Friday, August 5, 2011

Work on the 147.210 Repeater

Well after being plagued by problems with the 147.210 repeater over the last few years we finally were able to make some progress in determining it's future viability.  As you may know, this particular repeater is located inside one of the columns of the Talmadge Memorial Bridge which crosses over the Savannah River in downtown Savannah.  The problem has been the fact that the repeater would key up on it's own and just create a bunch of noise on the frequency.  The thinking was that it's location on the bridge over a major port authority corridor has become a very "noisy" RF environment with the addition of a variety of new radio sources since the post 9/11 increased security posture along the river.  Certainly all of that is true but we thought surely something must be wrong with our system to allow this increased RF to impact it so greatly.  We have been able to turn the repeater off by accessing the controller via DTMF tones but the problem started getting so bad that this was becoming ineffective.  Not very good operating practice to have a repeater out of our control.

So why haven't we been able to address this issue sooner and troubleshoot the problem?  Well that increased security posture that I mentioned makes accessing a major bridge over a major river very difficult to coordinate.  But after tasking the CARS club technical committee with coming up with a strategy to address the issue it was discovered that it may not be as difficult as we thought or at least as it once was.  Paul-KJ4FAV led the effort to figure out who we needed to coordinate with to gain access.  After a few phone calls, Paul had worked it out with Georgia DOT and we got a date on the calendar.  Paul and Mark-KA4CID coordinated with the folks at Savannah Communications to do some testing and analysis on the system.  So with a troubleshooting plan in place and bridge access coordinated, the day had arrived.

Paul and I met over at the Savannah Communications office this morning and we followed Mark and Ron downtown to the bridge.  When we arrived, GA DOT was already there and had the right lane blocked off for us.  The DOT guys opened the door to the southeast pillar for us to access the elevator which runs about a hundred feet up to the bridge cross section where the repeater is located.  The antenna is located in the top of the pillar about another 100 feet up accessible by ladders running up through the column.  The Sav Comm guys loaded up thier test equipment and headed up.  Paul and I followed with our tools, laptop, cables, connectors, gatorade, etc. 

Once we were all up to the area with the repeater we did a physical inspection to be sure everything was in place, connected, etc.  All looked good except for some reason the squelch knob on the front panel of the repeater was all the way open!  How the heck did that happen?  Sure would explain why adjacent noise or stray RF might be getting into the reciever section of the repeater and being retransmitted.  Mark adjusted the squelch and we power cycled the controller and the repeater came back up and started behaving like a normal repeater!  Well, almost.  There is still a tremendously high noise floor in the environment and there is a pulsing noise that can be heard when transmitting but nothing that causes the repeater to key up and belch all that noise like it had been doing.  We did a few radio checks and called Kevin-KW4B to give the repeater a try.  All seemed fine.

So, the Sav Comm guys went ahead and did a complete test and analysis of the repeater, duplexer, feedline, and antenna.  Everything checked out great.  We also connected one of our hand held radios to the antenna to verify the pulsing noise and it was still there so we know it's coming from the environment and not a problem with the repeater.  At least now we know that all of the equipment is in good shape.  That is except the controller which seems to have an intermittent power switch and configuration problems.  But it seems to be working well enough to keep it in place until we decide if we want to get a new one.  We may also go back to install a filter between the duplexer and reciever to see if that help at all with the noise. 

Made great headway and now we have a known baseline to work with as we monitor the repeater over the coming weeks.  Kudos to Mark at Savannah Comms for already compiling the analysis report and emailing it to us and to Paul for leading the effort on this project!

Guy McDonald, K4GTM
President, Coastal Amateur Radio Society

On the bridge roadway at the sooutheast pillar overlooking downtown Savannah

Access door to elevator

DOT and Savannah Communications Van

On the bridge looking into South Carolina

Paul-KJ4FAV going up in the elevator.  Close quarters!


Looking to the West in the span between the two south pillars

Looking up the pillar toward the top

Ron, Mark, and Guy-K4GTM

Paul-KJ4FAV at the top with beautiful downtown Savannah below

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