Try applying the filter on the input of the charger!
From Mike's Mobile Email
Sent from BlueMail
On Sep 29, 2018, 4:52 PM, at 4:52 PM, Randall K Martin <rkmassoc@comcast.net>
wrote:
>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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