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
Hi Al, W8KHP
Normally I have seen the resistance of the potentiometer to be less than 500 ohm but this is not extremely important.
BTW is very important that the potentiometer is linear.
I suggest to rotate the azimut just mid way of it's travel i/e 180° one side and 180° to the other side up to both the mechanical stops.
Disconnect the wires A1 A2 A3 from the rear of control box and than measure the resistance between A1 and A3 as well the resistance between A2 and A3
If the potentiometer is in good shape both resistance readings must be the same value less than 250 ohm each side but the same value.
Have fun
73" de
i8CVS Domenico
----- Original Message ----- From: tokens@myranch.com To: amsat-bb@amsat.org Sent: Wednesday, November 28, 2012 10:00 PM 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 _______________________________________________ Sent via AMSAT-BB@amsat.org. Opinions expressed are those of the author. Not an AMSAT-NA member? Join now to support the amateur satellite program! Subscription settings: http://amsat.org/mailman/listinfo/amsat-bb
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@amsat.org [mailto:amsat-bb-bounces@amsat.org] On Behalf Of tokens@myranch.com Sent: Wednesday, November 28, 2012 3:00 PM To: amsat-bb@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 _______________________________________________ Sent via AMSAT-BB@amsat.org. Opinions expressed are those of the author. Not an AMSAT-NA member? Join now to support the amateur satellite program! Subscription settings: http://amsat.org/mailman/listinfo/amsat-bb
At 21:00 28/11/2012, you wrote:
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.
Draw a graph of AZ vs Voltage... It should be a straight line, if not, the pot is not linear!
---- Original Message ----- From: "John Wright" ham@g4dmf.co.uk To: amsat-bb@amsat.org Sent: Thursday, November 29, 2012 5:40 PM Subject: [amsat-bb] Re: G5400B Rotor Problem
At 21:00 28/11/2012, you wrote:
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.
Draw a graph of AZ vs Voltage... It should be a straight line, if not, the pot is not linear!
Hi John, G4DMF
I agree with you and draw a graph of AZ versus Voltage to see if it is or not a straight line is a very good idea but you don't want to read the AZ on the control-box meter because the meter can be not linear.
BTW the idea to read the AZ as Erich DK1TB did is to me the best procedure.
In a previous message on Amsat-BB Erich writes :
----- Original Message ----- From: "Erich Eichmann" erich.eichmann@t-online.de To: tokens@myranch.com Cc: amsat-bb@amsat.org Sent: Thursday, November 29, 2012 7:52 AM Subject: [amsat-bb] Re: az-rotor
< snip>
I mounted the KR-600X in the shack over a big 360° linear scale with 1 m diameter and with a pointer that moved around the scale close above it. The rotor ran exactly an 360° turn from the starting position 180° in the south to the end position 180°.
-------------------------------------------------- 73" de
i8CVS Domenico
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