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Receiving Vertical Polarization

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kenshin03
Ex Member


Aug 15th, 2011 at 12:01pm  
Sir,

I cannot receive a vertical signal using my feedhorn and lnb, but if I replace it with LNBF I was able to lock the vertical signal. Is my feedhorn the cause of the problem?

I tried receiving horizontal signal and I was able to lock it. I already turn the feed 360 degrees and I really can't lock vertical signal.

I need to use the feedhorn/lnb setup because I am using it on tranceiving signal.


Thanks,

ken u.
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Eric Johnston
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Reply #1 - Aug 15th, 2011 at 1:19pm  
If you have the LNB on a side arm, coming out of the OMT junction, then
.   if the LNB arm is sticking out sideways that is vertical polarisation starting psoiton.
.   if the LNB arm is sticking out upwards (or downwards) that is horizontal polarisation starting position.

Having established the correct polarisation starting position, apply the appropriate polarisation adjustment amount.  For a positive (+) adjustment amount turn the feed system clockwise, as viewed from behind the dish and facing forwards towards the satellite in the sky.

If you use instead a general purpose LNBF, as typical for receive-only satellite TV,  then the LNBF has an internal 90 deg switch controlled by voltage (13V or 19V) to switch between polarisations.  You still need to apply the adjustment amount however.

See here for polarisation adjustment angles: http://www.satsig.net/maps/satellite-tv-dish-pointing-south-east-asia.htm
wxw
Best regards, Eric.
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« Last Edit: Aug 16th, 2011 at 11:21am by Admin1 »  
 
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kenshin03
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Reply #2 - Aug 15th, 2011 at 2:57pm  
Sir,

I already rotated the feed 360 degrees, the lnb made the position on both sides meaning they are vertically polarized but still I cannot lock the vertical signal. The horizontal signal is working well, when I reached the upward or downward position of the lnb.

My LNB is connected on a sidearm of the OMT after the filter.

Thanks,

ken u.
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Eric Johnston
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Reply #3 - Aug 15th, 2011 at 3:41pm  
1.  If you were able to get a good horizontal lock using the TV LNBF and you cannot get a good horizontal lock with the LNB on the sidearm check your modem tuning with regards to the LNB local oscillator frequency.

What is your wanted carrier frequency from the satellite ?
What is your L band modem tuning with the LNBF ?
What is your L band modem tuning with the LNB ?

A Ku band LNBF typically has 9.75 and 10.6 GHz LO frequencies (switched using 22 kHz tone).

A fixed LO LNB may have 10 or 11.3 GHz or several other possibilities. What is yours ?

So the L band tuning of the modem may need to be different using LNBF and LNB.

2.  You don't say what is your polarisation adjustment amount or if you have applied it ?   Where are you and what satellite are you pointed at ?

The adjustment amount may be anything from -90 to +90 degrees, depending on your location and satellite. If you are near the equator the polarisation adjustment amount may be very large and may change rapidly as you move from one satellite to another (or from one location to another).

To set vertical polarisation you need to put the LNB arm directly sideways (vertical polarisation starting position), then adjust it clockwise (+) or anticlockwise (-), as viewed facing forwards towards the satellite in the sky.

Best regards, Eric.
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« Last Edit: Aug 16th, 2011 at 11:25am by Admin1 »  
 
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kenshin03
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Reply #4 - Aug 16th, 2011 at 10:10am  
Sir,

I was able to lock the signal using LNB and LNBF on Horizontal,  the only problem is on receiving Vertical signal using a fixed LNB.

My LNB LO is 10750 and skewed to +30 degrees.
I am receiving 12390 GHz of Koreasat 5 from Philippines.


thanks
ken u.

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Admin1
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Reply #5 - Aug 16th, 2011 at 12:47pm  
12390 MHz on Koreasat 5 at 113E orbit position is a Vertical polarisation TV carrier.

If your LNB LO is 10750 your receiver tuning needs to be 1640 MHz.

If your LNBF LO is selected to 10600 your receiver tuning needs to be 1790 MHz.

If you use a "universal LNBF" with switchable polarisation (V and H)  and switchable LO (9750 and 10600 MHz), then you need to set it initially upright and then adjust it +30 deg clockwsie, as viewed from behind the dish and facing forwards towards the satellite in the sky. Select Vertical voltage option on your receiver LNB cable.

If you use a fixed LNB on side arm set the LNB side arm initially sidways, say on the left, for vertical polarisation starting position. Then adjust the LNB arm upwards, clockwise, by +30 deg.

Ref: http://www.satsig.net/maps/satellite-tv-dish-pointing-south-east-asia.htm
wxw
Best regards, Eric.
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« Last Edit: Aug 17th, 2011 at 8:55am by Admin1 »  
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