Engine interference on Amateur radio

[asgawth]

Folks,

Any hams out there operating HF in their 2nd gen Surf's?

I'm suffering from bad interference caused by something in the engine and I'm not sure where to start looking or how to address the problem.

The interference sounds a similar to that caused by spark plugs. The frequency at which the interfering 'pulses' occur and their intensity varies depending on how far the right foot is depressed. Its even present for about 1/2 a sec after switching off the engine! The interference is not directly coupled to vehicle speed. i.e. if doing 70mph and the right foot is lifted off, the level and frequency of the interfering pulses drops dramatically - much, much quicker than vehicle speed.

Any thoughts on common sources of interference on 2nd gens?

Truck runs perfectly.

I have a 2nd Gen, 3 ltr diesel SSRG

[Calos]

Can tell us how you've connected the CB, ie to wich feeds etc?


peace
cal

[T1z3R]

i think youll find hes using an Amateur Radio not a poxy CB LOL

i get the same problem in my 2nd gen too mate. havent gotten round to tracking the source down yet though so ill be keeping an eye on this thread.

mines is wired directly to the drivers side battery
an mines is a poxy CB

[Calos]

It may just need a suppressor on the live feed, cb or scanner or cd radio.

peace
cal

[Apache]

Injectors or injector drive circuitry. I see it regularly in my work (Military EMC Engineer - vehicle specialist) and it's going to be nigh on impossible to fix (cheaply!)

Might be worth trying some ferrites on the injector drive cables, but there's so much energy in them (very fast edges) that best you can probably hope for is a reduction.

If it's radiated noise, try moving your antennas toward the rear of the vehicle, however if its conducted noise coming down your power line, Cal's suggestion (or again a ferrite or two on the power lead as close as possible to the radio) might be worth a try.

[asgawth]

I suspect Apache is onto it. I've found a site last night that had a recording of injector noise and its pretty similar.

For info the radio is an Icom 706MkIIg and its an amateur HF set. It has a very good filter on both power cables which are fed from the drivers-side battery. The antenna is mounted on a bracket I've made and is attached to the towbar plate. Its 'ground' side is very well connected to the chasis of the vehicle.

I'm pretty sure the noise is radiated.

Any help identifying the injector cables would be much appreciated. Depending on how accessable they are, I'm thinking of screening them, maybe with the copper braid from some decent coax. I've also see reference to wrapping troublesome cables in specialist foil and grounding that......

Any thought's Apache?

Thanks to everyone for their posts.

[Apache]

Braiding the injector cables is a positive move. We usually recommend that to vehicle manufacturers attempting to pass Def Stan emissions.

A couple more suggestions - is your radio power a two wire back to the battery system, or do you ground the -ve to the chassis somewhere? If so, lift the ground and wire both power lines back to the battery. Ensure you have no ground at the radio chassis to the vehicle too.

Same goes for the ground plane. Try isolating it from the chassis.

Because there is no real earth on a vehicle (the whole lot is floating effectively) there can be some absolutely horrendous noise on the vehicle frame, which can couple straight into your antenna ground plane, or your -ve, and because it's not necessarily common mode on your radio power wires, the radio will see it.

In the past, I've had some really weird noise problems on military vehicles, and spent weeks chasing individual components, when it's been the vehicle body itself coupling a mixture of noise straight into the antenna grounds due to poor earthing strategy.

So, to sum up, I'd approach the following as well as screening the injector cables :-

1) Power to your radio - two wires all the way back to the battery. Twisted and screened is the ideal.

2) Experiment with bonding of your radio case, try none (no earth on the case) to short and thick braided bonds to chassis.

3) Same with the antenna. Try providing a groundplane not referenced to the vehicle incase the vehicle chassis is noisy. Noise into the antenna *may* not be radiated, it could be coupled into the ground plane.

[asgawth]

An update, and sorry its long but it gives the info:

With the Surf parked outside the house I started the engine and noted the level of noise on the radio's meter. Let's just say it registered 7 on a scale of 1 to 9.

Then I disconnected the radio from Surf power and connected it to a transformer run from the house mains. Result: Noise level unchanged.

Retaining this configuration I then pulled the antenna partially out of the radio, so that only the center conductor of the antenna remained connected. i.e. the ground/shield side of the coax was disconnected. Again absolutely no change in the level of noise received.

Finally, I disconnected the antenna completely. Result no noise registered on radio's meter.

So, I conclude the noise is being radiated by the vehicle electrics and is being 'collected' by the antenna and presented to the radio. i.e. its not on the power cables or just the coax screen.

Apache, I think this addresses your first two suggestions. For the third, I cannot unfortunetly provide an independent ground/counterpoise due to the nature of the antenna. Its a vertical section, ontop of which can be attached different 'heads' to make the antenna resonant on different frequencies. Any independent counterpoise would be too big to use on the Surf.

I still believe Apache is correct in suggesting its the injectors, but I know absolutely nothing about the injection system and how it works I will see what info is in the forum and then perhaps start a new post.

A link that I've found helpful and may be of use to others:

http://www.k0bg.com/ - See the 'Noise ID' section

Again, thanks for the help

[Calos]

Just to point out,

If the system has noise on it, then it has noise on it everywhere, have you tried a suppressor?

peace
cal

[Apache]

A power line noise suppressor will not help if the noise is radiated. It's looking more likely* that it is radiated because unplugging the antenna eradicates the noise.

*but not certain. Noise can still be conducted from the groundplane into the antenna depending on things like the impedance of the antenna at the noise frequency.

Can you connect the radio to a completely independent antenna off the vehicle just as a test?

[asgawth]

Connecting an external resonant antenna is not going to be that simple. Its not impossible and I'm willing to give it a try, but it may take a while. As an alternative would a few meters of insulated wire have the desired effect? - it won't be resonant but it may be a good enough antenna for test purposes.

I'm not sure I appreciate why doing the above is beneficial. In the earlier, test when I disconnected the ground/counterpoise, leaving only the centre coax core - ie the vertical whip - surely, that was the same test? Certainly that whip is electrically disconnected from the vehicle...

During earlier testing, the antenna was resonant at a frequency of 7130KHz at which it presented close to a 50Ohm load to the radio. Because the antenna is physically quite short(8 ish foot) (full size quarter wave antenna would be about 10m! - rather big even on a Surf!) at all other frequencies the antenna should present a high impedence/poor match to the radio (harmonics excluded) and thus attenuate signals on other frequencies.

What I should also mention is that the noise is broad-band. i.e. its present from 3MHz to 50MHz. However, its much worse at lower frequencies. So, by 28MHz and 50MHz the amount of interference, although present, is small. When checking other frequencies I made the antenna resonant on frequencies in those bands.

I have started another thread to discover more about how the fuel injection system on my Surf works: http://www.hiluxsurf.co.uk/forums/sh...ad.php?t=63004

Once again, thanks to all for the help. Its much appreciated.

[Apache]

I'm assuming because you know the noise is broadband, that you have access to a spectrum analyser. Try sweeping around likely areas with a near field probe?

You can have capacitive coupling of noise from the ground plane (not really ground, so can be as noisy as the vehicle frame remember) to the antenna itself, which is possibly why the noise appears on the centre conductor. I've seen it happen. There's a DefStan emissions test which finds it if its there (DRE04.B). It can be a problem to Bowman comms systems if the vehicle frame is noisy.

Doesn't help you find where the noise is coming from though!

PS - why is connecting an external antenna difficult?

[asgawth]

Cheers Apache,

It was connecting a resonant HF antenna that did not connect to the vehicle that was tricky. I would need to build one Connecting any-old antenna is easy - hence the suggestion of a piece of wire. The receiver covers 1MHz to 30MHz on HF, then 144MHz and 430MHz. The noise is mostly present across HF, hence my broadband comment.

This weekend I hope to have a poke around and see if I can improve the ground on the alternator, fuel pump, exhaust. Hopefully that will help... Its a first step.

Thanks for your help,
Andrew