On May 1, 6:01*pm, walt wrote:
On Apr 27, 2:13*pm, Cecil Moore wrote:



On Apr 27, 10:30*am, Wimpie wrote:

Depending *on the frequency resolution of your VSA, the frequency of
the injected signal can be well within 1 kHz of the carrier, so LC
filters in the PA will not distort the measurement. *In case of a 100W
PA and injection of about 100 mW, the difference in wanted signal and
signal to be rejected is 30 dB (not that large).

Would any competent optical physicist suggest that it is valid to
study the conditions associated with interfering coherent light waves
inside an interferometer by introducing an incoherent light source
into the system? Why would any competent RF engineer suggest that the
system source conditions associated with interfering coherent RF waves
can be studied by introducing an incoherent test signal?
--
73, Cecil, w5dxp.com
"Halitosis is better than no breath at all.", Don, KE6AJH/SK

Cecil suggested reading Chapter 19A in Reflections to view the results
of my extensive measurements of the output resistance (impedance) of
RF power amps, but except for Jim and Richard, it appears that the
others have not. Actually, *Chapter19A is an addition to Chapter 19,
which when taken completely will *provide some information that *will
hopefully change some minds concerning the maximum power delivered. It
should be understood that 'maximum' power delivered is that power
delivered with a specified level of drive.

For example, if the drive level is set to deliver a maximum of 100w,
and the pi-network is adjusted to deliver that maximum power into its
load, the source resistance (impedance) will be the (complex)
conjugate of the load impedance. We're not *talking here about the
very maximum power that the amp can deliver, with max drive, max plate
current, etc.

If you review the 19A portion of you will see beyond a doubt that the
conjugate match exists between the output of the pi-network and its
complex load impedance, and that the maximum power delivered at the
drive level that allows only 100w to be delivered as the maximum.

Further review of all the data presented there will also show that the
output resistance of the amp is non-dissipative, while the dissipative
resistance is that between the cathode and plate. The reason the
efficiency of the amps can exceed 50 percent is because the cathode to-
plate resistance is less than the non-dissipative output resistance,
where that R = E/I appearing at the output of the pi-network.

The earlier portion of Chapter 19, that appears in Reflections 2, can
be downloaded from my web page atwww.w2du.com, click on 'Read
Chapters from Reflections 2', and select Chapter 19.

I hope the review of my measured data will clear up some of the
confusion concerning the output resistance (impedance) of the RF power
amp.

Walt, W2DU

When a source is tuned (e.g. through a pi network or any other
matching network between a PA and its load) such that maximum power is
delivered to the load, it's axiomatic that the source impedance is the
complex conjugate of the load. Is there really a need for a whole
chapter for that?

You say, "We're not talking here about the very maximum power that the
amp can deliver, with max drive, max plate current, etc." I beg to
differ. That is EXACTLY what we are talking about. We're talking
about modern amplifiers that would be destroyed if not for protection
circuits, if they were loaded with a load that resulted in maximum
dissipation in the load. We're talking about even old amplifiers with
enough grid drive that they COULD be loaded to higher power output,
but for reasons of wanting the active devices to survive for a
reasonable length of time (or possibly other reasons), are not loaded
so heavily. If you want to exclude such amplifiers from
consideration, then I would hope none would disagree about the
relationship of the load impedance and the source impedance. You
needn't have made any measurements to convince me of that.

Cheers,
Tom