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On May 27, 4:23*am, Keith Dysart wrote:
If you are uninterested in source impedance (and many people seem
to be much more concerned with it than they need to be), then
by all means do not consider it, do not specify it, do not attempt
to compute it or measure it and do not make statements about what
the source impedance is.

The question then becomes: If the system box does not include the
source and the system exhibits characteristics consistent with a
conjugate match, can we say the system is conjugately matched? For
instance:

100V---50 ohm coax---+---1/4WL 300 ohm feedline---1800 ohm load

This system exhibits all the characteristics of a conjugately matched
system. Can we say it is conjugately matched?
--
73, Cecil, w5dxp.com

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Roy Lewallen, W7EL wrote:
"Nut the statement which was made was that "Maximum power transfer
occurs when the source and load impedances are matched."

Inelegant and bereft of qualifications as it may be, I am the author of
that statement, and I stand by it.

Roy says: "This is not true, as the example demonstrates."

Robert L. Schrader says on page 43 of "Electronic Communication":
"To produce maximum power in any load, it is necessary that the load
resistance equal the internal resistance of the source."

I believe our statements are equivalent. Load a battery of a given
internal resistance with the same resistance as a load, and for a short
time the battery will deliver more power to that load than to any other
resistance larger or smaller.

Best regards, Richard Harrison. KB5WZI

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Roy Lewallen wrote:
"Reduce the source imperance to 10 ohms."

FOUL!

In the case of a 10-ohm internal source, the load which extracts maximum
power is 10 ohms.

Best regards, Richard Harrison, KB5WZI

W2DU's Reflections III is now available from CQ Communication...
 

I stand by my position that when the source is an RF power amplifier,
and when all the available power is transferred from the source to the
load, the source impedance is the conjugate of the load impedance. In
a similar instance, if the load is a pure resistance, the source
resistance equals the load resistance.

And referring to a statement Dysart made concerning plate resistance,
Rp, it must be understood that in Class AB, B and C amplifiers, Rp is
NOT the source resistance. In those amplifiers the effect of Rp is a
negative feedback that reduces the effect of plate-current change
resulting from a change in grid voltage, thus reducing the power
output compared to what the output would be if Rp were absent.
Compensation for the power lost to Rp is accomplished by simply
increasing the grid drive.

Consequently, Rp plays no part in achieving a conjugate match at the
junction of the network-output and the load. Although lossless
elements are required to achieve a perfect conjugate match in both
directions, a perfect conjugate match is obtained in the forward
direction with real elements when all available power is being
delivered to the load. This condition is verified in data presented in
Chapter 24 of Reflections 3.

Walt, W2DU