Now back on air. See below for full details
GB7LR - Markfield, Leicester (next to J22, M1)
Repeater TX (User RX): 439.475 User TX (Repeater RX): 430.475
Colour Code 1 - Also called a "color code" apparently
Reflector talkgroup use
Fault on or around 21/7/2016
Whilst away in Spain and climbing the rock of Gibraltar to see the monkeys, I was contacted by Jon G4TSN who reported the repeater offline. Simple investigations resulted in reports of low RF power. Due to the non-standard nature of the amateur equipment (compared to our normal PMR equipment), we decided to fix it upon my return.
My suspicions were correct. We had installed a RF helical filter on the transmitter to avoid interference to GB3LE. Prior to the application for the repeater there had been significant opposition from the GB3LE group, so I wanted to ensure there would be absolutely no interference caused to them.
Therefore the helical filter had been tuned beyond its rated specs to provide >110dB loss at GB3LE RX freq. This meant the insertion loss was around 4dB.
During the recent hot weather the filter therefore had heated up beyond its rated max temperature (combination of dissipated TX power and high ambient temperature) and burnt out, passing no meaningful RF (1.5mW for anyone interested!)
It has now been replaced with a 3-cavity bandpass filter arrangement which has a far higher power rating (200W RF power as opposed to 20W), a far lower loss (1dB total) and slightly better off-frequency rejection.
This means the TX power has increased, more towards the full licensed ERP, and the out of band emissions are slightly better than before, so everybody is a winner!
Please enjoy and it is good to know that it was missed - it means it was being well used. Ice hot!
People keep asking me about the talkgroups. I have tried my best to put together the info, but the talkgroup settings are out of my control, they are controlled by the Brandmeisternetwork. I honestly have no idea how it is set and what is below has been discovered by trial and error. I hope it is correct. I have asked for the info several times and it has not been forthcoming.
TG9 is the only talkgroup available. This is linked to GB7DC (Derby), GB7LR (Leicester) and GB7RR (Nottingham).
TG9990: Echo testTG9: "Reflector talkgroup". See below for instructions for use.
Note - GB7LR does not have easy access to a local talkgroup without disconnecting reflectors, so GB7SK Slot 2, TG9 this is perhaps the best for a "local" chat around Leicestershire. GB7LR Slot 1, TG9 is best for a "regional" chat around the East Midlands.
Reflector talkgroup use
This works much the same as your normal Echolink/IRLP node, except the dialling is not DTMF. Set your radio to TG9 and leave it alone.
By default it links to reflector 4400. Just talk on TG9 and it will be linked into Reflector 4400 (UK).
To link/unlink, add the required reflector number to your contacts list and make a private call to that number. You will hear a synthesized voice talking back to confirm you have linked/unlinked.
Dial 5000 to hear current repeater status. Dial 4000 to unlink the repeater (operates then in GB7LR only mode).
To see the current list of reflectors, visit http://www.bm-dmr.uk/dashboard/bmreflector.html
The installation for GB7LR is intended to embrace the homebrew and optimisation element of amateur radio. All equipment was brand new in service for GB7LR and is not second hand. This should give a good lifetime, since it's not already worn out and tired upon entering service, as can unfortunately be the case with amateur installations.
Reciever and transmitter: Tait TM8000 series mobile (DDS RX/TX). Transmitter has been fitted with large heatsink
Controller: G4KLX MMDVM Arduino Due thing interfaced by Jon G4TSN modified with 0.1PPM clock
Preamp: Kuhne MKU LNA432A EME preamp, tuned for use at 430mhz
Duplexer: Procom DPF70/6-150 1/4 wave duplexer with 2x Procom BPF70/3-150 on RX and TX
Internet: BTnet 500mbps delivered over 1000mbps fibre to premises bearer
Antenna: Skymasts 4-stack array at approx 25m pointing 90 degrees (East) with 10 degree downtilt to optimise signal into Leicester
TX power: Running 10W ERP, licensed for 25W ERP
Transmit modulation fidelity: <1% error - better than most commercial DMR transmitters!
Receive sensitivity (measured at antenna socket of radio): 0.075uV (-129.5dBm) for 5% BER - Yes, 0.075uV, not 0.75uV!
Receive sensitivity (measured at antenna socket of duplexer): 0.089uV (-128dBm) for 5% BER
Duplexer loss at wanted frequencies: Approx 1.5dB
RX loss at 432.4902mhz: >65dB
RX loss at 433.100mhz: >80dB
TX loss at 438.000mhz: >60dB
TX loss at 434.700mhz: >110dB
Port to port isolation: >120dB
Prior to this repeater going on air there was significant objection from LRG (GB3CF/LE/UM group) due to worries concerning interference from GB7LR to the LRG repeaters, despite commercial equipment running at far higher power from the same site on 440mhz for several years.
Several tests have been carried out and no interaction between GB3LE and GB7LR have been noted. Tests to further LRG equipment have not been possible due to non-cooperation of LRG.
GB7LR was originally applied for, to run from our Markfield site (next to GB3CF, GB3LE, etc. NOT the same site I must add!).
I was particularly keen to embrace the hobbyist aspect of amateur radio and deploying equipment we have been using for over 10 years commercially feels to me to be playing "catch up", rather than pushing things forwards.
I was therefore keen to see a homebrew repeater deployed. From my previous experience of Leicester/Nottingham amateur repeaters I have always felt that there is a local connection between the two cities and that anything in Leicester should be able to interconnect with Nottingham.
I contacted Jon Lee (G4TSN) who recommended Brandmeister would be the best way forwards. I gave him two brand new radios which he returned a week later with some G4KLX thing attached. We plugged it into the duplexer, aerial and internet and then hey presto - it came to life!
However unknown to me there were actually two networks - Phoenix and Brandmeister.
Some local amateurs were dismayed that we chose Brandmeister over Phoenix, and others expressed concern about the quality of homebrew equipment. Therefore GB7SK was applied for (see to the right).
GB7LR is connected into the DLN (Derby / Leics / Notts) talkgroup on TG9, Slot 1. This means that using TG9 Slot 1 will come out on GB7DC, GB7LR and GB7RR, giving full East Midlands Coverage.