[RFI] automotive RFI from air conditioning
Sun, 20 Oct 2002 13:56:35 -0700
I recently installed my IC-706 in my 2001 Audi S4 and have been experiencing
some RFI issues... A little about the setup first. I ran power straight from
the battery, through the cabin and into the trunk where the base of the
IC-706 is. It's connected to an Icom AH-4 auto antenna tuner. I fabricated a
custom antenna mount using a piece of 3/4" thick aluminum bar which is bolted
to the towing loop beneath the rear bumper. The antenna is connected to the
tuner with a short piece of RG-213 with the outer insulation and shield/braid
removed. The antenna mount, IC-706 and AH-4 tuner are all grounded with short
runs of 14 guage copper wire to a bolt in the trunk that attaches one of the
luggage tie-downs to the chassis.
The first source of noise I'm pretty sure is the ignition. It's about an
S6 on every band with the noise blanker turned off. The noise blanker does
a really good job on 10 meters down through 17 meters, an okay job on 20
meters, and a so-so job on 40 meters. The tuner won't tune the 102" whip for
80 meters, so I'm not as worried about that (yet).
I feared that my long power run from the battery all the way to the trunk
might be the source of some noise, but with the tuner disconnected from the
radio, the noise disappears completely.
I would like to see the ignition noise go down to S2-3 with the noise blanker
turned off. I don't know if this is a realistic goal or not. Newer Audis
have an electronic ignition with a separate coil for each cylinder and no
ignition/plug wires. One of the motiviations for auto makers to move to this
kind of setup, ironically, is to reduce RFI from ignition noise...
The other noise is more complex and causes far greater reception problems.
It is narrowband and has two components --
a high-pitched whine and a lower note and is about S5 or S6. It occurs on
all HF bands about every 20 kHz, and rises gradually in pitch over time. I
made a key discovery that if I turn off the climate control, or press the
"Econ" button (which turns off the A/C compressor), the noise rises much more
rapidly in pitch for ~5 sec and then disappears completely. If I turn the
climate control back on, or turn off "Econ" mode, the noise comes back
instantly. I initially suspected one of the two electric fans that cool the
A/C radiator, but disconnecting one of both of them makes no difference.
I have called the service departments of several local Audi dealers, and they
seem totally unwilling to help diagnose RFI issues experienced by non-Audi
equipment. My next step may be to try to go in and demonstrate the problem
to a service advisor in person, but I don't have a lot of confidence that
I'll be able to make any progress that way.
In any case, if anyone has experienced and similar problems or has suggestions
for what my next steps might be, I'd appreciate it.
Jim Meehan, N9OYP
San Francisco, CA