[RFI] SO2R 2nd Harmonic Interference

[Randall K Martin]

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