Larry Benko wrote:
Michael Coslo wrote:

Should I put a 1:1 balun on the setup or not?

- 73 de Mike KB3EIa -

Mike,

I'm sure there are a lot of opinions but here is what I do. Assuming
your mobile antenna is pretty well matched and you are running 100W then
the differential current in the coax will be about 1.4A. I have an
industrial clamp-on current probe that connects to a small battery
powered RF power meter (you can use something else) and I would measure
the common mode current on the shield of the coax. If the common mode
current was greater than 10% of the differential current in the coax
(0.14A) on any band of interest then I would use a good quality 1:1
balun. Why 10%? I have no real reason but I have done many mobile
installations and have nearly 30K mobile qso's and have no equipment
interactions or problems.



HI Larry,

As an update, and not specifically about th ebalun issue, I tweaked my
system over the weekend.

Noise was an issue. When I first installed the antenna, it was on a
fairly quiet day, RF wise. The unmodified Vitara pumped a slew of noise
onto the radio. Without the engine running, I was seeing around S3-4
Noise. Turn the ignition on, and we're looking at S-9 worth of noise.
Obviously not too cool.

I installed ferrite snap ons onto various lines, such as the alternator,
the power lines to the rig, the power to the radiator fan. I then ran
wire braid from the hood to ground, and grounded all the doors the same way.

Yesterday afternoon, I tried a test drive of the system. Much much
quieter, although I hesitate to say exactly how much, since the band was
a lot noisier to begin with.

I still have to ground the exhaust system, and try a ferrite on the fuel
pump, which puts a little noise into the system. I still have to find
the fuel pump, though. I'm assuming it is on the tank - but I think a
call to Suzuki is in order.

40 meter operation was quite successful as far as the antenna working.
Good reports all around.

As also expected, there were a few in-vehicle issues.

One minor one is that the oil pressure light turned into a nice little
modulation indicator. This was whether the vehicle was running or not.
I'll probably put a ferrite on the power line to it in hopes of knocking
that out.

The other issue was that my voice would come out of the car stereo
speakers. A bit distorted but legible. I'm not sure if this was the
signal getting rectified somewhere or what. It would do this regardless
of if the stereo was turned on or not- thought oddly, it would start
only when the vehicle was turned on, and would go away gradually. At any
rate, I'l have to be sure to get that one fixed.

Finally, and this is not noise related, but I put a capacity hat on the
antenna as suggested by many. Being a homebrewer, I used what would best
be described as a "big freakin' pizza pan", a 16 inch pan mounted
upside down.

Turns out that I can adjust quite a bit lower in frequency than I
expected, and I will definitely have to shorten something up to run
higher than 20 meters.

- 73 de Mike KB3EIA -