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Re: [RFI] SO2R 2nd Harmonic Interference

To: rfi@contesting.com
Subject: Re: [RFI] SO2R 2nd Harmonic Interference
From: "qrv@kd4e.com" <qrv@kd4e.com>
Reply-to: qrv@kd4e.com
Date: Sat, 29 Sep 2018 20:05:21 -0400
List-post: <mailto:rfi@contesting.com>
I've used an IOTA PS with IQ/4 battery manager across a large deep-cycle
battery for years.

Dead quiet, gear runs off clean battery power, and has power for a while
when the grid goes down.

Best of all worlds.

YMMV ... 73, KD4E

I have been trying to solve an interference problem for quite a while here at my QTH. Symptom is that when I transmit on 40M CW, even at QRP power levels using bandpass filters and transmitting stubs, the second harmonic on 20M is a wide signal, covering 30-40 KHz. As per advice given by Frank W3LPL regarding RF flooding, I started searching for an electrical device (probably charger/wall wart).

I eliminated my own home as the source by testing with battery power and all circuit breakers turned off. Through more testing, I found that even at 100 milliwatt output on 40M, I still got the 20M wide band hash, but only when I pointed my 40M antenna at my neighbors house.

Today, I got together with the neighbor and he let me snoop around with a portable Rx. Voila! Culprit is a cheap little trickle charger.

DBT Auto Electrical Products PTE LTD Part no. 021-0123
"Household automotive battery charger" 120V input and 12V output at 750 mA

Question: Is there a battery charger that any of you can recommend? I tried wrapping the 12V leads of the current charger roughly 10 x through a large toroid and there was little if any reduction in interference.

73 Randy K0EU
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