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Author Topic: Eliminating Impulse noise from running engine?  (Read 3179 times)
G7MRV
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« on: April 19, 2012, 02:08:38 PM »

Heres the scenario - S7 impulse noise on 144.300 Mhz (USB mode) with engine running. Vehicle is 2007 Ford Fiesta, 1.2L Duratec petrol engine. Noise is present at low level when idling/steady speed, but increases in level and pulse rate when accelerating. Radio in use if Yaesu FT-857D, trunk mounted, HF antenna port currently to test load (no antenna yet so protective measure), VHF/UHF port to 5/8 whip roof mounted, through panel fixing.

Im no mechanic, but think this noise is likely to be from the ignition or injectors? or possibly fuel pump, based on the way it increases with acceleration, but dies away when at steady speed.

I'd like to know which area of the engine to concentrate on with a view to inspecting and/or improving the grounding and suppression.

Of course, i have enabled the noise blanker, and have to say im very impressed with it, it takes the impulse noise to below what the S meter can read, and i only know its there as im listening for it. But i'd much rather eliminate it than rely on the blanker.
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K0BG
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« Reply #1 on: April 20, 2012, 04:58:35 PM »

This specific Ford is a single-rail diesel. The injectors are the root cause of the RFI. No matter what anyone tells you, you can't fix the problem at is source. Rather, you have to squelch it as best you can. The requires bonding the hood, and the exhaust system in several places. Rather than go into great detail here, visit my web site.
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WA8FOZ
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« Reply #2 on: April 20, 2012, 07:55:42 PM »

Petrol = gasoline in Amurrican. So there are likely COPs producing noise that might be attenuated by toroids. Ford fuel pumps also have a reputation for noise, at least in years past. Bonding will still be very important.
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G7MRV
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« Reply #3 on: April 21, 2012, 11:14:25 AM »

Alan, have read the bonding section of your site thoroughly, I will begin working on that just as soon as I can.

FOZ is correct, the engine is a gasoline type. Ford engines used to be named Zetec for petrol models and Duratec for diesel, for some reason this one has the duratec name.

Not sure what you mean by COPs?
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G8YMW
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« Reply #4 on: April 21, 2012, 02:47:58 PM »

The diesel is the Duratorque, Duratec is the successor to the Zetec petrol engine.
Agree re bonding,
Look to see what state the ignition leads are in, just in case
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73 de Tony
Sent by WW2 Royal Navy signal lamp
G7MRV
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« Reply #5 on: April 22, 2012, 01:15:57 PM »

Well, its in the shop for service and MoT tomorrow, I'll ask them to have a nosey of the leads and the engine block bonding. (which reminds me, need to take the 2m 5/8th off!)
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M6GOM
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« Reply #6 on: April 22, 2012, 01:19:44 PM »

Well, its in the shop for service and MoT tomorrow, I'll ask them to have a nosey of the leads and the engine block bonding. (which reminds me, need to take the 2m 5/8th off!)

Completely and utterly pointless. They'll be looking for an electrical ground which is not the same as a RF ground. If they shove a continuity tester on the block and they get a reading on the ground point of the battery they'll go no further because it starts and if there was an electrical problem with the ground it wouldn't.

Automotive electricians are not trained for RF installs in this country other than putting in a new car stereo.
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G7MRV
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« Reply #7 on: April 22, 2012, 02:18:57 PM »

Not pointless at all. Its an oldish car, if an earth bond has failed it can cause issues with the vehicle systems as well as the radio. I never said i expected them to do RF work, but they are going to be inspecting the vehicle and if they see a corroded or failed earth conenction whilst in there it can be fixed. Besides, my mechanic will look for things i ask him to, above and beyond the requirements of the MoT, and it will save me carrying out the same inspection at a later date.
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M6GOM
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« Reply #8 on: April 24, 2012, 04:27:51 AM »

Not pointless at all. Its an oldish car, if an earth bond has failed it can cause issues with the vehicle systems as well as the radio. I never said i expected them to do RF work, but they are going to be inspecting the vehicle and if they see a corroded or failed earth conenction whilst in there it can be fixed. Besides, my mechanic will look for things i ask him to, above and beyond the requirements of the MoT, and it will save me carrying out the same inspection at a later date.

I'm a former mechanic with a BTEC HND in electronics engineering.

When it comes to electrics, mechanics don't know their arse from their elbow which is why auto electricians exist. And as I said, they'll be looking for an electrical earth and if there was a problem with the original one such as it being broken or corroded, the car would struggle to turn over. Does your car struggle to turn over? The engine management is grounded to a different point than the engine block. The dashboard uses yet another ground point in the cabin of the vehicle, the rear wiper is grounded to the tailgate, likewise the front wiper motor is grounded near its mounting point so in either case, a problem with the engine ground wouldn't necessarily show up in other systems.

Your mechanic will not be looking for the same things as you are. He'll be inspecting it from a "does it work" point of view, not "does it cause RFI"?

Good luck with your HF mobile. If you're mounting the antenna where you've posted in your blog you're going to need it. If I were you I'd be buying a lot of 31 mix ferrites.

But what do I know, I'm only a Mx call.
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K1CJS
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« Reply #9 on: April 24, 2012, 09:14:24 AM »

You didn't mention whether the noise appeared over time, started all at once--or was simply there when you put the transceiver in.  With respect to the more learned members here, for impulse noises like that you can also suspect a bad spark plug or a ignition wire that has a break in the conductor.

Sometimes it isn't the usual suspected parts at all, but the thing that you may well have overlooked.  73!
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G7MRV
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« Reply #10 on: April 24, 2012, 01:15:46 PM »


I'm a former mechanic with a BTEC HND in electronics engineering.

Good luck with your HF mobile. If you're mounting the antenna where you've posted in your blog you're going to need it. If I were you I'd be buying a lot of 31 mix ferrites.

But what do I know, I'm only a Mx call.

I appreciate your training - Im a current broadcasting engineer, also with HND Electrical and electronic engineering, and 10years experience installing and repairing public safety radio systems.

Once again, i never expected my mechanic to look for anything to do with RF. I do expect him to locate corroded, damaged and work electrical parts that may be contributing to the issue.

As it happens, yes i had been having some starting troubles, and as a result have had the plugs changed.

The antenna mount on the blog is only one of several options in use on the 'dodgem', and is intended to allow very tall antennas beyond what can be roof mounted.

I will be conducting tests on the noise level tomorrow.
CJS - Only noticed after fitting this radio, previous rig was 2m FM only and wasnt affected. Suspect it was there all along.


Oh, and incidentally, my mechanic went into motor repair after leaving the Royal Signals, where he'd spent two decades on rebro vehicles.
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