Snaefell Antenna Update 16 July 2013
Update 16th July 2013
The continuing good weather afforded us an opportunity to get the water-logged feeder replaced. The cable installed in its place is WestFlex W103 and the difference it has made has been little short of amazing.
Allowing for the low height of the antenna, we are getting remarkably good coverage with practically no sign of the burps, buzzes and gurgles that have plagued us up to the present.
Unfortunately, due to other commitments, I was unable to attend the site whilst this work was carried out but I would like to extend my thanks to those who were involved.
Our present situation, then, is likely to be the status quo until such time as we can make the final move up the tower. When that will happen is still unknown.
Updated 23rd June 2013
GB3GD was today returned to service but with disappointing results. There is a significant de-sensitisation problem which is not apparent when the system is connected to the test set, indicating that external factors are at work.
With the aerial connected, stations that can be heard with the repeater's transmitter off, become noisy and unreadable when the transmitter is turned on.
Whilst that is not a good thing, what makes matters worse is that today we came across the one sight that would make any radio person's heart sink (click image for larger picture):
This is not what I thought was meant by a Leaky Feeder!!
Whilst things appear to be working at present, this is likely to become an issue quite quickly unless the cable can be replaced.
Our status at present, then is as follows:
TX output to the antenna is approx. 22 Watts.
Receiver suffering external noise issues, making it difficult to use for all but the strongest incoming signals.
Snaefell site - TX output 20 Watts, Receiver working well.
Carnane Site - TX output 1 Watt (5W ERP). Site fully operational
Bride Site - Same status as Carnane
Andy Morgan (GD1MIP) took a short video of the conditions on site today. Thanks Andy.
Updated 22nd June 2013
Today a group of volunteers ventured up to the summit of Snaefell for the dual purposes of looking into our noise issues and looking at the scenery. I was grateful for the help as there was a fair amount of kit to carry (Spectrum Analyser, Marconi 2955 test set, Replacement radio for GB3IM-S, tools and documents). Had I been alone, I'd have still been up there fetching and carrying!
We began by assessing the present situation. This was done by radiating a weak signal from the test set and listening to see how the two repeaters responded - not well!!
There were burbles and buzzes everywhere. Connecting the antenna to the spectrum analyzer revealed a mess of noise within the 70cm band.
Since the temporary antenna is fed with UR67 (not ideal for a site like snaefell where there are two broadcast transmitters in the same room, along with a bunch of other stuff), we thought that perhaps some of the problem might have been pick-up along the cable. It turned out that the feeder was bundled tightly with half a dozen other cables, so we released our feeder from the clutches of its friends and routed it as far away from them as we could manage. That made a significant difference, which was fortunate as there would have been nothing else that we could have done.
GB3IM's radio has been replaced with another of the same type (Philips PRF1060) except that the one now installed has a logic module of a similar type as that in use on 'GD. There are a couple of differences between the 'IM logic and 'GD, most notably in that CTCSS generation and detection as well as all audio gating and tone generation are all carried out within the logic board.
GB3GD exhibited some rather odd symptoms whilst on site, including a rather nasty hum on receive and apparently poor receiver sensitivity. Rather than struggle with these issues up on the hill, it was decided to retrieve the radio back to the bench for checks. As I type, the transmitter is on full power soak test into a dummy load and the receiver has been checked out.
I hope to return 'GD to service tomorrow (23rd).
[Pictured - Procomm antenna in its temporary location at roof height.]
On Monday 17th June 2013, the Communications Division rigger took the opportunity to install our new dual-band antenna in a temporary location on the Snaefell tower.
He had previously installed a Watson "White Stick" dual bander in the same location but, due to the poor construction quality of the antenna, it only lasted a month.
The new antenna is very rugged and we are confident that it will survive a winter or two (hopefully many more than that). Its current position is only temporary, pending a move to its agreed location at about 25 metres AGL in due course.
Since its installation, very good coverage has been observed and it is especially noteworthy given the fact that the mounting location on the west leg of the tower is at the same level as the roof of the building, making it about 3 metres above ground, with a brick building to the west and a tower to the east. It really is between a rock and a hard place.
Unfortunately it has not all been plain sailing.
We are experiencing extreme de-sensitisation on the receivers of both repeaters, making them unusable at present. The origin of the interference is unknown and, at present, all we can do is speculate until we have visited the site to investigate the matter further.
For the latest on progress, please check back here from time to time.