Re: 3cm receive only system
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The problem is that the supply of LNBs is very unpredictable. Even those with the same part number often have different insides.
The Octagon LNBS were at one time very popular but QO-100 has caused the supply of those to dry up.
Basically any PLL type LNB will probably do what you want but there is always an element of chance when ordering. Feed it with 18 V via a Bias T and listen on 618 MHz with a SDR Dongle.
You can get away without modifying if you are happy to cope with quite a lot of drift. The frequency can be expected to be off by 100s of KHz at 10GHz with temperature drift. But it is normally fairly slow so you can still receive beacons OK. If you have a strong beacon to act as a marker it is not too much of a problem to compensate for the drift but if you only have weak beacons then you may struggle to find them.
It is fairly easy to modify most LNBs to feed in an external high stability reference, once you do that they work very well. I have had one on my mast without a dish for some years now and I can often hear beacons by rain scatter.
From: Dave Brown
Sent: 18 February 2021 21:48
Subject: [UKMicrowaves] 3cm receive only system
I want to set up a receive only 3cm system to monitor beacons etc.
I understand that there are a few LNBs that use a crystal controlled LO and
some of these are being used (with mods) to receive QO-100. As this
application is 3cm receive only I believe I should be able to use the LNB,
I have no real limitations as regards IF frequency as long as its below
2GHz . I'm looking for recommendations as to which of the few LNBs available
that fall in this category I should get. If I can get away with no LO mods
so much the better but happy to eventually use an external frequency source
if I find stability inadequate. Had a trawl through earlier posts re QO-100
etc but no clear picture has emerged re which LNB might be best for this