Advertisement
Field Service Procedure – Replacement Pol Pot Kit, 6003A/6004
1.
Brief Summary:
Troubleshooting document for diagnosing a fault with and replacing the pol pot on the 6003A/6004 series antennas.
2.
Checklist:
Verify Range of Motion
Verify Pot Feedback
Measure Resistance
3.
Theory of Operation:
A polang potentiometer is used to provide a feedback reference for the position of the feed assembly for linear
polarization. The pot acts as a potential divider giving an output voltage which varies from 0Vdc to 5Vdc. The PCU
converts the voltage output from the pot into the numerical value displayed on the DAC. A failure with the pot causing it
to output an incorrect voltage will result in the feed assembly not being aligned correctly causing bad cross pol isolation.
One indication that there is a fault with the feed alignment of the system is that the target light will be permanently
illuminated on the DAC and the antenna won't target correctly. It will sit 8 degrees above or below the satellites
elevation look angle, as part of the antennas targeting procedure is to target 8 degrees above or below the satellite,
calculate the auto threshold setting based on the noise floor level and then align the feed for the correct reception
position based on the vessels GPS position and the lookup table in the DAC.
If the system is unable to drive the pol motor to obtain the correct feedback, or if the pot has failed and won't give the
correct feedback, the antenna can't complete the target process and the antenna will stay in this position. Setting the pol
type to "0009" will make the antenna target by removing the auto pol function from the targeting process; however the
mis‐alignment of the feed will cause bad cross pol isolation.
4.
Verify Range of Motion:
First verify the settings in the DAC are correct; the pol scale should be set to 0090 to give the feed 180 degrees of motion.
The default pol offset is 0030 (however these may have been modified slightly to "trim" the pol angle). Ensure tracking is
off then drive the elevation to 0 degrees to make it easier to view the feed assembly for diagnostic purposes.
Set the pol type to "0009" to set the mode of the pol assembly from automatic to manual. Now enter the pol window and
hold the down arrow to drive the feed assembly into its end stop. At the lower end of the range the pol count should be
approximately 28, at which point the LNB should be horizontal with the coax cables pointing towards the left when view
facing the feed assembly. At the upper end of the range the count should be approximately 210 and the LNB should have
moved 180 degrees, i.e. the coax cables are now pointing to the right.
If no pol motor drive is present verify the pol reading on the DAC isn't out of range (i.e. displaying a value of either 0 or
255). If one of these values are displayed it's possible the pot isn't aligned correctly and that adjusting it may bring it back
to with the scale the DAC recognizes. Back the pot off from the main gear and rotate the pot, verifying that the feedback
value changes on the DAC. If so, calibrate the pol pot and verify operation as described in the later stages of this
document. If the pol count on the DAC doesn't change when the pot is adjusted the pot has failed and is outputting a
default value. See Verifying the Resistance of the Pol Pot section below. If this is the case no drive will be issued to the
pol motor as the value is out of the range which the system operates in.
Page 1 of 7
Copyright © Sea Tel, Inc 2011 - The information contained in this document is proprietary to Sea
Tel, Inc.. This document may not be reproduced or distributed in any form without prior written
consent of Sea Tel, Inc.
Document No
135301 Rev B
Advertisement
