Electrical interference with HF radio

I was away last week and found my Codan Hf dead to the world, hissing and no legible voice transmissions heard. I had the radio working a couple of weeks earlier, clear as a bell in Melb. I started on the troubleshooting route whilst camping and swapped out antenna, cables, isolated voltage booster, still high noise signal on all frequencies. i rang the Codan rep and he suggested powering up the radio with an 'isolated battery'. and disconnect the other vehicle batteries. result, radio full receive and next to zero background noise, beacon requests from 4 stations across different frequencies - great, must be something in the car or atmospheric getting into the antenna. So, start putting things back one at a time and monitoring the interference, bugger me, everything dead quiet and crystal clear, except around the 7-8.5MHZ area, which was still full of noise. prior to this everything was noisy from 3 - 29mhz. To my surprise the Corrosion device had little if no impact on the noise level, but it remains disconnected for the time being.

Problem I have now is I have not changed anything apart from disassembly and reassembly of the battery connections. All earths are fine and there are a number of links between body, chassis and batteries. So now its a hunt to find a frequency generator in my local area around this 8meg point. I will need to go for a drive into a 'quiet area', free from power supplies, cables and transmitters to see if this is resolved, but again, bit at a loss as to how it has 'fixed' itself in most regards except the 8meg area - annoying, but have another 6 weeks now to sort it i guess.

@TPC. Tony, Mate are you able to troubleshoot this one?

Anything with a switching converter can cause interference across a broad spectrum. My fridge causes problems but most chargers are OK for me.
Try disconnecting everything off that battery except the radio and reconnecting 1 by 1 and see when the problem re-appears.

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Originally Posted by Brissieboy

Anything with a switching converter can cause interference across a broad spectrum. My fridge causes problems but most chargers are OK for me.
Try disconnecting everything off that battery except the radio and reconnecting 1 by 1 and see when the problem re-appears.

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Yes did that, and every tuned frequency except those in the 7600 - 8200hz freq band are silent or 0 - 1 bar/5. If I disconnect the co-ax cable all goes quiet, as expected, so the interference is coming thru the antenna - tried two antennas and different configs of both, same result. I don't have a problem with the fridge either. I am wondering about the vast array or woreless networks around the house and street - watched an interesting youtube clip last night of a guy - amateur radio operator - hunting down his background noise sources and wifi modem and computer were the culprits,

You could make up a simple directional "loop antena" to find the source of the interference.

Sounds like you have the coax grounded at both ends with a difference in potential between those earth points causing current in the shield. Quite possible one of your grounds is not good. Try removing the antenna from where ever it is mounted so that it does not contact ground and just relies on the ground from the radio.

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Originally Posted by BillsGU

You could make up a simple directional "loop antena" to find the source of the interference.

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OK how do I do that?

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Originally Posted by Brissieboy

Sounds like you have the coax grounded at both ends with a difference in potential between those earth points causing current in the shield. Quite possible one of your grounds is not good. Try removing the antenna from where ever it is mounted so that it does not contact ground and just relies on the ground from the radio.

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Thanks BB. I run a braided earth from the antenna base to the chassis. Connection is assured with conductive paste as well. i run a second earth cable in 10mm round to a different location on the chassis, again connections soldered to the lugs and conductive paste. the radio is earthed to the body also, with conductive paste, all connections tight. I will run an independ earth from the antenna to the same earthing point for the radio as you suggest, however since the body is earthed to the chassis in 6 places, and the battery earthed to the body and then to the chassis, I reckon the earth is secured. the Codan tech discounted the earth as a problem, he thinks its a generated Rf so either find the source and eliminate it or I am investigating a device to try and null it out, such as this. i am waiting on a return call from Strictly
ham to get their thoughts. I have a pre amp I could try however whilst i could probably enhance the legible signal, I think i will also raise the floor level of the interference - will see. thanks for the input also.https://www.ebay.com.au/itm/MFJ-1026...frcectupt=true

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Originally Posted by PeeBee

OK how do I do that?

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Here is one example.

https://www.minikits.com.au/eme234

I haven't used one of these for many years but they are very directional and can find the source of interference or separate a very weak signal from noise and other signals. You can buy them already made. Check out eBay.

Mystery deepens. Strictly Ham suggest it could be an earth loop as BB suggested, so I am going to go around and undo-clean up and re-do all earths and see how I go. The MFJ unit would not have helped it seems. Another wild goose chase - getting good at these!

My HF Codan NGT AR interferes with my UHF 80 channel CB. I can only have one on at a time when the vehicle's moving. Haven't tried both on when stationary yet. I get intermittent to full time static in my UHF from the HF.


@the evil twin might be able to help.

I haven't posted as there is not much that others haven't already suggested... IMHO it seems suspiciously like a couple of issues IE I think there was /is an earth loop which improved when everything was disturbed and possibly something else is leaking HF interference.

HF is a black art at the best of times so sacrificing a virgin chicken at midnight on the solunar equinox using a crystal blade with a unicorn bone handle shaped by dwarves can often help...

If you can't do that the next best thing I found to help with dodgy comms kit during my time in the military is swear a lot while kicking the shit out of it.
Rarely gets it too work but you def feel better for it.

Thanks gents, I am going to launch into the earthing checks next monday after the wife goes back to work and I have an uninterrupted period of time to work thru it. Strange its only in this particular band around 8meg, but it affects 4 channels from 7.2 - 8.5meg - damn annoying.

Hi Phil, if you want to pm your phone number I could give you a call to chat about the problem.
Noise on HF can be a bugger of a thing to track down and is worse with older vehicles as earthing between different parts of the car can be resistive.
If you were close I would try and track it down with a spectrum analyser but you Covid 19 infected Mexicans can't mix with the rest of us.

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Originally Posted by TPC

But you Covid 19 infected Mexicans can't mix with the rest of us.

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When you're near Mt Gambier, Phil could come here for a visit. We could drive past Nelson, and push his driverless Patrol across the border. You could fix it and send it back:)

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Originally Posted by mudnut

When you're near Mt Gambier, Phil could come here for a visit. We could drive past Nelson, and push his driverless Patrol across the border. You could fix it and send it back:)

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I like that idea, but will take a few to get this barge rolling! I will speak with Tony tomorrow sometime and see if he has any specific ideas or different starting points. This forum is great for stuff like this I reckon.

Haha, problem is I was in the mount this week

OK, I finally got to this issue and think its resolved. I cleaned off the earth points across the whole vehicle, and also added a second flat braid earth strap between the 9350 auto tuner and the chassis, all using a conductive paste at the joints. the background noise on receive went down on most channels to 1/5. on anything between 6.8 and 10.1mhz, the noise level dropped to 3/5 from 5/5. I am able to hear traffic even in Metro Melb with Covid-19 virus in the air, so am happy i think. The next bush trip will be the telling point. What is interesting though, if I then select a channel and push the tune button, the background noise rises to 4/5 on those pesky freq's above, and the 3/5 for the other quiet frequencies. I might end up taking the set across to lara Electronics and have Peter James run his expertise over it just to be sure.

Do you know anyone else that has the same set up? Swapping items one at a time to eliminate each is the way to go. Otherwise you just keep chasing your tail.

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Originally Posted by BillsGU

Do you know anyone else that has the same set up? Swapping items one at a time to eliminate each is the way to go. Otherwise you just keep chasing your tail.

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Unfortunately no, I am working thru a process of elimination, however even with the radio powered off a totally independent battery, not connected to the car, the base noise level is high, so I will see what its like next time I am out in the bush, away from all the passive metro noise. If its still noisy then the radio may need checking. From what I can see, the installation is fine.

All it takes is a bad connector or a faulty cable and you get all sorts of issues that are very difficult to find unless you have a known working system to swap / compare with. I am surprised there is no one on the Forum that has a similar setup.

Thanks for the thoughts. We are in lockdown for a further four weeks, might get out into a quiet area by December, it can wait. The higher background noise in the range 7.5 - 10Mhz is suggesting something local generating it. Its nothing i can find in the immediate area of the vehicle, and all cables are factory new, well earthed where required and the set has been totally checked and upgraded by a Codan service agent who i have used for 20 yrs. He also serviced the auto tuner when upgrading the radio. Its not the radio, the installation or the earthing. I would have picked overhead power, but ours is underground. There are a lot of wireless connections in the area, but they are way off frequency to the ones getting interference. I am just a bit stumped. The vehicle is in the driveway, 5m from the nearest power, except an inverter a/c unit right next to the car - just thought about that - might be something there, but its a slim chance. If I can't resolve it its going back to the dealer as installed and he can cast his eye over it. I have had a couple of my amateur radio mates look at it also from the club, and they can't fault the installation. Playing around today it is possible to drop the background by 2 pts/5 simply by application of the internal filtering, so maybe its simply a case of detuning it when in the metro areas and amping up the sensitivity when out bush?

@PeeBee

I've got a Codan NGT AR HF radio and I have interference problems when I have the UHF CB and the Codan on at the same time. It only happens when I'm moving, not stationary.

It's like the squelch on the UHF keeps cutting in and out.

Rossco.

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Originally Posted by DX grunt

@PeeBee

I've got a Codan NGT AR HF radio and I have interference problems when I have the UHF CB and the Codan on at the same time. It only happens when I'm moving, not stationary.

It's like the squelch on the UHF keeps cutting in and out.

Rossco.

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Thanks Ross. I an starting to wonder about the a/c unit hanging on my neighbours wall, approx 2m from the radio. I know they are C tick approved, however field effect from inverter drives can be large and under most circumstances not interfere with other devices, but you can bet the requirements dont include the recreational user frequencies which are typically the freq bands that industry can't use effectively. I might back it out into the street a few metres and see what I find. Thanks for the contact. If it does improve, I will move back into the original to confirm degradation, but it would be a really interesting finding, no the least that the neighbour had the a/c unit installed on the wall of here house and it hangs over my boundary, plus is right at the front of the house and is a total eyesore, but she is an old lady and can't take this oversight on board, - will see. The a/c won't be moving and it may simply mean I cant use the set in the driveway, which I dont do in Metro Melb.

I have the SR NGT, still learning the ropes on it - upgraded from a 9323 as wanted the amateur band flexibility - legally.

Righto, I think I have found the source(s) of the interference. i have my NGT mounted on the cargo barrier, alongside a Victron MPPT solar controller, a Renogy 50amp DCDC charge controller and a 3500W Pure sine wave inverter. The noise floor on 8mhz os 4.5 - 5/5, 6mhz close to this, and everything else from 3 - 14.7mhz lower down to 1 s point.

I spent a couple of hours removing and letting any charges dissipated from each of these devices and they all contribute to the background noise plane. With everything totally dead, the noise floor is now 2 - 2.5/5, so i put that mystery down as a win. Now it will simply be a case of total isolation of each device, not just an 'off' to start getting some better receive results. My transmissions are fine and strong from vic to Adelaide and tassy, even borderline acceptable for Alice.

I also might look to physically relocate the HF to a quieter location inside the vehicle, away from this noise.