Watt the Hell......

[M0GVZ]

Common mirror mount onto truck backrack with solid contact between mount and rack. Rack has body ground and 10 ga. ground wire to chassis. I do have a coax ferrite core I could try.

They're terrible. Its the metal under the antenna that counts, not what is alongside it. The fact there is DC continuity between the rack and the body means nothing and because RF floats over the surface of a conductor wire, even 10 ga, is quite poor for RF bonding.

A ferrite core will only be of use if it is the correct mix. 31, 43 or 52 mix is what you want.

Don't worry about not getting it right or asking questions which may seem daft. Mobile antenna installation isn't straightforward, especially the RF ground side.

 

[Captain Kilowatt]

I still think you have a radio tuning issue, and no amount of shielding, bonding, or coax will help if the output from the radio itself is splattered.

Im running a 100 watt General HP40w in a 2012 Silverado with zero issues. But the radio was tuned correctly.

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Out of band or even in band splatter should not be an issue as the ECM is not a radio receiver and therefore can't tell splatter from the desired frequency. The issue is shear fundamental RFI to it.

 

[The Jerk]

After dealing with this in a Dodge truck, I can tell you for fact a clipped/hacked/chopped radio will cause this...and that was just a Cobra 29. Some of the electronics are susceptable to ANY rfi, no matter what the band.

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[Brake Weight]

At a red light in my beater car one time, I had the airbag light flicker for a few seconds and then started getting chatter over my stereo speakers. What had happened was...a big ol' 4wd truck with a big ol' radio, tuned and clipped I'm sure, pulled up next to me. He left, interference left.

 

[vkrules]

Keyed a Cobra 200 up in the truck, Instrument panel went ape shit. All lights but 2 came on, Fuel gauge went empty, and while driving, Speedometer kicks it own ass back to 0 very fast. Repeatedly. After the 3rd time the security light came on and stayed on. This truck doesn't have a factory alarm. According to my RS SWR meter I have a 1:1 match at PEP on 27.185. No Ant. indicators kick on. Coax is not coiled, pinched, sharply turned, etc... On my buddies mfj-259 it shows anywhere from 4.8 to 10 db coax loss at different freqs. It also shows high as SWRs where all my other test equipment shows low.

Specs:
'01 Silverado Base LT
3' Firestik II
K40 50-ohm coax (Not sure type, Pulling dash apart in the morning to look.)

I'm thinking I need to bond the body together with straps since the chassis isn't doing it.

Ok the mfj shows high swr and high loss , that with the symptoms your reporting makes me wonder if you have no connection on the coax shield.Check the connection on the pl259 could be a bad solder joint. You should see 0 ohms between plug outer and earth and maybe 0-2 ohms between centre and the ant.Get your buddy with the mfj to do a sweep and see if the ant is resonate somewhere.Going off on a tangent! where have you taken the power from ? Not from an acc plug I hope, that can cause issues with the vehicles electronics.Straight back to the battery is best. If all else fails borrow a mag mount ant and try different mounting locations around the truck

 

[Captain Kilowatt]

After dealing with this in a Dodge truck, I can tell you for fact a clipped/hacked/chopped radio will cause this...and that was just a Cobra 29. Some of the electronics are susceptable to ANY rfi, no matter what the band.

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The bold text highlighted above reinforces my statement. Because the ECM is not a receiver it cannot distinguish between in band transmissions (any band) or out of band spurious emissions. I had a bone stock Yaesu FT-857 that was clean and not modded in ANY way....not even for 11m. The vehicle it was installed in had a tach that would bounce like a modulation meter and the check engine light would come on when I transmitted. It had nothing to do with splatter or dirty signal. It was simply because it could not handle the 100 watts from the radio. Oddly enough it was a Dodge as well. The same radio and same antenna on my Ford Escape had no affect whatsoever. I haven't tried it yet in my Toyota Tundra. Have to wait until spring for that I guess. Getting too damn cold to do antenna and radio installs in a vehicle now. I don't have a garage to work in.

 

[The Jerk]

Then explain why a DTB repair/tune on the Cobra 29 solved all my problems? It was the ONLY change.

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[vkrules]

Not wanting to get into a heated discussion about causes of RFI I would just like to say that I worked for a communications company for years as a tech and later as a service coordinator. I have had to deal with hundreds of RfI problems in vehicles .Never once was the problem a "dirty" tx.Not to say it doesn't happen but it is rare. Some problems are frequency dependent I had a trunking radio one time that would only cause problems on one ch. So I guess if you had a radio that was producing lots of strong harmonics of the fundamental frequency it could be problematic.Electronics in modern vehicles aren't well shielded and just a whiff of Rf can send a CPU haywire. Big wiring looms under plastics dashes and Companies cutting costs with shielding all contribute to the problem Rf can and does come in through the glass just because everything is grounded and installed correctly doesn't mean your safe. I had a ford courier pickup one time that the stereo would turn on and wind the volume up full everytime you tx. Problem was the coax used by ford ,the braid looked like a bald man with a comb over. 1 strand of wire for the shield and the coax routed along the top underside of the dash looking straight at the ant through the window.The fix in that vehicle was replace the stereo coax and drop the coax straight to the floor behind the dash, after I moved the ant all round the vehicle.I have seen cars that would shut down on the freeway, petrol gauge , indicators,tipmeters etc do strange things. Most are cured by rerouting the coax or moving the ant, replacing the coax, improving the earth or rewiring the power back to the battery, all the usual fixes . Sometimes nothing you do works .

 

[Captain Kilowatt]

Then explain why a DTB repair/tune on the Cobra 29 solved all my problems? It was the ONLY change.

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Perhaps it was because the radio was now putting out a bit less power than before. Who knows. Todays vehicle electronics also have computers that run at certain clock speeds which also have RF generators. Entirely possible one such clock freq may have had a mathematicl relationship to a spur from the radio. This would mean that even a super clean radio would cause an issue if it transmitted on the right freq. This is what I meant by it not being a dirty radio issue as much as an overall susceptibility issue. Yes cleaning up a dirty radio MAY cure it but the susceptibility to RF problem still exists. One ham I know only had a problem on 15m. The vehicle would stumble and sputter with 100 watts. He also had a lot of wideband noise on 15m in the rx. He made an aluminium box for the ECM module which he grounded and no more noise on rx or sputtering on tx. The issue was that he evidently was interfering with a data signal the vehicle used and not a dirty signal. A lot of people tbink a dirty radio will interfere with computer speakers and that a filter will help. Since the speakers are not a radio receiver a filter will not help. The problem is power getting into the device regardless of spectral purity. Some freqs. may have an eazier path due to resonant lengths of cabling or layout etc.

 

[Ratfink]

Out of band or even in band splatter should not be an issue as the ECM is not a radio receiver and therefore can't tell splatter from the desired frequency. The issue is shear fundamental RFI to it.

Someone listen to him. Your not going to fix anything with your mouth open. Headache rack spells disaster can it be done? Yes is it worth the trouble? No. Is hard mounting and bonding and grounding the best way for any application ? Yes if you want the work involved and the better end results. But have it your way it's better to do it right once than wrong twice .... Or more.

 

[Shockwave]

Your coax is radiating your signal because you have no ground plane under the antenna and the coax braid is loaded with CMC. That's why the only thing that has helped at all so far is the ferrite core near the antenna. Adding more may reach a point where the RFI level is acceptable but chances are you will be plagued with this issue until you relocate the antenna to the roof. Nothing fixes these problems like sheet metal under the antenna because it's the only way to address the root of the problem.

 

[AudioShockwav]

Your coax is radiating your signal because you have no ground plane under the antenna and the coax braid is loaded with CMC.

You have two choices, put the effort into ensuring that the rack is adequately grounded or move the antenna.
Just because the rack is bolted to the frame/bed/sheet metal means nothing,and the 10 gauge wire from the mount to the rack is about useless.
You have to bond the bed to the frame, and bond the rack to the frame
You have to insure you have RF ground....not just a DC ground.
I have done several headache racks, including my own.
Often the additional 4 to 6 inches in increased height from the rack will NOT outweigh the extra work needed to have a good install.
Yes, some guys get lucky and it will work tits the first try, but often it is a lot of extra work.
The Choke on the coax that helped slightly improve the problem is a indication "of the problem" not the cure to the "real problem"

Your coax is radiating your signal because you have no ground plane under the antenna and the coax braid is loaded with CMC.

73
Jeff