# [amsat-bb] Re: G5400B Rotor Problem

Alan wa4sca at gmail.com
Wed Nov 28 14:01:39 PST 2012

```Al,

The output from pin 6 parallels nicely the meter reading.  If you do a
linear fit:

Measured		Calculated

.024			.0062
.606			.626
1.27			1.25
1.864			1.865
2.489			2.48
3.074			3.10
3.69			3.72
4.35			4.34
5.00			4.96

Those variances are all within the 4% accuracy claimed.  This implies the
meter electronics are good, or at least consistent in reporting what the pot
is telling them.  However,

>> The difference in voltage from reading to reading varied from 0.582 to
0.660 V. From left to right they were 0.582, 0.664, 0.594, 0.625, 0.585,
0.616, 0.660, 0.650.

Apologies, but I am not clear on what this means.  It does represent
approximately 45 degrees.

The fact that the pot total resistance is less than 500 ohms, and the fact
that it has a jump (non-linearity) in the readings, implies there is a
shorted section in the pot

Alan
WA4SCA

-----Original Message-----
From: amsat-bb-bounces at amsat.org [mailto:amsat-bb-bounces at amsat.org] On
Behalf Of tokens at myranch.com
Sent: Wednesday, November 28, 2012 3:00 PM
To: amsat-bb at amsat.org
Subject: [amsat-bb] G5400B Rotor Problem

Got some unexpected time today to look at the rotor. First I set the output
at pin 6 of the external control output jack to 5.0 V. Then I got readings
every 45 deg from 180 at the left to 180 on the right. The readings are of
course subject to parallax in reading the needle. Readings from 180 on the
left to 180 on the right were 0.024, 0.606, 1.270, 1.864, 2.489, 3.074,
3.690, 4.350, and 5.000 V. The difference in voltage from reading to reading
varied from 0.582 to 0.660 V. From left to right they were 0.582, 0.664,
0.594, 0.625, 0.585, 0.616, 0.660, 0.650. I then took resistance readings on
the 500 ohm pot in the rotor (removing connection from control box each
time). Starting at the left resistance from 1-2, 1-3, 2-3 were 415, 416, and
1.7 ohms. With the rotor halfway around (360) (dial reading 345) resistance
from 1-2, 1-3, 2-3 were 241.7, 416, and 176.1 ohms. With the dial at 360
resistance from 1-2, 1-3, 2-3 were 220.4, 413, and 193.6 ohms. With the dial
at the right 180 resistance from 1-2, 1-3, 2-3 were 30.4, 414, and 383 ohms.
First observation is that the pot in the rotor is considerably less than 500
ohms. Next with either the rotor being halfway around or the dial reading as
if it were halfway around I would expect the 1-2 and 2-3 readings of the pot
to be somewhat similar but they are not. So, are these results glaringly
pointing to the 500 ohm pot as the culprit? Or does someone see something
else?

I'd appreciate any opinions on this. Thank you once again.

73 Al W8KHP
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