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VSAT technology and installation >> iDirect Forum: hubs and terminals >> iSCPC Link

Message started by Habib D on Aug 29th, 2014 at 1:09pm

Title: iSCPC Link
Post by Habib D on Aug 29th, 2014 at 1:09pm

I'm struggling to establish a SCPC connection with two infinity 5300. I have generated the options file for the two modem and applied them. From the VSAT operator prospective each tx carrier are seen, but i'm not able to lock the RX on both modem.
This is the first time i'm trying to establish scpc connection with iDirect 5300.
My need should be broad, i don't see which parameter to check.
modem_1.png (25 KB | 198 )
modem_2.png (25 KB | 216 )

Title: Re: iSCPC Link
Post by Admin1 on Aug 29th, 2014 at 8:19pm
I have no experience with iDirect options files.  Maybe someone with iDirect experience will identify some obvious problem.

Can you see your L band receive spectrum yourself on a spectrum analyser?  If so, verify the L band carrier frequencies and C/N ratios. Adjust your transmit levels under supervision from the network operations centre so that the C/Ns at your receive sites are both nominal. Make sure your carriers 'look right' with appropriate bandwidth, clean shape and with no interference humps, spikes or sidebands.  Turn them off and check the noise floor is clean underneath.  Record on paper for future reference.

If you have no analyser, ask the NOC to help you set the transmit levels correct for your size of dishes and location. It is likely that the modem tx powers will be different at each site. i.e. not both exactly -25 dBm at each site.

It may be that your levels are far too low to be received on small dishes at your locations, but fine for reception at the large teleport dish at the NOC.

Other possible problems could be:

.  that you are using co-pol rather than x-pol feeds, or vice versa. Almost all C band systems use x-pol feeds but a few satellites operate co-pol.

.  that you are using linear rather than circular polarisation or vice versa. If this was the case the NOC should have picked it up but if there is some giant carrier on the opposite polarisation they might miss the error.  You however would get dreadful interference on your wanted frequency.  It is really best if you observe your own L band receive spectrum on a good analyser.

.  that your LNB stability is worse than +/-50 kHz.  Only you can see this. If you have low stability DRO LNBs then the tuning may be in error by +/-500kHz or more. Check that your LNBs really have +/-50 kHz stability or better. If the entry really means "rx acquisition range" it might help to increase the setting to +/-100 kHz.

. Is the transmit reject filter that protects the LNB missing? If so when transmit is on the LNB might be overloaded with wanted receive signal suppressed.  In this case turning the tx off should make reception of the carrier from the other site ok.

Best regards, Eric

Title: Re: iSCPC Link
Post by fluffymassive on Sep 3rd, 2014 at 7:23am
Hi Habib D,

You need to make sure that the FEC Blocks per frame are the same on each modem. Then they will lock up.

[i]Transmit Side[/i]
FEC Blocks per frame: Select a frame length that is as close as possible to 125 ms.

Receive Side
FEC Blocks per Frame: Enter the same value as configured for the transmit properties of the peer remote.

Title: Re: iSCPC Link
Post by Habib D on Sep 19th, 2014 at 4:23pm
Hi Fluffymassive
As mentionned,  it was due to the FEC parameter. I just set it as indicated in your post and it's working.

Thank you all for your assistance, it was helpfull.

Title: Re: iSCPC Link
Post by fluffymassive on Sep 23rd, 2014 at 1:40am
No worries.

Glad it is now working! :)

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