Lowband and ABS brakes

jim · Post by **jim** » Thu Dec 04, 2003 8:17 pm

In case some of you installers and techs didn't know this:

When installing lowband radios in any heavy trucks (fire, Freightliner EMS unit, commercial trucks) with Wabco and/or Bendix ABS systems, the ABS computer must be specked for the frequency you are operating on.
If you are bidding an install, know someone ordering a truck that uses lowband or are troubleshooting a "radio problem" that involves the brakes....

There are four different computers available depending on what frequency you are on. Yes- it does matter, too. The ABS computer must be compatible with your frequency or you will experience inadvertant ABS activation when braking normally (while transmitting) or malfunction lights.

If ordering a new truck with ABS, inform the manufacturer that you are on lowband and what frequency. Also, tell them WHY you are telling them this, since most dealers and salespersons have no idea about this problem.

I thought about this after reading the one recent post about lowband interference and decided that this was important to bring up because many FDs are on lowband yet and many techs/installers are unaware of this problem.

RADIOMAN2002 · Post by **RADIOMAN2002** » Fri Dec 05, 2003 10:32 am

I would hope every tech is aware of eratic ABS and other vehicle computer operations as a result of using 2-way radios in vehicles. Every Motorola radio used to have a sign that came with every packed radio, and was to be left with the customer after installation, advising about unwanted ABS operation while transmitting. Some early Ford computers would freak out with any radio install doing over 50 watts. The best were the Cadillacs, you could pull up alongside of them on the highway doing 55, key your radio and you would see the car have to pull off to the side of the road. The car would stall and then not start. Sounds to me like the ABS brake manufacturers havn't done their homework in resolving RF interference to their product. All the car companies have, and I would tell them that!

apco25 · Post by **apco25** » Fri Dec 05, 2003 2:50 pm

Most any field of design is woefully inadequate when it comes to RFI issues. Many devices are built without giving the radiated or received RFi a second thought.

Post by Pj » Fri Dec 05, 2003 4:00 pm

Good point. I remember see all sorts of manuals around 1994/1995 that had it right in the install manual--especially the AVA's. Since than, I have not seen the warnings other then the standard airbag ones.

kens · Post by **kens** » Sat Dec 06, 2003 3:28 pm

Thanks! We are in the process of specing new fire engines and we are still using low band as secondary comm.

Jay G. · Post by **Jay G.** » Sun Dec 07, 2003 2:21 pm

What I have done in every rig I have spec'd or been involved in, is place specific clauses: No part of the vehicle shall cause interference or shall be effected in any way by RF transmissions on any or all of the following frequencies:_______"

Never had a problem!

RADIOMAN2002 · Post by **RADIOMAN2002** » Tue Dec 09, 2003 1:52 pm

The worst interference problem I ever saw was when the contractor I was working for, had to correct an errant braking problem on some NYC transit subway cars. Seems the WABCO braking system didn't like the new radios. We found that the car manufacturer had installed the railroad antenna, right next to the brake controller. The old radios were 2watt and the new ones were 12watt. We ended up having to turn the radio power down to 2 watts to prevent the braking problems.

jim · Post by **jim** » Tue Dec 09, 2003 3:46 pm

Whoever installed an antenna next to a brake controller should not be allowed to touch any tool more complex than a broom.

WB2IID · Post by **WB2IID** » Thu Mar 04, 2004 10:26 am

Does anyone have experience with interference FROM the ABS on low band?

I have a 1997 Explorer, with a LB Maxtrac tuned to the 46 MHz fire band. Occasionally - but not always - when in scan mode the radio breaks squelch when I apply the brake. I delete the offending channel but it actually appears on more than one frequency at a time.

The other day I discovered that this happens even with the engine off!

I did not notice this problem with the old radio, although it was more fixed-frequency and in PL mode all of the time.

Any and all suggestions would be appreciated.

jim · Post by **jim** » Thu Mar 04, 2004 10:51 am

It is possible that this may be from LED brake lights.

Try to disconnect ABS main power and retry. If it works fine w/o ABS powered up, contact the manufacturer of the system, as they may have a different module.Do this before trying anything else to avoid pulling your hair out!

Another option is to tighten the squelch threshhold on the Maxtrac.