Thread: SI Disco: Poor Range for 315MHz Security Remote

I have a problem with poor sensitivity for the remote keyfob on a '96 SI Discovery - it works at no more than 1.5 - 2m from the vehicle. It's a 315MHz 2-button remote with the receiver in the green box above the passenger side footwell. I suspect the problem lies with the receiver's antenna.

The Rx antenna exits the alarm on pin26 of C225 (the larger connector of the 2). In some SI Disco's the antenna is 150mm of stiff yellow wire dangling from the connector behind the kick panel. In others, mine included, the yellow wire disappears into the loom heading for the driver's side and, according to the (Rave CD) wiring diagram, arrives at the multifunction unit (C204 pin 18) behind the fascia fuse panel. Suffice it to say that after considerable effort and skinned knuckles I am positive that it does not arrive there (the wire colour on pin 18 is wrong and a continuity check with a multi-meter confirms there is no connection.

I suspected it might head up the driver's side windscreen pillar but this was a dead end (and I now have to repair the plastic tabs on the pillar trim!). Can anyone enlighten me as to where the antenna wire does go in this model? Can anyone offer any help on this subject?

On a positive note, I have some tips I've discovered (er... no pun intended) along the way, which might help others:

Sensitivity is severely compromised if there are any dry or broken solder joints in the key fob - check the battery holder tabs and the solder tabs on the surface-mount pushbutton switches (rock the switches while inspecting with a jeweller's eye-glass). Repair requires a fine tipped soldering iron, a steady hand and great eye-sight. Before fixing these problems my remote would only work when held over the gap between the front door and the front guard (which gives a clue as to where the antenna probably lies!).

The previous owner assures me that I've restored operation to as good as he had at new, and despite complaints to the dealer under warranty they were never able to improve it for him. I've also been told that this is typical, if not excellent, performance for the 315MHz remotes, and I should be grateful. However a friend with a '95 SI Disco and the same alarm has at least 15m range so I'm not inclined to believe that. I can understand that a UHF remote will always have better range since the Tx antenna in the remote will always be far too short to be efficient at 315MHz due to the limited size but this is ridiculous. There has to be a fault and I'd be very grateful for any help anyone can give me to track it down.

And yes, you can assume I'm a tech, and I have a fetish for cleaning oil spots off the driveway (I've owned LandRovers since I left school in 1974).

Thanks in anticipation .....

OK Chaps, I have made some progress on this issue. My apologies to those of you who have been hanging out for an answer, as I’ve been distracted with other issues for a couple of weeks.

First, the short term solution of holding the key-fob remote to the chin to increase its range. I approached my experiments to investigate this with a high level of scepticism – I have a background as a technician and for me, this falls into the realms of pseudo-science. Much to my surprise, however, I found that holding the remote to my chin did, in fact, appreciably improve the range of the remote – generally from about 1.5m to 2m out to 3m to 4m. At this stage I can’t provide a satisfactory explanation for why this works, but I have a colleague who has a deep understanding of these things and I’ll try and get an answer and post it later.

Despite the fact that holding the remote to my chin helped, I simply can’t bring myself to wander around a car park with a keyfob to my chin in public – not in daylight anyway!

I got the chance to have a close look at the Disco with good range for the security remote owned by a friend of mine, and found it has a third variation on the location of the antenna for the theft alarm module (the other two are the short tail hanging down behind the passenger side kick panel, and the wire disappearing into the loom heading for the driver’s side as in my vehicle). This ’95 Disco has the antenna wire encased in a length of protective sleeving and heading up the passenger-side windscreen A-pillar and then across the top of the windscreen. This is pretty much how I expected the antenna wire to be run in all Disco’s and I was surprised to find that, apparently, most aren't.

Back in my car, I removed the sun visors and front roof console from the headlining and this allowed me to feed a stiff wire from the hole in the centre of the headlining (above the rear view mirror) to draw a length of 1mm2 (yellow insulated) wire from the opening for the LH side sun visor mount to the centre, and then did the same for the RH side and used the latter as a draw wire to pull the first wire right across the windscreen. I removed the plastic trim on the driver’s side A-pillar (more on that later) and formed a loop in the end of the wire at the top of the door pillar and fed a cable tie around the steel tab which holds the wiring loom in place at the top of the pillar and used this to secure the end of my new antenna wire.

I then used the stiff wire to pull a draw wire up from the top of the passenger side A-pillar to the hole for the sun visor and used that to pull the end of the yellow antenna wire back down to the top of the pillar. It was then quite easy to tuck the wire in behind the plastic trim on the A-pillar and feed it down to the kick panel trim and around the back of the passenger-side foot-well to bring it into the loom to connector C225 on the alarm module. A quick snip with the side-cutters and crimping some connectors onto the wires now had my new antenna wire connected. (I’ve explained in detail how I ran the wire to help anyone wishing to do this avoid some of the dead ends I ran into on the way - you should be able to do this in about 2 hours.)

And has it worked? You bet your skinned knuckles it has. I have yet to perform a set of (objective) comparative tests in an open area but early indications are that it has increased the range of the security system to around 5m to 6m to each side and to the front of the vehicle. It still has very poor range to the rear but this isn’t too surprising considering where the antenna wire is located; it is, after all, tucked in behind the vehicle’s metal roof and is therefore somewhat screened from the outside world.

If you were having the windscreen replaced it might be possible to run an antenna wire in the rubber seal and this should provide a bigger improvement in range as it would bring the wire out from behind the metal screen of the roof – I’m not sure that this would be practical however.

And the A-pillar trim? Well, can anyone tell me how to remove these trims without breaking off the 3 plastic tabs that lock into the spring clips in the pillar? And having broken the damn things off, my hunch is that using the adhesive for gluing PVC drain-pipe together is going to be a more permanent solution than using a cyanoacrylate (instant) adhesive. I’m also considering bolting some metal tabs onto the trim in place of the broken bits with M3 hardware. Any thoughts anyone?