Re: Wideband 70cms racket


John Fell
 

About 20 years ago , when the civil services introduced the still current digital comms system ,I was looking after GB3SZ , the UHF 1.6MHz split Repeater in central Bournemouth.
Being based on the usual Pye deck + Amateur band tweaks ,the RX squelch was hammered when the local Police started the new system from 150m LOS.

The late Nick Foot G4WHO and I had to spend considerable time adding cavity filtering and tweaking the system using R&S sig gens , comms Rxs and Spec Anns on top of a 10 storey office block.

We got our own back when some months later I was rung up by an officer from the RF investigations division in Bristol .He asked if I knew about an RF device sending "something one of our lot thinks is Morse " and after several mins thinks it sends GB3SC .

I was able to confirm being the Keeper and that it was a VHF Repeater .

He said they were getting occasional breakthrough on a newly installed multi-site repeater , which had a node 150m away .....

I referred him to Nick ,who just happened to be the Owner/MD of AQL EMC .

Nick had a chat and agreed to go to the Bournemouth site for  alook .

Turns out a contractor had gone through the Control Room and removed some cylindrical objects that had " nothing to do with the new system  " .i.e. they had dissed the antenna filtering components used to provide selective performance from out of band high level sources of RF .

As it turned out they had kept the items in a store room and Nick was able to refit - the complete multi-site system performance improved considerably and Nick picked up another Consultancy contract .

70cm is a shared Secondary allocation and has been for many years . I hope the current crop of QRM crap fails fast .

73
John
G0API

On Wed, 27 Jan 2021 at 11:54, Colin Ranson <g8lbs@...> wrote:

John,

 

On the input of IH its like ‘chuff........ chuff,chuff’    ‘chuff.........chuff,chuff’ on weak signals and  as you say, at various times, also very broadband.

 

 

Colin de G8LBS.

 

Sent from Mail for Windows 10

 

From: G8ACE
Sent: 27 January 2021 11:21
To: UKMicrowaves@groups.io
Subject: Re: [UKMicrowaves] Wideband 70cms racket

 

There have been several different 70cm rackets in recent months.  Is this the one that sounds like 1pps marching on the spot.  It moves around and can occur on repeater inputs and outputs.  Its audible  at various times on all the 70cm repeaters I can receive .  It starts up and goes away without warning and seems very hard to get a bearing on.  I suspect its multiple sources and we are likely stuck with it from now on as I guess its almost certainly a licence free qrm machine.
73s John G8ACE

 

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