Chip Interference from CB Radio

[Bammo]

Has anyone else experience interference on their engine management chip from radios in the MN? I had a Chip It DPS210 which would completely fritz out if I transmitted anything more than about 1W on UHF or 500mW on VHF from the radios in the car.

I pulled the chip apart last night to note with surprise that the casing is resin not metal and none of the cables are shielded. I'm going to refit the PCB into a metal box and replace the wiring with shielded cables and I reckon this should solve the problem once and for all. Anyone else experienced this?

[kitemanwest aussie]

One of the cables could be acting as a tuned aerial, or the device you've plugged it into may be acting as the aerial (via a coil?). Will be interesting to see if yr shielding solves anything.

[Bammo]

Nah - if one of the sections of cable was acting as a tuned stub antenna the level of interference would be quite frequency dependent - this is broadband so it's just RF coming into the box and messing up the timing chips I think. A die cast metal box should fix most of it but whilst I am there I'm upgrading the cables just to be sure.

[Giovanni]

Another cure could be the fitting of ferrite beads and rings to the effected item

[RHKTriton]

Location of the antenna and coax wrt to chip location is one point.

Power supply is your next direct link between both, so ferrite rings around each units power wires another easy one to test.

Professional radio installations usually run supply wires direct from battery to two-way to provide clean power and minimise interference with vehicle electrics.

[Bammo]

Bugger. I installed the chip into a grounded metal case and I replaced all the wiring with double shielded wiring looms with a shielded power feed direct from the battery. Used a secondary antenna on a mag base and installed that on the back of the vehicle so that there is maximum physical separation between the antenna route and the engine bay - the coax goes nowhere near the engine in other words.

The interference level is certainly reduced - it no longer cuts the engine completely when transmitting @ 50W on VHF but @ 5W on VHF it still noticeably interferes with the chip. 5W on UHF is OK so I reckon anyone with a normal CB would think this was fine.

I suspect part of the issue is the nature of the radios I run in the vehicle- not your normal CB!

I'm going to try some ferrite beads next. If that doesn't work I think I might have to flog the chip Anyone know what a used Chip IT chip (with a new wiring harness!) is worth? Mine comes with the fully unlocked programming set since I had the very first chipped MN in Australia and they guys gave me full access with source code etc so this one can tweaked almost any way imaginable.

[RHKTriton]

50W! That'll punch through.

Have you tried chokes on the DC lines into the metal enclosure and on your radio supply lines?

Another thought, form any of the wires (where there is a signal and associated ground wire) into a fairly tight twisted pair.

I have a client who has a variable speed exhaust fan in one of his lab setups and it plays havoc with a data logger measuring thermocouples. We've tried ferrite rings, shielded dedicated mains, etc. End game, his replacing the whole fan setup.

A band-pass filter on your coax feed may also reduce any harmonics and consequent radio energy being presented to the chip. Is. Tighten up what's going up the stick.