"Roy Lewallen" wrote in message
...
Richard Fry wrote:
. . .
The source impedance of most transmitters is not published even today.
If
it was, probably we wouldn't be having all of this confusion about it,
and
its effects.


Who's confused? It has no effect.

Roy Lewallen, W7EL

Hi Roy,

Going back to the Slick discussions of last winter, Was that you who made
the statement that you can have 100% re reflection from a transmitter, even
if it has a 50 Ohm output impedance? At first I thought this was all wet,
but after making some low power experiments, I am convinced it is true.

Tam/WB2TT

"Richard Harrison" wrote
I`d design for a conjugate match at the rated load and include overload
protection for an output short circuit or near short. For solid-state
I`d provide overvoltage protection.in addition to overcurrent
protection.

===================================

To obtain a conjugate match it is first necessary to know what the source
impedamce is. How or from where is that elusive figure obtained?

It is not given in a transmitting tube manufacturer's data sheets. Perhaps
it doesn't matter what it is - not needed?
----
Reg, G4FGQ

Walter Maxwell wrote:
Thus, no transmission line is necessary. For example, the device can be
connected directly to the antenna terminals, or any other device you desire to
determine the mismatch, and power it directly from the signal source--no
transmission line is needed on either port for the device to indicate the degree
of mismatch.

Assume a 100+j100 ohm load and a 100-j100 ohm transmitter
directly connected with no transmission line. The system
is matched. Are there any reflections? Now install a
transmission line. Will an SWR meter read the same thing
in both cases?
--
73, Cecil http://www.qsl.net/w5dxp


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Reg Edwards wrote:
And the accuracy of any instrument depends on how it is used rather than on
what the manufacturer says about it.

Presumably, including the "Bird wattmeter" and "SWR meter". :-)
--
73, Cecil http://www.qsl.net/w5dxp


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Tam/WB2TT wrote:
Going back to the Slick discussions of last winter, Was that you who made
the statement that you can have 100% re reflection from a transmitter, even
if it has a 50 Ohm output impedance? At first I thought this was all wet,
but after making some low power experiments, I am convinced it is true.

It is true by definition. All reflected power incident upon a
transmitter is re-reflected, by definition. Never mind that
reflected voltage can cause an over-voltage condition and/or
reflected current can cause an over-current condition *inside*
the transmitter. By definition, any reflected power dissipated
in the source after making a round trip to the load was never
generated to begin with.
--
73, Cecil http://www.qsl.net/w5dxp


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Ian Jackson wrote:
Call it an RLR meter, which is what it IS really measuring.

How about an "SVI", Superposed Voltage-sample(+/-)Current-sample,
named for the math function that it is performing?
--
73, Cecil http://www.qsl.net/w5dxp


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Reg Edwards wrote:
To obtain a conjugate match it is first necessary to know what the source
impedamce is. How or from where is that elusive figure obtained?

If no reflections are allowed to reach the source, the source
impedance doesn't matter (except maybe for efficiency).

It is not given in a transmitting tube manufacturer's data sheets. Perhaps
it doesn't matter what it is - not needed?

Install a matching network that achieves a quasi-conjugate
match between the network and the load. That's what I do. :-)
--
73, Cecil http://www.qsl.net/w5dxp


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On Mon, 6 Sep 2004 06:20:23 -0500, "Richard Fry"
wrote:
I won't try to soften this

Hi OM,

I kin take it ;-)

: your conclusion above doesn't just _appear_ to
be wrong, it IS wrong. 100% wrong.

Hmmm, in light of what is about to be said by you this continues to be
amusing.

How do I know? I was the author of all of the brochures and technical data
sheets for Harris' entire FM product line for the ten years before I
retired.

Yes, your patter sounds like a publicist rather than a design engineer
- I've snipped your commercial fluff as it is pretty soft still.

It
is designed for a 50 ohm load.

Imagine THAT! Of course I won't hold my breath for your explanations
WHY (or -gasp- how) it is designed for 50/75/100/300 Ohms and not just
slap the output into any load - that would be an engineering issue of
matching which seems to be foreign to your discussion. Glad to see my
inclusions of so much of your copy brought back you memory that
rejected this:
On Sun, 5 Sep 2004 11:25:02 -0500, "Richard Fry"
wrote:
The source impedance of most transmitters is not published even today.
I can accept that perhaps under your hand it was not, but Harris has
returned to the fold of conventional design specifications:
MW-10B SPECIFICATIONS
RF OUTPUT IMPEDANCE: 50 ohms, unbalanced.
Other output impedances available on special order.

Harris Platinum Z FM transmitter
100 ohm output impedance (unbalanced)

HARRIS SW-50 A
RF Output Impedance 300 ohms balanced, 2.0 to 1 maximum VSWR
Don't bother rummaging up you own drafts lingering in the musty
corners of the web, there are newer spec sheets available that easily
eclipse you in numbers to the contrary, but typical engineering
regards for specifying the output impedance.

I would suggest you review the works of a real engineer, Geoff
Mendenhall (you know, the guy you dissed) who explicitly offers
formula and specifications that correlate to current Harris equipment
design considerations for matching source Z to load Z. This has been
fairly common material available from Terman (One of Geoff's
references) for 70 years now and even the digital age has not changed
this:

It sounds pretty simple, in fact,
each module has a torroid (coil) which is the load for that
module; all those torroids are lined up and an iron pipe is run
through these torroids so that the combined output of all the
modules is coupled into this pipe. One end of the pipe is at
ground, the other end is the RF output of the transmitter. There
is an output network to match impedance of the pipe, which is
probably only a few Ohms, to the required output impedance which
is usually 50 Ohms, although sometimes high power transmitters are
set up to provide 75 Ohms, once in a while even 300 Ohms, to drive
an open wire type transmission line system.

From the Goatman:
"It was necessary to determine the plate
load impedance (formula) = 1000 Ohms
where Emin min drop across the tube in saturation
I1 ac plate current.

"Since this Zp was to be coupled into a
Z output of 50 Ohm, a impedance transformation
of 20:1 was needed."

Perhaps this is too many words for the publicity department style
sheet, but to engineers there isn't an iota of difference in the
design considerations of the final over the course of 1968-2004. It
goes much further back than this - we will skip that so as to not
appear to be roughing the receiver.

However, to this subject I am quite used to the rebuttal "You are not
going to change my mind." Impeccable logic such as this and
variations offered by you have scant foothold in the sweep of time. I
especially enjoy the sharp swerves to avoid the Goatman's simple
expression above. Reminds me of the Chinese contortionist acts that
used to be the staple of the Ed Sullivan show.

73's
Richard Clark, KB7QHC

On Mon, 06 Sep 2004 11:11:56 -0500, Cecil Moore
wrote:

Reg Edwards wrote:
And the accuracy of any instrument depends on how it is used rather than on
what the manufacturer says about it.

Presumably, including the "Bird wattmeter" and "SWR meter". :-)
Not if you are measuring mud (data missing)

Richard Clark wrote:

Cecil Moore wrote:
Presumably, including the "Bird wattmeter" and "SWR meter". :-)

Not if you are measuring mud (data missing)

And I have indeed measured mud.


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