GB3MH and GB7MH

The following was a report to HARC on our recent talk on GB3MH and GB7MH. This was written by Alister, G3ZBU and we thank him for permission to reproduce it here.

Your hon sec went along to our friends in Crawley for their monthly talk which was on the Ashdown Forest Group’s repeater GB3MH, which is located at a church in Turner’s Hill. This 2m repeater is co-located with a 70cm D-star repeater and they share the same aerial;
the aerial is a 2m/70cm co-linear cunningly disguised inside a flagpole. Power is about 5W ERP, and the aerial height is about 600ft above sea level, so it covers from the North Downs to the South Downs. Coverage is not so good to the West.

What is interesting about the 2m repeater is that it has an Internet link to the rest of the world. It can be used as a normal repeater for local contacts on 145.625MHz/145.025MHz, and it gereates a Morse ‘K’ between overs. However, if you have a DTMF keypad, you can make contacts all round the world using either Echolink or IRLP modes. To access an Echolink node, press star/asterisk/* before the node ID, e.g. to access an EchoTest node, press *9999.

Echolink nodes include mobile phones, so it is possible to access someone’s mobile phone. We had a demo where a phone runs an ‘app’ that has a soft PTT button on the touchscreen, so it makes the phone work in simplex mode. To use a phone, or computer for that matter, you have to send off a copy of your licence and become registered.

IRLP is a mode where the two ends of the link must be done by amateur RF. One doesn’t need special registration because using RF sort of infers that one is licensed, or maybe a pirate…

When linked, the ‘K’ signal is replaced with a ‘courtesy tone’ ( 3 tones rising or falling in frequency ). If you hear the ‘K’ you know the linking has been undone! To unlink, key in 73.

Dave 2E0DDG accessed repeaters around the world but no-one replied! Possibly it was very early in the morning in ZL-land! He impressed upon us the operating procedures to be used: always listen first, then ask if the repeater can be linked. Of most importance is to leave a large pause between transmitting to allow all other repeaters to change from tx to rx. This can take up to 3 seconds if the end point is on the other side of the planet. Without a large pause, the repaters can end up in silly states e.g. locked in transmit!

The reader may like to read an article originally published in the Feb 2010 issue of RadCom by G4ULF.

The aerial had to be professionally erected, and considerable expense went into all the legalities of planning permission. It cost something like £2,000 to get the kit on the air. Most of the electronics was kindly donated. Annual running expenses are mainly for internet access and electricity, as the site rent is a ‘peppercorn’ rate.

The tone levels are not quite correct as the ‘K’ is far louder than the received audio. If enough people complain then this may get sorted out.