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7 IV PROGRESS
Update on progress of GB7IV, this has been a long haul project due to problems getting a suitable set of duplexer filters, these filter allow us to connect both the transmitter and receiver to a common aerial, which has all ready been installed, and is visible in the site photographs.
To get GB7IV on air from SMC Chandlers Ford, Chris G4HCL and Andy G4MYS We were able to borrow the GB3SH duplexers, which have been returned, and thus SH is available and on air. Chris G4HCL tracked down what seemed to be a suitable set of filters from North east England and brought them down to Whitby and Andy Went and got them from Whitby, the place famous for its oddball connection to the North Yorkshire moors steam railway as much as its beach.
Unfortunately the supplying repeater group were not are that the filters they sold us were totally unsuitable, the markings indicate they were, being as they are on the 220Mhz band great for a 74cm repeater in the USA, but not here in Blighty!
So we set about trying to convert the British Gas filters were got given by then some 10 years ago, We were then fortunate to get brand new old stock Sinclair duplexers from SMC which we clubbed together to obtain, which also promised to work, but tests quickly showed they played up if they were operated with more then 2 watts - not very useful!
The state of play currently is Alan G8IPG is working on getting the British gas filters to work with the Sinclair filters to have enough "notch" which is more then 60db per channel ( Tx & Rx ) One filter is in situ and is connected to the test transmitter in site a Tait TM8100 so show we can operate a GB7IV without problems to GB3SH, and this is so. The test beacon of GB7IV is a sent around every 7.5 minutes and is running the ERP of the licence, it sending: GB7IV TEST.
Soon We have have
all the filters on site, and then we will be able to connect it to the
repeater and test as a repeater, that will be soon be not yet, this GB7IV
will be a C4FM unit, capable of connection to the internet as soon as
we can get a stable reliable internet connection available to us, It will
not be connected to Either MT or PO. In this way we will be providing
4 separate repeaters from site each with its own unique identity and possibly
Our engineers have been to site again to sort out the lacks of pips on both GB3SH & GB3SU and is common with most of these things, a common problem was harassing both repeaters. Simply put RF energy was getting in to the area that the logic is in, and more importantly on to the DC supply cable, and the simple cure was to wrap the DC cable through a ferrite ring several times both cured and a lesson for us all in areas of high RF field stop RF entering electronics with RF filters !
The camera and weather station are back after engineers for there respective companies who run the internet and wifi system We rely upon worked on the cables and the distribution system, and found the signal to be around 6db below a working level, while We cannot say exactly the cause, we know someone there has shifted much, and has got favours done to get us and our camera -back on and We say a big thank you to Peter & Dan. It is good to know our supporters help us in different ways.
Other problems were
looked at too esp the " coaxial experiment " which will be done
on another day.
Additional work is
being done to our DC systems to ensure a " fail to battery"
goes smoothly, with each output DC port having its own relay, fuse, and
fuse fail indicator, additionally an easy fit battery "2" has
also been introduced, for when we have an extended outage.
Off board battery
chargers have also been introduced, ensuring a recharge of the batteries,
and maintaining a healthy float voltage.
Research made by Alan
G8IPG, and confirmed separately by the keeper of GB3IW: G4IKI indicate
that our coax may be the seat of the problem. We should be familiar with
what happens if you put a diode or even an accidental diode across an
RF circuit, in repeater systems rusting bolts on the guy lines, and other
nearby metal work can become diodes, rectifying the RF, and making a broad
band clicking and noise.
So now let us turn
our attention to the installation: having proved the GB7MT transmitter
is squeaky clean, and that the circulator's have cleaned up the incoming
RF to the SU receiver, but the QRM persists, we need to look at other
parts of the repeaters installation.
We use quality commercial
grade low loss coax called: LBC 400, on the length we use this is a good
compromise between sheer cost per meter, performance, coupled with and
plug cost, about a fiver each, the coax too was around a fiver a meter,
and half the loss of RG213, its a good choice for us! However research
asks the question - or is it?
LBC 400 has an inner
core of stranded copper, a solid dialectic, surrounded by "bonded"
aluminium foil, which of course has the current carrying copper braid
around that, and the outer " weather proof jacket" around that.
This is common design for quality cable, be it TV or communications cable.
With TV of course its not carrying watts of power, and of course at our
homes We don't have a sensitive receiver connected to the same aerial!
So such coax at home is great its quality and low loss, a tad expensive,
so where is the suspect problem?
This is with the different
metals of the aluminium foil and the copper braid, ( this is not 1st April
joke BTW ) which under certain conditions have been shown to create a
diode effect,.. a very low level broad bandwidth RF noise can be generated,
small enough only to be heard on nearby receivers, and too small to be
detected more then a few feet away! the cure is to replace the coax! So
hands up who wants a lot of very high quality coax then?!
Further research shows
that even the connections between the RF plugs and the coax can, and does
cause problems due to the different metals used!
Thus coax replacement
needs to be a fully copper system, such cable is known as "hard-line"
consists of usually a tube, for the inner line and a almost copper pipe
as the outer, its available in different sizes from around 12mm to whatever
at megger quid per meter and about 25 quid a plug!... We further understand
that many RF sites only permit the use of hard-line cables, there must
be a reason why!
First however we will
do an experiment, at a time to suit a team will go to site and run out
two 33M lengths of fully copper RG 213, two aerials and see what happens!
We'll let you know
when this experiment happens, its likely to be a Saturday or Sunday afternoon
as we got to be off the roof by darkness!
We will need some
not scared of heights on site ( we have keys to the bog on site, ) and
amateurs on air: , locally, and DX stations too, - so are you in for a
true amateur radio experiment?
Dont worry we wont
change the aerials or coax that day, this will be a prove / disprove experiment
only with the aerials stood only on transportable tripods.
We are considering removing the Broadcastify facility due to lack of use, and on going interruptions of service.
Rather then switch off straight away, We are considering turning it off on 30 Sep 2021, as this is a remote off air receive facility only service, discontinuing it will in no way effect the operation of any of the repeaters.
We are grateful to the loaners of the equipment used, and that will be given back directly to them soonest after 01 October 2021
LATEST - PROGRESS
We are pleased to say We have started on upgrading the DC supplies, Battery charging and the DC PDU ( Power distribution unit ), in addition We are building a 24 Volt Power supply with battery changeover unit, this will provide a long battery back up in time of AC power failure, for the 24 Volt equipment, More on that later.
Today We tried to swoop the loan GB7MT out for our own, but the equipment suffered from a Mini USB socket mechanical failure, thus the Repeater is now on its way back to YMUK for repair.
This we still have
the loan unit on air as GB7MT and as such there is no change in MT behaviour.
The Beacon is on
air, though its duplexers and one filter, as We wanted to prove that we
can run two VHF repeaters on one site with out mutual jamming either way.
The tests are a beacon
which appropriately is every 7 minutes and sends at around 14 WPM the
following: GB7IV TEST
The equipment an ex commercial PMR radio: Tait TM8110, the repeater Duplexers from SINCLAIR, and one filter ex British Gas, the aerial is the purpose fitted dual band colinear attached to the top of the GB3SU aerial mast.
Today We extend our thanks To
Alan G8IPG, Andy G4MYS, David M0XIX, Bill G0XAZ, who were directly involved, and several others who helped on the day with reports and moral support!
Unfortunately, the Thames Valley Repeater Group (TVRG) has to announce that the GB3AW UHF repeater located 7 miles SSW of Newbury, at Ashmansworth. in Berkshire will be moving site. The existing site at has been sold and is being developed. We have managed to find another site fairly close at a similar height. There is a fair amount of work to be done, taking down the existing mast and erecting a new one at the new site. The equipment is being rehoused to occupy less room and it is probable that the logic will be different.
Timescales at the moment are flexible but it is most likely that the existing GB3AW will go "off-air" by the end of July. When it returns is dependent upon on a number of factors, not least when we receive approval from OFCOM for the move. Although the new site is fairly close to the old one, the distance is such that it has to be regarded as a new repeater application. Having said that, we would do not expect there will be any problem is obtaining approval. As a guess, we would hope it could return by the end of September/October.
An application for the new site was submitted yesterday.
GB3AW has been on air from the present site since 1978 and has been run by the TVRG since 1992. Still all good things come to an end, and we hope you will find the "new" GB3AW useful to you.
P.S. GB3RU is currently
off-air. We're investigating why this is.
ENGINEERING UPDATE 21st JUNE
It does not take us
long to do an upgrade, suggestions made at the Southampton Amateur Radio
Club meeting last Wednesday,. were put in to another IC, and that was
fitted into GB3SH on Sunday 21st June.
The GB3SU logic is currently a Zetron Model 38A, which is odd school commercial repeater logic, which is why it sends up to 4 pips and only CWIDs during overs. We will introduce M0XIX logic onto GB3SU soonest. Alan G8IPG is working on GB7IV duplexers with a view to getting it on air soonest. He is making progress tuning the brand new SINCLAIR duplexers and old British Gas filters to allow us to run GB7IV at full licenced power.
We like to thank
in particular David M0XIX for his attention to detail in producing the
new logic for GB3SH, as this is around the 7th one he has made!
Another visit to the
repeater site, resulted in MT being off air for 2 1/2 hours as SH was
removed with its integral power unit which also charges the batteries.
Another SH has been fitted, see picky 1312, pictured here while being
built with the yet to be fitted GB7IV duplexers.
Time out is ( as per also on GB3SU ) is 4 minutes after which your over is marked with time out pips to let everyone know you have timed out,.. total time out is 8 minutes, if you rabbit on that long SH will chuck you out and close down. This feature is to prevent jammed PTT holding the repeater open for hours, this same feature exits in SU also, that's the way We ( G8IPG has ) have programmed them.
SH sends a distinctive
"double bleep" at the end of each over, and access. However
and but, should we have a power fail, then instead of the double bleep
the Repeater will send a "B" in Morse ( _...),! at the end of
an over, this repeater is a stop gap machine, ... the revised and yet
to be fitted repeater will have a modification to the CWID to indicate
loss of AC power, which will be a double B being sent in the CWID the
first one being the code for 71.9Hz CTCSS, and the second being "Were
running on batteries!"
SH is running on
a stop gap PSU too, to which were thankful to Chris G8BAL, this goes to
show a little " maas " switch mode 22Amp PSU force cooed by
a fan, can run our repeaters for 1& 1/2 hours continuous transmit
when push comes to shove ! If there is any doubt in the capability of
these little wonders we doubt no more. We understand Nevada flogs them.
Also fitted was a
beefed up battery charging unit, which will enable faster recovery time
when We have a fail to battery event.
Weather camera..As a result of all the unplugging the mains we lost the camera output for some time as this takes up to 12 hours for some unexplained reason to re emerge after a power loss, we are looking into power this with battery back up.
That Tv aerial you'll recall We removed the fallen TV aerial from the roof, the pickys here explain
Picky 1424 is the installed aerials as is 6 June, The disused top aerial is what remains is still up, the middle and front section of the failed aerial, below is an upside down TV aerial the one in use, its normal to fit the cable connector to the top of the boom, thus keeping rain out!
Picky 1428 is the fallen section, we were interested to show you the fractured boom which is the failure point
and the amazing amount of rust on the aerial connections, picky 1426.
We checked over all
the masts wall mountings on site, ours & SCC, and all appear well
after the long winter and its winds.
Thank you to Geoff G4ICD of RF Comms supporting the S.H.R.G.
Check out his page, we have just bought over 4000 cores any many top grade materials at silly prices WWW.RFCOMMS.CO.UK
G4MYS onbehalf of the group
New licence condition for spectrum licensees confirmed
Ofcom has today confirmed a new licence condition that now applies to the vast majority of spectrum licensees.
The changes mean most licensees will need to take action to ensure their equipment operates within international guidelines on electromagnetic fields (EMF) for the protection of the general public. Most licensees will also need to keep records demonstrating their compliance.
Following the publication of our policy statement on EMF in October 2020, we wrote to licensees in March this year to inform them of our proposals. We have considered licensees' feedback carefully and made some changes to the new licence condition and guidance documents. Today we have published full details of our final decision on the licence condition.
We have also published guidance on what licensees should do and how long they have to ensure compliance - this is dependent on the frequencies they are using. Our EMF compliance flowchart tells licensees whether or not they need to take action and, if they do, what action is needed.
A simplified version of the full guidance and specific advice for holders of amateur, ship radio and aeronautical licences will be published next month.
We will shortly be writing to affected licensees to inform them of our final decision and provide a replacement/update for their current licence.
REPEATER SITE WORK SATURDAY 22nd MAY
Alan and Andy have been back to the repeater site with the intention to rid GB3SU of the QRM from GB7MT once and for all time, the result of this visit was plenty of test tones on GB3SU from the test set as they tried various filter configurations on GB3SU and GB7MT. Basically whatever was tried did not really improve the situation. In the process GB7MT was put back on its 4 stack UHF dipole array, and this made the situation worse, so its back on the GB7IV colinear!
While it may seem a little crazy to fit a filter to the transmitter of the effected repeater,.. one would think rightly so that filters need to go on the effected receiver, one needs to bear in mind that RF will also go down into the transmitter of nearby repeaters ,.. in here.. the transmitter of GB3SU.. whether it is transmitting or not, the high powered unwanted RF can cause problems by "mixing" inside the transmitter, and it was this signal we were seeking to reduce., So we fitted a circulator, the drawing explains what happens. In this drawing Port 1 is connected to GB3SU Transmitter, and port 2 is connected to the coax which goes to the duplexer. Port 3 is connected to a 50 Ohm dummy load rated at the same power or more then the transmitter. Thus any RF entering down from the duplexer on port 2 is dumped by the Circulator in to the dummy load on port 3. In this mode its known as an Isolator. The working of Circulators are not covered in the RAE, and you can see why normally we have no use for such a devise, they are big enough to sit on the palm of your hand, are heavy for size and at UHF around 5MHz wide, they also need careful tuning, however very important is not to drop them as they contain ferrite material.
The circulator has not cured the problem completely to the frustration of our lads, and the users, no doubt, however the Lads will go up gain with other parts to try and work out where the problems is and how to cure it!
They also fitted a circulator to GB3SH to try and rid ourselves of the data QRM from the co sited SCC system, hopefully that will do the trick. We will only find out as the week goes by as We cannot stimulate the SCC transmitter in to operation! ( and rightly so )
The other important work was to test the all brand new GB7IV, this is built form a pair of "New" old stock Motorola GM360 mobile transceivers, they have been fitted in to a 3U 19" rack tray, the idea today was merely to check that they would work together successfully side by side without miss-behaving in a repeater set up. Users were puzzled by the behavior of "GB3SH" as it gave no pips or callsign, and had a squelch tail! - as of course its to be fitted with a Raspberry Pi and other electronics to allow it to become a data repeater on R7, 145.775MHz. We will tell you more as this project progresses.
So why had it fallen?
This TV aerial is the type which sits on a twin support boom, the clamps
on the boom grip the aerial l towards the front, and rear, the rear one
is where the aluminum of the boom has fractured and snapped. As to why?
The rear section has a 20 element reflector which is also clamped on the
the boom, this had worked itself lose and was able to rattle itself back
and forth along the boom for around 30mm, Why it was taken out of use?
- We will never know but - the F plug aerial connector had no weather
VISIT & CHECKS
Alan and Andy made the first visit to the repeater site this weekend and found one little problem which was causing QSB last year, with GB3SH.
Oddly enough only one station, 2E0ZBE reported QSB from GB3SH last summer, and it was noted then that the power level was going up and down, this could be clearly seen form the trace of the Farnham SDR. With gratefull thanks to them for their useful facility.
The cure to this was to plug in the cooling fan Tray DC connector which had fallen out of it's socket, so we now know to screw up those silly D plugs dont we ?!! The reason for the QSB was the PA was getting hot and automatic thermal protection was kicking in and the effect was the Power was being turned down! The fan runs on the transmitting being activated, and it runs on for another 3 minutes, after the tx goes off air.
We refitted the filter which should keep GB7MT out of GB3SU receiver,... all be it not as well as we'd like, Both Alan and Andy have been on the trail of more Narrow notch filters to try and keep one repeater out of another.
Additionally measurements were taken so we can make up new coaxial cables for extra filters for the VHF digital repeater GB7IV, these filters will enable us to test GB7IV at full power hopefully before installation.
While They were on
site the winds were reaching 59.9MPH, they watched our aerials from the
ground, moving with the wind.
WEATHER CAM & WEATHER STATION DOWN
Were sorry to report
that there is a failure in the link somewhere which has downed our system.
We are aware that our camera and weather station went down at 00:07BST on Monday 12th April 2021, at time of writing We have no news at all, of when we can expect a re-connection. GB7MT will operate as normal as it uses a Microwave RF link to GB7PO.
Were pleased to say were back!
Our logging kit records we returned at 1354Local Wednesday afternoon.
FT 70D RAFFLE
Well done to the winners
of the prizes and thank you to you who purchased a ticket. The profits
made go in to the running of our repeaters.
2nd Prize - Alpha Tronix Power Supply (Ticket 351) G7NKZ Keith
3rd Prize - High Power Glass Insulators (Ticket 377) M0VBD Rob
4th Prize - Ceramic Insulators (Ticket 3) G8IPG Alan
GB7IV UNDER TESTS D-Star / C4FM / FM
Behavioral Tests were made on Saturday 6th March to establish if our "Sinclair" Canadian built duplexers would work successfully on the 2M band.
These test followed others where the D Star repeater would not behave and We were seeking a second test to try theory's out.
We tried with an Icom Repeater "GB7IV ", between 0800 & 1130 also Yaesu DR2 " fusion" type repeater, from around 1200 to 1800L and a pair of Tait TM 8110 mobiles which will form a complete standby GB3SH. from 1800 to 1845L
The tests used in D star, C4FM and FM this allowed different modes to be tested and with FM other non digital users could try it should they have wanted.
The tests consisted around attempting to run the transmitters at different power levels, with in the licence limit, to establish if the transmitter was happy and also importantly if any De sence was happeing, in other words if the transmitter was deafening the receiver, It difficult to establish this with the D star repeater as it wont run FM and neither does it have an S or RSSI meter. But what We did find out was that even at 17 watts our limit the D star repeater was happy.
After lunch it was the go of the Yaesu DR2, We put this in to dual mode, and found out how it operates in dual mode configuration. For the record it only sends its CWID on FM, and it will wait for the end of an over to CWID in FM, however when its time to CWID and its idle, even if the previous QSO was in C4FM, it still goes over to FM and sends the CWID. One or two may of had the surprise then of hearing " GB7IV " as a CWID and may of wondered wat's that?! This is when We started to note the desencing issue, while We were playing on FM.
In the evening We tried the Two Taits bearing in mind : We have had them at the repeater site on air behaving impeccably at 17 watts as GB3SH in to the SH duplexers without a hint of problems for several hours.
These Taits also played up when used on the IV channel and the IV duplexers, curiously it was beaconing as " GB3SH" of course,.. and anyone puzzled by finding a "GB7IV" in the afternoon must of wondered how GB3SH had QSYed! and perhaps even better why there was now two of them!
So the conclusion
So were glad We tried off site as it is more easy to fathom out what is happening when not working in the restrictions, of the repeater site be that the COVID Threat, The cold, it struggled to get above +5C today! And of the dragging all the kit to site in the first place.
We gratefully thank:
2E0TGE 2E0ZBE G4MYS G6DLJ G7AFN G8IPG & M1PVF for working through and help test the repeater system.
Thanks to: ICOM Yaesu and TAIT for some rather good radios to play with!
IMAGE TO OPEN IN FULL
The Yaesu DR 2 from the tail connections note "callsign" GB7MT on the repeater, and "GB7IV" on the duplexers. The DR2's are dual band so it was no problems to reprogram GB7MT to become GB7IV!
IMAGE TO OPEN IN FULL
The almost complete standby "GB3SH" on GB7IV channel just before its "go", sitting on top of the on air DR2, the top unit is the monitoring unit showing volts and current drawn, also holds the RSSI or S meter and a convenient " tx test inhibit and normal" switch on the front panel, and the electronics to enable the operating "On Battery " ident to be transmitted. Also fitted a thermal probe on the transmitter heat sink, with its display on the panel, this curiously worked from two 1.5 volt button cells in parallel !
SPARE REPEATER & DUPLEXERS
New 145Mhz duplexers
work very well !!
We are pleased to say our desire to have a fully spare working VHF FM repeater ( cold standby ) has been built with Tait TM8100 mobiles, built in New Zealand, it's been soak tested in to a dummy load for several days, for thermal reasons, and tested on air, with the logic, a brand new design by M0XIX to our specifications with some features for ease of use and information. For instance when running on battery back up, a special tone will replace the end of over "Beat". This repeater has been tested with our brand new old stock Sinclair Canadian built Duplexer which was aligned to R7, 145.775 Mhz by Richard G4WFR.
The next thing to
do is take them to site and air test both of them on our aerials. A date
for this has yet to be decided as with everything its COVID dependent.
GB7IV DUPLEXERS GB7SU DMR
After around five
years of trying to get a set of working duplexers for GB7IV, a brand new
set has been successfully obtained privately.
We will need your
help with this experiment.
You will not need
special equipment, for these tests, just a FM transceiver on either the
usual GB3SH channel, or a transceiver on 145.775MHz FM, the old GB3PC
channel with CTCSS on 71.9 Hz. on transmit.
SOUTHAMPTON AMATEUR RADIO CLUB & REPEATER GROUP CLUB NIGHTS ON ZOOM
Since the Covid outbreak
the Southampton ARC holds now a regular get together on Wednesday Evenings
at 19:30 on Zoom Meeting.
Topics range from
projects sharing of information, to subject not radio related but a good
For the Zoom access code e-mail Andy G4MYS at GB3SHSU@gmail.com
Radio history story from the BBC
We are pleased to
announce that our GB3SU & GB7MT Broadcastify links are back on and
connected up. The GB3SU link has been back on for around 6 days.
WEATHER STATIO0N UPDATE
The weather station
returned online today at 16:00. The Weather Cam is still off line and
should return in the next 24 hours
STATION & CAMERA
Update: An engineer is on the way today to fix problem in West Southampton
While the fault in the network has been cleared, it has the effect of this has knocked out our connection to the internet. This fault is a variation on a theme on around 50% of the reason's as to why we lose connection, some of the faults are to do with the linking equipment, all of this as such is is all out of our control. Due to the COVID restrictions We can't go to our site to make our standby alternative arrangements work - frustratingly.