We have added a form to allow Repeater Signal Strength Reports as it is always useful to receive reports of how well our repeaters are being heard and we really appreciate it when people take the time to tell us. If you have time please fill in the form to provide feedback on repeater strengths in various locations:  http://www.cambridgerepeaters.net/repeaters/

Repeater Timeouts – and why we have them.

Some people, as you know, seem to enjoy timing out on the repeaters in the CRG area. But why do we have a timeout in the first place? No, it’s not a hindrance, it’s there for a good reason.

While the repeater PA could handle 100% duty at its current setting, the idea of the timeout is to give other people a chance to make use of the repeater. The idea of the repeater in the first place is for mobile stations (in vehicle, or on foot etc…) to extend their operating range. It is not a platform for broadcasting, and it should be remembered that at peak times, with heavy traffic, there is a chance that a amateur mobile operator may come across a situation where they need to make an urgent call, and that means pretty well “now”, not in 3/6/9 minutes time.

What do I mean? Well, GB3PI has a 3 minute timeout. But some people think it’s OK to timeout, grab a reset, then have another bite, maybe another timeout, and some more…. That’s not good operating practice, and they should know better. Especially those who work in the commercial radio comms trade where we often set timeouts to 1min, AND have “hog” timers where users that monopolise community base stations suffer a further lockout if they exceed a pre-defined amount of use. It’s all to promote fair usage, and give other users a chance to utilise the equipment.

What does this mean for CRG repeaters? Quite simply, if the current situation continues, I am going to investigate a number of options which include an aggressive timeout policy on CRG repeaters, where the timeout is set at a generous 3min, but will reduce to 2min if the repeater times out again in a given period, and if it times out again, it will reduce to 1min, then 30seconds, and finaly the repeater will shut down for five minutes.

Another option includes utilising a transmitter signature system to identify offending stations and adjust the timeout according to their behaviour. That last option may be a little draconian, but it’s on the table!

Why has it come to this? – Comments have been made by some people that they don’t use our repeaters much these days because they can’t get a word in edgeways, and when they do, their journey is over before they get to have a proper go. So they just don’t bother turning it on. The next step is not having a radio in the car, followed by leaving the hobby. So why should the selfish actions of one of two people ruin the hobby for many more?

Look at it from that perspective. Your journey to work takes 15 mins. Enough time for a few overs in normal QSO. Then take it with our repeater hog on air – taking 2/3 x timeouts @ 3min each = 6/9mins per transmission. You *might* get one go, you probably will only get the chance to announce yourself on the repeater, and the next time it’s 73!! Not good at all.

Education has been tried, and it’s failed. It’s time for action!

Hi all,

Thanks to everyone for the updates regarding the loss of power at the Madingley site on 20/01/12, it sure gave the batteries a good test and I would say they worked well.

If you look at the telemetry MB7UM sends out here http://goo.gl/C6g7f you can see the 4th graph down showing the mains power state (010 for ON and 000 for OFF). Power went for somewhere between 16:50:41 and 17:02:20 and came back on between 00:00:17 and 00:11:53 (how cool is it we can tell this now!). That was a duration of about 7 hours.

Back on the telemetry, the 24v graph (2nd one down) shows a drop in voltage from ~27.5v to 25.0v, 27.5v is the charging voltage, but held steady at 25.0v for most of the time after, some slight fluctuations towards the end. The 12v (top graph) didn’t change at all (the fluctuations between 13.9v and 14.1v is probably ADC error). Note the graphs are the actual value x10 which allows greater resolution.

The only thing I need to work out is why the temperature jumped 8C when the power can back on (between 00:00 and 00:47). This *might* be an ADC reference voltage error, but I can’t see how as it is run off a 5v rail which shouldn’t have been affected. There is a heater in there so maybe it’s just a very good one!

Anyway great work by Phil G4BIK who not only updated GB3PY’s logic to send a ‘B’ between overs instead of a ‘K’ when on batteries, and for plumbing in the new rectifier and battery backup system which worked a treat over the 7 hours.

Gavin M1BXF

CRG Technical Coordinator

The story of GB3PE – from the CRG perspective!

In October 2010, the group operating GB3PE took the decision to close it down, together with GB3PB (70cm), partly due to equipment unreliability, partly due to those working on the kit having no time to do so. When I heard that this had happened, I immediately set about finding out if the original keeper – G1ARV – would transfer the NoV to the CRG, and we could then re-establish it.

He had already issued the “E0″ form to the ETCC to formally close the repeater down, so we would need to ask Ofcom. Sadly, Rod Wilkinson was on extended sick leave, so was unable to help.

I contacted the original site owner, Dalmark Grain, and asked if we would be able to re-establish the repeater on their site. They were most accommodating and agreed – subject to licencing. The NoV appeared on my doormat in early January 2011, and to be honest, caught me unawares! I was expecting it to take a number of months, not a number of weeks!

Work commitments meant that I had no time to really work on the repeater until June/July, even though I had a base station programmed and tested, with a controller, all ready to go at the CRG Rally at Easter. The delay was caused by the filtering.

The grainstore at Thorney Toll has a loft cavity (where the repeater is housed), and this is subject to some large swings of temperature through the year. I expect to see temperatures in excess of 45degC in the summer, and ambient external type temperatures during the winter (so could be freezing!).

I’ve covered the filtering woes and issues in previous posts, so won’t go into that any further now. With everything finally ready to go in late October, all that was needed was some kind weather, and site owner’s permission to get in there and do it.

The first week of November was sporadic with its weather, though I had quite a lot of work on, so couldn’t spend the time. I planned for Thursday 10^th November, the long range weather forecast looked favourable, low wind levels, no rain, and reasonably temperate for the time of year. Dalmark grain were happy for us to go on Thursday, they only operate the site one or two days a week, and Thursday was one of those days. Once on site, Andy G6OHM, struggled up to the loft to see what we were dealing with. He admired the view, and took a few pictures.

Starting with me….

Getting the LDF4-50 and bits out of the van ready to go up the silo.

Looking out to the south west over the A47.

Looking from the end of the building where the kit is, a little dusty!! At the other end, you can just see the top of the stairs where we enter the loft.

The building, with the aerial hoisted up, but not fitted properly yet. The top is 30m AGL.

To get the equipment up there, we threw a rope down, attached it to a large black bin, and I pulled it all the way up. A touch tiring!!

Having a breather…..

Bolting the mast (6m pole) in place took a bit of work, Andy held on to the pole for dear life, while I climbed up and attempted to kick him off the gantry! (Sorry Andy!)

Luckily the electric motor was not going to be on while we were working!!

Final tweaking of the folded dipole for the planned MB7PE APRS relay.

With it all up there, and our breath back, nearly all of it went into the cupboard. The batteries had to be placed on the top of the cupboard for now – until a suitable box/shelf can be built to put the batteries and the charger under the main cupboard.

There is room in the rack for the APRS relay, and at the bottom is a 19″ radial fan that will eventually be used to offer airflow/cooling for the repeater in warmer times.

I’m still thinking about ways of keeping the whole thing cool for stability and reliability, but the issue will be getting stuff up into that loft! I’m thinking about a fan blowing air from outside into the cupboard in the summer months – all temperature controlled.

Within minutes of GB3PE going back on air, we had calls from around the area. Reports of end-stop signals in areas where I would have expected it, and other areas where I would not! G4KSW(?) reported end-stop at Colsterworth on the A1, and later that it was S7 in the centre of Grantham.

G1SAA reported end-stop in Histon!! Later, Gavin M1BXF, worked it from his IC92 portable on it’s rubber duck, in Trumpington, Cambridge. OK, there were lift conditions, but still, it was working well.

On my journey home, I was able to work it right back to the Bedfordshire border on the B1040, and then in my yard at Sutton, Bedfordshire. That was using a 1/4wave and a Motorola GM950 PMR rig, so no 50W radios with 7/8waves!!

The Cambridgeshire Repeater Group can now stand up and say clearly that it covers Cambridgeshire!! (having not checked coverage out to the far west properly, it’s a bold statement, but PI covers out to the Northants border and beyond!).

I have to re-iterate my thanks to Andy G6OHM for his help on the day. Without him, there’s no way it would have been installed. A Mk2 version is going to be built, using the fabled G1YFF logic, which will pip and bing and do lots of things! The basic controller at the moment does CTCSS detect, ID, and timeout – which is set at THREE minutes.

Comments on the operation of the repeater and its performance are welcome to technical@cambridgerepeaters.net.

Remember – the CRG AGM is on Wednesday 23^rd November, to be held at The Sun public house, Waterbeach, Cambs. Members and Non-Members are welcome to attend, however, only paid up 2011 members (and life members) may vote.

VY 73

Rob

M0ZPU

Chairman

The Cambridgeshire Repeater Group

A short – but very BIG update.

GB3PE is now operational as of 1530hrs Thursday 10^th November 2011.

Many thanks to Andy G6OHM for his help on site getting it all bolted in place.

Reports please to technical@cambridgerepeaters.net or post via the Camb-hams reflector

A full report on the kit and installation will be posted later.

Vy 73

Rob

M0ZPU

Chairman

The Cambridgeshire Repeater Group – serving the whole of Cambridgeshire!

And there’s more….

GB3PE’s hardware is now complete, sorted, and ready for installation on-site.

The last issue was one of noise/interference causing up to 20dB of de-sense. Spending a number of hours on it, tuning, re-tuning, tweaking, perfecting the filters I reached a point where the answer was staring at me, but I couldn’t see the wood for trees!

So a call to one-time CRG Technical Co-Ordinator – Phil Richardson – GW8MLA pointed me in a number of directions to resolve the issue.

The first was to decipher the cause of the de-sensitisation, even though the filters were giving 95dB of TX to RX isolation. Was it due to noise caused by a transmitter instability? FX5000′s are known to become unstable if the exciter produces too much RF. Was it due to transmitter generated Intermod? Receiver generated intermod?, Aerial generated intermod? Broadband noise generated by the transmitter, or in the receiver? So many questions.

So, let’s start at the start.

Transmitter instability brought on by an over excited exciter! : The FX’s transmit driver needs to be set to a maximum of 1.5W o/p. Checking this with my test set showed 1.59W, and with a Bird Wattmeter, 1.7W. So I turned it down to 1w, and then checked the output level through the filters. Still at 11W where I’d set it before (more on that level later).

Now while I was at it, I decided to double check the receiver tuning. I found another dB of RX sensitivity taking it from -124 to -125dBm (better than 0.2uV).

When I put the whole thing back together and checked it, I noticed a intermittent change in the noise level on received weak signals when the TX was on, which happened when I moved some of the internal cabling. Setting about that, and checking for damaged cabling, I found that careful re-routing of the receiver aerial feed tail minimised the noise to reduce the de-sense to around 0.5dB, and then it was only an increase in the noise level on the signal.

Going back to the TX output – 11W, we’ll call it 10W. That’s 10dBW in new money. The aerial has a gain of 6dBD, add them together and you get 16dBW. We’ll, we’re only allowed 14dBW ERP for a 2m repeater. What about the other 2dB, that’s feeder/system loss.

With that all done, the next thing is to install it on site at Thorney Toll. For that, the weather needs to be right. 20mph gusts are not good when you’re trying to manhandle a 6m long co-linear at the top of a 90ft high grain silo! The forecast for the end of next week (10^th/11^th November) is looking favourable, though I’m keeping a “weather eye” on things!! The site owner – Dalmark Grain – need 24hrs notice so they can arrange for someone to be on site when we want to be there, to unlock, and supervise.

More news as it happens!!

Just a quick update.

GB3PE is close to being back on air. It’s currently on test in my workshop – just needs a little fine tuning as the latest test has shown a 14dB de-sense when it looked like it was spot on before!!

I am looking for a nice beech tree so I can find a good branch to thrash it with!!

I have clearance from the site owners to go an install now, something I’ve been trying to get sorted for a few weeks. Just need to give them a couple of days notice so someone can meet us on site (weekday) to let us in.

With the weather looking a bit breezy (or wet) for next week, and with a 6m co-linear on a 6m pole to man-handle up a 90ft elevator tower, it needs to be quite calm for the sake of safety. The best day looks like Friday at the moment, though the week after may be better, I’ll keep an eye in the forecast as I obviously need to contact the site owners ahead of the day of action.

It’s take far too long to get to this point, but work commitments, filtering issues (!), as well as family, etc.. have all played their part in holding things up. It is a hobby after all, but a great learning process for those involved!!

More news as it happens!!

vy 73

Rob

M0ZPU

Chairman

The Cambridgeshire Repeater Group