It also depends on the station strength, atmosphere conditions, electronic noise
from other things like being near a high tension line or a cable TV dish farm.
It all depends on what is causing the noise as to the fix if there is one. Not
all AM noises can be stopped, one of the reasons AM is not the major media it
If its am only I vote for an antenna problem. Check the cable for any rusty
spots and loose connections. If there is any rusty spots on the cable it is
most likely corroded inside too. If its an aftermarket radio it could just
be a crappy am reciever too.
Radio Shack or any radio shop worth beans probably sells the car radio
power line noise filter what you want. It's a coil/cap combo in one little
black box. Hot and ground to the car, noise free hot and ground to the
radio. It's essential a filter that shunts audio frequency noise in the
power line to ground. After installing one, try the radio with and without
the optional grounding strap that's on the back of most radios to see
which way sounds best. Use a plastic insultating jury rig to hold the
radio with the strap if you need something to hold the back of it and it
sounds better without that extra ground. Every big city has one or two
decent AM stations and FM has gone to the crapper for sure in Cincinnati.
I had a persistent AM only engine interference problem on my '86 Lincoln
Mark VII for almost ten years since I purchased it used. I tried
everything. Even replaced the automatic antenna with a special design
optimized for AM reception. I installed multiple braided wire
connections between, the hood and body, tailpipes to body etc. The fix
was accidental and not entirely understood. One day when checking the
radio chassis ground with the radio connected but out of the dash, I
noticed that the reception was great until I replaced it in the dash. It
turns out, if the radio was grounded both at the radio and also through
the antenna shield at the point of the antenna body intrusion, I would
experience the problem. When the radio ground was removed at the metal
chassis to body connection, it worked fine. I insulated the ground at
the chassis to body by removing the metal tab that engaged the body
mount and it has worked great for the last 2 years before selling it
My Chrysler did the same thing. I bought a power filter, removed the
radio, and damn it already had one installed. I tried it without the
grounding strap for the heck of it while it was all hanging out and it
: I had a persistent AM only engine interference problem on my '86 Lincoln
: Mark VII for almost ten years since I purchased it used. I tried
: everything. Even replaced the automatic antenna with a special design
: optimized for AM reception. I installed multiple braided wire
: connections between, the hood and body, tailpipes to body etc. The fix
: was accidental and not entirely understood. One day when checking the
: radio chassis ground with the radio connected but out of the dash, I
: noticed that the reception was great until I replaced it in the dash. It
: turns out, if the radio was grounded both at the radio and also through
: the antenna shield at the point of the antenna body intrusion, I would
: experience the problem. When the radio ground was removed at the metal
: chassis to body connection, it worked fine. I insulated the ground at
: the chassis to body by removing the metal tab that engaged the body
: mount and it has worked great for the last 2 years before selling it
: last year.
: Stan K.
I have had that problem on my last several Fords including a
'90 Taurus, my '93 F150, a '90 F150 and a couple of CV's.
The problem has been resolved on each of them with a power
supply filter. The one I have been using looks like a small
tomatoe can about 3 inches tall and 1 1/4" across. There is
a single wire on the feed end, a line to the radio and
another on the radio end that attaches to ground. There is
already a filter in the system as on other but, I have
simple cut it from the system and replaced it with the
aftermarket unit. I picked up another this afternoon at
Fry's to go on my current CV. The problem has typically
gotten worse as the vehicle gets older for some reason.
Those who only listen to the FM side of the world may never
have a problem.
I've had good experience with noise free AM reception for distant, weak
stations on my '87 Taurus, '92 Grand Marquis and now my '96 Lincoln Mark
VIII. All have had the premium sound systems and standard powered mast
antenna. Only the '86 Mark VII had the problem and it wasn't coming from
the power supply...it was antenna induced. Limiting the grounding point
of the radio chassis antenna shield to only one location resolved it
completely. BTW, I rarely tune the FM band.
On Fri, 08 Oct 2004 20:56:58 -0500, Stan Kasperski
Several months ago, I spent a bit of time (too much)
researching the possible causes. I understand the antenna
is many times the cause. I was finally able to get the
service manager ot the Ford dealer I usually frequent to
tallk to me about the problem and the fact that it seems to
be prevalant in older higher mileage vehicles. One of the
primary sources he pointed out is the fuel pump which tends
to get noisy with age. The fuel pump problem is somewhat
less in vehicles like the CV which have a steel fuel tank
that tends to shield the noise which is picked up through
the antenna. Their internal solution to this source of
noise is to install a filter on the pump power supply inside
the fuel tank which, of course, requires dropping the tank.
The filter kit is a Fomoco parts item which is still
available. Their recommendation in this case for a vehicle
with miles is to install a "Delco" fuel pump instead of
installing a filter. According to him, the Delco pump does
not require a filter to correct the noise problem.
Other common problems in their shop are antenna and radio
grounds. I did quite a bit of testing on my current CV and
F150. Although not terribly noisy, the CV radio did have a
problem as the AM signal weakened or the car went into a
garage or under a bridge. The loss of signal on the F150
was so bad, I thought the radio was bad and replaced it to
learn the noise could get even worse. The radios are not
yet entirely quiet but, much more useable and acceptable
with the addition of the can filter. I suspect that your
solution of isolating one of the ground points, inhibits
reception of the RFI by interrupting it's path into the
system whereas the filter is shunting it to the radio
chassis ground where it is attached. I know very little
about the electrinics or theory of RFI. I did try an
antenna filter which introduced a loud popping into the
system while greatly reducing signal strength - that did not
work for me.
I kow and freely admit that my observations and experience
are all anecdotal but, what the hell - it seems to be
working. I am always looking for a better solution if
anyone knows of one.
If you're experiencing weak reception on AM, perhaps replacing the
standard antenna with a special one may help. I installed this loaded
coil antenna on the older MarkVII in an attempt to improve the signal to
noise ratio. You may want to look into it.
AM FM Auto Antennas
On Sat, 09 Oct 2004 11:21:27 -0500, Stan Kasperski
Thanks for the tip, The power part of my CV antenna no
longer works. I will look to see if they by chance have a
power antenna that my work. The factory power antenna uses
a rather large hole in the fender to mount.
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