Transponder With Weak Signal

[sabre1fv]

I have checked other threads on transponder mounting and didn't see my issue mentioned, so hopefully someone can provide some insight or better suggestions.....

My hardwired AMB transponder apparently is providing a "weak" signal to the Timing and Scoring folks. I discussed this with them and they recommended that I elongate the hole through the floor pan. I can do this but wonder if that will really help and so am curious if others have run into this problem. My transponder is mounted to the front bulkhead so it is seated on the floor pan and has a 3/4" diameter hole directly below so that the transponder is 'looking' at the track 2.5" below. This is not an intermittent problem, such as a loose wire/bad connection, and it has been noted at two different track events by T&S. I will add that the hole is through an 1/8" thick steel plate. The transponder was purchased when they were first required many years ago, so it is an older unit. This is a essentially a new car, so the car and transponder have never been used together before; the transponder was last used in 2011 with no problems, though it was mounted outside the chassis.

Anyone have a similar problem?

Thanks in advance.

[Keith Carter]

We typically mounted ours outside the profile of the floor plate. Either on the front bulkhead (nose cone side) or on the front side of the body panel under the suspension. Metal tends to hose up the signal.

[sabre1fv]

Yes, I agree that mounting it outboard would be better. My thought process was that for the price these are going for, it would be worth protecting it by mounting inside the chassis. Since I don't know the signal 'pattern': conical, straight and what diameter,... mounting so the signal end would be flush to the floor with a 3/4" through hole seemed like it should be adequate.

-Jim

[DaveW]

I had that issue several years back. I had to borrow a rechargeable one for an event because they were not able to see the one I had. The transponder had been doing the same as yours (slowly getting weaker), so I bought a used replacement and that fixed the problem. It sees the road through a ~1" hole in the bottom of the aluminum front crush structure and the fiberglass nose (no hole). That's worked fine.

[Lotus7]

We ran a GT3 car this summer at 6 different tracks. Our transponder is the 'old' hard-wired non-subscription style we've all used for years. It's mounted in the driveshaft tunnel looking down thru a 4" x 4" fiberglass sheet 'window' grafted in to a solid-carbon floor.
Although we changed nothing in our configuration, at two tracks they said we were reading "intermittently", and at the other four we were fine. I can't help think the track wiring is also an aspect of the issue for some people.

[Purple Frog]

I believe it is a conical signal. So, the higher it is mounted the larger the pattern that hits the track surface. I had mine about 8" high (with no metal between it and the track) and never had an issue. Shooting through a small hole may make the pattern smaller on the track.

[Bob L.]

some used transponders listed on prodracing.com currently. FYI.

Okie

[DaveW]

I had that issue several years back. I had to borrow a rechargeable one for an event because they were not able to see the one I had. The transponder had been doing the same as yours (slowly getting weaker), so I bought a used replacement and that fixed the problem. It sees the road through a ~1" hole in the bottom of the aluminum front crush structure and the fiberglass nose (no hole). That's worked fine.

I believe it is a conical signal. So, the higher it is mounted the larger the pattern that hits the track surface. I had mine about 8" high (with no metal between it and the track) and never had an issue. Shooting through a small hole may make the pattern smaller on the track.

Thanks, Mike.

My transponder is only ~2" above the hole in the crush structure, so the small hole doesn't do much to restrict the width of the beam to the ground. However, what Frog says is correct. If it were mounted higher, it would.

Also remember that beam strength at any 1 point on the ground is inversely proportional to the transponder's <distance-from-the-track>^2 since the area it covers increases proportional to D^2, just like a flashlight beam. When I had the weak transponder issue I quadrupled the hole area (~doubled the diameter), but that didn't help.

[tige00]

We run it in nose cone floor about 3 inched off the ground 1/8" fiberglass no hole works flawlessly

[Hardingfv32]

The signal is magnetic for both old and new units. The signal shape out of the transponder is more like what you think of as emanating from a horseshoe magnet. Ferrous metal can cause issues.

Brian

[sabre1fv]

Thank you Brian, that is helpful and puts the suggested elongated hole in perspective.

-Jim

[sabre1fv]

In thinking about this further, do you know the orientation of the signal: parallel with the mounting flanges or perpendicular?

Thank you.

-Jim

[bob darcey]

The wires in the track loop are supposed to be ~24" apart. If both wires have to "see" the signal simultaneously (I don't know if that is so), the mounting geometry would have to accommodate that and elongating the hole fore to aft might help.