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Author Topic: Getting rid of hash noise in semi truck  (Read 237 times)

KF4KQS

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Getting rid of hash noise in semi truck
« on: February 18, 2023, 07:47:16 AM »

When on 75/80 through 20 meters i get an overwhelming garbly hashy noise through the receiver. My truck has a huge power inverter installed from the factory and i have tried grounding it but the noise wont go away. It kind of floats around the bands and is about 20 db over s9 when it starts.  Any suggestions on how i can filter this out so i can actually enjoy mobile hf? Thanks!
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AI5BC

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Re: Getting rid of hash noise in semi truck
« Reply #1 on: February 18, 2023, 08:41:45 AM »

Do you have the battery negative wire connected directly to the Battery Term Post? If so, that is your problem, you placed yourself in ground loop. Do you have a tilting cab?
« Last Edit: February 18, 2023, 09:03:12 AM by AI5BC »
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WA3SKN

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Re: Getting rid of hash noise in semi truck
« Reply #2 on: February 18, 2023, 08:58:23 AM »

Have you checked with the truck company?
It may or may not be the inverter.  There are lots of tests that can be done, but the company will probably know both the causes and cures.  Just guessing is not enough to cure the problem!

-Mike.
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K6AER

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Re: Getting rid of hash noise in semi truck
« Reply #3 on: February 18, 2023, 09:28:51 AM »

Pull the fuse to the inverter to see if the noise goes away. If not the source of your RF noise is something else.

I won't matter where you connect the DC ground. A ground loop is not the problem. The inverter is generation RF noise with the AC wiring on one side and the DC wiring on the other side. Think of this as a transmitter with a AC/DC wiring as a dipole. Plus the fact that most truck bodies are fiberglass and your antenna is only 6 feet away and you can see the problem.

If the inverter is the source, what you need to do is connect a couple of .01 mFd 200 volt caps on the plus and minus inverter input and two more caps on the AC output connections to the frame ground of the inviter. Once the RF hash gets into the truck wiring it will radiate to your HF antenna.

Good luck,

Mike K6AER
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KD6VXI

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Re: Getting rid of hash noise in semi truck
« Reply #4 on: February 18, 2023, 09:38:08 AM »

Do you have the battery negative wire connected directly to the Battery Term Post? If so, that is your problem, you placed yourself in ground loop. Do you have a tilting cab?

Which would do nothing like he is describing.  Period.

He has an rf hash issue.  Which could be inverter driven, can uod be the PWM signal to the injectors, etc.

Having operated mobile, at legal limit, for years while I drove truck.... No, his radio doesn't have a ground loop.

He said hash.  Not whine.

--Shane
WP2ASS / ex KD6VXI
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KF4RQH

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Re: Getting rid of hash noise in semi truck
« Reply #5 on: February 18, 2023, 03:15:10 PM »

There was a couple of drivers (CDL ) that were having the same problem with their Cb's they had s9 noise and they knew I was a ham operator, they asked me what to do. I killed the power to the inverters and the noise went away, hooked it back up noise came back. I always had a bunch of chokes with me, so I went to work finely got the noise lvl from s9 to s3 and they were happy. This was 20 years ago, the inverters they had were in the 1000-watt range. Just remember that was on CB's amateur equipment does have better filtering might take less work.
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KF4KQS

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Re: Getting rid of hash noise in semi truck
« Reply #6 on: February 21, 2023, 09:07:01 PM »

Its definitely coming from the big inverter. Disconnecting/killing it completely gets rid of the noise. I would just keep it off but it runs my fridge and other appliances. It renders most of the 80/75 and 40 meter bands useless. I have tried moving my ground around with no change at all. The company mechanics dont know anything about it and look at me like im a moron hihi. I have tried wrapping the power wires around ferrites a few times with no difference.
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WA3SKN

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Re: Getting rid of hash noise in semi truck
« Reply #7 on: February 22, 2023, 02:24:55 PM »

OK, it sounds like you do not have a pure sine wave inverter.  You probably have a modified sine wave or even a square wave inverter.  Both have lots of noise/harmonics.  You can try and filter with coils and capacitors (see older Handbooks) or you might look into getting a pure sine wave replacement.
Just how much power is the inverter designed to provide?

-Mike.
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K0UA

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Re: Getting rid of hash noise in semi truck
« Reply #8 on: February 22, 2023, 09:19:45 PM »

Did you try Mix 31 ferrites?  Multipe turns thru a 2.4 inch mix 31.  If you don't know the mix of a ferrite it will likely be useless for you purpose.
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73  James K0UA

K5LXP

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Re: Getting rid of hash noise in semi truck
« Reply #9 on: February 23, 2023, 09:33:59 AM »

Knowing it's conclusively the inverter is 90% of the battle.  There's only so many points of noise egress there can be.  Depending on the kind of interference will require different mitigation.  Could be conducted, radiated, or both.  The trick to taming interference like this is first characterize the noise - note the bands/frequencies the interference is present and corresponding S meter levels with your standard antenna setup.  Then try something, like putting ferrites on the input and output leads.  Re-assess the noise again - better or worse, maybe just some bands and not others?  Or maybe no effect at all?  Any result, including no result, is a clue as to what the interference is and what to do about it.  Depending on the dollar value of this unit (any more inverters aren't very expensive) it might be time/effort ahead to just replace it, betting that a "better" one will have reduced emissions (may not...).  So you start with a band/level noise survey and spend some quality time with ferrites, caps, chokes and EMI filters and noting cause/effect.  With any luck it's not coming straight out of the plastic inverter housing and into your antenna, and standard I/O mitigation techniques tame it down.  Another point to address is common mode.  If your antenna/feedline isn't isolated, then even small amounts of interference can couple efficiently into your radio via the coax.  So improving isolation there can also help reduce noise.

Mark K5LXP
Albuquerque, NM
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