PCS-Electronics

One thing, it is best to place amp and exciter in separate boxes. This is why all major
big-power transmitters are always separated above, say 200-500W of power.
Yeh i would do if it was that kind of power.

I know it cant be audio getting into the RF stage on the exciter. Its the power to the ...

Just tested it properly. There is still some hum there but not as much.
However, when i power the exciter with my bench PSU and run the rest as normal there is no humm atall so the problem lies in the supply to the exciter i imagine?

I am just using a 7812 regulator decoupled with a 0.1uf and 47uf ...

I think ive done it!

A ground loop i belive :evil: :evil: (you may be able to verify)


Took me a while to find it but i fixed it by just connecting the negative of the rectifier straight to ground instead of having a ground wire going from the smoothing cap to the amp ground plane. So no ground ...

Ok i am using one of the 150w amps (BW do them aswell i think) and just a standard PLL driver (500mw-1w)

I have boxed it all up and all is working fine but i get a hummmmm when i turn the radio up full when on the dead carrier.
I have used a 300w toroidal transformer and two 10000uF smoothing caps ...

Thanks Marko, this seems to work fine.

Have you got a pic of the board? im not sure if its the one im thinking of

This is the bias circuit to the base of the BLF244:

I already have the SWR pickup strip which goes low when the SWR gets high . Im just not sure how to use it to pull the bias voltage down, where to connect it on the bias circuit etc. I cant just short out the regulator supplying the bias voltage.

Either works well. Pulling the bias voltage down or cutting off the drive.

Just make sure your amplifier is stable with exciter output turned off, especially
if it still produces small amount of power.

Some flimsy RF AMP designs can oscillate under such conditions.
thanks for that.

like i say ...

Whats the best way to incorporate this on a band 2 amplifier?

Anyone got any schematics or docs handy?

is it best to just turn down/off the bias supply to the driver transistor (im using blf244 driving sd1407) or bypass the exciter into a 50ohm resistor.


I actually have an amp here with swr ...