[Boatanchors] line cord question

[Robert Nickels]

On 2/18/2019 9:59 AM, McDonald, J Douglas wrote:
> The only thing that helps is a TRIfilar choke with all three line cord leads, with 0.01 uF safety caps connecting all three together at the line cord end,three .01 caps grounding all three at the chassis end, and a TUNABLE variable cap across the chokes

I agree that safety capacitors (X type from line to line and Y type from 
line to ground) won't do a lot if you have conducted EMI on the AC 
line.  I've never done the tunable thing, but I nearly always use a 
filtered IEC power entry module in homebrew gear, and have had good luck 
also mounting them in a small enclosure with a receptacle for the radio 
to plug into (also a good place to add fusing for those with the 
dastardly fused plug).  Here's an example of a stock Schnaffner product 
that is a little over $6 from DigiKey:

https://www.digikey.com/product-detail/en/schaffner-emc-inc/FN9222R-15-06/817-1449-ND/1929030

Not only can you be sure the proper components are used in a commercial 
module but you can view the datasheet from the link above and see the 
attenuation curves.   I bought a bunch from MPJA when they were a buck 
apiece, and while those are no longer available, this filter module 
looks interesting because it incorporates a two-stage filter for about 
the same price:

https://www.mpja.com/IEC-Power-Inlet-Module-RFI-Filter-Switch-Fuse-Holder/productinfo/33931+FH/

These modules are easy to integrate into homebrew gear;  you just have 
to get creative when applying a filtered module to a boatanchor radio.  
But they absolutely work - totally quieted down a cheap PC replacement 
power supply where the "cheap" came at the cost of eliminating the AC 
line filter!

73, Bob W9RAN