GT3000 air purifier creates noise on 154.4 MHz VHF radio.


I bought a GT3000 Air Purifier. It works great to clean the air in The whole house. Problem is that the 24 VAC, 50 HZ fan creates a lot of noise.
I first noticed it when I walked by it and my pager starts making a lot of noise.
I have been working with the owner and the engineers to fix it. First the sent me a new fan. No change. I then wrapped aluminum foil around the copper windings. It significantly reduced the noise. The noise no longer opens up the squelch/fire tone circuits.
Using a VHF scanner with a controllable squelch circuit I can still detect it is putting out a lot of noise.
I added a .01 UF capacitor in shunt with the fan leads. Almost no difference. I put 3- .01 UF capacitors in parallel with the fan leads. This increased it to .03 UF capacitance. Still no improvement.
I?m leary of increasing the capacitance much more. Eventually it will short out the power supply.
The unit if fed from a 38 VDC power supply, from which it creates all of the required voltages.
I?m looking for any ideas on how to eliminate this Harmonic noise.
Jim Altmiller

Michael Bush:
You did everything I can think of except better shielding... maybe a Faraday cage of #8 hardware cloth...


--- Quote from: Michael Bush on November 04, 2019, 09:25:00 am ---You did everything I can think of except better shielding... maybe a Faraday cage of #8 hardware cloth...

--- End quote ---
Thanks Michael. I will try that. I will start with one on the out side of the unit. If that works, I will try to put it inside.
Jim Altmiller

I built the Faraday Gage today.
Here are pictures of it.

When I place my scanner near it I could still hear the noise. When I back away 10 feet or more I cannot detect any noise.
When I received calls I can still hear the noise on my Pager and radio but not as bad as before.
I?m going to see if I can find copper Faraday Screen and order it and make another one from it.
I used to work in a mobile radio shop that was completely enclosed in this screen, including the door to eliminate radio interference while testing units.
Jim Altmiller


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