GB3PE – 2m Voice
GB3PE is the groups 2m repeater near Peterborough.
|Location||Thorney Toll||Access Method||CTCSS Only|
|Input Frequency||145.075MHz||Timeout||3 minutes|
|Mode||Speech (NFM)||Reaccess Period||NA|
|Polarisation||Vertical||Aerial||Jaybeam end-fed colinear|
|(Site) Height ASL||-1m||ERP||25W|
Last week I visited site at Thorney Toll to change out the repeater controller for one that improved the audio quality through the repeater, and to give an inter-over indication.
It is still planned to change to a G1YFF logic in the future, though Jake has other projects to complete first, and this one will be his first FX5000 integration – not just plug in the back of the box, a proper connection into the repeater control module.
For now, I have swapped out the recalcitrant Zetron 37 for a far far better Zetron 38Max that I have purchased and loaned to the CRG for the job.
The first thing you noticed is the quality of the through audio – it’s much much better (couldn’t be any worse!), being fuller and far louder. If anything, it’s a little more “punchy” than it is when the FX5000 is placed in it’s own talk-through mode without the controller plugged in. It’s certainly easy on the ear when mobile.
And then there’s the “K”. I had considered using trailing pips, but that may cause issues with the Echolink that Andy G6OHM kindly provides for GB3PE.
When you drop carrier, you’ll notice a little squech tail. I have set the Zetron to do this so weak signals chopping in/out don’t send K K K K K K as they’re falling out (one of the reasons why the old box didn’t have a pip was it sending the pip the moment that CTCSS decode was lost!). People who have radios that provide a “reverse tone burst” when they de-key will have no squelch tail. (A “reverse tone burst” is a period of around 300mS where the transmitter remains keyed after the PTT is released, with NO CTCSS on the signal – it allows the repeater to close it’s input before the signal is lost, so there’s no squelch crash. It’s a feature on just about every PMR radio, yet only a few ham rigs do it).
Echolink is working correctly via GB3PE (when Andy has it switched on – see the CRG homepage for the status indicator). There were a few issues initially, but Andy has resolved those now. We still hope that at some point in the future we’ll be able to have Echolink, and other facilities like IRLP or AllStarLink on GB3PE 24/7.
MB7IPE – our new APRS iGate, built up by Gavin M1BXF, went on site too. At first there was a problem where PE’s TX was getting back into the RX and keeping the repeater open, but appearing like a very weak signal. Turning MB7IPE off made it go away. After some searching and testing, it was found that the power cable for the APRS unit was pretty well a 1/2wave at 2m, and causing some kind of parasitic re-radiation into the RX. Chopping it to “just long enough” cured the issue, as well as winding the aerial feeder into a choke, just in case.
The other issue I found was MB7IPE causing de-sense to PE’s input, even with a filter inline. Something that didn’t appear on any bench tests. So it was removed back to my workshop for tests & mods where necessary. With PE’s input only 275KHz away, it was going to be a problem! However, following a little head scratching, and a good suggestion by Rob M0VFC, I have added a relay into the PTT line, which is energised by the “COR” signal from the repeater (Carrier Operated Relay). This means that MB7IPE’s TX will be disabled when there is a valid signal on the input of GB3PE. I had hoped to use COR to control the DCD in the TNC, which would allow it to buffer packets until the coast was clear to transmit. Sadly the TNC-X that is used for the APRS digi does its DCD in software, and there are no hardware means of providing this.
I hope to get MB7IPE back on site early next week (w/c 29th Oct).
Again, at some stage in the future, we hope to have internet connectivity for our systems on site, which will enable the iGate for MB7IPE.
What we did find, during its short tenure on site last week, is that it can hear MB7PI, and MB7PI can hear it, which puts it in direct contact with our main iGate at Barkway.
Coming up next is the CRG AGM on November 28th at The Sun, Waterbeach, Cambs. All welcome (only paid up CRG members can vote) – I look forward to seeing you there!
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 10th 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 email@example.com.
Remember – the CRG AGM is on Wednesday 23rd 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.
The Cambridgeshire Repeater Group
A short – but very BIG update.
GB3PE is now operational as of 1530hrs Thursday 10th November 2011.
Many thanks to Andy G6OHM for his help on site getting it all bolted in place.
Reports please to firstname.lastname@example.org or post via the Camb-hams reflector
A full report on the kit and installation will be posted later.
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 (10th/11th 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!!
The Cambridgeshire Repeater Group
CRG Chairman, Rob Compton, M0ZPU, has submitted an application to (re)establish GB3PE from it’s previous Thorney Toll site. The group hopes that it shouldn’t take the RSGB ETCC long to process the application, and that GB3PE can be returned to service in North Cambridgeshire/Peterborough as soon as possible.
Following agreement with the site owners – Dalmark Grain, the CRG is to apply to re-instate GB3PE from it’s site at Thorney Toll. An application is being put together to send the the ETCC for approval, and it’s hoped to have that back quickly.
It is planned that the initial installation of the repeater will be using a Philips FX5000, controlled by a Zetron Repeaterman. The aerial installation is going to be tricky as there is only space for one aerial pole on the site, and that will determine what we can use. The original aim was for two aerial working, with the TX and RX aerials separated to give greater than 40dB of isolation, then the use of a barrel filter in the RX leg to increase that to over 80dB of isolation which is what’s required for 600KHz split operation.
The RX aerial will be at the top of the pole, with the TX below it by around 15ft. The RX aerial will have 6dBD gain, where the TX aerial will have 3dBD. ERP will be 25W (14dBW). As this will be a new application for the repeater, it will be CTCSS access only, with 94.8Hz required in accordance with RSGB ETCC guidelines for Cambridgeshire.
A brief spec is as follows:
Repeater callsign – GB3PE
Input/Output freq – 145.175 / 145.675
CTCSS (decode/encode?) – 94.8Hz
1750Hz Access? – No
Lat/Long – TBA
Antennas height – TX – 30m, RX – 35m AGL (site at -1m ASL)
Antenna type – Omni – two aerial working
Timeout period – 3 minutes.
Any comments or suggestions, please send them to email@example.com