How To Protect AM Signal in A Car

I usually just notice that on stations that are getting weak.
I know at one time they sold spark plugs that didn't cause interference. That's the only in car thing I've heard of.

Start with the basics,be sure the hood (if its steel) has a good ground wire on it. I had to put a grounded foil tape matrix under my fiberglass hood! Then its on to individual items,I had to add a filter to my heater blower,fuel pump,ect.. A good source of info can be found in any ARRL Handbook under the mobile operating section. Available in most public libraries.

First, identify the mechanism by which the noise is reaching the receiver. It is either being conducted in through the wiring or is being radiated and received through the antenna.

If possible, disconnect the antenna and assess if the noise is present. If so then it is conducted.

If not then it is being radiated to the antenna.

In either case, check the grounding of the receiver. I have found that a poor ground in the antenna circuit will allow noise to be picked up by the antenna.

My truck radio whines sometimes on weak signals and the noise seems to be related to me pressing the brake pedal so I think it is coming from the ABS system. I didn't pursue it because I mostly listen to a strong local station and it is not too annoying.

IF things appear grounded properly then ask a service manager about this. It may be a known problem for which a factory solution is available.

Neil

Thanks for all the info and to Geoff - yup, I have
the same problem.

It's my wife's car. When my station was just on
1700 KHz, the steering wheel put all kinds of
strange noise into the radio. Listening to my
station and tracking where it covered was really hard.
At about the same
time I noticed the interference, a pirate station started to
broadcast on 1700, also, not too far from me.
That's when I moved
my station down to 1690. As a bonus, there was hardly
any interference from the steering wheel electronics
on that AM channel on the car radio.
Most of you guys know the rest of the story. I
built a set-up so my station ran 1690/day, and
1700/night. (The pirate was not on at night.)

So Geoff, what is the color of your Sentra? Ours
is black. There are so many black Sentras in our
town, that I started to get into the wrong car once -
(the lady sitting in there was pretty surprised) -
another time a guy thought OUR car was his, and he started to
get into ours. When he saw me sitting in there he
apologized a bunch of times for picking the wrong black Sentra.
Both times it was in the same strip mall parking lot.

Best Wishes!
Bruce, MICRO1690/1700

Haha, well, my FIANCE's Sentra is the maroon red color, and I see them EVERYWHERE around here in Baltimore, and I must admit it is a really nice car, just a joy to drive around

I guess it is a huge improvement over my Geo Metro which is on its last legs as I type

That's a great story though

UPDATE:

I have been currently broadcasting oldies during the day, and at 8:00pm, I stream the ABN Antioch Broadcasting network, Antioch 1710 AM Old Time Radio, which is just fantastic the guy who runs it does a great job, so that goes overnight from 8:00pm till 6:00am, then back to oldies, I have really been enjoying, and I hope if I am enjoying it, other people will too.

Still angry at the damn Radio Disney station that crapped all over my signal at 1640 in the evening, forcing me to go to 1630, now my station ID's are all screwed up.

So, Bruce, how do you go about ID'ing when you switch frequencies?

Happy Part15ing,

Geoff

This probably won't help, but it might trigger someone's memory.

I worked in early FM when car radios were just beginning to feature the "new" band. An engineer friend of mine got a state-of-art Motorola FM for his car, and it came with a big fat capacitor "to be installed somewhere in the engine compartment" to prevent noise.

That's all I know.

Hi everyone:

Sorry about this late reply, Geoff.

My AM Part 15 station is off right now, because I
started to redo the ground system, and some
family stuff started taking up my time. I really want
to get it back on. I'm going to go into my back
yard and do a lot more sanding and resoldering of the
radial connections. (Soon, I hope.)

I had no IDs at the frequency change. It was and still
is my intention to do that, but I never got that far. There
was a different problem I was working on. The day frequency
(1690) was stronger than the night frequency (1700.) It
was the same transmitter and the same tuning coil. Even
with cochannel interference, I could tell 1700 was the
weaker of the two. I had more adjusting to do for the
night channel when life got in the way.

At the height of my success with automation experiments,
my ID at the top of the hour would give the time and ID,
and the music would fade down automatically, and come
back up when the announcement was over. There was
also an ID at the bottom of the hour with no time given
that worked the same way.

I have to go but I'll be back.

Best Wishes to All.

Bruce, MICRO1690/1700

I just wanted to add that my automation
scheme did not use computers. (Our
family doesn't have one to spare.)

There were two audio mixers. The different
music sources (Or NOAA Radio) went into the
first one. That was followed by a second mixer
which was hooked to several cassette decks with
timers that would play the various IDs. When a
timer came on and a tape deck was playing an
announcement, an on the air light would come on.
Also, an attenuator would come on between the
first mixer and the second mixer lowering the music
volume, or NOAA, or whatever. Because I have an
audio processor, the transitions with the announcements
would sound very smooth with regard to volume.
Also, the station originally would sign on and off with
timers. "This was when I was just on 1700. There were
also sign on and sign off announcements. It was always
fun to hear the station music go down, hear the sign off
announcement, then there would be a few seconds of
silence, and the transmitter would shut off.

Again, this was all without computers because I don't
have one to use. The funny thing about using a whole
lot of digital timers was that, I would have to check them
fairly often to make sure they were all in sync. Almost all
of the timers drifted. In a week, some timers would be
a few seconds off and sometimes things didn't work quite
right. But this was all part of the fun.

I hope this wasn't too boring.

Best Wishes to All.

Bruce, MICRO1690/1700