Topband: Elimination of Treadmill RFI on 160 meters

[Bill Wichers]

Ganged outlet boxes are no longer a good option. In years past, they were fairly beefy. Modern ones are lighter gauge steel and too flimsy to hold together outside of a wall (and too flimsy in the wall too, IMHO). They also usually use internal cable clamps with a screw that sticks out the back so they don't make a nice assembly to use in the field. Extension rings suffer from the same flimsy problem these days.

If you use a "4 inch box" (usually called a "4 square" in the trade), I recommend getting the drawn kind (one formed piece with round corners) instead of the more common welded kind (two end plates tack welded to the rest of the assembly with sharp square corners). The drawn kind I think are made by Steel City and Home Depot has them. If you can get the deep version (2-1/8" deep), you'd have more room for filters inside than with the more common version that is around 1-1/2" deep.

I think 4-11 boxes are even better if you need to mount things inside, but I've only ever seen them in the welded style. Note that the extension rings for 4-11 boxes are DIFFERENT! They have a round cutout between the box and the ring instead of the square cutout you'd expect! They are probably NOT very suitable for this application!

The BX clamps work but the rubber cable glands are better for not much more money. Home Depot actually does carry a Halex version of the cable gland, but the Appleton and Hubbel ones are MUCH MUCH better.

And why would the manufacturer spend 15 cents when their customers can spend $50 of their own money instead? ;-)

  -Bill

> A deep "4 inch box"? Add extension rings if necessary? Ganged outlet
> boxes?
> 
> http://www.mcmaster.com/#standard-outlet-boxes/=vohae8
> 
> I know I've seen on the web somewhere, a Grow-Light filter with 3 big 2.4"
> toroids all in a 4 inch box. I don't think there was any room left for outlets.
> 
> I use 4 inch boxes for all sorts of ham accessories (having nothing to do with
> 120VAC power). They are nice and heavy and stay put.
> 
> The 3/8" BX clamps work great for cable strain relief.
> 
> If the treadmill manufacturer had just included 15 cents of waveshaping at
> the MOSFET, all the external filtering would be completely unnecessary.
> 
> Tim N3QE
[snip]