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Old 10-20-2010, 10:01 PM
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Radio interference from fuel pump

I receive radio interference on my ham radio in my TJ in the form of loud static. I'm a radio amateur and use low frequencies by modern day standards. These HF freq's are very susceptible to static, especially the fuel pump which is afterall, an electric motor. For continuity sake,
the following narative is my original question which was in another member's post. :
================================================== =====
Mellissas6570, interesting background. I believe that if any AC currents are flowing due to EMF or low freq. RF, it would be better for the PCM to be grounded/connected in order to return such current to ground. As opposed to the PCM floating without a ground. I'm a radio amateur, N3JQD, and Xmit high power RF from my Wrangler, typically anywhere from 3.8Mhz to 7.29 Mhz at up to 500W. My only problem is the darn fuel pump noise be received by the Xcvr. My entire frame and body are grounded everywhere using braided flat cable. The hood, the frame, the exhaust is even grounded thus all metal is bonded to ground and creating a suitable groundplane for Xmit. So, anyway to attenuate the fuel pump noise or eliminate it?
================================================== =====
For those that responded, I thank you. I use braided multi-strand, flat grounding cable to the body and frame. The antenna mount is also bolted thru the body in the right rear qtr. panel. I then grounded that to the frame as well.
To mellissas6570; access to the fuel pump wiring isn't easy. I don't think that there would be enough wire to wrap a ferrite. As an interesting footnote, this 'static' is not being transferred into the Xmit side. i.e. no one is receiving my transmissions with the same static that I am hearing.

Here's the bottom line. I don't want to remove the fuel pump and replace it, just to have the same static all over again.

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Old 10-20-2010, 11:06 PM   #2
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You should be able to find the power wire and ground to the pump right at the pump - actually where the wires go over the tank. Try hanging a small capacitor across them, or even an LC trap.

Not being transmitted but hearing in your receiver makes me suspect it's coming in on the power lead.
Can you hear the noise with the volume down? That's a sure sign the noise is on the power.

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Old 10-21-2010, 02:17 PM
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Hmmm. I didn't try that, but, it does make sense.
VHF/UHF are not any problem due to the much higher freq.
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Old 10-21-2010, 02:33 PM   #4
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Those are the 80 and 40 Meter bands? I loved those - 40M was my normal place. I always wanted to get on 160M but never did.
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Old 10-21-2010, 02:33 PM   #5
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I'm tellin ya, its the braided flat cable you have going everywhere. Motorola mandates that every tower site be free of braided flat cable because of the noise it creates/generates
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Old 10-21-2010, 02:57 PM   #6
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I'm curios - Why would braided flat cable make more noise than regular stranded wire?

Is it the Skin effect?

Towers, you mean high freq cellphone towers?
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Old 10-21-2010, 03:13 PM   #7
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Here's a quote out of the motorola R56 manual

"Braided grounding conductors shall not be used under any circumstances. Braided
conductors corrode easily and become a point for RF interference"

And its true, we took all those straps out of our sites and it cleaned up the signals alot.

Yes cellular sites, and fully loaded two-way radio sites with multitudes of transmitters on location
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Old 10-21-2010, 03:23 PM   #8
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Thats what I was saying about you picking up the noise in your speaker. How do you have the antenna cable routed in the jeep to the back of the radio? Did you go from the antenna mount into the cab, or did you go from the antenna under the jeep tub then into the cab? I still think the noise is being coupled from the pump power leads into the radio, on the antenna shield or the common power that they both share. I think if I were going to play with caps I would do it on the radio, and not cut or tap on the pump power. If it were to short on the radio the worst that could happen is need a new radio. If it shorts on the pump power, well who knows you may not have any problems ever.

I tell you what, can you post pics of your setup? antenna mount, cable run, radio mout, radio power? I think that would really help by seeing how things are setup.
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Old 10-21-2010, 03:27 PM   #9
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It may be an isolated incident because we have been running antenna cables under bodys of cars for 50+ years without a problem. We don't do it on every install, but more times than not its easier to run underbody.
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Old 10-21-2010, 03:30 PM   #10
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Quote:
Originally Posted by bobsalmon View Post
I receive radio interference on my ham radio in my TJ in the form of loud static. I'm a radio amateur and use low frequencies by modern day standards. These HF freq's are very susceptible to static, especially the fuel pump which is afterall, an electric motor. For continuity sake,
the following narative is my original question which was in another member's post. :
================================================== =====
Mellissas6570, interesting background. I believe that if any AC currents are flowing due to EMF or low freq. RF, it would be better for the PCM to be grounded/connected in order to return such current to ground. As opposed to the PCM floating without a ground. I'm a radio amateur, N3JQD, and Xmit high power RF from my Wrangler, typically anywhere from 3.8Mhz to 7.29 Mhz at up to 500W. My only problem is the darn fuel pump noise be received by the Xcvr. My entire frame and body are grounded everywhere using braided flat cable. The hood, the frame, the exhaust is even grounded thus all metal is bonded to ground and creating a suitable groundplane for Xmit. So, anyway to attenuate the fuel pump noise or eliminate it?
================================================== =====
For those that responded, I thank you. I use braided multi-strand, flat grounding cable to the body and frame. The antenna mount is also bolted thru the body in the right rear qtr. panel. I then grounded that to the frame as well.
To mellissas6570; access to the fuel pump wiring isn't easy. I don't think that there would be enough wire to wrap a ferrite. As an interesting footnote, this 'static' is not being transferred into the Xmit side. i.e. no one is receiving my transmissions with the same static that I am hearing.

Here's the bottom line. I don't want to remove the fuel pump and replace it, just to have the same static all over again.
I have one other question, Why did you add so many grounds to the Jeep? were you having problems with something or trying to fix the radio problem?
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Old 10-21-2010, 03:36 PM   #11
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Quote:
Originally Posted by Ibuildembig View Post
It may be an isolated incident because we have been running antenna cables under bodys of cars for 50+ years without a problem. We don't do it on every install, but more times than not its easier to run underbody.
Yes that is very true, but depending on where you run the cable, what is in the bundle with the cable etc. you can pick up noise with the cable. Plus the length of the cable could cause it to be tuned and cause a problem.
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Old 10-21-2010, 03:39 PM   #12
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Yeah I understand the theory, but after 50 years worth of work and not a single problem its not something that ever crosses my mind.
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Old 10-21-2010, 03:56 PM   #13
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Originally Posted by Ibuildembig View Post
Yeah I understand the theory, but after 50 years worth of work and not a single problem its not something that ever crosses my mind.
Well thats not completly true. That exact reason is why the 461 standard was developed.
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Old 10-21-2010, 04:34 PM
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The coax is run inside the cab. It comes thru a hole in the rt. rear qtr., lays on the floor on upto the radio. The radio, "rig", is grounded to the body with #16 black mutlistrand wire. Just regular hookup wire, etc..
Ah, the reason for all the grounds is to create an effective groundplane when Xmitting. Every mobile HF ham has recommended that every piece of steel become electrically bonded together and grounded. Then it supposedly behaves as if all steel parts are in one big, albeit, mobile groundplane. Xmit isn't any problem as I get good reports on my signal strength. The noise is to the point where I have to park somewhere to hear on the rig. So, its not very effective as a mobile HF station. Now, when I'm on battery only, the receive and antenna system are great because my relative signal strength meter shows a strong signal is present. When I start "Jeepers", then the static begins as soon as the fuel pump starts to whine.
To answer Melissas6570 question; no pics are available because I recently removed everything due to this problem. i.e. it can't be used while driving. I removed it just before starting in the Wranglerforum website. But, it can all go back in an hour or so. I'm still thinking that the EMI from the pump can be "clamped" somehow externally.
Oh, as a sidebar: several produts exist that remove this EMI before it enters the rig. But these active filters are very expensive, about $300.
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Old 10-21-2010, 04:39 PM   #15
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braided grounds....thats all I am saying
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Old 10-21-2010, 05:11 PM   #16
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Remember the frequencies he's talking about are nearly DC compared to cell phone stuff.

All kinds of strange stuff happens when the wavelength is shorter than the strands on a flat cable.
Who ever hear of an 80 meter waveguide?
He's still operating where logic rules.

If the capacitor was across the power leads to the radio - then shorted - all it would do is blow the fuse - not the radio.
Same with at the pump - it would just blow the fuel pump fuse - same as when the pump motor shorts out.

You could also try hooking a diode across the pump's power line. Cathode + toward the
+ power side - reverse direction. It will clip 1/2 of the noise pulse. There usually is one across the pump motor right on the motor, but it may have come loose. (AC clutches, relays, even your winch motor uses capacitors and/or diodes to keep RFI down - it's the law!)

Killing the noise at the source is always better than trying to suppress it somewhere else.

Cell phones - too bad they aren't really usable yet. I've had quite a few with different carriers - they all fade in and out, noisy, and totally unreliable. They aren't even as reliable as smoke signals! You can stand close to the tower and watch the signal fade in and out! I rarely even bother to carry one anymore.
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Old 10-21-2010, 05:11 PM   #17
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How do you know for sure its the fuel pump, and not part of the ignition system? I would expect WAY more RF from the ignition system. I seen tons of weird issues from high powered ignition systems.
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Old 10-21-2010, 05:25 PM   #18
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rrich...Humor me for just a second....wouldn't it be easier to disconnect all that crap and try it verus reinvent the wheel with a bunch of hodgepodge components in line that should never be needed? As I said earlier, we have done installs in vehicles for more than 50 years,,,,including HAM, satellite, GPS, cellular, VHF, UHF, 700, 800, and 900 radios as well as marine and aviation, not to mention full out car audio competition and display vehicles...we have even built from scratch mobile command centers with one of each freq radio installed in it, as well as a complete audio and video system and guess what....no noise. I am as well versed in mobile communications as anyone on this site, so I say what's it gonna hurt to try something that doesn't cost anything?
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Old 10-21-2010, 05:48 PM   #19
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Certainly wouldn't hurt to try it!

As a radio ham he probably already has a bunch of capacitors and diodes laying around. Poking the ends through the connector would be easy to try too. Backprobing them into the connector is easy. He He - the hardest part is sliding underneath to get to the connector - in my case, my stiff old body protests!

The possibility of ground loops with lots of cables is always a potential. But they aren't "producing" the noise he's hearing. IF the noise is from the pump motor, then the grounding system may be carrying it too much.

I just looked at a pump motor - not from a Jeep, Chevy I think, it has a diode across the motor.

A quick test to verify it is the pump - key on, engine off, the pump will run a few seconds, then shut off. The noise in the radio should do the same.

He He - gotta go cut some more firewood now - to replace the wood I used when I called my wife. (smoke signals.)
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Old 10-21-2010, 09:58 PM
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That's exactly how I determined the noise origin. Key to the on position without cranking or idling. The rig is wired directly to the battery. So the off/on button stays on while I cycle the key switch and the noise follows the key position. I can temporarily move the rig into my Shaguar to test the noise from that fuel pump. Also, did I mention that I have a YJ at my disposal, ( one of my cars for sale ). I'll try the radio in both of those vehicles. I'm curious how the YJ's pump may sound.

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