SatSig topic:

Unable To align On Yahsat 1A C-band

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Feb 22^nd, 2012 at 8:54am

Hi

I am unable to align my Prodelin 2.4m antenna on Yahsat 1A C-band . Can anyone help me with polarizer setting.

Feb 22^nd, 2012 at 1:30pm

Check that you are located within the beam coverage and ask your service provider what polarisation name you are supposed to receive (and frequency, symbol rate, FEC etc).

Yahsat is at 52.5E orbit position.

If you contact Yahsat, ask what is the polarisation of each of the two beacons at 4198 / 4199 MHz.

For circular polarisation read this:
https://www.satsig.net/pointing/circular-polarisation-set-up.htm

Trial and error also works very well and does not take long. If your initial circular polarisation is wrong, change it. There is a 50% chance of getting it right first time !
wxw
Best regards, Eric.

Feb 22^nd, 2012 at 2:52pm

Eric, your last sentence is 100% true!

When it comes to polarity, there is so much confusion, not only among users, but also among field engineers, NOC engineers, service providers, satellite operators and equipment manufacturers... This is true also for linear polarity, but with circular things are becoming even worse. LHCP is counter clock wise or clock wise? From what point of view? Watching behind the dish or front of the dish? Now we have a polarity marked on the feed - does it means the polarity of the Tx or the Rx? And for Tx for example - is it the polarity transmitted from the feed or the polarity transmitted from the dish after being reflected from the reflector (and therefore changing from LHCP to RHCP and vice versa).

For example, the polarity marking on Prodelin dishes represent the polarity of the Tx as it is transmitted from the feed, before the reflection from the reflector. In Andrew feeds, it shows the polarity of the Tx AFTER reflection from the reflector...

My advice for our field engineers is always - if you dont know this specific service, try both polarities. Usually it saves lot of confusion and time.

Regards,
Nimrod

Feb 22^nd, 2012 at 3:46pm

Even if you perfectly follow my instructions in https://www.satsig.net/pointing/circular-polarisation-set-up.htm there is still a good chance of getting it wrong because you may have been provided with incorrect information from your service provider or even the satellite operator.

It is no suprise to find instances of operation in the wrong transponder for some time due to mutual misunderstandings involving the NOC operators and the end users.

If you can see the C band beacons on a spectrum analyser this often clarifies matters. The telemetry beacon(s) may RHCP (A pol) and tracking beacon (CW) linear. In such a case the linear tracking beacon will always be visible (-3dB down), while the RHCP telemetry beacon will only be visible if you are set to RHCP down.

One thing to be thankful for however with circular is that it needs no angle adjustment - it either works perfectly or not at all. I am really pleased that circular has become the standard for Ka band. They seem to have learned from experience with Ku band. Even with trained installers and close supervision on line-ups, the actual in service cross polarisation interference is bad. If you look in a Ku band cross-pol transponder opposite to a TDMA return link you see multiple high level interference bursts - some even demodulatable !!
wxw
Best regards, Eric.

Mar 18^th, 2012 at 9:26am

Hi,
I think i have the same problem here,in my case i am using a 3100 modem and a 1.8m channel master dish, i have RX SNR of 14.8 and as soon as i connect the TX cable the remote state to say rx lock,rx unlock continously on my telnet page,and when i remove the TX cable the RX stays stable but as soon as i plug back the TX the issue starts again
If i go by what dhrisht say,if i try it on a prodelin dish it will work well,but i do not have a prodelin dish here and ISP is just clueless about the issue.
Please any help will be appreciated.

Jul 3^rd, 2012 at 1:16pm

Please check your feed horn
this is may be the transmit reject filter
is not working and the tx signal is suppressing the RX.

Best regard