SatSig topic:

Strange iDirect Problem pointing to NSS7

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May 4^th, 2011 at 3:35pm

Strange iDirect Problem pointing to NSS7
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The VSAT dish, a 2.4m offset C-band antenna dish (Patriot) on NSS7 (22WL) dropped off the network 2 months ago after more than a year in operation.

Several attempts to re-align this antenna have been unsuccessful.

I have the following equipment on site:
1. iDirect 3100 modem
2. TXFCC-240CSCN 2.4M C-Band Antenna Patriot
3. NJT5669 5W BUC NJR
4. NJS8476S PLL LNB NJR
5. IFL RG6 cable (30m)

The highest Rx signal strength on iSite is 8.3v. This signal strength fluctuates between 0, 0.3, 2.3 and 8.3v in no particular pattern.

I have done the following in trying to isolate what could cause this problem where i cannot get more than 8.3v on iSite:

1. Swapped the entire feed assembly (BUC, LNB, Feed-OMT/Polarizer/Filter/TXRX) with another feed from a working site. it worked perfectly at the 2nd site but the feed from the second site does gives the same volts on iSite at the faulty site)
2. Loaded the option file from this site with issues to another modem at another site (about 1k apart) and had both a Rx and Tx lock.
3. Used cables from a working site to connect the modem at this faulty site but it didn't get more than 8.3v.
4. Swapped the modem from a working site with the modem of the faulty site. None of the modems got more than 8.3v on iSite but both modem had a Rx and Tx lock at the working site.
5. I have used a spectrum analyser and got a clear channel but cannot get the modem to Rx lock.

The site geo statistics for the VSAT location is N 6.445 and E 3.41151.

I am not really sure at this point why I can’t get more than 8.3v on iSite. Any further data that maybe useful to resolve this will be provided.

Your input will be of great help.

May 5^th, 2011 at 1:37pm

Maybe you are pointed at the wrong satellite.

Compare the observed spectrums at both sites with spectrum analyser.

If the spectrums don't match up you have the wrong satellite (or polarisation or LNB freq). Measure the elevation angle very accurately at both sites and adjust.

If the visible carriers are same then you have the correct satellite. What difference is there in the measured (C+N)/N for the wanted carrier ?.

A widely varying receive signal could be due to observing an intermittent carrier on the satellite (e.g. TDMA traffic), a loose LNB cable connection or antenna swinging in the wind. Low signal levels that vary smoothly up and down over the day could be due to severe mispointing, say -5 dB down the side of the beam.

Do you get a steady reading when you put several layers of wet towel over the feed horn ?

Best regards, Eric

Nov 7^th, 2011 at 7:19am

Hi,
this is not the LNB BUC or modem problem this is the OMT Filter problem. Change the antenna location bring it 10 or 20 meters away from this location or get a OMT reject filter
because C band not working in case there is some wimax in front of antenna .

Reqards
Noor Ahmed
AFSAT Communication
Kabul, Afghanistan