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AMC12 Line Up

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Ex Member
Ex Member


Aug 15th, 2006 at 3:04pm  
we are having a problem trying to line up our 2.4M VSAT in Liberia (Monrovia) to the AMC12 "bird" but we are having alot of problems.

We have done EVERYTHING right and we still are getting a "blinking" lock light on the CDM570L modem.  We did all the frequency conversion from Cband to Lband.  We put in the LO for the BUC and the LNB but still "NOTHING".  We just cannot seem to Lock on.

PLEASE HELP -  SOMEBODY PLEASE
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Eric Johnston
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Reply #1 - Aug 15th, 2006 at 6:35pm  
What have you set for:
L band receive frequency
Symbol rate
FEC rate
Type of FEC
Data differential encoder ?
Data descrambler
Spectrum inverted ?.

If in doubt about any of these ask the hub what to set for each of these.  All must be correct.

C band LNBs normally have an LO=5150 MHz.  It may be written on the label.   L band freq = 5150 minus C band downlink frequency (inverted spectrum).

What is the name your receive downlink polarisation is called: Horizontal or Vertical ?.   To set the polarisation:  For Vertical, START with the LNB waveguide with its broad faces on top and below.  Then, for a positive polarisation angle,  rotate clockwise so many degrees, while facing the satellite.    In your case the rotation  angle is large like +77 deg so you have a lot of rotation to do.  Do it carefully and accurately.  If something hits the metal start again from an LNB position on the opposite 180 deg.

Set the elevation angle and sweep across.  You should find the satellite.

Check that you have selected LNB power ON.  What is the LNB current showing ?  

If you have external reference PLL type LNBs make sure that you turn ON the LNB 10 MHz reference.

Two futher thoughts:  

There is the possibilty that the carrier towards you is pulsing on and off - causing your RX LED to flash all the time.  You may be correctly pointed and normal.   This is unlikely as it is normally the other way round - a remote site receives a continuous carrier and transmits an intermittent pulsing TDMA carrier.

A flickering or pulsing RX LED may indicate that one or more of these is wrong: FEC rate, Type of FEC, Data differential encoder, Data descrambler, Spectrum inverted.   I have seen that problem, with wrong type of TPC FEC selected at the receive end.  Go through the list checking that every one is identical with the hub transmit modem.  

Who is your hub ?   Once you are receiving OK the hub should be able to take control of your modem and save the settings.

Best regards, Eric.
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