MOTOROLA SPECTRA VHF NOISE HELP

[rydzewski]

i have a motorola spectra low UHF that sounds and works great.

i recently bought a motorola vhf hi power a9 and installed the same way as the low uhf a9 and i get alot of noise in the backround when i accelerate or when the car is on, when the car is off and the batterys are running it sounds fine.

i have a ford 2000 crown vic p71 and the radio's positive connector is ran from the batterys to the trunk. the negitive it grounded to a grounding bolt in my trunk.

if i run a negitive from my batterys to the VHF radio will it cut down on the backround noise? i dont want to buy a noise reducer, i am just looking for a cheap fix.

Ben

[Jim202]

You might want to be some what more detailed in the noise your getting.

Popping noise that changed with engine speed is probably the sparkplug high voltage ingition causing it.

A whine that changes with engine speed is probably from the alternator.

You could be getting fuel pump noise when you first turn on the ignition, but don't start the engine. It should stop when the fuel pressure gets built up.

There are a number of solutions, but no need in going into them till you narrow down the problem.

Jim

i have a motorola spectra low UHF that sounds and works great.

i recently bought a motorola vhf hi power a9 and installed the same way as the low uhf a9 and i get alot of noise in the backround when i accelerate or when the car is on, when the car is off and the batterys are running it sounds fine.

Ben

[Rick Rock]

Also trace your power lead run and make sure it's not tied to the alternator power lead (zip-tied or taped to it) or any other current-carrying wires in the engine compartment or along the frame rail where the fuel pump power runs.

If you have a heavy-enough power wire run for your other radio, you can also put in a fused distribution block in the trunk area then run your 2 radio power leads to that.

[rydzewski]

its a whineing sound when i accelerate, and i will check the wire placement but i dont think it's next to the alternator. it's only a 10 guage wire, could that be the problem?


If you have a heavy-enough power wire run for your other radio, you can also put in a fused distribution block in the trunk area then run your 2 radio power leads to that.

i would like more information on that if pobbible.

e-mail me at [email protected]

thanks.


jim, thank you for your responce also!

[Jim202]

What you descibe is coming from the alternator. However,
lets ask a few more questions.

1. How old is the battery? If it is close to 3 years or
more old, replace it before you do anything else. As
batteries age, the internal resistance starts to go up.
First problem that shows up is a whine on some radio
receivers. Next thing that shows up is the digital clock
starts to be reset when you start the engine. Last thing
that happens is you can't start the car on a cold morning.
With winter about over, that probably won't happen this year.

2. Have you tried a load test on the alternator? Simple
way to do this is to use a digital volt meter. Measure the
battery terminal voltage before you start the engine. Do
this after the car has not been run for several hours. You
should see something about 12.6 to 12.8 volts. Start the
engine and measure the voltage again. You should see
anything between 13.8 and maybe as high as 14.8 volts.
Write these numbers down. Next with the engine running,
turn on the headlights on low beam. Measure the voltage.
Next turn the headlights on high beam. Measure the
voltage. Next turn on the heater to high. Measure the
voltage. Last turn on the wippers. Measure the voltage.
Try and speed up the engine RPM slightly after adding
the additional load. Watch the voltage.

What your looking for is the point where the voltage
starts to drop. If the engine RPM is normal, the alternator
will just hold the electrical load through all this. If it drops
and a slight increase in the engine speed brings it back up,
your idle adjustment might be slightly low. Be carefull here
as the idle adjustment will cause transmission banging if it
is set too high.

Next, take the same digital meter and put it on the AC
voltage scale and look at the battery voltage again. Set
the range to the most sensitive scale you have. What
your looking for is any AC output at the battery terminals.
If you see more than a few milivolts, you probably have a
bad diode in the alternator. A bad diode will produce low
current output and you won't be able to maintain normal
battery voltage with increased load.

An alternator with a bad diode will normally show up with
a higher AC ripple on the output.

You can go to Sears, or one of the other auto stores and
have them do a load test on the battery and electrical
system. But you will probably find the problem before you
need to go that far.

Jim

its a whineing sound when i accelerate, and i will check the wire placement but i dont think it's next to the alternator.
e-mail me at [email protected]

thanks.


jim, thank you for your responce also!

[viper314]

I have the same alt whine with a high power vhf spectra. I have two identical radios but only one of them has the alt whine when I swap them back and forth any thoughts ??

[wx4cbh]

A really long shot, but open the mic case and see if someone has tied the blue wire to the black wire in order to avoid the trouble of grounding the mic hanger for PL/DPL operation. The mic may not be original to the radio, and this is a common back door trick in some radio applications, especially when the vehicle has a positive ground and the mic hanger is consequently not mounted to a metal surface, or also in normal polarity systems where the mic hanger is not in contact with a metal surface. When the blue and black wires are tied together, there's a fair chance that there will be alternator whine and maybe more present when the modified mic is placed in a grounded hanger. The quick and dirty way to tell on a Maratrac is to lift the mic out of the hanger when the condition is present and see if it stops, but that may not work with Spectras since they're different animals.

[thebigphish]

...check the fuel pump next.

[Jim202]

Viper brought up an interesting point. He swapped radios and the problem went with the radio. This
would point me to looking rather close to the radio.

Has a ground gone bad in the radio?

Has a filter cap gone bad in the radio?

Are there loose board mounting screws?

Was there a poor ground connection made when the control cable was mated to the radio and head?

I would try putting back the suspected radio that was having the problem and see if the noise does come
back with that radio, if I was Viper.

Jim