Ignition noise tips for your mobile uBITx

Robert N4FBZ has been experimenting with locating his µBITx in his vehicle, but says, “I’ve given up on trying to use my Bitx40 as mobile. Nothing I’ve done eradicates the ignition noise (and the alternator whine came back).”

Robert’s comments, and those of other constructors provide pointers to addressing ignition noise that may be helpful to others seeking to take their µBITx mobile.

Bob shares a couple of tips from this…

1) the radio is awesome, but very sensitive to impulse-type noise. The more barriers you can throw up between the noise source and the radio, the better! That means chokes in the power line, filter caps, and so on – and if possible, shielded wires! The noise may actually be getting in somehow via a path besides the antenna and knowing the spectrum could give a clue as to how it gets in.

2) if you’re trying to go mobile, grounding grounding grounding!!! While Bob’s best attempt  wasn’t good enough, it might be good enough in another situation. Ground everything you can… and don’t just trust to bolted-together sheet metal (frame). Also, usually drawing the power from a very low impedance source (direct to the battery) with good shielding and filters is the usual fix. In the case of Bob’s µBITx, it wasn’t enough.

Other suggestions:

  1. Ensure your µBITx is in a metal enclosure without large penetrations (like Nextion screens)
  2. Is everything inside the radio grounded to a common ground? (Power, antenna, board, raduino, mic and key jacks, etc.)
  3. How and where your antenna is mounted is important (i.e. far away from ignition sources, and with a good RF bond to the chassis)
  4. Use a common mode choke using ferrite material and with a number of turns of coax through it.
  5. Check for alternator whine.

Vic WA4THR observed on his first BitX40 trip that he didn’t have ignition noise, but the alternator whine was horrible.  He found it was coming through the power line, and not the antenna.   The noise didn’t change when the antenna was disconnected.

He used a Radio Shack “Heavy Duty Automotive Electrical Noise Filter” (cat. no. 270-051B) in series with the power lead and was amazed that it actually quieted everything.  This was subsequently installed inside the BitX40 plastic case.

On the road, the receiver now sounds as good as when at home on a power supply. Vic suspects that these filters were designed for CB radios, and are the right size (rated 10 amp) for QRP.   You can often find them quite cheap, too.

A good resource:

  1. K0BG’s website contains information on bonding surfaces, dealing with ignition noise, spark plug wires, etc.