[RFI] SO2R 2nd Harmonic Interference

[Jim Brown]

On 9/29/2018 1:52 PM, Randall K Martin wrote:
> Is there a battery charger that any of you can recommend? 

What your neighbor has is a switch-mode power supply (SMPS), which are 
notoriously noisy and cause problems like this. I suggest that you 
search your junkbox for an old linear wall wart rated for 12V at 750mA - 
1A. If you don't find one, head for second hand stores. These are one of 
the things I search out at hamfests and flea markets. The going price is 
a buck or so.

They can usually be identified by weight -- the linear units are much 
heavier than the SMPS. A more reliable way to identify them is to plug 
them in and hold a portable radio next to them tuned to the high end of 
the AM band. I use a Kenwood talkie that can tune to 2 Mhz. An SMPS will 
be noisy, a linear unit will not.

Once you have the linear supply, cut leads on the two units and splice 
the linear supply to the cable running to the device being charged.

There's a lot of detailed advice on this in the piece I wrote for NCJ a 
few years ago on finding and killing RX noise. It's on my website, and 
includes the suggestion to buy one of the little inline voltage and 
current meters. I have several of them, have put PowerPoles on both 
ends, and put Power Poles on the leads from the good supplies and the 
leads going to stuff that they power. This can be important, because the 
linear supplies are nearly always xfmr-rectifier-capacitor units, almost 
never regulated, so their open circuit (no load) voltage will rise to 
the peak value of the low-voltage waveform, typically 1.3 - 1.4x the 
rated DC voltage, but will drop to the rated voltage at rated current. 
With the meter, you can verify hook things up and verify that you're not 
over-powering the device. I've done this to dozens of devices and never 
blown anything up. :)

k9yc.com/publish.htm

The last time I bought these meters Tenergy was the cheapest, but you'll 
have to add the Power Poles. Other vendors sell almost exactly the same 
unit twice the price. And for even more bucks, you can buy one with the 
PowePoles installed. :)

https://www.amazon.com/gp/product/B017YCTRKK/ref=oh_aui_detailpage_o01_s00?ie=UTF8&psc=1

73, Jim K9YC