MB7IBK Gateway, 144.9625
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Last updated Jan 27th 2021, mike@g4kfk.co.uk



MB7IBK was switched off on September 19th 2020, having fulfilled the aim of introducing DMR to Bracknell Amateur radio Club members who did not yet have DMR equipment.

I am leaving this information here, as it may be helpful to others planning to build gateways or repeaters with Motorola radios and Arduino-based controllers:

MB7IBK is an analogue simplex gateway, linking the Bracknell Amateur Radio Club’s Brandmeister talkgroup 23529 and 144.9625MHz FM, providing a means to access the TG for those members who do not yet have DMR capabilities.

Sited at 51.4256ºN, 0.7375ºW, the system provides 2m FM coverage for Bracknell and the surrounding area.

The 2m FM radio is a Motorola GM350, set to its lowest power level (5W), then fed via a 3dB attenuator to a dipole antenna, 8m above ground level. After allowing for cable losses, the ERP is estimated at slightly above 1W. The 2m FM receiver requires 118.8Hz CTCSS. The transmitter sends 118.8Hz CTCSS.

The system is controlled by an Arduino Uno, the code for which may be found below. The Arduino is powered via an RTU5024 GSM controller, from which it provides a switched 12V supply to the “ignition sense” pins on each of the radios. In this way, the whole system can be remotely shut down with a single phone call to the RTU5024. The use of the ignition sense pins also means that system will power up in an active state either after restoral of AC power, or after a second phone call to the RTU5024.

Higher resolution images of the above can be emailed by request to mike@g4kfk.co.uk

During an inactive state, the system sends the following beacon in Morse code at 1450Hz, approximately every 10 minutes: MB7IBK J IO91PK

Calls from the DMR network are accompanied by a single MB7IBK in Morse code at 1000Hz. If there is no further activity with approximately 20 seconds, the beacon is sent again at 1450Hz.

Calls on 2m FM are acknowledged with a (very) brief K, and the beacon is sent again at 1450Hz after approximately 20 seconds of no activity.

The Arduino Uno controller code may be downloaded here.