2nd Gen Non-Engine/Transmission 20 meter RF into '02 'puter...

[Gary - K7GLD]

I've been steadily fighting a losing battle with RF getting into the accellerator circuit of my truck when transmitting on 20 meter SSB with my IC-706MKIIG - I mostly use Hamstick monoband antennas, they load perfectly and I get great reports - but while accellerating and transmitting at the same time, I get noticeable surges that follow voice peaks - no problem while traveling at a steady speed... Several times it's been bad enough to set codes and light the CES light - I've installed ferrite chokes in nearly every circuit under the hood - especially those in, out and around the ECM and VP44 - but no luck so far in significant RFI reduction... I'm not about to start butchering the wiring itself, unless someone who has "been there, done that" has specific info on exactly what and where to make modifications - surely some other ham out there also has a truck like mine and has had the same problem? OR, if some of you other hams are using 20 meters WITHOUT problems, maybe we can compare notes as to what we're doing different...



I'm NOT looking for wild "shots-in-the-dark" or guesses - but someone who has had this same problem, and found a specific cure for it...

 

[jmeehan]

Originally posted by Gary - KJ6Q



I'm NOT looking for wild "shots-in-the-dark" or guesses - but someone who has had this same problem, and found a specific cure for it...

OK, but I'll give you one any way .

Would shielding the accellerator circuit wiring with foil and grounding the foil help?

If not please explain why. I know shielding is used in some automotive applications. This seems perfect, but I don't know much about radios yet.

 

[Gizmo 007]

had that problem while running a linear amp on a CB radio. I ended up having to move the amp to the back of the cab, and rerouted all the wires as far away from the firewall as I could. Not sure how you could reroute the ham so as not to interfere. It's got a lot of power, and the computers are really sensitive.

 

[fest3er]

I'm not a ham, nor do I play one on TV. But Dad's been a ham operator for 60 years or so, and I picked up a lot of RF experience in my 10 years at Motorola. (I even learned about building EMP-proof faciliites for computer and communication equipment during my 5 years at GTE. ) So whilst I don't have 20M ham experience, I do have a fair bit of RF knowledge I can share.

Try narrowing or defining the problem. My guess is your rig is interfering with the data busses. (The CCD bus is a 3-wire bus - send, receive and ground; it likely is not terribly resistant to RFI. And the PCM-to-ECM data link is quite likely similar. )

Is the interference due to the signal radiated from the antenna or the EM field (if any) around the transceiver? Is the antenna located near the front of the vehicle? Are the chassis of the transceiver and the co-ax well and solidly grounded? Did you run a twisted pair for the power and ground to one of the batteries?

If all else fails, build an 'RF shield box', using a wave cutoff tube (I forget the exact technical term) to pass the power and control wires into the box, and using a panel-mount connector to pass the RF co-ax into the box. This should pretty much isolate the transceiver from the outside world. As a first attempt, you could try using copper screening to 'encase' the transceiver, ensuring that all joints are well soldered and that the screen is well connected to vehicle ground.

The most common practices for solving RFI include moving the transceiver, antenna, co-ax and power as far from the affected equipment as is possible and/or practical. Less common is building an RF isolation chamber.

[EDIT] Oh, your rig is probably inducing current flow in the accelerator circuit. There are three potential solutions to this *particular* problem. First, you can try shielding the accelerator circuit with foil (as 85CJ suggested), and grounding either one end or both, depending on which works. You can replace the accelerator circuit with a balanced, twisted pair circuit which should be much more immune to RFI (or replacing it with a short fiber link, which should be all but immune to RFI). As a last resort, you could try adding 1-5 feet of wire to the accelerator circuit, so it doesn't 'resonate' so strongly at 20M. BTW, *this* is almost purely SWAG. But, as you know, SWAGs are part and parcel of being a ham!

Good luck,
Fest3er

 

[Lazy-Boy]

Possibly related TSB?

Gary,

There was a TSB for "Radio interference To/From Two-Way Radio Receivers" for the 01's.

May not do anything to help your situation but it might give you some more ideas...

TSB 08-18-00

 

[Gary - K7GLD]

Thanks for the DC TSB - unfortunately, it is for RECEIVER interference, and does not apply to my problem - my receive conditions are perfect!



To the rest, much thanks, I appreciate your interest and good intentions, I really do, but mostly it's the type of info I was trying to avoid - I've been doing this stuff myself for over 40 years - and am WELL aware of all the usual fixes and work-arounds - I don't want to reinvent the wheel - this is a SPECIFIC problem that at this point will respond only to a SPECIFIC fix... I have not the slightest doubt I am getting 20 meter RF into an ECM throttle circuit due to its poor shielding or lack of RF bypass protection. I've tried different antennas in different locations, I've tried running the radio on a completely isolated,separate battery - the radio is extremely well grounded, the antenna is well matched, I've tried different feedlines mounted in different locations, I've carefully rf-choked just about every circuit in the cab and under the hood - this list could go on for many paragraphs, and was exactly what I was trying to avoid - I've done this stuff before, and am VERY familiar with all the steps usually required - honest!



But what I need NOW, is someone else who has faced this SAME problem, on a truck like mine, and found a specific method to cure it, not a shotgun approach that sends me down endless paths - most or all of which I've already traveled...



I too suspect something will be needed in the TPS-to-ECM-to-VP44 - but it SEEMS like all those are extremely short and hard to get at leads - and I really hate to start screwing around on what are undoubtedly pretty fragile and sensitive circuits, unless I know exactly what it is that needs to be done and HAS worked for someone else - and so far, RF chokes in those areas has NOT helped, and it's gonna take stronger measures!



When I encountered a similar problem with alternator whine in my '91, I ended up wrapping virtually ALL the underhood wiring in aluminum foil - it worked great, but sure looked unusual - and made servicing or troubleshooting underhood stuff a real pain... Was hoping to avoid that in the '02 - but looks like that is where I'm headed...

 

[sheldon]

Hey Gary, where did you install your antenna, run your coax, and your power leads? My antenna is on the front grill guard with power and antenna lines running along the right frame rail. So far, no problems on the tech bands. Other bands depends if I learn the code or not... ... .

 

[rweis]

Not mentioned yet, does the interfearence vary with RF power output?

 

[FDziurda]

20 Meters

Gary,

I have my 706 mounted under the driver's seat and the control head mounted on a bracket located in front of the center seat console.



Make sure you ground the radio, itself, to the truck's body under the seat (for RF). Run separate #10 wires for positive and negative, directly to one of the batteries. I have been using hamsticks and other types of antennas with no problems, however, my truck is a 99 and probably a little different. My antenna mount is located at the rear of my truck, on the side of one of my racks on a camper shell (7' from the pavement) I also found that I had to have one of the matching coils at the antenna feed for 75 & 40 meters (non necessary for 20 mtrs and up).



You might also look into placing some large ferrite beads (common mode choke) over the outside of the coax, as close to the feedpoint as you can. This will help prevent RF from flowing on the shield of the coax back towards the radio. Some of those ferrite beads on the power cable might help too.



Going out of town for the weekend.



Good Luck,



Frank - K7SFN

 

[Gary - K7GLD]

LESSEE...



1. Antenna(s) mount in bed on each side of fuel/tool box - fed with mini-8 coax, lead was run temporarily thru rear window slider, has since been permanently installed by running it over under driver-side seat to door sill, where hole was drilled for coax passage on back to bed of truck - no change. And I stress, this so far has only occured on 20 meters - other bands are fine. Unfortunately, 20 and 40 are my main bands of interest!



2. Radio itself is grounded directly to adjacent seat framework with large braid - coax is ferrite choked at base of whip - has been tried at other various locations, no improvement - reducing power helps, but obviously is self-defeating...



3. I have tried (as pointed out above in another post) running the radio on a totally isolated, separate battery right next to the radio on the floor, and with ferrite choked leads - no improvement! It's not RF getting directly into truck wiring thru power leads to the 706!



4. I have ferrite choked the Edge Comp - thinking THAT might be the problem - and also have several other ferrited RF chokes at other locations relative to the Comp sensor attachment points - no improvement... Makes no difference what setting the Comp is on, or even if its turned off...



I mean, all the above is COMMON stuff in troubleshooting problems of this type - *I* am WAY past "common", and am now way out in the Twilite Zone!



Matching coils/capacitors for bands below 20 meters are pretty common - not usually required for 20 and higher with proper mobile antenna design - my 20 meter antenna is perfectly flat, with SWR measured at either the base of the antenna OR at the 706. I don't rely upon merely the mechanical attachment of the mobile mount to provide RF ground, but also provide an alternate ground path via large braid directly to the bed of the truck to several bolts.



AND, I suspect that differences between a '99 and my '02 could be pretty significant as far as various specific computers, harnesses and RF is concerned. My receive situation is absolutely dead quiet - no change whether engine is running or not - and I really want to be able to eventually install my Ameritron ALS-500 solid state amp in the truck as I did in my '91 - but don't dare until I get this RFI problem eliminated - sure don't wanna blow a $1500 ECM out on some lonely stretch of highway...



Unless some more specific info comes in, I'm becoming pretty convinced the only real avenue of correction will be to totally wrap all underhood wiring in aluminum foil, carefully bonding that at various points to the body - it's not very hard to do, I've done it before with great success - but with a new vehicle still under warranty for many items not voided by my Comp, would hate to have to then REMOVE all that for some stupid electrical problem needing dealer attention... :{

 

[JRodgers]

Gary,



Did you ever get this issues sorted out? I just got my last in the state 02 model and was planning on doing virtually the same install in the truck with a IC706MIIG as well. I am wondering if I am going to encounter the same problem.



Joe N5WY

 

[Gary - K7GLD]

The problem was basically RF getting into the added leads of the Edge Comp - several turns of each of those leads around a clamshell donut ferrite toroid choke as close as possible to where those leads connect to the Cummins circuitry, completely cured the problem - of course, by the time I found that out, I had ferrite-coiled nearly every wiring harness under the hood and lotsa ground bonding at various points as well - dunno how much that contributed - but the problem persisted full-force until I treated the Comp leads as describe above... Currently running 500-700 watts out on 20/40 meters with NO problems!

 

[The patriot]

Originally posted by Gizmo 007

had that problem while running a linear amp on a CB radio. I ended up having to move the amp to the back of the cab, and rerouted all the wires as far away from the firewall as I could. Not sure how you could reroute the ham so as not to interfere. It's got a lot of power, and the computers are really sensitive.

You gotta tell us how big that amp was... ... .

 

[The patriot]

Originally posted by Gary - KJ6Q

LESSEE...











I don't rely upon merely the mechanical attachment of the mobile mount to provide RF ground, but also provide an alternate ground path via large braid directly to the bed of the truck to several bolts.

I'd bolt it directly to the frame.

Did you call DC about this? Sometimes they have bullitens on things like this.

Eric