Al Arduengo wrote:
Carl - w5su writes:

snip

I'd opt for a 108" steel whip plus a small antenna tuner at the end of
the coax by the radio.


Where in te heck are these 108" whips? I would like to get it local
instead of waiting for mail but all there seems to be are up to 39"
whips for CBs.


Now, back to the noise problem...


snip

Out of curiosity, why doesn't this noise show up on my FM/AM that the
truck already has? Is it that the noise and its' harmonics lie in
the same band as sw?

I really need to break out the old college books and refresh my rf
theory.

Cheers,



You've partially answered your own question. Harmonics from the
ignition and other electical noise do, indeed, fall within certain
spectra. Although these spectra may be quite broad.

However, AM/FM broadcast signals are often 10 to 100 times
stronger than SW signals, largely masking impulse noise from the
vehicle two ways One is simply overwhelming it with signal, the
other is the often reduced sensitivity on broadcast bands.

If, while listening to your favorite AM station, the carrier
drops out, you will likely hear these noises. Even some factory FM
receivers will render these noises if tuned to interstation dial
positions.

SW signals being much lower in amplitude, will not offer the same
quieting that a city grade signal will, and will permit some of this
impulse noise to be heard. You can experiment with this by tuning
between stations. Strong broadcast SW station signals will be less
encumbered by vehicle noises, than weaker signals which may be
covered up entirely.

Good sheilding of the antenna transmission line, as well as
effective grounding of the receiver, transmission line and antenna
mounts will help reduce much of this noise. Make sure the hood and
deck lids are making solid contact with their copper grounding tabs.
And ascertain whether the antenna transmission line runs through
well shielded areas of the frame, isolated from ignition generated
electric fields.

My 308 had the antenna cable running through the engine bay right
across the ignition cables. But then what do the Italians care
about my listening habits. It took quite some effort to re route
that cable before my Becker 2340 would render quie3t SW.


Once measures were applied, the listening was quite good.