SatSig topic:

zero burst

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Apr 19^th, 2010 at 4:12pm

Does anyone experience zero burst on HLC's?in version 6.0.9.7.
the acq bursts are there as shown in spectrum analyzer, but cannot be detected by HLC. usually it was solved by switch off the frequency hopping to carrier grooming mode. the reference clock is got from internal clock of RCM.
Any idea?

Thank's

Apr 23^rd, 2010 at 12:01am

Upgrade.. That happened a lot back in the old revisions.

Apr 23^rd, 2010 at 11:51am

Wbailey is correct. What you describe was noted in previous versions (espp 6.X).. Are you familiar with the peek and poke process to adjust the agc setting on your Rx HLCs?

Apr 29^th, 2010 at 12:12pm

Agree with Mike....we had a lot of trouble with older iDS versions and we had to do the peek and poke procedure and also enter a custom key on the HLC. We found that the HLC's had real trouble letting the first remote on a network in.

May 2^nd, 2010 at 1:44am

I've done the peek and poke procedure and set the custom key on each HLC. but, it still happened sometimes...

Sep 12^th, 2010 at 3:58am

Dear guys,

It's getting more crazy at the moment. it happens almost every hour. The HLC's are set with custom key already, but no changes.
Is there any solution other than upgrade?

Thank's alot,

dean

Sep 12^th, 2010 at 1:40pm

You really need to move away from 6.0.9.7. Preferably to an iDS that automatically sets the agc. Are you certain that your power levels on the remotes are set appropriately? If they are not within the sliding window of the UCP they will likely be ignored. Double check your remote power levels to ensure they are not too low, or too high.

Sep 12^th, 2010 at 4:40pm

I'd also make sure there is no interference and that the satellite is still performing according to spec first.

Sep 14^th, 2010 at 1:51am

I'm sure there are no interference and the UCP is working fine. it doesn't happen to all HLC in the same time, but randomly.

Thank's

Sep 14^th, 2010 at 11:14am

Since you say the UCP is working fine.....when you dump the acquisition bursts (-a) on the RX line card(s) of the inroute group... what are the SNR values of your remotes attempting to burst in?

Sep 14^th, 2010 at 2:12pm

in normal condition (no zero on line card's burst), the SNR are above 8dB when acquiring to the network according to the initial tx power I've set.
but when zero burst happen, it drops below 4dB even the SNR shown on SPEC AN are normal (as it was 8dB)...

Sep 14^th, 2010 at 3:11pm

If the demod shows 4dB and the burst as seen on the spec an looks normal ( 8dB ) I would suggest:

There is phase noise in the burst - power supply or VCXO in the transmit modem ?

There is ampitude drift during the burst - power supply to the BUC, DC ohms in too long cable ? Does the burst start with a high amplitude overshoot ?

There is interference due to spectral regrowth from bursts on adjacent return link frequency slots. Use spec an in peak hold mode and wait to see if the gaps between the burst carrier frequencies fill up.

Other interference. Turn off or move all the sites on that return link frequency elsewhere. Use spec an in peak hold mode and wait to see if the carrier slot remains empty.

The wanted burst is from a BUC at or beyond saturation. Reduce the BUC drive until the output level starts going down dB for dB.

The burst is off frequency. PLL problems, digits on freq settings not exactly the same.

Just some ideas - not in any kind of order and may not be relevent at all..

In a similar context, I have seen the burst error rate degrade on all burst receivers at a hub due to a noisy DC power supply for the LNB or IF distribution amplifiers - even though the bursts all looked good on the spec an. The secret was to look at the receive IF spectrum between 25 Hz and 200 kHz.

Best regards, Eric.

Jan 4^th, 2011 at 1:39pm

Finally I survived from this zero burst problem and it's been back to normal for 2 months. I didn't know what was really happened exactly, but I did some changes like:
1. rearrange carriers for getting some more space
2. switching the operating RCM from A to B
3. Replace the IFL cable with better one
4. add a line amplifier right before the LNB DC power supply

anyway, thank's for the advices, Guys, Eric...

Best Regards