Cachemobile upgrade: Part I

10 10 2011

A GPS is useful on it’s own for showing you where you are and in conjunction with some kind of radio transmission system it can also be useful for letting others see where you are as well. Many new smartphones have built in GPS and they transmit your position via the phone which is also a radio transmitter/receiver but one that is not fully in your control.

However, amateur radio operators have an alternative – APRS! (Automatic Packet Reporting System). When my car is in use and APRS is activated, it’s possible for others to see where the car is, and hopefully where I am as well. It can be useful for those times I zoom off geocaching on my own. I don’t limit myself to caching in good weather and if something should happen then at least the starting point for a search is easy to find.

Until recently my cachemobile was equipped with an APRS set up that used my old Garmin eTrex Legend to provide the NMEA Location input to my Kenwood TM-D700 transceiver. Every time I got in the car I had to turn on the GPS and then remember to turn it off when I get out. I am forever replacing batteries and it always seems that the batteries die when I am on an interesting cache trip and I don’t have spares. I wasn’t all too happy either with how the transceiver was placed on a makeshift bracket in the car. In other words, an upgrade of my cachemobile APRS set-up was in order.

While I was at it I wanted to reposition my second radio, a Yaesu FT1500M, so that I am better equipped for the rally operations that I am involved in. The TM-D700 has two channels, of which the first is dedicated to APRS and the second is used for voice operations on either the 2m or 70cm bands. The only problem I have noticed is that every time an APRS position packet is sent the traffic on the other channel is disturbed. On most occasions that’s just a nuisance but on rally operations it could be more critical in certain circumstances. Most of the rally transmissions between the stages and HQ are on the 2m band which is where APRS operates. Other transmissions are on the 70cm band and so to monitor both I need to use the FT1500M on the 2m band to avoid interference from APRS and the TM-D700 to monitor the 70cm band.

The TM-D700 was fed by a fixed antenna on the car and the FT1500M with a separate magnetically mounted QP antenna. I now have both radios fed by fixed antennas, but with the possibility to use an external antenna where warranted. An example of that is when a rally is in forested hilly terrain and for those situations I use a 4m mast mounted antenna to improve reception and transmission.

Pictures of the new set-up in the V70

TM-D700 radio control head

TM-D700 Main radio unit

External speaker in the centre consol

Now that I have the radios and antenna mounted it’s the turn of the GPS. As this will be a fixed unit powered by the car’s battery it becomes a bit of a different project to just connecting my handheld Garmin GPS as I did previously. The new GPS is a GlobalSat MR-350 designed for fixed mounting.

GlobalSat MR-350 GPS


I will write about how that was installed in a coming post.

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