[Boatanchors] line cord question

[McDonald, J Douglas]

Because of the way line noise works these days, one really needs to get the caps 
as close to the place the cord comes in as possible. Ideally there should be feedthrough
caps at the chassis, or better a "bathtub" filter with four caps and two inductors.

In general, however, this only does good if the chassis is well-shielded, with 
a good tight bottom plate. 

IF you're are SERIOUS about getting rid of line noise, and don't have a really really
well balanced input with excellent common mode rejection, line caps are useless
for noise rejection. 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 (in parallel because of the 
.01 uF caps), rotor grounded. You tune the cap to resonate at the frequency being
received. The results are amazing if the receiver is located at an outside wall ...
tune to resonance and the noise simply disappears. But remember, this will NOT WORK
if you ground the ground lead to the chassis. Its only connection has to be through 
the big fat (to carry the current) trifilar choke. The ground lead of course IS grounded
for 60Hz and safety purposes, through the big fat choke wire. Just not grounded for RF. 

It works! With of course the nuisance of tuning the filter.

Doug McDonald 

-----Original Message-----
From: boatanchors-bounces at mailman.qth.net <boatanchors-bounces at mailman.qth.net> On Behalf Of Michael Bittner
Sent: Monday, February 18, 2019 9:13 AM
To: rls19 <rls19 at psu.edu>; RAY FRIESS <rayfrijr at msn.com>
Cc: boatanchors <boatanchors at mailman.qth.net>
Subject: Re: [Boatanchors] line cord question


Where should you put line noise suppression capacitors in this setup and 
what value should they be?  I'm thinking .01 uF, 600 V, one from each side 
of the power transformer primary to chassis ground?  Or should they be 
directly across the line input? Before or after the fuse or power switch?

Mike, W6MAB




----- Original Message ----- 
From: "rls19" <rls19 at psu.edu>
To: "RAY FRIESS" <rayfrijr at msn.com>
Cc: "boatanchors" <boatanchors at mailman.qth.net>
Sent: Monday, February 18, 2019 06:41
Subject: Re: [Boatanchors] line cord question


> Ray,
>
> For any boatanchor that is to be used rather than intended to be a shelf 
> queen, the 2-wire cord should be replaced with a 3-wire one. The hot lead 
> should go through a fuse of the correct value and then to the power 
> switch. The neutral goes to the other side of the transformer(s) and the 
> green safety ground lead goes to the chassis. If the fuse holder is a 
> chassis-apron type, the hot lead should go to the far end of the holder 
> from the chassis so that if someone forgets to unplug the rig before 
> removing the fuse, the fuse will not be hot when it is pulled part way 
> out.
>
> 73,
> Bob AD3K


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