Yet another military HX thread

I would be interested to see some photos of your antenna/feed arrangement.  Please send to eric@satsig.net

The LNB position for vertical downlink receive polarisation would be with the LNB at the side, 9 o'clock or 3 o'clock  position, as viewed towards the satellite. Note the broad faces of the rectangular LNB input waveguide will then be on top and underneath.  This is the definition of vertical polarisation.

Using https://www.satsig.net/maps/satellite-dish-pointing-pakistan.htm

The polarisation adjustment required for the AM22 Pakistan/Afghanistan beam coverage is approx +10 to +30 deg clockwise. This means adjust the polarisation by turning the entire dish so many degrees clockwise, while facing towards the satellite.  The big scale on the back of the dish is perfect.  Calculate your particular polarisation adjustment needed, using your location.

I am particularly interested in your feed arrangement, so close up images showing the 505, the single and dual tick marks and the fat side of the feed throat are of interest.  I can say for certain that the fat side of the feed throat must be exactly towards the feed arm and the 505 directly away from the feed arm.

How the OMT/side filter/LNB are attached is another matter.  The orientation of the side filter LNB sets the nominal receive polarisation.   If the filter LNB is up on top that gives horizontal receive polarisation, as used for W3A satellite for Iraq.  With the filter/LNB at either side you are set for vertical receive polarisation, which may be applicable for AM22.



The OMT/filter assembly I have here is marked P/N 110196-7 and it is a cross-pol device.  

The Transmit module has its own polarisation.  The unit has an obvious underside and top.   The transmit unit works vertical when its top is uppermost (or underneath).

In the case of AM22 your service may be configured for co-pol operation.  This means that the OMT/filter block may need to be changed for a diplexer/dual filter, which will have different model number.

If your AM22 service is a co-pol operation and you have a (wrong) cross pol assembly then when your receive is perfect your transmit signal should not get to the hub at all.  It should fail completely.

Ask WAFA what kit they have supplied to you and clarify on which polarisations you are supposed to transmit and receive.

Are you supposed to transmit and receive co-pol, i.e. both on the same polarisation ?  
wxw
Best regards, Eric.

You say "The RPR states Horizontal Transmit and Vertical Receive."  I have spoken with the operator who says that this is in error.  You should be transmitting and receiving, both on Horizontal polarisation.

You have the correct co-pol feed assembly with a pair of diplexer filters.  Your transmit and receive will be the same polarisations.

I've put my explanations of your images below:


Image above shows co-pol arrangement with nominal horizontal polarisation for transmit and nominal horizontal polarisation for receive.
A polarisation adjustment of approx -30 deg has been applied by turning the entire dish anti-clockwise, while facing towards the satellite. There is a big scale on the back of the dish to set this adjustment.



Image above shows co-pol arrangement with nominal vertical polarisation for transmit and nominal vertical polarisation for receive.
A polarisation adjustment of approx +30 deg has been applied by turning the entire dish clockwise, while facing towards the satellite. There is a big scale on the back of the dish to set this adjustment.



Image above shows co-pol arrangement with nominal horizontal polarisation for transmit and nominal horizontal polarisation for receive.



Image above shows the mode matched horn at the top.  This is correctly oriented.  The 505 is away from the support arm.  The fat lump (not visible and underneath the throat) is towards the feed arm. The single tick mark on the tapered spacer tube is away from the feed arm.  These positions apply regardless of the nominal polarisation settings.  Polarisation is achieved by altering the joint marked. As shown the diplexer (two filters) is vertical for both transmit and receive.

My recommendations:

The 505 is away from the arm, fat bit towards the arm, single tick mark away from the arm. (This is always the case)

The LNB needs to be directly away from the feed arm for Horizontal polarisation.  Looking at your pictures you need to undo the six tiny screws between the taper adaptor tube and the diplexer filter and rejoin with the LNB upwards, same as the 505.  The BUC will be on its side.

The entire dish should be turned for the polarisation adjustment.  Positive (+) angles mean clockwise while facing the satellite.  You need to determine the polarisation adjustment angle using your lat long and AM22 orbit position.  See  https://www.satsig.net/maps/satellite-dish-pointing-pakistan.htm  Set the pol adjustment angle exactly using the large circular scale.
wxw
Best regards, Eric.

Dear Sir

This is BW I agree with USN retired get the dish right away from that transmitter yagi it will definitley affect the the signals , you need to move it at least 15 meters away or more if the cable permits ,this is a co polar installation so recieve and transmit are in the same plane , please contact directly us or Wafa although we are the HX noc our contact is found on the BW web site www.bentleywalker.com or contact me directly anthony@bentleywalker.com

Dear Sir

For Kabul region the position of the feed/LNB is anticlockwise 33 degrees , hope this helps
Best Regards,
Anthony Walker

Well, went out again with the new information in hand (-33 polang and horiz/horiz orientation) and a horizon meter. We swung around and to the previous location we had been looking for seasat and had no success. Could not achieve a signal of more than 63 on the horizon, that was the peak after vertical/horizontal adjustment using my method (which works quite well).
The odd thing was, when we switched the horizon to look for W3A, we were able to get over 70db on the meter after a quick peak-up. I'm thinking there might be something wrong with the LNB hardware itself,  but the fact that we are able to get good gain off of W3A seems to obscure the issue even further.

I agree with Greg.  -33 deg is in error by 55 deg relative to +22 deg, so you would be lucky to get the wanted signal from AM22.  It would require there to be no traffic on the opposite polarisation and the wanted signal would be 5 dB low.  The opposite polarisation traffic, if present, would be higher than the wanted signal so no hope at all...

The entire dish should be turned for the polarisation adjustment.  Positive (+) angles mean clockwise while facing in the direction towards the satellite.  You need to determine the polarisation adjustment angle using your lat long and AM22 orbit position.  See  https://www.satsig.net/maps/satellite-dish-pointing-pakistan.htm  Set the pol adjustment angle exactly using the large circular scale.

I agree the angle should be in the range about +12 to +30 deg for the Afganistan/Pakistan area, but since the exact angle is important, the customer should do it themselves privately with their own known lat/long position.

The co-pol feed is intended for use with this AM22 service.

The service on W3A needs a cross pol feed. In Afghanistan, the W3A 7 East beam coverage is poor, the signal is low level and also low elevation angle (20 - 10 deg) so I would not recommend attempting to use it. 

Best regards, Eric