Just a 50 cent plug for the yahoo group rfamplifiers. You might join the
group and ask your question over there. More than one RF Amp Engineer
hangs around to bounce your questions off.

good luck
cheers
skipp

just go to the main www.yahoo.com page, type in yahoo groups. Then type in
rfamplifiers and join.


: Bill N2CQR MOHBR wrote:
: I've built a little RF amp (for 20 meters) using a single MTP3055V
: MOSFET.
: Class AB, binocular core RF transformer in the output. I drive it
: with
: a homebrew 20 meter DSB rig.

: Here is the problem: The amp works fine IF I take the low pass filter
: out of the circuit. I'm using a groundplane antenna with a T network
: tuner.
: I can adjust it to make it look like 50 ohms. Without the low pass
: filter,
: I get a very nice clean output (looks good on a scope, and SWR is low,
: so I don't think it is putting out spurs or harmonics).

: But if I include the LP filter in the circuit, the amp takes off,
: turning
: into an 18 Mhz oscillator!

: I checked the filter with a sig generator. The cutoff freq is where
: it is
: supposed to be.

: I've had this kind of problem before, with other amps.

: Any suggestions?

: 73 de Bill M0HBR CU2JL N2CQR
: http://planeta.clix.pt/n2cqr