From: BITX20@groups.io [mailto:BITX20@groups.io] On Behalf Of Robert D. Bowers
Sent: Sunday, March 31, 2019 7:07 PM
Subject: [BITX20] Changing direction - ignition noise intractable #bitx40
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). I've gone with direct power from the battery, extra grounding on the 'doghouse' of my van, plus extra grounding on the antenna base and vehicle frame. I've tried filtering on the power, then multiple layers of filtering - then even a separate battery entirely (no connections to van). I added chokes to the outside of the coax... trying to stop that as a source of entry. I did find that the original grounding scheme for the doghouse (internal cover to the motor on a van - in my case a 90's GMC) was seriously insufficient and improving that reduced the ignition noise by probably 30db or so... but it's still way too loud to use the radio. I even took the coax out of the van and ran it over to a table, where I had the radio. As soon as the coax fitting touched the antenna connector, ignition noise. (You could even faintly hear it with a piece of wire stuck in the antenna connector.) At the same time, using an old TS-520 on my fan dipole, I could not hear the slightest bit of ignition noise, with the van parked only about 30-40 feet from the 40m portion of the antenna. I could hear the contest, however.
I'm really tickled with my BitX40... it's very sensitive and works pretty well (I haven't tried making contacts with it - yet, but the rx is good and filtering seems more than adequate). What I did with it was put it in an old metal case (like a toolbox in a way), with battery, coax, and external noise filter/AGC. It's pretty slick there - a complete portable kit in a box, as long as I have an external antenna along (a dipole would probably fight right in). Someday I may try to shield the case that the radio came with... that might (or might not) be the problem.
I had to pull my 'good' radio (Alinco DX-70) from my shack for repairs, so I'm going to put it in place of the BitX40 in the van... it has a rock-crusher noise blanker and good filtering - once I get it back in operating condition. It should help a lot in solving the noise problem - maybe eliminate it.
A couple of tips from this... first, 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! If I had the equipment (broadband spectrum analyzer), I'd characterize the noise - it may actually getting in somehow via a path besides the antenna and knowing the spectrum could give a clue as to how it gets in. (I don't have a good bandpass filter right now, that might also be a trick to try.)
Second, if you're trying to go mobile, grounding grounding grounding!!! While my best attempt (I don't have lots of time to throw at the radio) 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 to the sort of noise I'm getting. In this case, it wasn't enough.
So now I have an awesome portable (emergency) HF station, that works good - I just can't use it mobile in our van. (Third tip: if it doesn't do what you'd like, find a use where it does!)