On Mon, 23 Nov 2009 19:18:37 +0100, "Ronald" wrote:

Suppose we feed 20 watts in a p.a. but don't want to use a dummyload
in the p.a. Come on this is done all the time.

The only reason that works is that the transmitter has a protection
circuit that detects high VSWR and either reduces power or shuts down.
The idea is to not destroy the output xisitors. Into an infinite VSWR
load, you can easily find twice the collector voltage across the
output stages, which on many radios, will destroy the xsistors. With
other type of loads, the output stages could easily draw twice their
rated current, this time destroying them with too much dissipation.

Judging by your wording, I don't think you have a clue what a dummy
load does or where to install it. It's not "in" the PA stage. It's
after the PA, after the low pass filter, after the T/R switch, and in
place of the antenna. You use a dummy load for testing and
measurement so that you don't pollute the airwaves or fry your radio
tuning into an unknown load.


--
Jeff Liebermann
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558