Re: 3cm receive only system

Colin G4EML



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.


Colin G4EML





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,

mechanically unmodified?

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



Dave, ZL3FJ

Christchurch, NZ










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