Re: Question about antenna noise filters

"MOSFET" <ntanner@xxxxxxxxxxxxx> wrote in message
news:KOCdnZvvDuhGMivbnZ2dnUVZ_q6hnZ2d@xxxxxxxxxxxxxxxx
That Radio Shack guy was on crack.

I know the item you're reffering to and it goes inline between your HU and
amplifiers or signal processors, NOT SPEAKER CABLES.

TAKE IT BACK!!!! And then use Google to find someone who sells EMI
filters
for antennas.

If your HU is not making this noise when playing the radio (AM/FM) or
CD's,
CLEARLY it is an EMI problem through your antenna that is causing the
problem.

MOSFET


"Cartrivision1" <doidy1@xxxxxxxx> wrote in message
news:1186364026.551322.56700@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxx
On Aug 5, 3:35 pm, "Christopher \"Torroid\" Ott" <spamtrap at
ottelectronics dot com> wrote:
"Cartrivision1" <doi...@xxxxxxxx> wrote in message

news:1186348029.307176.231030@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx





On Aug 5, 1:28 pm, "MOSFET" <ntan...@xxxxxxxxxxxxx> wrote:
Just to be clear here, you are saying you bought an aftermarket Sony
HU
(head unit) that as well as having CD (perhaps cassette) and AM/FM,
it
also
has shortwave capability. Correct? It is not a seperate unit.

If so, are you also using any type of aftermarket amplifier to
boost
the
signal before it goes to your speakers? If so, that is where I
would
look
first (a ground loop).

If not, you may be picking up EMI (Electromagnetic Interference)
from
the
various accesories in your car. Car's produce A LOT of EMI
especially
from
the alternator.

Does it make this noise if you are just playing AM/FM or CD? If
not,
the
EMI problem is more than likely the problem.

You MAY want to try a larger ground wire from your HU or try
different
grounding spots, but I'm not sure this would help.

Your best bet might be a filter between your antenna and your HU. I
believe
Radio Shack makes just such a device and it may solve the problem.
If
not,
you can always take it back.

MOSFET"Cartrivision1" <doi...@xxxxxxxx> wrote in message

news:1186331021.530215.259930@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx

Hi, I recently bought a Sony head unit that has shortwave radio
coverage. It has fairly good sensitivity using the car's power
antenna, but on one channel that I like that broadcasts in the day
time, I pick up a lot of noise from the engine, power accessories,
etc. I notice that when the engine is off the reception is just
fine,
but with the motor running and fans running and such the noise
pretty
much drowns out the reception.

I thought about adding some kind of noise filter but not sure how
these are installed. Are they installed inline at the antenna, or
at
the head unit? Also, I did talk to one local car stereo place and
they said to check the ground wire. I am pretty sure that the guy
who
installed the deck, which is aftermarket, probably just used the
ground connection from the stock radio. BTW, radio reception on
AM/FM
is just fine.

Any help would be appreciated.

thanks,
CTV- Hide quoted text -

- Show quoted text -

Hi, thanks for the reply. I believe you are correct that it is EMI
because the reception is great with the ignition and accessories off.
And yes, it is a Sony head unit with shortwave coverage, no external
box of any kind. And no, I do not have a problem with noise on the
other radio sources such as cassette or AM/FM. Just on shortwave
which is very susceptible to outside electrical interference.

You might have some luck with the folks over on rec.radio.shortwave
regarding how to protect the signal until it gets into the radio. It's
pretty obvious that the problem is EMI, finding which of the several
sources
in the car and correcting it is a little more specialized. SW is really
low
power and the signal is easy to overwhelm in a car.

Thanks for the advice. I went to Radio Shack and they no longer carry
the filter for the antenna. They did manage to sell me a ground loop
isolator for $16 though! The sales guy seemed to think that since it
was engine noise that was causing most of the problems that it would
be the best bet. I went home to connect it to the system when I
realized that I have a 4-channel system, and I only got one of them.
A question though........is it OK to connect it at the amplifier end
as opposed to the head unit to save myself having to yank out all of
the wires from the front of the dash?


thanks,
CTV


Yeah, I agree (see above), that ground loop isolator isn't going to do
anything for your problem. The interference is either getting in from the
antenna or the ground of the head unit. SW signals have to be amplified alot
more than the AM/FM or CD which opens poor grounding up as a real
possibility. Even if nothing else has noise the SW receiver is still
susceptible because there's so much amplification.

So you need to focus your attention first on getting a good, short chassis
ground on your head unit. Do not use factory wiring for this. Try not to
wiretie any other wires to the ground line either. If you still have noise
after this, you'll need to consult with some HAM guys in the other groups
for possible filters for your antenna. Or even an alternate antenna if
that's an option.

Chris


.

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