Amateur Radio Hardware

Mobile Radio Upgrade

I’ve had great service from my trusty Yaesu FT-7800E transceiver for around 15 years. It’s lived in a few different vehicles, performed really well and been easy to operate on the go. That is until a few months ago, when I started to get reports from other stations that my transmitted audio was weak intermittently…

Mobile radios can sometimes suffer, given the harsh conditions of mobile radios in terms of vibration and extremes of temperature. Cleaning all of the plugs and sockets on the connecting cables would usually fix things, but sadly not this time. Even swapping the microphone didn’t help.

Studying the circuit diagram, I found there are a few semiconductors in the transmitted audio signal path which control gain and it seems one of these might have become faulty. Due to lack of time and the small surface mount nature of these parts, I decided the easiest fix was to upgrade the radio to a newer model. I’ll repair the FT-7800E in due course, as I need a dedicated radio in my shack to park on the local FM repeater channels.

I chose another Yaesu transceiver for the replacement, and went with the FTM-300DE. This offered more features than the radio it replaced:

  • True dual band allowing simultaneous reception and transmission
  • C4FM Digital Voice capability, and access to internet gateways
  • APRS (Automatic Packet Reporting System)
  • Bluetooth
  • MicroSD card for easy programming of channels
  • And finally, a fancy colour screen!

The only drawback compared to my current radio was that the microphone attaches to the radio body, rather than the display head so I had to reroute some cables in my vehicle:

A mess of wires behind a dashboard

I also had to change the antenna on the vehicle roof. My previous antenna was designed only for UHF use on 70cm. The new radio would need to transmit regularly on 2m VHF as well as UHF, so I swapped to a dual band antenna, which was also slightly shorter. I’ve lost some of the range I had on 70cm, but I’ve gained 2m TX capability and of course APRS.

After an afternoon of fiddling around, the new radio body is hidden away with the control unit neatly on the dashboard and an extension speaker providing crisp audio directly into the cab:

Final install with dashboard refitted

I didn’t really think I needed APRS, but it has been interesting so far. I’ve had text messages from stations in neighbouring countries who have received my position beacons, which has allowed me to assess how far my signals are travelling. I can see local amateurs driving around near me, so I know to give them a call. One day, I started receiving position reports from lots of stations I don’t normally hear. So the radio is automatically giving me a ‘heads up’ on enhanced propagation events without me having to pay too much attention. Finally, the location of my vehicle is recorded by the APRS internet system, and so I can be tracked live on websites such as Google Maps APRS and this has resulted in a fresh cuppa being ready as I pull up outside home!

I’m usually monitoring the local repeaters GB3GD and GB3IM as well as the FM and Digital Voice calling frequencies when I’m driving around. Feel free to give me a call!

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