Sudden and persistent 'flutter' on VHF only

Discussion in 'On the Road' started by W4EAE, May 27, 2021.

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  1. KB3WFV

    KB3WFV Premium Subscriber QRZ Page

    Hi Ryan,

    Try installing a mag mount antenna with coax and a different VHF radio. Borrow one for testing if you need to. This will eliminate the current radios and antennas. It is worth noting that there has been alot of VHF ducting from MA down to SC in the last week or so. Does this fluttering occur during all times of the day?

    Something has desensitized the RX on the radios. Is there attenuation turned on causing reduction in signal? Is there a pre-amp turned on causing an overloading of the receiver? It could also be a change in the repeater that is simply reducing the signal to that area of town. If you drive a different direction while keeping the distance from the repeater about the same does the fluttering change?

    Interference from near by devices in the car will usually occur at all times. So, the suggestions to check for RX noise while the car is sitting still is not a bad idea.

    Take a ride in the car without any cell phones, tablets, hot spots, gps, or laptops in the car. It could be possible that one of those devices is causing a interference and desensitizing the RX.

    Brian
    KB3WFV




     
    AG6QR likes this.
  2. W4EAE

    W4EAE XML Subscriber QRZ Page

    It was, in fact, interference de-sensing the receivers.

    The source was the DC-DC charger I use for my auxiliary battery. It was putting out noise from 145.1 to 156MHz that was only detectable in the near vicinity of the car. My IC-R30 was showing it to be S2-S3 in the car, and S5 if I touched the antenna to the charger. As soon as a walked a few feet from the car, it disappeared. I disassembled it and every looked OK (nothing was burnt), so I put it back together and wrapped it in some copper foil. That brought the noise down to the point that is wasn't discernible from the constant band noise.

    I think that that relatively small amount of noise was de-sensing the receiver just enough to make the formerly hidden constant flutter which occurs during motion quite obvious and annoying. When I was parked, the signal from the repeater was strong and constant enough that I didn't notice anything, even though the noise was still there.

    Thank you all for your suggestions. They were very helpful.
     
    G0CIQ and AG6QR like this.
  3. KB3WFV

    KB3WFV Premium Subscriber QRZ Page

    Nice work Ryan.. Thanks for posting the solution.

    Brian
    KB3WFV
     

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