MB7UNE – Magor, Caldicot

MB7UNE is an APRS gateway system running on 144.800MHz. The setup consists of the following :


  • PSU : 13.8v SAMLEX SEC-1235G
  • Radio : Motorola GM340
  • Time out timer (ToT) : 30 second
  • Maximum Deviation : +- 2.5KHz
  • ERP permitted : 14dBW (25W erp)
  • 13W at back of radio


  • Diamond X300N
  • Gain : 6.5dBi
  • Height : 11m agl (permitted 15m)
  • Elements : 2 x 5/8th on 2m
  • Max wind : 50m/s or 112mph
  • Length : 2.9m
  • Max Power : 200w
  • Nominal Impedance : 50ohm
  • SWR @ 144.800MHz : 1.4 : 1
  • ~18m Ultraflex7 from Messi & Paoloni

EMF Compliance

Compliance based on maximum power output of 25w erp defined by the frequency co-ordination and certificate. Details Here


MB7UNE uses a WX3in1 Plus 2 from MicroSat. It provides the following features :

  • Digipeating – receiving of APRS RF packets, decoding and if valid will repeat them out if required. The hop count is used in this decision, and decremented if the packet is digipeated. A trace is also added. The packet will be dropped if a number of checks fail.
  • iGate – will take APRS-IS gateway packets and will send them out over RF. There are a number of conditions required for this to happen, such as if a station is local and has it been heard in the last 30 minutes. There are also a number of filters that prevent RF ‘flood’.  MB7UNE will also inject APRS packets heard via RF into the APRS-IS internet system.
  • Monitoring – temperature and psu voltage are included in the position aprs packet, sent out every 15 mins or so. This temperature sensor is attached to the back of the WX3in1 and as such is shack temp, not outside temp.

If the are any issues please contact me via [mb7une <at> grange-lane.co.uk]

Change Log

MB7UNE as of 9:30 12/03/24

3.5w at back of radio = 35.44dBm

18m UF7 feeder loss = -1.2dB
connector/other loss = -0.5dB
total loss = -1.7dB

X300 gain = +4.5dB (+6.5dBi)
total gain = +4.5dB

erp = 35.44dBm -1.7 +4.5 = 38.24dBm = 6.7W erp

MB7UNE as of 12:00 12/03/24

13.09W at back of radio = 41.17dBm

18m UF7 feeder loss = -1.2dB
connector/other loss = -0.5dB
total loss = -1.7dB

X300 gain = +4.5dB (+6.5dBi)
total gain = +4.5dB

erp = 41.17dBm -1.7 +4.5 = 43.97dBm = 24.95W erp