"Tim Wescott" wrote in message
...
Frank wrote:
Hi all
Let me preamble this by saying I am new at this, and need your
help. But I am a quick learner!
I have a few specific questions and perhaps you can help. I am
trying to troubleshoot a Fm static problem
1) Is the car coax cable lead one or two wires? I am quite sure
it is two (one outer (the ground) and one inner wire) but I'll
ask to confirm
"Coax" is short for "coaxial conductor", i.e. two conductor one
outer
one inner.
2) Should a "in-glass" rear winshield antenna be grounded to the
car's body? If so, from which end of the coax cable? (see Q 3)
That depends on the antenna, but if yes it would almost certainly be
the
outer conductor. If the antenna has two symmetrical conductors then
it
should either have a balun (which would be a little gizmo, probably
cubical) between the coax and the antenna.
3) Does the expression "grounding the antena" (in the case of a
glass mounted antenna) be as simple as soldering a grounding wire
from the outside coax lead end that plugs into the HU to a metal
ground of the car? Or should it be done closer to the actual
antena? SUch as at the junction of the end of the coax and where
the antenna starts...
"HU"? Yes, grounding in a car means to the car body.
Here is more detail on my problem if this helps: inconsistent FM
reception ( static) with in-glass antenna where I use to get
crystal clear reception with old car. However, there is a twist
to my problem: I noticed that the coax cable (inner cable) from
the HU is not truly connected to the antenna even if it looks
like it is. I tested it with a continuity tester and it is not.
When I try to connect the inner coax wire directly to the antenna
(using a wire and soldering), then I can test it and it is well
connected. In other words, the inner wire of the coax makes a
continuous circuit from the HU's to the end of the antenna. Yet,
I still get some static on some FM station (which is not induced
by the engine or the car's electrical systems).
Any suggestion? It is an RSX 2004 (Acura). I changed the HU twice
(two models) and the problem persists (same issue with the OEM)
TIA
It may just be a crappy antenna. If you were really determined you
could try a mag-mount external antenna just to see. If it were a
symmetrical antenna I'd build a balun for it (actually I'd probably
_think_ about building a balun for it any time I drove it, but
wouldn't
get around to it for years).
--
Tim Wescott
Wescott Design Services
http://www.wescottdesign.com
You have both overlooked the fact that the antenna is also most
probably the heating element of the heated (rear?) window. If this is
the case then there has to be a d.c. block for the antenna and
something to stop the supply cable shorting out the signal. This is
usually as small (often cylindrical) device somewhere near and within
a short distance of the window connections. If this is faulty it is
most likely the cause.
The other question - if it is the heating element then does it
completely work? Elements often get minute breaks in them: if the
element only partly works then the working part is all you have for an
aerial and so you may be suffering from lack of signal.
The most important point however is the nature of the
signal/interference. Is it lack of signal - which will give fading and
hiss on FM - or is it crackle being produced by the vehicle? If the
latter, make sure the earth bonding is good between battery, engine,
and chassis. Also make sure it has the right type of spark plugs -
most vehicles these days use the type that have a resistor inside them
and that is singularly the most effective way of cutting spark
interference.
Finally make sure the radio earth is good. If the aerial is
disconnected does the radio still work? It is not uncommon for the
earth in the main harness to fail and the radio to be earthed through
the aerial - which means there will be impedence (i.e. signal
resistance) in the supply route which will definitely cause crackle.
--
Woody
harrogate2 at ntlworld dot com