Topband: plasma TV RFI?

[Tom Rauch]

>>Jim, can you tell us what kind of cap is rated for AC line 
>>voltage?
>
> I'm not as "up" on specific capacitor types as I should 
> be, but I
> believe that a DC rating of 600V or so should be safe on a 
> 120VAC
> circuit.

They are not safe. Don't use them.

Normally a line rated cap, at least from the ones we used at 
Zenith/Heathkit and Ameritron, were 1400Vdc or higher (when 
stamped with a dc rating). Most important they clearly state 
they are specifically rated for line bypass use, and are 
rated for AC line voltage. Zenith and Heath were very 
concerned about conforming to UL requirements and not 
burning down anyone's house. Even if you do everything right 
there is always a fire or safety risk, but stay away from 
regular caps on power lines. I've seen a regular cap sit and 
make a large ball of fire for several minutes. The 
UL/CSA/VDE line rated caps extinguished in less than a 
minute in the same tests.

> The key issues are dissipation at power frequencies, as 
> well as low
> stray R and L at RF.

The key issue is if it more likely to burn your house down 
or not.

The capacitor, since it is on a system that cannot be fused 
at a few watts of power level, must be able to handle a 
sustained not-shorted not-open fault where it can have 
anywhere from a few to a few hundred watts without causing a 
fire.

Mouser and every else sells suitable capacitors.

My own experience with a plasma TV isn't very good. Even on 
lower bands there was substantial radiation from the screen 
area. All the normal bypassing and external lead bonding did 
nothing at all. I couldn't very well screen the front of the 
display, so it never was fixed.

**This isn't to say other cases will be like this, but I 
think that is a system that the old FCC (when it wasn't run 
by lawyers) would never have allowed.**

Anyway, watch what you put across the power line. Don't use 
the wrong parts, and by all means make sure they are in a 
flame proof housing.

73 Tom