Tracking a noise source(s)

[JRichard]

I realize this question is asked often but please indulge me a moment of your time.

I'm using a Pro-97, running off batteries, hooked to an NMO roof (hole) mounted 1/4 wave antenna and I'm experiencing significant static with the engine running. Here's the strange part, if I'm near the transmitter(s) the noise is almost entirely canceled out. It usually manifests itself when the signal is weaker but it's only there when the engine is running, and the characteristics don't change, much, it's usually constant. It also doesn't sound like picket fencing. I have experienced that as well but that's more of a terrain thing.

The static is there when using the stock duckie as well.

If anybody is wondering, the car radio is symptom free.

It's a bit of a pain but I'm thinking alot of this is a result of using a handheld instead of a mobile in a vehicle. Handheld's plastic cover versus metal shielding in a mobile.

Thanks,

Jeff

 

[JESSERABBIT]

Does this happen on all frequencies? Is there a specific band ie: aircraft, public safety, or all of them?

 

[Viper43]

Also, does the noise change while accelerating, will it do it with just the key on?. There are a lot of things that can cause it. Some Fords the fuel pump causes noise and adding torrids to the wiring takes care of it. There are a lot of other things that can cause the noise, knowing the make model and year will help in locating the cause.
V

 

[datainmotion]

Lower incoming signal level closer to the noise floor?

 

[Don_Burke]

Here's the strange part, if I'm near the transmitter(s) the noise is almost entirely canceled out.

That is good news. It means the noise is not saturating the receiver.

It usually manifests itself when the signal is weaker but it's only there when the engine is running, and the characteristics don't change, much, it's usually constant.

Concentrate on the changes it _does_ make.

Starting from engine off:

1. Turn the ignition on without starting the engine.

2. Crank the engine.

3. Let the engine start.

Tell us about the noise at each step.

 

[JRichard]

The vehicle is a Pontiac Pursuit (pre-G5).

I'll let you know how it behaves at the various stages.

 

[DiGiTaLD]

Ignition noise is what it is. A wide-open front end on a scanner will definitely pick it up. The reason you are not hearing it or not hearing it as much near the transmitter site is probably because the received signal is overtaking it. The further away you get, the weaker the signal will get and the more the ignition noise can get in to the receiver.

 

[Don_Burke]

Ignition noise is what it is. A wide-open front end on a scanner will definitely pick it up. The reason you are not hearing it or not hearing it as much near the transmitter site is probably because the received signal is overtaking it. The further away you get, the weaker the signal will get and the more the ignition noise can get in to the receiver.

How did you rule out the fuel pump and the fuel injection system?

How can it be ignition if it is relatively constant?

 

[N_Jay]

How did you rule out the fuel pump and the fuel injection system?

How can it be ignition if it is relatively constant?

Because he "knows". :roll: :roll:

:lol: :twisted: :lol: :twisted: :lol:

 

[eorange]

How can it be ignition if it is relatively constant?

"Ignition noise" is often - and incorrectly - thought of what happens when you turn the key. In reality, ignition noise refers to the energizing of the spark plugs, so it can be a constant source of noise.

 

[N1508J]

Another check.

I realize this question is asked often but please indulge me a moment of your time.

I'm using a Pro-97, running off batteries, hooked to an NMO roof (hole) mounted 1/4 wave antenna and I'm experiencing significant static with the engine running. Here's the strange part, if I'm near the transmitter(s) the noise is almost entirely canceled out. It usually manifests itself when the signal is weaker but it's only there when the engine is running, and the characteristics don't change, much, it's usually constant. It also doesn't sound like picket fencing. I have experienced that as well but that's more of a terrain thing.

The static is there when using the stock duckie as well.

If anybody is wondering, the car radio is symptom free.

It's a bit of a pain but I'm thinking alot of this is a result of using a handheld instead of a mobile in a vehicle. Handheld's plastic cover versus metal shielding in a mobile.

Thanks,

Jeff

All the replies you received are on the right track. I would emphasize checking alternator whine and ignition noise (spark plug) primarily. Also, check the coax shield for good continuity (less than one ohm) for a 10 foot run of RG 58 from the antenna ground mounting point to the connector on the radio. Poor or open shields will allow "noise" to radiate from the shield to the inner conductor. However, since your duckie picks up noise the shield of the coax is most likely ok, but check it anyway. Determine what the noise sounds like...whine siren sounds that vary in frequency with engine speed are due to the alternator while buzzing-popping is due to the ignition system. In more troublesome cases, random noises are due to poor electrical bonding of metal parts (chassis) of the car.

Alternator whine is easy to fix with a coaxial capacitor. Ignition noise becomes more interesting.

 

[N_Jay]

"Ignition noise" is the energizing of the spark plugs, so it can be a constant source of noise.

Except the noise tends to change with engine RPM, hence not "constant".

 

[JRichard]

Thanks for the replies. I can't add a lot but when the key is turned over, there's a short higher pitched whine until the engine starts and then it's the constant static after that.

 

[Don_Burke]

"Ignition noise" is often - and incorrectly - thought of what happens when you turn the key. In reality, ignition noise refers to the energizing of the spark plugs, so it can be a constant source of noise.

So....you have a vehicle with an engine that runs at a constant RPM?

What are you driving? A locomotive? A DC electric cruise ship? A generator?

 

[Don_Burke]

Thanks for the replies. I can't add a lot but when the key is turned over, there's a short higher pitched whine until the engine starts and then it's the constant static after that.

I would go for the fuel system first. Everything else mentioned here would change pitch with RPM.

The easy way is to find someone who has beaten this in your model car.

If that does not work out for you, we can start talking toroids, capacitors, and shielding.

 

[JRichard]

You might be on to something. I decided to listen to one of the main freqs opened up and when turning the key short of turning the engine over, I hear a very short click noise then it goes away. When I turn the engine over the noise comes back constant.