"Rich Grise" bravely wrote to "All" (26 Feb 05 16:01:31)
--- on the heady topic of " 1/4 vs 1/2 wavelength antenna"

RG From: Rich Grise
RG Xref: aeinews rec.radio.amateur.antenna:26047
RG sci.electronics.design:194
RG On Sat, 26 Feb 2005 08:33:25 -0600, Cecil Moore wrote:

Rich Grise wrote:

On Fri, 25 Feb 2005 22:35:28 -0600, Cecil Moore wrote:

Rich Grise wrote:
If that's not impedance matching, I don't know what it is! (Oh, "Load line"
matching? What are the two parameters of the load line? Voltage and
Current,
right? What's the slope of the load line? Impedance!)

And there's the catch. If the load line is the source
impedance, the load (not the designer) effects the source
impedance.

Apparently, I'm not following the same conversation here, because I
thought that the impedance matching network (in the instant example, the
pi-net output of the transmitter) was what translated the load impedance
to the source impedance, matching both in the process.

Maybe I inferred wrong. From your "load line equals
impedance" statement above, I inferred that you were
implying that the load line *is* the source impedance.

RG No, just trying to make the point that it does, in fact, _have_ an
RG impedance. (even if it's running class E.) What that exact impedance
RG is, of course, is left as an exercise for the reader. :-)

RG And another thing - in a transmitter, the impedance matching only
RG happens at the one frequency, which is a lot different scenario from,
RG say, a stereo. This could be a confusion factor here.

RG Thanks,
RG Rich

There are a couple of things meant by matching. The usual notion has
to do with the plate resistance of tubes. When used in a linear mode a
tube has a given plate resistance. To get the most power output from a
tube its plate resistance must equal the load. The available plate
current curve and equivalent load then must match the supply voltage.
A transformer is needed to adjust the typically low value load
resistance to the much greater plate resistance.

The other notion of matching has to do with using a switched voltage
to synthesize the right output voltage and current to drive a given
load. This type of transformation is done by using sampling over time.

Another type of transformation uses a resonnant tank circuit which,
like the above transformer, can adjust the load resistance to equal
that of the source resistance by a choice of the proper tank network
reactances. This is a single frequency only matching however.

Transistor audio impedance is never matched since an extremely low
source resistance is desirable for speaker damping. Musical instrument
tube amplifiers are somewhat between these since the tube power must
be transformed to match the high voltage supply low plate current to
the high current low voltage load, but yet must present a low source
resistance damping to a speaker so uses negative feedback for this.

A*s*i*m*o*v

.... Ok, I pulled the pin. Now what?.....Hey! Where are you all going?