[RFI] SO2R 2nd Harmonic Interference

[Grant Saviers]

I have found the "Battery Minder" products quiet and reliable. Not to be 
confused with Battery Tender which have had a high failure rate for me.  
The Minder brand uses a pulse charge float technology and has recovered 
partially sulfated batteries for me and has the lowest water loss of any 
float charger I have used.

Two are on 24x7 24v 2 to 4a outside (48v x 220AH), one 12v 1a outside on 
24x7 (12v x100AH), and one inside 12v 2a on 24x7 (12v x 220AH).  I 
haven't added chokes on any of them.

Not cheap but worth it as batteries really last and are always ready to go.

Grant KZ1W

On 9/29/2018 13:52 PM, Randall K Martin 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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