To Shield or Not to Shield

[W1RKW]

Got the 813 RF deck built but I'm wondering if I should enclose it to shield all other equipment from RF even though the rack has doors to provide shielding.  What's going into a transmitter rack with the RF deck are the 813 modulator, PS, PS control unit and exciter.  Speech amp is on the modulator and is shielded as well.  All low level audio equipment will be in a separate rack.

[K1JJ]

Bob,

I know many guys use cage shields around their HF RF final decks.

However, out of all the rigs I've built, some big linears up to 10M, I've never double shielded the final sections. They just sit in the rack with the rack cabinet and bottom plate acting as the shield to other equipment inside or outside the rack. I ground the metal cabinet to the station ground system.

I don't have RF in the audio, even on 10M, nor problems with RFI within the house.

But, if ya have the motivation, it's a good engr practice anyway. Just like using feedthru bypass caps as insurance for in/out connections.

My exception here is the 6M 1500W 8877 amp. I did put in a final cage just cuz of potential RF radiation, even tho it's in a metal enclosure/19" rack. The amp sits near me during operation.

I'm presently building up quite a few new HF rigs, as you know... and could easily add cages at this point. Maybe someone here can cornvince me to do it for a compelling reason, other than the old wive's tale of dying from HF radiation induced cancer..

T

[W1RKW]

Hi Tom,
Thanks for the input.  The reason I was asking I have a very tight clearance with the chassis of the RF deck and the rack side rails.  Although I was considering enclosing the RF deck I may just give it a try without a cage.  I'm dealing with a little less than a 1/4" total clearance between the rack rails and the chassis.  I've seen several transmitter racks on the net that don't have shielding so it's worth a try.  And if you and others have had success without shielding then I won't worry about it.  What worries me is my construction practices.  Hopefully something has rubbed off of  you experienced HB'ers and I didn't cut corners. Still got a ways to go before putting the fire to the wire.

[Steve - WB3HUZ]

What would be your reasons for wanting to shield?

[K1JJ]

Rack clearance for the homebrew unit has always been a problem for me too.  We all tend to build them so that they have max width while still fitting into the ~18" wide rails of a standard 19" rack.

I used to make my rig chassis 17.5" wide, and had occasional clearance problems, but now do 17" max. This allows for mistakes and for adding shielding, braces, etc later on.

T

[W1RKW]

What would be your reasons for wanting to shield?

Steve,
I was thinking of homebrewing a modulation monitor in the form of a crude o'scope in the same rack setup with the RF deck and I didn't know if RF from the RF deck would give me any grief.  I was planning on enclosing the RF deck and o'scope as they're going to share the same rack cabinet.  But maybe the o'scope will be fine being enclosed by itself. And of course there's the RF in the audio issue.