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Thread: Electrical interference with HF radio

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    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.
    Last edited by PeeBee; 8th July 2020 at 06:03 PM.
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    Patrol God mudnut's Avatar
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    @TPC. Tony, Mate are you able to troubleshoot this one?

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    PeeBee (8th July 2020)

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    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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    Quote Originally Posted by Brissieboy View Post
    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.
    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,
    Manufacturer of the Complete Camp Oven System

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    Patrol Freak BillsGU's Avatar
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    You could make up a simple directional "loop antena" to find the source of the interference.

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    Expert Brissieboy's Avatar
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    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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    Quote Originally Posted by BillsGU View Post
    You could make up a simple directional "loop antena" to find the source of the interference.
    OK how do I do that?
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    Quote Originally Posted by Brissieboy View Post
    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.
    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
    Last edited by PeeBee; 9th July 2020 at 02:58 PM.
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    Patrol Freak BillsGU's Avatar
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    Quote Originally Posted by PeeBee View Post
    OK how do I do that?
    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.

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    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!
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