Receive interference Jeep Jk

Discussion in 'Mobile Radio Systems' started by KN4BMK, Sep 23, 2018.

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  1. KN4BMK

    KN4BMK Ham Member QRZ Page

    Good Afternoon, I have been having receive issues with my mobile setup and was needing to see if anyone else with a JK or someone more Tech then i am can help solve the issue.

    Radios testing:
    Kenwood TM281a and Yaesu 2500 (using both to test)

    Antenna Testing: (have switched both between each coax)
    MFJ 1/4 wave antenna with NMO mount and small (cant remember name) coax
    Comet CA-2X4SR with NMO mag mount with small coax.

    Issue description:
    When the Jeep is off: Great Transmit and Great Recive
    When the Jeep is off but key turned to Run: Great Transmit and Bad Recive
    When The Jeep is on and going down road: Good Transmit (was told they are a bit of noise, but could just be wind noise), If it receives i get Crackling, "skipping" words.

    2 different radios, 2 different antenna setup on 2 different coax, removed all LEDs in Jeep to see if i was picking up interference with the led drivers, Moved from a lip mount on hood to the rear (seems to of helped a tiny bit)....

    Only thing that comes to mind is im picking up interference from the Alternator, but what really confuses me is when i first put the radio and lip mount in jeep, it worked great, had to take it out for a few months, installed leds and removed carpet, then when i got the rig back in the jeep it then started to mess up. Thought ok, LED interference, but i removed all the drivers and it still appeared so im at a loss...

    I ordered some clip on power filters as well as a coax to nmo converter so i can try with some better shielded coax, has anyone had this kind of issue also for the jeep owners, any recommended mounting if i cant mount on the hood?
  2. K0BG

    K0BG Ham Member QRZ Page

    First, it is NOT the alternator! And, the clip on power filters will NOT correct the problem. The real issue is the on-board electronics, primarily the B-CANs (Body-Chassis Area Network), and the transceivers themselves to a lessor degree.

    I don't remember the exact frequencies of the three B-CANs Fiat-Chrysler uses in the Jeep, but they are digital. Their harmonics stretch well into the VHF spectrum. This "hash" effectively reduces the receiver's SNR.

    We'd all like to think the FM gear we buy would be immune to AM noise sources. The truth is, they're not! We (collectively) amateurs like to have transceivers with wide receive coverage, including the AM-based aircraft bands. This fact makes them much more prone to AM noise interference, in this case, B-CON harmonics.

    You can install common mode chokes on the coax cable as close to the antenna as you can. This will reduce some of the RFI, but probably not all. For VHF/UHF, a single-turn, Mix 31 split bead, is adequate for the purpose. But don't expect miracles.
    KK4NSF likes this.
  3. KN4BMK

    KN4BMK Ham Member QRZ Page

    Thank you very much Alan, i will look into adding the chokes Mix 31, the information on the B-CANs is great to know.
    Last edited: Sep 23, 2018
  4. KN4BMK

    KN4BMK Ham Member QRZ Page

    Also would using LMR-Flex instead of RG-8x (current) or RG-8u? or would it just be a waste of cable? ~ 10ft run.
  5. K0BG

    K0BG Ham Member QRZ Page

    Waste period.

    RG8 sized coax is never warranted, unless you're a fanatic. The difference in attenuation at the lengths we use in a mobile, are measured in tenths of a dB.
  6. KN4BMK

    KN4BMK Ham Member QRZ Page

    My apologies, i miss typed on the current its: RG-58, but you just answered my question none the less :) i was thinking from a shielding stand point. if something with more shielding like a rg-8 or even an lmr would be warranted in using. I'm still really new to communication and learning the different uses and applications of the different coax. Thanks again for your help
  7. K0BG

    K0BG Ham Member QRZ Page

    If someone nailed me down, I'd insist on using the RG8X RF Connection sells, if for no other reason than price. It is as good as any other brand, even LMR. And, I'd use crimp on connectors (using the correct crimp tool which costs about $60). The best choice are the ones with a soldered tip. I'd also use double-walled, poly-olefin heat-shrink tubing to seal the crimp area. Do it correctly, and they will outlast any other type of connection. The only drawback, is the fact they can't be R&R everyday. For that issue, use slide-on, PL259, adapter shells. RF Connections sells those too.
    KN4BMK likes this.
  8. KN4BMK

    KN4BMK Ham Member QRZ Page

    FYI your site is very informative and has been very helpful! just wanted to throw the kudos out there for it!
  9. K0BG

    K0BG Ham Member QRZ Page

    Thank you.
  10. N5AF

    N5AF Premium Subscriber QRZ Page

    You didn't mention the model year of your Jeep, but as the owner of a late model (2012) Ram 1500 4.7L V8, I can attest to what K0BG said regarding the Fiat-Chrysler onboard electronics. My truck is a rolling RFI nightmare. I've not bothered with any mobile gear for that very reason.

    I have observed a "quirk" with my 1500 - you might test and see if it also applies to your Jeep. Start it up and turn on the transceiver to the worst-affected frequencies. With the vehicle in park, apply the brakes and see if the RFI disappears or is reduced. With my truck, the digital "hash" and RFI is reduced by about 90% when the brakes are applied in park, and almost 100% when it is in drive.

    Can't drive around hitting the brakes every time I want to receive. :D

    Our other vehicle, the XYL's 2014 F-150 5.0L V8 Crew Cab is dead silent, no RFI issues as far as I can tell. (No, she won't trade with me...)

    Good luck with your Jeep. If you find a cure, let us know.

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