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Author Topic: Christmas Tree RFI  (Read 181 times)

KT0DD

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Christmas Tree RFI
« on: December 03, 2022, 09:39:53 PM »

We have a Christmas tree with built in bulbs that makes quite a bit of RF noise on 75m and a little on 40m. I know it's the source because it goes away when I shut it off. The transformer is a cheap Chinese Ting Shen square transformer with the male plug prongs right on it. It's rated input @120V 60hz, and its output is 29V DC at 0.45 amps. Can I find a 29V capable DC regulated and filtered supply and wire the tree to it to see if that cleans it up? My wife is getting tired of having to turn it off when I want to use the radio. Christmas is her big thing. Constructive replies are appreciated.

Todd - KT0DD`
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KF4HR

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Re: Christmas Tree RFI
« Reply #1 on: December 03, 2022, 10:15:07 PM »

There are several adjustable 0-30vdc regulated bench power supplies on Amazon that would do the trick.  I use one of these on my test bench I haven't had any RFI problems with it.
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K5LXP

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Re: Christmas Tree RFI
« Reply #2 on: December 04, 2022, 06:56:26 AM »

A combination of wall warts in series will get you there too.  Two 12V and one 5V would be one option.  Might be a hunt to find quiet ones but you're not bound to using the stock wart.

Mark K5LXP
Albuquerque, NM
« Last Edit: December 04, 2022, 07:12:54 AM by K5LXP »
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AI5BC

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Re: Christmas Tree RFI
« Reply #3 on: December 04, 2022, 07:50:04 AM »

Live with it, that is what hams do, generate and fix noise they create.
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WA3SKN

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Re: Christmas Tree RFI
« Reply #4 on: December 04, 2022, 07:58:33 AM »

A couple of .01 caps across the input and output wires would probably do wonders.  Since the output is DC it shouldn't hurt anything.  Also, ferrites on the input and out wires would help.  And you could shield the transformer a bit with aluminum tape from the hardware store.
It sounds like the "transformer" is really a switching DC supply with no filtration and the wiring is acting as an antenna to radiate the harmonics and trash of the rectifier.
Do you have a scope to see the noises?

-Mike.
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KT0DD

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Re: Christmas Tree RFI
« Reply #5 on: December 04, 2022, 02:33:16 PM »

A couple of .01 caps across the input and output wires would probably do wonders.  Since the output is DC it shouldn't hurt anything.  Also, ferrites on the input and out wires would help.  And you could shield the transformer a bit with aluminum tape from the hardware store.
It sounds like the "transformer" is really a switching DC supply with no filtration and the wiring is acting as an antenna to radiate the harmonics and trash of the rectifier.
Do you have a scope to see the noises?

-Mike.

I may try a new supply and a mix 31 ferrite on the DC side.
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