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[ghondie]

hi peeps, goint to fit my radi ogear in the car, and im gunna use a window mounted antenna, just wondering if anybody on here installs pmr gear or has ever done it in a meega?

just need to know what cables to avoid running the aerial cable near to and if there are any specific emc requirements for this car. maximum im going to be running is about 10 watts at 144mhz and 10watts at 430mhz  

cheers all
nathan

[Kevin Wood]

I'm a licenced radio amateur although I don't operate mobile.

I doubt you'll have any issues at that power level. If I were going to do it I would run any wiring down behind the driver's side sill trim panel because, aside from the car radio / mobile phone antenna lead and BOSE, if installed, there's not much for it to interfere with. Most of the car wiring goes down the passenger side.

Good practices should ensure that the feeders don't radiate any RF anyway. I'd give them a couple of turns round a ferrite bead at the antenna end just to remove any common-mode RF from the feeder and do the same to the power supply connections to the radio as close to the radio as possible.

I would also be tempted to remove my (defunct) mobile phone antenna and use the hole in the roof to permanently mount something. Glass mount antennas are a bit lossy and can radiate a bit more power into the car.

Kevin

[ghondie]

hi, indeed this is what its for, i rarely tx in teh car anyway but its useful for aprs use, and coastguard comms on the way to a lifeboat call. i do intend to use the roof aerial hole, but need to get a decent mount for it. i will eventually have 2 antenna's on the car, one soley for aprs tracking use and the other for voice comms.

cheers for the advice, i just wasnt sure on where the important cables run, and although i dont intend for my cable to be a bit leaky i thought it be a good idea to keep it away from them.

cheers
nathan

[zirk]

Hi ghondie

I’m new to this site (today), but I am a Radio Comms Engineer, so may be of some help.

Your install should be straightforward, simple things to remember are the basics which are as follows.

Wire your PMR Radio straight to the Battery rather than tapping into of the Cars Loom (decent cable and both Positive and Negative Fused near the battery). Keep the Coax Cable as short as possible and without any sharp bends or kinks (I personally wouldn’t wrap it around ferrite beads or coils), if your running Tx High Power i.e. more than 25  Watts, upgrade to Double Screen Coax (make sure its 50 Ohms though).

The most important things are Connecters and using the correct Aerial, connecters should be made as per the instructions insuring both the inner and outer coax is connected properly (you should be able to give them a good tug without them falling apart). Try a run the coax cable above the roof lining rather than down a sill.

The Aerial needs to be matched to the frequencies your using, a good PMR Installer would be able to do this using a Forward / Reverse Power Meter (or worse case a VSWR meter) and then adjust the Aerial Whip to its correct length. As you’re using the Amateur frequencies, these are quite narrow band compared to the PMR bands, so as long as you get a decent Amateur Aerial for the correct bands then you should be OK.

Ideally the aerials should be body mounted (i.e. the coax earth at the aerial base is connected to the body work). If your using ¼ Wave Aerials (simple whip type without coils or matching boxes) then these need to have, what’s called a ground plain, which would be an area of the Cars body work around the base of the aerial with a radius approximately equal to or more than the length of the aerial whip, (i.e. aerial is fitted in the middle of the roof or near middle front or back of the roof and not fitted to the edge of the roof or Cars wing.

If your fitting what I would call an High Gain Antenna (sometimes known as Ground Plain Independent Antenna) which will have a Coil at its base or in the middle (or both) of the whip, then these can be fitted without the required Roof area, i.e., wing, rear door, roof rack etc..

Finally if you’re fitting 2 or more aerials together on the same car try and keep them away from each other.

If you follow the above basic rules you won’t go far wrong and it should give you the best radio performance.

Thanks Chris.

[ghondie]

hi thanks for the above advice, im no stranger to radio coms installs, and have been doing so for a few years, just have never come across an install on omega's before, i was mainly worried about the elctronic systems onboard, ie airbags and light checking etc,
will take your advice onboard, and hopefully it will all go smoothly