Installing an AM CB in a Tdi Defender

**VladTepes** · 19th September 2006, 03:09 PM

except i haven't been able to find any contact details for them anywhere.

**VladTepes** · 12th October 2006, 08:57 AM

Bump.

I'm still looking for advice as to where I might mount this unit. It's a single-DIN sized unit. The 'space' where a radio is normally mounted in a Defender is already in use. I was vonsidering the trans tunnel between the tunnel and the handbrake but I'm not sure how I'd mount it up ?

I also need to know how to tell if my antennae are ground plane dependent or not.

Please help.

**dmdigital** · 12th October 2006, 09:31 AM

Just going through this thread (as I am going to fit a radio to my Defender soon).

You said the aeriels are different lengths. If you notice in the models you posted the link to one aeriel only comes in 910mm whislt the other comes in 3 sizes. Have you measured them? This might give you a clue as it sounds like you have one of each or 2 the same in which case the one longer than 910mm is not specified as requiring a ground plane.

I'm not big on radios, I know enough to be of danger and only about UHF. When I've put them in Disco's I've owned I always wired them back to the 2nd battery (+ve) and the negative back to a ground pin on the body.

I get my Defender next week so I'll be able to have a good look as to where I'll mount mine. I'll be looking for ideas!

natanchris · 12th October 2006, 10:01 AM

Definitely wire it direct to the battery(with fuse of course). The AM sets in particular are very susceptable to electronic interference, so a direct power feed minimises the problem. Also when you run your antenna wire, try to avoid running it close to other power wires for same reason. A ground-plane independent antenna should have a metal "extension" at the base of the whip; some look like a bulb, others like a metal rod. This is the bit that tricks the antenna into thinking its mounted on a big metal ground plane. The ground plane dependent type just has the hex fitting where you screw it onto the standard base. Hope this helps....Cheers Chris.

**Tusker** · 12th October 2006, 11:02 AM

Originally Posted by VladTepes

Bump.

I'm still looking for advice as to where I might mount this unit. It's a single-DIN sized unit. The 'space' where a radio is normally mounted in a Defender is already in use. I was vonsidering the trans tunnel between the tunnel and the handbrake but I'm not sure how I'd mount it up ?

I also need to know how to tell if my antennae are ground plane dependent or not.

Please help.

Space is at a premium in a Defender.. your stuck with either the trans tunnel, or buying/making an overhead console.

Just assume its ground plane dependent, and fit accordingly. If on the bullbar, it just needs a circular disc around the base. You see these fitted this way every now and then. If on the roof, not such a problem.

How big should the disc be? I'll leave it to the experts. They don't need to be that big, less than a foot across from the ones I've seen. There will be a formula somewhere in cyberspace I'm sure.

Regards
Max P

**one_iota** · 12th October 2006, 11:54 AM

Originally Posted by Tusker

Just assume its ground plane dependent, and fit accordingly. If on the bullbar, it just needs a circular disc around the base. You see these fitted this way every now and then. If on the roof, not such a problem.

How big should the disc be? I'll leave it to the experts. They don't need to be that big, less than a foot across from the ones I've seen. There will be a formula somewhere in cyberspace I'm sure.

Regards
Max P

The gospel according to Mobileone:

http://www.mobileone.com.au/antennas/default27.htm

**cewilson** · 16th October 2006, 06:29 AM

Originally Posted by VladTepes

Bump.

I'm still looking for advice as to where I might mount this unit. It's a single-DIN sized unit. The 'space' where a radio is normally mounted in a Defender is already in use. I was vonsidering the trans tunnel between the tunnel and the handbrake but I'm not sure how I'd mount it up ?

I also need to know how to tell if my antennae are ground plane dependent or not.

Please help.

I ended up biting the bullet and buying a roof console. Best damn thing I ever did for the Defender.

**VladTepes** · 16th October 2006, 01:20 PM

Yeah problem is I;m tall and a roof console across the front top of the windscreen actually wold restrict my vision.

**cookiesa** · 9th February 2007, 02:44 PM

As said before most important thing with wiring on AM is avoiding noise caused by other electrical wiring and devices. Try keeping both the power and antenna cables away from these items as much as possible. Being second hand aerials (I think that is what they are, ignore this if not) be very careful using them. As mentioned before AM requires the antenna to be "tuned" (SWR meter needed). This is done by trimming the length of the antenna. If they are used and have been tuned to another vehicle the SWR (signal to wave ratio) may be far enough out on your vehicle to fry the radio.

Most antenna shops/auto electricians can tune the antenna for you (and usually charge next to nothing to do it, less than a swr meter will cost you probably)

When I used to use one (think it is still in the shed.... might have to get it out!) I wired it up, mounted the unit then just got it tuned as done properly also makes a big difference to performance.

**BradM** · 9th February 2007, 05:23 PM

Hi, The 27 MHz AM antenna needs to use a groundplane but this will be provided by the landrover chasis. For AM sets it is best to mount the antenna as high up as possible and a roof gutter mount bracket obtainable from a communications shop wiil do the job. It is best practice not to run the antenna cable through the engine bay with 27 MHz AM if possible as this can pickup noise from the electrics in the engine bay even though the cable is shielded. Many installers do it though if the customer wants the Antenna on the bull bar.

UHF sets are reasonably immune and I personally have the Ae mounted on the bullbar.

Some AM sets if they have been tweaked up for their power output can draw a reasonable amount of dc amps from the 12 volt supply. I would highly reccomend as stated earlier that you run it direct from your battery with an 8 or 10 amp inline fuse. This just keeps it tidy but the big "Hotwire" to the fuse panel would be able to handle it. Easier just to run it to the battery.

Just remember if you forget to turn it off the set and it runs for a fair amount of time even without transmitting it like the inside light senario left on can flaten your battery. I run my UHF to the Aux battery in the Disco.

If the antenna was origionally installed with this set it is more than likely been SWR 'd. This means tuning the antenna to be a precise 1/4 wave stub so it does not reflect power back into the set. Get it checked..as a really bad match will blow the output power amp in the set and any mismatched antenna will reduce output power into the air. Hope this has helped.

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