N1ATP

RF NOISE IN THE CAR

Have you experienced RF noise coming “out of the blue” and effectively shutting down your VHF communications?

It seems only the ham-band (144-148) are affected by electronic RFI from consumer electronics. Here are a few examples:

  • My first experience with RFI was shortly after getting my first iPhone. While driving, my favorite D-Star repeater range was suddenly reduced dramatically. Since D-Star is digital, I could not hear a RFI noise. The radio seemed deaf, but was actually drowning in the frequency specific noise-floor. Other frequencies were not predictably affected. I could sometimes see the S-meter bounce around. But not always. My routine was to get in the car and use the opportunity to charge my iPhone. One day i happened to disconnect the iPhone from the charger while looking at the radio. The S-meter what at zero. No noise? I unplugged the non-Apple, but name brand, plug in charger and all noise was gone. Could a famous battery name brand 12vdc to USB really almost shut down VHF communications? The answer is YES! The cheap voltage converters are cheap because filtering is sub-standard. 
  • Years Later, New Car (yeah!). New radio setup. Works great! Let’s add the rest:
    • 12Vdc LTE Router with ethernet ports for onboard intranet – no problem.
    • 12Vdc WX3in1 TNC for APRS and I-Gate – no problem.
    • 5Vdc SharkRF OpenSpot for DMR Mobile HotSpot – Unit is OK. Power Supply???
    • 12Vdc to 5Vdc USB type converter. Suspect to become noise. Chinese hardwired unit – appears quiet?
    • Changing antennas – appears to have no effect – still quiet.
    • Remounting all remote radios from “laying around” to a plywood plate and adding a computer network switch. No big deal, right?
    • Running short on ethernet ports (do not like WiFi when possible to use wire). Added a MOXA EDS-305 industrial multi voltage router to survive the fluctuating dirty voltage in a car. – NOISE when cables are plugged in., however, not when not transferring data.