I just finish building a 1.2ghz video transmitter . Work great . When install it in a metal case it goes to pot . Can it be cause by the pcb dielectric . How can i correct this problem . If i left the board off themetal botton of the case it works fine . Put a paper spacer betweem the case and pcb it works fine

 

post schematic...........

 

I just finish building a 1.2ghz video transmitter . Work great . When install it in a metal case it goes to pot . Can it be cause by the pcb dielectric . How can i correct this problem . If i left the board off themetal botton of the case it works fine . Put a paper spacer betweem the case and pcb it works fine

attached is my circuitView attachment 1.2ghz 2.sch

 

Are we supposed to guess what program created that file? Why don´t you post a .png picture or a pdf?

 

View attachment 1[/ATTACH]

I just finish building a 1.2ghz video transmitter . Work great . When install it in a metal case it goes to pot . Can it be cause by the pcb dielectric . How can i correct this problem . If i left the board off themetal botton of the case it works fine . Put a paper spacer betweem the case and pcb it works fine

 

First, are you sure you are not shorting the connections with that metal box?
Second, have you checked how far from the box you need to be to get it to work?
Can you post some photos of the actual board and enclosure?

 

i not shorting the b+ out .the circuit is not touching the casel

 

the circuit board is about 1/8" from the bottom of the case when it works

 

well, the schematic looks really dodgy, for example the capacitor close to the VCO looks connected wrong, the emmiter of the second transistor doesn´t go anywhere, etc.
Really, a good design starts with a perfect schematic.

As to your problem with the case, you are clearly seeing the effect of the stray capacitance that this metal plate creates when close to the pcb components and tracks, so just mount it on standoffs and call it a day.