> the box itself or the USB connection. I have put toroids on the cable
> ends.
> I have also tried different computers and it is the same. Any ideas on
> what I could do
> to remedy this.  I can cut power to the rotor and all is fine. But the I
> have
> to restart NOVA each time. I could live with it if I could just switch
> the Rotor control off and on without restarted NOVA etc..
> Thanks
> Joe
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