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Engine Noise Filter

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BlueDevil

BlueDevil

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We have an engine noise problem in our Fire Truck. We are using an Icom radio integrated with Firecom Wireless Headsets. The engine noise can be head through the headsets and on the receiving end of transmission if speaking through the headset. If the radio mic is used to transmit then the noise is not heard or very minimal.

Any suggestions of a filter to put in-line with the power supply.
 
rescue161

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Put a scope (not a multi-meter) on the output of the alternator. You should see straight DC. If you see a sine wave, then one or more of the diodes is bad and the anternator should be changed. If you do see 13-14 VDC (No sine wave), then you should look for a loose ground. Using a filter to cover up noise is not good practice. I consider it putting a bandaid on an amputation.
 
BlueDevil

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Thanks for the reply. This is a brand new Ladder Truck (1yr old). All the charging systems seem to be working fine. The noise is also consistent with the turbo wine. Not sure that a turbo could cause this but the noise is consistent with that.
 
rescue161

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Diodes, as well as any electronic device, can fail. We see them all the time in our shop. Do you have access to a an o-scope?
 
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cabletech

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Couple questions here: Did the truck come with the Firecom interface preinstalled or did your people install it?

Where is the power for the firecom connected? Must trucks come with a filtered +12 for radios and equiptment.

Have you tryed a differant 'channel' for the headsets? Some times changing channels will remove the whine.

Have you contacted Firecom about the problem and or a filter? They have very good support.
 
rescue161

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None of the fire trucks that we've done installs on have had filters or filtered 12V tap points. Most of the trucks we do installs on are Pierce. If there is noise, it is either coming from the alternator or you have a bad ground somewhere. You can try to filter it out, or you can fix the underlying issue.
 
J

jackj

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whine

If you are talking about a whine and you aren't having a problem with the alternator not carrying the electrical load then look for a ground loop. A difference in potential between the antenna ground and the radio ground can sometime result in alternator whine in the transmitted audio. Double check all the radio grounds, including headset(s).

rescue161's suggestion of using a scope on the alternator output is a good one but you will see some ripple. It won't be a pure DC but it will be close with a few millivolts of ripple. Sitting on the power pole in our back yard.
 
BlueDevil

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I will try getting in contact with FireCom. I don't have an oscilloscope, yet. The FireCom was pre-installed and to my knowledge there are not multiple channels to choose from. I have tried different power sources and grounding spots without any changes in the receiving audio or transmitting audio. Like I said it seems to be isolated to the FireCom headsets/system.
 
J

jackj

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Hummm...What is sitting on the power pole? And where in hell did that come from?

If you don't have the whine when you use the hard-wired mic then the problem is with the FireCom. If the FireCom is powered by the truck's electrical system then you might try a alternator noise filter in line with the power lead to the FireCom. Radio Shack used to carry them, they consist of a choke and a filter capacitor. But make sure that the truck's electrical system is okay first.
 
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ofd8001

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Two cents from another fire guy-

With the Fire Comm being something installed at the fire truck factory, this might be something to have the factory service folks deal with. If it's less than a year old, it may still be under warranty (and owing to how good of a rapport you have with the factory, they might stretch that out a bit).

I don't think installing a noise filter is the answer. There has to be something going wrong and you probably ought to see what it is just so it doesn't get worse, as in "cure the disease not the symptom".
 
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