SatSig topic:

vertical polarized signals

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Apr 4^th, 2012 at 6:27pm

It is observed that, the Vertically polarized signal are difficult to receive from 66 degree east and 76.5 degree east satellites from Dhaka, Bangladesh. Horizontally polarized signal have good quality of reception.

I use the LNB which have single output terminal for the V & H polarized signal.

Please help to find the reason.

Apr 4^th, 2012 at 6:59pm

This could be that the carriers have different levels, or it could be that your LNB has degraded performance on one polarisation.

Try turning the LNB physically by 90 deg.

If the problem remains unchanged then the cause is different carrier levels on each polarisation.

If the problem now appear the other way round then it suggests that one side of the LNB is faulty. Try turning the LNB physically when you want to watch on the other polarisation, or get a new LNB. Check it is dry inside ! If switching the polarisation involves a magnet or actuator check it works.

Review all the possible channels etc on Intelsat 17 (66 east) and APSTAR 2R (76.5 east) and the beam coverage patterns by going to https://www.lyngsat.com

Best regards, Eric.

Apr 5^th, 2012 at 2:35pm

Thanks eric,
I tried the ways as you explained .

But the V polarized signals are found always weak in almost all the satellites with different LNB's.

Anyway thanks again for your quick help.

Apr 5^th, 2012 at 5:05pm

I am having to stretch my imagination to think of any explanation for your observation.
- maybe your dish is made of wire mesh and the wires with a particular orientation in the mesh are corroded ?
- maybe your satellite TV receiver is sending out very low DC volts when set to vertical ? It should be +13 V for vertical and +19 V for horizontal. Is your cable very long or maybe corroded internally due to moisture, causing high resistance ? If this is the case then you should get good reception using Horizonal selected and if you then turn the feed 90 deg physically then you should get good reception on vertical as well.

As seen from Dhaka, Bangladesh, when you point your dish at the 66 or 76.5 deg east satellites you will need to apply polarisation adjustment amounts of approx +43 or +29 deg clockwise as viewed looking towards the satellite in the sky. The satellites are to the west of South.

For example, to align the LNB for the 76.5E satellite you need to set the LNB initially upright, then turn it +29 deg clockwise as viewed looking forwards towards the satellite in the sky. Your Horizontal and Vertical polarsations will both be tilted be the same +29 deg amount clockwise.

For exact polarisation adjustment angles see https://www.satsig.net/maps/satellite-dish-pointing-india.htm
wxw
Best regards, Eric.

Apr 9^th, 2012 at 4:29pm

Eric
Thanks for attention .
My dish is made of wire mesh. Corrosion can not be avoided in a humid country.
I have a very good satellite receiver even to get HD and MPEG-4 signals.

I targeted 7 satellites which are working well and I am satisfied. Sometimes corrosion are found. I have no signal meter, but takes my receiver and monitor on the roof and do it manually. !

Recently the TV concerned, TARA MUSIC shifted their transmission at 68.5 degree(Horizontal). Till now , I have the same problem. All other V & H programs from 68.5 degree Intelsat 10 are displayed except TARA MUZIC.

The main cause may be the C/N lock for TARA MUZIC is 7.9 at Dhaka ! I am really in despair to solve the problem.

I will let you know , If there is any progress. Thanx again

Apr 9^th, 2012 at 7:52pm

See: https://www.lyngsat.com/Intelsat-7-10.html

Are you receving 4012 MHz H TARA Muzik ?

If so, there may be a cross pol 'feeds' carrier, also at the same frequency, but perhaps not all of the time.

I note that this is C band operation, with linear polarisation, just about in the tropics.

C band linear is not a good idea in the tropics as it suffers from ionospheric Faraday rotation. The two polarisations (V and H) stay at right angles to each other and the baseline angles are as calculated, clockwise to the south west. Anticlockwise to the south east. But, the polarisations are rotated by the ionosphere by varying amounts. As your feed rotation is fixed, you experience varying levels of cross polarisation interference.

At S band and L band the polarisation may rotate completely. At C band there is problem. At Ku band and Ka band Faraday rotation is not a problem, but the higher do frequencies suffer from bad rain attenuation and rain noise.

Do you adjust your linear polarisation angle when you repoint to different satellites. Use this to get your adjustment angle https://www.satsig.net/maps/satellite-dish-pointing-india.htm but note that the actual optimum angle will be varying according to the sun's output (space weather.)

In the tropics, C band circular polarisation is preferred.

Best regards, Eric

Apr 10^th, 2012 at 6:09pm

No,I do not.
I will try again in a few days as per your kind suggestions . I could get it from 66 degree east but with very low signal.
At 68.5 degree , I do not get it at all. HD and all V& H polarized signal are well received except the 4012 Mhz.

I do not know , TARA Muzik says that, they transmit at 4013 Mhz at S/R of 7203 kc/s , which actually does not matter too much.

I think that my 2.5 meter mesh dish should work well with the signal strength of 38 db. Does not it ? Local operators retransmit TARA MUZIC which faces lack of synchronization as well.

Any way, hope to assure you my reception report by next week.....Thanks.

Jan 1^st, 2013 at 5:11pm

I am sorry. I could solve the problem in last July,2012.

A solid mesh of 6 feet diameter solved the problem but with too much precise alignment. Thanks to all who helped me.....