RadioBanter - Noise from vehicle

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Noise from vehicle

The noise you're picking up is obviously radiated and being picked up by
your antenna and not coming thru the power lead, as you have
demonstrated by using a separate battery. If you're using the wind-up
antenna, it's picking up every single ounce of stray radiated rf energy
from all the noise sources in the vehicle. You don't want the antenna
to receive anything until it gets outside of the vehicle, so you need
shielded coax from the radio to the antenna on the outside. But given
the confines of space, you obviously can't throw out 100' of wire, so
you're limited to some sort of vertical whip antenna...a 108" steel whip
is about as long as you can practically get - but that's still pretty
short for a shortwave antenna. So the way antenna manufacturers get
around that is to add a loading coil to make the radio "think" the
antenna is longer than it actually is...kinda'/sorta' what a hamstick
is. BUT - - you get them on a frequency other than where they're
designed and they suck! So to cover the shortwave spectrum, you'ld have
to get a BUNCH of hamsticks. I'd opt for a 108" steel whip plus a small
antenna tuner at the end of the coax by the radio.

Now, back to the noise problem...

I just picked up an MFJ-1026 "Noise Canceller" that I've experimented
with in the shack for both my ham rig as well as general coverage
receiver. I bought it as somewhat of a "crapshoot" figuring that I'd
throw something new at the noise and if it worked...fine; if not...it
was worth a shot. Few things you gotta' know about this noise
canceller...it's not like a noise blanker or DSP. The receiving antenna
and a 2nd antenna (to pick up the noise) are each plugged into this
unit, then a cable goes from it to your receiver. The way it works is
to "mix" the signals from the 2 antennas after it changes the electrical
phase of the signal from the noise antenna so it is knocked way down.
So it does require another antenna (can simply be a piece of wire) and
also quite a bit of a learning curve - - you tune this thing - carefully
- you don't simply switch it on and off. But it DOES work (at least, in
the shack). My next step will be to try it with my hf mobile rig (the
infamous Ford Explorer) - I *think* it should work but just haven't
tried yet. If so, it should make a dramatic improvement. More, later...

/Carl - W5SU
Dallas TX

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,
--
~/.signature

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.

Al Arduengo wrote in message

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?

MW is just as prone to noise as SW if you listen to weaker stations.
Maybe more so. The reason you don't notice it on that radio, is it has
a properly designed and mounted antenna system. MK

Peter Maus wrote:

(snipped)

Hi Peter, how's the bike? Well I hope.

mike

m II wrote:
Peter Maus wrote:

(snipped)

Hi Peter, how's the bike? Well I hope.

Goes in for a tuneup this week.

Other than that...seriously fine, quiet and smooth.

p

mike