Re: Dual Link Margin script SR1lm.pl


David J Taylor GM8ARV 🏴󠁧󠁢󠁳󠁣󠁴󠁿 🇪🇺
 

On 16/11/2021 20:02, Ernst Lobsiger via groups.io wrote:
David,

yes the LM of HVS is normally the problem. With a reasonably sized antenna BAS
almost always has a considerable LM.
Of course the constants I use are only "empirical" as far as I have found those
from looking at an SR1 status display.
The SR1 people have certainly calculated those from MODCOD and maybe max symbol
rate and other HW settings.

FYI: Yesterday I also did the test with two other SR1 EUMETCast receiver
stations on your page:

Loughborough SR1 #1:   SNR (EsNo) = 13.9 dB   /  LMbas = 8.0 dB  /  LM hvs-1 =
4.6 dB
Rungsted Ayecka SR1:   SNR (EsNo) = 13.6 dB   /  LMbas = 7.7 dB  /  LM hvs-1 =
4.3 dB

Both SR1 receivers fulfill my simple equations.

But those do not work exactly with Thorsten's Novra S300N. The Novra staff has
a slightly
different idea what LM = 0dB means. This might also be to some extent HW dependant.

Cheers,
Ernst
Yes, empirical, but good enough to compare across the same devices. My guess
is that the passband shape will come into it, and how that affects both the
noise distribution across the passband, and the shape of the recovered digital
signal. It wouldn't surprise me if different companies had different definitions.

Some definitions talk about "when the receiver stops working", but what does
that mean? With digital systems there isn't a sudden stop between LM := +0.1
dB and LM := -0.1 dB, so should the "acceptable" bit error rate come into the
definition?

I see the value of these measurements as being for individuals to watch for any
gradual degradation in their system or to monitor improvements they may make,
or for comparisons across Europe to answer questions such as "I live in
Helsinki - what dish might I need?".

The more monitoring stations sharing their data the better!

Cheers,
David
--
SatSignal Software - Quality software for you
Web: https://www.satsignal.eu
Email: david-taylor@blueyonder.co.uk
Twitter: @gm8arv

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