Re: Gaps in AVHRR images yesterday.


David J Taylor GM8ARV 🏴󠁧󠁢󠁳󠁣󠁴󠁿 🇪🇺
 

David,

Sorry for the delay in responding - just seen this 'way down the pile.'

My SNR is always around 13.00 dB in clear sky conditions, so I guess that is not the problem and disabling HVS-1 won't make much difference?

- check both TelliCast for [ideally] zero packet loss, missed and recovered.
There are some systems where there is steady stream of missed and recovered
packets, but with the same count for each. Temporarily disable HVS-1 and
check again. BAS should have zero packet loss.

This is a bit 'worrying' as I don't remember ever having zero MP's even before HVS-1.
And the old version of Tellicast.


Remember, I have an SR1 that regularly indicates minus (into the 1,000's) value of traffic for up to 5 seconds.
And, as Ernst and I think, we get missed packets when we 'switch on' (use) another quad LNB port on another receiver on the EUMETCast LNB.


At the moment my statistics from 2020-09-10 14:31 (13 days) are:


BS MPb4 FEC 2284. FEC RP 181.


HVS-1 MPb4 FEC 1763 FEC RP 14.


SR1 statistics for same period Bad Frame Count 139. Bad Packet Count 281.


I would not add too much weight to these figures, although through a clear sky period, as I've been moving around in front of the dish doing patio work and we had a period of heavy rain last night.


Regards,
John.
==================================

John,

I'm pretty sure that Robert's issue with large EARS AVHRR gaps is something other than simple lack of link margin, so I'll wait until he can report back.

Missed packets can be caused by a variety of reasons, and EUMETSAT's document TD 15 goes into a lot of the causes, slow or busy disks being the most likely culprits. That's why a number of us now use a RAMdisk for both tmp and received data, with a e.g. Robocopy running once a minute to move any received files onto an HDD for further processing. For BAS alone, I'd recommend ~1.5 GB RAMdisk.

Obviously obstructing the dish will cause data loss, and heavy rain and thick cloud (ice-crystal-topped) too.

Cheers,
David
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