SNTWRSML.JPG (7456 bytes)

GB3SN
_______

History


A very brief history of the repeater....

GB3SN was one of the first UK repeaters to go on air back in 1975.  The 1970s was the period when repeaters were novelties, mobile setups were things like Pye Cambridges installed in Morris Marinas, and 2m was gradually being dragged into FM and channels from AM and tuning high to low.  When the rot set in some would say....

Of course, not everyone was that keen on repeaters, and the repeater was subjected to various forms of abuse as well as bona fide users.  The worst attack suffered by the repeater occurred when someone forced an opening in the hut where the repeater lives, and put in a smoke device.  Try and justify that to your landlord.... The logic developed in a way designed to withstand a certain level of abuse, and the receiver sensitivity was restricted.  Luckily, over time the conditions changed, repeaters became more accepted, more repeaters came on air and the pressure on the early repeaters was reduced.

In the early 1980s, a new repeater was put under development.  However, there was also a radical shakeup in the group as well, and the repeater was handed over to a new group of people to complete the engineering, shake out the bugs and get it on the air.  This job was completed in late 1984, when the MkII was put on air.  Compared with the MkI unit, MkII was much more sensitive, and the logic was made simpler and more predictable to use.  This was in turn gradually evolved over the years; battery backup was instigated, a backup repeater was engineered (actually based on the MkI unit, but with a lot of the insides replaced), commercial cavities replaced the original homebrew items, and a commercial colinear antenna was put on the tower, which gave markedly improved performance.

In the year 2000, repeaters on 2m were migrated to 12.5kHz channel spacing, to release extra FM channels on the 2m band.  A new repeater was built based around the much later Storno CQF9000 series base station to conform to this, and at the same time to add CTCSS.   See 'specifications' for more information.

The one perennial problem on the site has been local sources of noise which are generated when the transmitter is in operation.  These are probably a combination of rusty bolt effect from an ageing reinforced concrete structure that is full of water, and possible interaction with other electronics on site.  This has made desensitisation of the receiver by the transmitter a continual problem with a sensitive receiver.  We also have suffered from limited lifetime of the 6dBd commercial colinears, possibly due to movement at the top of the 20ft pole which in turn is mounted on the water tower.  In October 2015, the antenna system has been replaced, and a second antenna mounting on the tower repurposed to allow twin antennas to be run.  The feeder has also been changed, to two runs of LDF4-50.  The transmitter uses a 4.5dBd colinear on a 10ft pole, and the receiver uses a 6dBd colinear on a 6ft pole.  Our hope is that the shorter, stronger poles will be more stable, and give better antenna lifetime, and the use of twin antennas will prevent the rusty bolt effect desensitising the receiver.

 

 



Home page

Copyright 2015 The UK FM Southern Repeater Holding Group