Grounded-collector 14MHz power amplifier
 

Wonder if somebody else has experience with grounded-collector
amplifiers for amateur radio applications? See the notes on
http://home.online.no/~la8ak/c23.htm

73
Jan-Martin
---
J. M. Noeding, LA8AK, N-4623 Kristiansand
http://home.online.no/~la8ak/c.htm

Sure looks complex for a circuit that only delivers 10W and 10dB gain at 14
MHz. Also, the common-collector configuration ("emitter follower") is
notorious for becoming an oscillator when driving reactive loads.

What's the advantage of this circuit supposed to be?

Joe
W3JDR

"J M Noeding" wrote in message
...
Wonder if somebody else has experience with grounded-collector
amplifiers for amateur radio applications? See the notes on
http://home.online.no/~la8ak/c23.htm

73
Jan-Martin
---
J. M. Noeding, LA8AK, N-4623 Kristiansand
http://home.online.no/~la8ak/c.htm

On Mon, 27 Dec 2004 03:05:57 +0100, J M Noeding
wrote:

Wonder if somebody else has experience with grounded-collector
amplifiers for amateur radio applications? See the notes on
http://home.online.no/~la8ak/c23.htm


While the collector is grounded for RF the circuit is NOT an emitter
follower. The drive is impressed via a link to the E-B of the
transistor and taken off the emitter not the base. A two port
analysis makes the characteristic behavour similar to
common emitter. The low gain was devices of the time rather
than the circuit itself.

I've seen this used in older Aircraft comm radios, at least two
different older solid state CB (ca-1969) and varios other places.

It's weakness is rather high rf feedthrough making CW and AM
system require keying the previous stage (driver) or there will be
poor keying and/or modulation. Also reflected RF (load mismach)
was reflected back to the driver resulting in poor operation under
less than optimum loading.

The upside was it made it easier to cope with the fact that the
collector was a high capacitance to a heatsink for RF.

Using modern devices and circuit techniques makes this a less
than desireable design.

Allison
Kb1gmx

Verizon News wrote:
Sure looks complex for a circuit that only delivers 10W and 10dB gain at 14
MHz. Also, the common-collector configuration ("emitter follower") is
notorious for becoming an oscillator when driving reactive loads.

It's not actually common-collector. The input is applied between the
base and emitter, and the output extracted between the emitter (ignoring
ballast resistors) and collector. It's an ordinary common emitter
amplifier but with the collector grounded.

Unlike the emitter follower, which is almost guaranteed to become
unstable with sufficiently large capacitive loads, this circuit is
devoid of feedback external to the transistor. The circuit should be
fairly stable assuming the tank circuit is well behaved at all
frequencies up to the transistor Fc.

What's the advantage of this circuit supposed to be?

Insulator between collector and heatsink is unnecessary.

bart
wb6hqk