Re: Signal Drop


Prem
 

A hot dish can expand or shrink when cooling. It can also distort it's shape very slightly which can affect your signal. There is also your coax cable, mainly copper which will expand and/or shrink to a greater extent than your dish. This can also affect the length of cable which again will slightly affect your signal strength. All coax cables should be cut to the correct length for the frequency that they are being used for. As has already been said, atmospherics plus numerous other spanners in the works without me adding further.

Prem Holdaway (G0DCP)
Phold29@talktalk.net

-----Original Message-----
From: MSG-1@groups.io [mailto:MSG-1@groups.io] On Behalf Of David J
Taylor via groups.io
Sent: 27 May 2020 10:31
To: MSG-1@groups.io
Subject: Re: [MSG-1] Signal Drop

David,

Interesting comments.

A problem is, I'm not an RF engineer and I'm just reporting what my SR1 and
SatPal meter are showing.
What it all means, is another matter :-)

Last year(?) Klaus Peter suggested I looked into 'atmospherics' effecting
satellite signals which I did and I think I wrote a GEO article on my
findings.
Of course the sun is very high in the northern hemisphere at the moment so
I
guess we should expect some 'turbulence?'

LNB umbrella is in place and the LNB is shaded from the sun and keeping cool
at 09:00 UTC.
However, my dark grey 1 m dish gets hot enough to fry an egg - so that will
be radiating 'thermal energy.'
I wonder if that is a factor?

I have a plan to temporarily deal with the dish warming - watch this space.

SR1 TP 1 SNR down from 13.0 dB last night to 12.6/5 dB at the moment with
cool LNB.

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

John,

First thoughts are that a hot dish means the LNB is looking at a warm source
rather than the cold sky! Warm means more noise, poorer SNR, lower link
margin. However, it depends on what the dish "looks" like at 11 GHz.

Perhaps that grey surface is fully reflective at that frequency, so the LNB
is looking at a cold sky. I don't think it will be a perfect reflector, so
some dish temperature rise will result in SNR loss.

The other effect is that the LNB will have at least /some/ "seeing" outside
the disk of the dish, so a warm background is not desirable. Moving the LNB
nearer the dish will result in "seeing" less outside the dish, but having a
smaller capture area and hence get a smaller amount of signal.

Keep monitoring!

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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