History

THE HISTORY OF THE BRISTOL 70cms REPEATER GROUP

 

GB3BS is one of the oldest Licensed UHF Repeaters in the UK. It was first licensed in 1974 and after negotiations with what was then Frenchay Hospital Trust; we gained permission to operate from Cossham Hospital in Bristol and commenced operations in 1976. The exact date has been lost in the winds of time.

The Pye Westminster W15U

This setup stayed on air until 1982 when GB3BS had a full revamp, we moved away from the W15U to a Pye F462 a PMR Base Station. We Also changed the Antenna system to a pair of stacked Finglas SA460 folded dipoles. Our Logic also was upgraded to the G3RKL Logic which was based on GB3US’s Mark 1 Logic.

We further upgraded the logic in 1984 to the Mark II Logic from G3RKL again this was based on the GB3US Mark II logic.

Our first repeater was based on a Pye Westminster W15U Boot mount PMR radio, The logic was totally home brew! The first antenna system was a pair of UHF dipoles, nothing spectacular, but we were on the air!

Unfortunately not many records exist of the actual station, nor do any photographs, such a shame that we cannot display anything of the original history of GB3BS.

GB3BS first antenna's

The Mark II Repeater

CTCSS Encoder/Decoder board

On the left is GB3BS as it was the day it was removed from site on the 19th April 2008.

 

On the Right is a picture of the Mark 2 BS Logic.

Left is the CTCSS encoder and decoder unit which was also capable of DTMF remote control. This was an add on to the logic pictured right.

On the Right is a picture of the Mark 3 BS Logic which was based on the 1802 processor.

The Mark 1 G3RKL Logic

The Mark 2 G3RKL Logic

 

All the above systems performed well, with only minor outages mainly caused by mains power failures when the hospital was testing their backup generators.

 

In 1996 we were contacted by the hospital management to inform us that they suspected GB3BS was causing access issues to motor verticals on site, this was a shock, and the group were concerned that we would be asked to vacate site. However working with the Hospital management we investigated the problem, and it was confirmed that GB3BS output was causing the problem on site. This was not due to GB3BS becoming faulty, but as a direct result of the poor design of the receivers used in the Car Keyfob system (for more information on this subject please visit Ofcoms website and search for RAKE). Once we had confirmed that the fault was not with GB3BS we were able to design and implement a solution that the Hospital were happy with

 

The Solution was a 418MHz Encoded transmitter that operated from a control box in the porters lodge. Pressing a “Stop button” on the front of the box transmitted a signal to GB3BS. The Receiver simply operated a small relay which was inserted into the repeaters Squelch line, thus breaking the line, and forcing the logic to think that the QSO had finished and no further traffic was using the repeater and moving the repeater back into standby mode.

 

This design was submitted to both ofcom and the Repeater Management Committee (Now the Emerging Technologies Committee) and was approved for use by both parties. We understand our solution has been used by several other repeater groups that suffered the same problems.

 

It simply offered the Hospital staff a method of forcing GB3BS to stop transmitting for a short period of time (Approx 2.5 Minutes). Because the solution only broke the Squelch line, it did not turn power off to the repeater so no issues to our licence conditions in reference to authorised persons turning on and off the repeater.

 

This solution stayed in place until 2007. When we were contacted by the new local administrator of the Hospital who informed us that we were now causing problems to the local Doctor’s surgery. We conducted several tests that suggested this new problem was not actually being caused by GB3BS, but obviously with our history of car keyfob problems it was not so easy to convince the hospital.

 

The Group decided to investigate the feasibility of moving GB3BS to one of the newly allocated wide split. Once we were happy that this route would fix our keyfob problems once and for all (Transmitting a 100W signal directly next to a car that we knew suffered from GB3BS blocking its keyfob on a wide split channel had no affect). Within a couple of day’s of us conducting our last tests we were again contacted by the new hospital manager, who was un aware of the button solution that we had already put into place, she was concerned that with the increased usage of the hospital the problem was becoming more and more disruptive. At the meeting we put forward our plan’s to move, and results of our tests we had been conducting. Thankfully the hospital Manager we were meeting was interested in our pro-active approach to the problems, and our attempts to resolve the issues prior. She also understood that the issues were not with GB3BS but the car alarms.

 

The New GB3BS

The Group decided if we were going to all the effort of moving GB3BS to a wide split, it would be sensible to replace the now aged transmitter, as we were not 100% sure if the tuning coils slugs would survive a re tune! We also decided that it would be sensible to upgrade the repeater Logic as the operational box was getting hard to source spare parts.

 

In September 2007 we settled on the RC210 Repeater Controller. Once it arrived in the UK, we started to build the new Mark III repeater. While we were waiting for the new logic to arrive, Mark obtained our new Tait transceiver system.

 

After many late nights, Electronics interface designs, conference calls (Both between the group and with Arcom in the states) and more coffee that is sensible the new GB3BS was switched on in its test environment in January 2008. It remain on the bench in test mode until we had our N.O.V. then it was off to site and the new GB3BS was officially switched on, on Saturday 19th April 2008.

All was fine, Car alarm problems gone, well, all except one elderly Gent who was convinced that GB3BS was still causing him issues with his old Skoda, a new set of batteries in the keyfob soon had the gent back on the road so to speak.

 

Although GB3BS was on the bench for such a long time, we did find a few bugs and quirks with the live production version. These we worked with Ken Arc in the USA (Who I must say is one of the most helpful people I have ever spoken to) and have resolved most of the problems. In fact we bought a spare logic unit and spare radio parts so that in the event of failure we have all the parts we would need to get the box back on air quickly. We use the spare logic as a “Sand pit” environment for testing, and have been able to Beta Test software for Ken.

 

All has been fine with GB3BS until May 2009 when, out of the blue we were served noticed to leave site by South Gloucester Primary Healthcare trust (The new owners of Cossham Hospital). Although this was not un-expected due to our knowledge that Cossham was due to have a £18m refurbishment, it was still a shock

 

The Group had several meetings which were to plan what we were going to do, if we were going to attempt to re-gain access to Cossham once the refurbishment was complete (Finding a Temporary site while the work was being done), find another site, or just simply turn the box off, walk away and add it to the ever increasing list of repeaters that are going off air.

 

I am glad to say we went for the second option of finding a new home!

 

Mark and I drew up battle plans, we did have some restrictions with potential sites due to the very high saturation of UHF repeaters around the Bristol area. Also the lay of the land so to speak had a big influence on potential sites.

 

It was decided we would create an information pack that we could send to potential sites, both to introduce our selves, but more importantly to make a direct request for help with securing a site for the repeater. We nicked named the pack “The Sales Brochure” as it was trying to sell the group to a potential site.

 

10 packs were sent directly out to a number of high profile sites, some instantly wrote back stating Health and Safety restraints on accessing their sites. One company offered us some tower space but wanted £5K Plus a year in rent, something we would never be able to afford!

 

Another site did offer us some space, and we started exploring working with them, at the same time I cold called a few more sites, and finally hit a site manager that was already knowledgeable of Amateur Radio, and what it can bring to the community, we were invited to forward an information pack to him.

 

Which of course we did. A follow up call was made a week or so later, primarily to ensure delivery of the pack. While speaking to the site manager he requested we contact BANES Raynet Group as they already have a presence on site, and to ensure that our equipment would not interfere with their operations.

 

I contacted the Area coordinator, and after a site visit, meeting up with Phil from Raynet and the site manager, it was discovered that we as a group could benefit Raynet, and they could benefit us.

 

We have been continuing to work with the site owners, and at the start of September we received an official invite from Avon Fire & Rescue to use their site at Lansdown.

 

Further meetings were held to finalise where we could go equipment wise, and we were put in touch with another company that are already onsite. I was put in contact with a lady who was the third party companies senior technician. Working with the 3rd party company it became apparent that they were about to abandon one of the buildings they occupied and they were more than happy to sign the building back to Avon Fire & Rescue, and for us to take over ownership of this building. What was also a surprise was the building came with its own 3KW Generator.

 

So after spending several months tying to find a site, we have now secured a site, our own building for the repeater to be fitted in, own backup power supplies. And access to a 30mtr tower. Everything the repeater group could ever need.

 

We have also appointed a commercial rigging company to install our new antenna system on the tower! (It was decided to abandon the original antennas firstly to save group funds, but secondly as the original antenna's are over 20 years old, and we know that the upper element has a fault).

 

Our NOV for a site move was submitted the day after our official invite was provided. This I am pleased to say was issued on the 9th of October 2009 and at the time of writing this; we are working on the site refurbishment and planning on move dates which we hope to be by the end of November 2009.

 

Updated 23/05/2010: we moved GB3BS to Lansdown on the 19th December 2009. Although the repeater was on a temporary antenna system for a few months, this reduced the service area of GB3BS, some users understood, others did not. However on the 19th April 2010 we finally had our main antenna installed.

 

The new GB3BS Rack

November 24th 2013 the repeater group applied for a N.o.v. to operate a Digital Mobile Radio repeater. DMR is a true digital mode, providing internet linking, very narrow bandwidth and two situations QSO on a single channel. On top of this, this new mode also allows features such as checking a person has their radio switched on and tuned to the same timeslot you are using, send them a simple text message or request a private QSO with them, although the latter is frown on as not being in the spirit of repeaters, or amateur radio.

 

On the 20th January 2014 we were issued a NOV by Ofcom for GB7BS, we were not expecting such a fast turn around as normally delays are in excess of 7 months.

 

Also in January we took delivery of some radio samples from BFDX in china, these radios are DMR hand portables, the TD501. The radios are brilliant for the money, BUT lack CTCSS which make them useless for Ham Radio use. BFDX then sent us some samples of the BFDX TD503 (we had serial 003 and 004 !!) These looked better, and had the CTCSS, and a nice colour display. BUT again were no good as they had several issues with firmware, something BFDX were not willing to talk to us to find a fix, even after we sent them a full technical breakdown of the faults. It was desided not to continue working with BFDX as we were not getting anywhere with customer services.

 

On the 20th April (after a lot of research and conversation between Mark and I) we had a brand new shiney DR3000 repeater in our hands, funded by Mark and I and not the Repeater Group as funds would not allow it. We selected the Motorola DR3000 over the Hytera repeater, not on Technical engineering, but simply on compatablity grounds.

Over May and June 2014 (while I was off seeing parts of the USA not many tourists see), Mark concentrated on building a duplexer and combiner antenna system. It was the intention to use the GB3BS main antenna, combine both repeaters and use it (The antenna) for both boxes.

Part of the combiner system and circulator

A PROBLEM

Mark was seeing some very strange results of the combiner system, something was unstable. We hoped to launch GB7BS at the Frome Rally June 2014. But tests conducted and tweaks to the combiner system all indicated the Repeater Group had a problem with the main antenna. We were also seeing GB3BS entering a failsafe mode and backing off the forward RF power, this would happen even if the old antenna system was re-installed. Finally Mark was able to capture it, and get to site to conduct tests while this fault was happening, one of the problems of intermittent faults.

 

The Motorola DR3000 Repeater

We had been discussing with the keepers of GB7AA, GB7JB, GB7DR and GB7SD on a linking project. Mark and I had been following the ever growing DMR-MARC repeater groups within the UK, and found it to be VERY over complicated in its operation, and a political hot pot, something we ALL wanted to keep well away from so it was planned to form the "South West Cluster" of DMR repeaters.

The Southwest Cluster coverage map

The long and short of it was the Repeater Group had a problem with our main antenna, or its feeder. what ever happened, we needed a tower climb to inspect the coax and antenna. With the cost of hire of a crew to climb it made financial sense to simply replace the antenna (the most likely fault).

If needed, we had enough feeder spare to replace the existing run. On the 21st September the Antenna WAS replaced and a visual inspection of the feeder showed it to be water tight and in good conditio (good old Denso tape :) ) . See our 2014 newsletter for the full story and autopsy of the antenna. Durring testing a problem was identified and resolved with the circulator and the steel chassis it was mounted to. Also some fine tuning "Tweaks" were needed to finalise isolation of the two repeaters.

With the proof "Two does go into one" The Repeater GB7BS was officially commissioned on the evening of October 16th 2014. Our thanks go to the stations that helped test the repeater during its commissioning.

 

Since its launch, there has been a steady increase of activity on GB7BS as the mode becomes more accessible to people, something of a flashback in time to the launch of repeaters on the 70cms band back in the 1970's. There has also been no reduction of activity of its older sister GB3BS. Something we are glad about!

 

Once GB7BS went like (In local mode only, no internet linking) we moved our attention to the next step in the very long list of thing to do.

 

Getting Broadband on site.

 

The Finanlised antenna combiner (C)Bristol 70cms Repeater Group.

30th November 2014, we had installed a 2.4GHz link from my home QTH to Lansdown. Although this worked (most of the time) there was network drop out, something initially assumed to be alignment at my QTH, but non long after having the dish at my QTH re-aligned and the fault returned.

I investigated the 2.4GHz noise floor at Both Lansdown and my own home QTH.

 

The Lansdown end had a noise floor in excess of -130dBm, with a received signal level of around -81dBm.

 

At my end the levels were shocking. I could RX Lansdown at about -79dBm BUT and this was a BIG but, the noise floor was one minute -90dBm and then next was at -60dBm, at least it proved the kit was working, it was simply the receiver at my QTH was being swamped by nearby wifi links.

 

The only choice we had was to move to the 5GHz band, a full site survey was done, and this time both ends were in excess of -130dBm, By January 26th we had a network on site, and GB7BS was already linked to GB7AA. By the 15th February 2015 GB7SD was linked, followed by GB7JB and GB7DR, both were on air and linked in by the 24th March 2015. The South West Cluster was up and fully operational.

 

The (now defunc) 2.4GHz dish in place

The Noise floor at G7FBD QTH

In January 2015. G7FBD secured an NOV to operate a APRS Digipeter/Igate to compliment the Bristol and surrounding area APRS network. The project, although not funded by the repeater group, has its home at Lansdown along side our main line repeaters. MB7VV went live early April 2015. We know APRS operates on 2m an yet we are the Bristol 70cms Repeater Group, but.. see MB7VV Technical for more information.

Our new Ubiquiti 5GHz Dish prior to installation.

MB7VV on the bench being tested prior to install

APRS traffic on the local "Network"

Over the last 38 years+ The Repeater Group has grown and changed, and moved. It has and still is at times a thankless task to keep repeaters on the air. But the support we receive from our members keeps the Group alive, and pushing forward.

More history events will be added as future events unfold.

 

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