[amsat-bb] Re: G5500 Rotor Drift Issue

i8cvs domenico.i8cvs at tin.it
Mon Jul 13 17:16:15 PDT 2009

Hi Mark, WA8SME

Sometime the voltage regulators tends to self-oscillate in a very low but
very wide frequency band.

In this condition the regulated voltage is unstable not clean and dirty as
can be seen using an oscilloscope.

This problem is well know by the microwave people when they try to
get a local oscillator clean and stable.

To eliminate the self-oscillation an effective cure is to put a ceramic
capacitor of  0.1 uF in parallel to an electrolitic capacitor ranging from 1
to 10 uF both at the input and the output of the regulator and check
again with the oscilloscope any trace of oscillations at the regulator

73" de

i8CVS Domenico

----- Original Message -----
From: "Mark Spencer" <mspencer at hughes.net>
To: <amsat-bb at amsat.org>
Sent: Monday, July 13, 2009 8:42 PM
Subject: [amsat-bb] G5500 Rotor Drift Issue

> There have been a couple of recent posts about a G5500 voltage drift issue
> and some solutions.  I'd like to thank those gentlemen for the posts and
> solutions.  I am in a unique position to be able to work with nine G5500
> rotors side-by-side in preparation for the Teachers Institute II that I
> hold at the end of the week.  I noticed the same warm-up/calibration issue
> mentioned in the posts.  I discovered that it took on average 10 minutes
> warm up time for the voltage to stabilize, and this voltage is the
> on which the antenna position indications are based.  The difference
> the cold start and warm up position was around 10 degrees for AZ and 4
> degrees for EL.  Minor but irritating.  I thought I'd try the easiest
> solution suggested first (changing the output cap on the regulator to
> before I tried the more dramatic solution of changing out the voltage
> regulator.  I simply tack soldered the .1uF cap on the exposed leads of
> existing .01uF cap, and it worked like a charm.  All nine rotor
> fire up at 6.12 volts and hold that voltage throughout the operation of
> rotor.  This sure will make instruction of rotor setup and calibration a
> heck of a lot easier.  Thanks for the suggests.
> Mark Spencer, WA8SME
> ARRL-The national association for Amateur Radio
> Education and Technology Program Coordinator
> mspencer at arrl.org
> http://www.arrl.org/FandES/tbp/
> 530-495-9150
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