I was attracted by the "usually" qualification. Under what circumstances
is the line SWR affected by the source impedance which feeds the line?

Roy Lewallen, W7EL

Richard Harrison wrote:
. . .
SWR depends on the match between load and transmission line and is
usually unaffected by the source impedance which feeds the line.
. . .

Roy Lewallen wrote:
"Under what circumstances is the line SWR affected by the source
impedance which feeds the line?"

None that I kbow of, but I can imagine a control mechanism that adjusts
the impedance presented to the antenna to reduce SWR.

To avoid responding to: "But, how about the "Matchmaker System", which I
never herd of, I added the word "usually". As far as I know, there is
usually nothing that can be done at the transmitter end of the line to
affect SWR. Match between the load and line controls SWR.

Best regards, Richard Harrison, KB5WZI

On Fri, 5 Sep 2003 12:02:02 -0500 (CDT),
(Richard Harrison) wrote:

Richard Clark wrote:
"Motorola (in their confusion) offers:
For example, in the 180 Watt version the input transformer is of 16:1
impedance ratio, making the secondatry impedance 3.13 Ohm with a 50 Ohm
interface."

Does not seem confused to me.
16 x 3.13-ohm= 50 ohms by my calculation.

Hi Richard,

The expression of "confusion" is not original, nor embraced by myself.
It represents my wry comment, an irony in that this term (confusion)
applied to Motorola's specifications is rejected by data, experience,
Motorola (except through a particular reading of one application note
that seems to bear no relation to any known experience), and at least
three more vendors that I have supplied who all conform to this
practice.

Technical literature for RF Design Engineers is chock full of this
consideration that is taken for granted in academic texts (it would
only muddy the waters for students, I suppose). However, when
unmentioned, except in the footnotes, endnotes, or appendix (all
unread at hazard to speed readers) this academic shortfall gives the
impression that the topic is of no interest. Hence we read of
Motorola being confused about their specification of source Z that
everywhere in their literature is expressed with deliberation and
planning. To date, and through more than several inquiries to expand
upon this "confusion" I have been offered no data, other form of
specification, how it bears on application, or any correlation to
personal experience.

If you follow the thread back up several, you will find Tam struggling
to find negative confirmations, and through his lack of close reading
his "condemnatory" sources in fact supply me with all the engineering
details I had described as being part and parcel to a common RF
Finals' Deck.

73's
Richard Clark, KB7QHC

Richard Clark wrote:
On Fri, 5 Sep 2003 12:02:02 -0500 (CDT),
(Richard Harrison) wrote:

Richard Clark wrote:
"Motorola (in their confusion) offers:
For example, in the 180 Watt version the input transformer is of 16:1
impedance ratio, making the secondatry impedance 3.13 Ohm with a 50 Ohm
interface."

Does not seem confused to me.
16 x 3.13-ohm= 50 ohms by my calculation.

Hi Richard,

The expression of "confusion" is not original, nor embraced by myself.
It represents my wry comment, an irony in that this term (confusion)
applied to Motorola's specifications is rejected by data, experience,
Motorola (except through a particular reading of one application note
that seems to bear no relation to any known experience), and at least
three more vendors that I have supplied who all conform to this
practice.

Technical literature for RF Design Engineers is chock full of this
consideration that is taken for granted in academic texts (it would
only muddy the waters for students, I suppose). However, when
unmentioned, except in the footnotes, endnotes, or appendix (all
unread at hazard to speed readers) this academic shortfall gives the
impression that the topic is of no interest. Hence we read of
Motorola being confused about their specification of source Z that
everywhere in their literature is expressed with deliberation and
planning. To date, and through more than several inquiries to expand
upon this "confusion" I have been offered no data, other form of
specification, how it bears on application, or any correlation to
personal experience.

If you follow the thread back up several, you will find Tam struggling
to find negative confirmations, and through his lack of close reading
his "condemnatory" sources in fact supply me with all the engineering
details I had described as being part and parcel to a common RF
Finals' Deck.

Tam is innocent!

I take full responsibility for planting the word "confusion" in
Richard's mind. What he's done with it is something else again...


As the records of this newsgroup show, the context in which I used the
word (actually, the word was "confused") was:

QUOTE *************************************

Some manufacturers state the conjugate, others don't. Even Motorola have
changed their terminology over the years: sometimes it's "output
impedance" or "Zout", sometimes it's "Z(subscript OL)", sometimes it's
"Z(superscript *)(subscript OL)".

Motorola's AN1526 was written in the 1990s to clear up this mess.

[...]

AN282, from which you quote, was first published in 1968. The truth
about load impedance is in there to be seen, but I'd be the first to
agree that it's not stated clearly. Motorola then confused the issue by
continuing to talk ambiguously about "output impedance" for at least
another 20 years.

AN1526, from which I'm quoting above, supersedes AN282. It was written
about 25 years later in an attempt to clear up that inherited mess of
loose definitions.

END QUOTE *************************************

I stand by those statements and take full responsibility for them.
Motorola's ambiguous use of "output impedance" - and three different
symbols, over the years - when all the time they meant "load"
impedance", has indeed been confusing.

The way Richard has subsequently misused the word is purely his
responsibility.

If he twists the facts again, to mislead others about what was actually
said (as he has just attempted to mislead Richard H, carelessly accusing
Tam in the process) then I will simply post the above quotation again.

The beauty of newsgroups is that everything that anyone has ever posted
is on the record, for any reader to judge.


--
73 from Ian G3SEK 'In Practice' columnist for RadCom (RSGB)
Editor, 'The VHF/UHF DX Book'
http://www.ifwtech.co.uk/g3sek

On Thu, 28 Aug 2003 07:20:28 GMT, Richard Clark
wrote:

The scenario begins:

"A 50-Ohm line is terminated with a load of 200+j0 ohms.
The normal attenuation of the line is 2.00 decibels.
What is the loss of the line?"

Having stated no more, the implication is that the source is matched
to the line (source Z = 50+j0 Ohms). This is a half step towards the
full blown implementation such that those who are comfortable to this
point (and is in fact common experience) will observe their answer and
this answer a

"A = 1.27 + 2.00 = 3.27dB"

"This is the dissipation or heat loss...."

we then proceed:

"...the generator impedance is 100+0j ohms, and the line is 5.35
wavelengths long."

Beware, this stumper has so challenged the elite that I have found it
dismissed through obvious embarrassment of either lacking the means to
compute it, or the ability to simply set it up and measure it. It
takes two resistors and a hank of transmission line, or what has been
described by one correspondent as:
There is no institutionalized ignorance, just a
lot of skepticism regarding the reliability of the
analysis methods and the measurement methods.

Hi All,

One emailer provided the following solution:
Total loss = 2.0 + 1.26639 + 1.57316 = 4.83955 dB
which varies from the citation by about 0.06dB.

The math offered:
1.Effective length of 50-ohm coax is 5.35 l – 5.0 l = 0.35 l = 126°.
2.Using W2DU program HP2, Page 15-35, Reflections, 1st ed.,
input impedance on 50-ohm line = Zin =31.10025 – j26.14159 ohms.
3.Using W2DU SWR program (Appendix 4, Page Appendix 23.7),
mismatch between the 100 -ohm generator and impedance
ZL = 31.10025 –j26.14159 = 3.456687:1
4.The problem now simplifies to determining the insertion loss
due to the mismatch between the 100-ohm source resistance
R of the generator and load ZL = 31.10025 – j26.14159 ohms.
5.Input voltage reflection coefficient rin = 0.55125
6.Input power reflection coefficient r2in = 0.551252 = 0.30388
7.Input power transmission coefficient t2 = (1 – 0.30388) = 0.69612
8.Power transmitted is then 69.612%, insertion loss expressed in dB, 1.57316 dB.
9. Using ITT terminology, P/Pm = 1.43654, which is also 1.57316 dB.

As I said, all achievable through references that many here have
available to them, but fail to read, or practice at the bench through
the angst of low self confidence or being too imbued with the kulture
of institutionalized ignorance. There are other sources that approach
this problem through more elegant means, but they are equivalent to
reaching for the stars when NONE here can pick the fruit from their
own orchard.

73's
Richard Clark, KB7QHC

On Mon, 08 Sep 2003 12:59:42 -0500, Cecil Moore
wrote:

Richard Clark wrote:
As I said, all achievable through references that many here have
available to them, but fail to read, or practice at the bench through
the angst of low self confidence or being too imbued with the kulture
of institutionalized ignorance. There are other sources that approach
this problem through more elegant means, but they are equivalent to
reaching for the stars when NONE here can pick the fruit from their
own orchard.

I tend to deal with these problems on a conceptual level:
"There's no such thing as a free lunch!" :-)

Cecil, what does a free lunch have to do with rho?

Walt

Richard Clark wrote:
"As I said, all achievable through references that many have available
to them---."

Richard Clark`s question was:
"A 50-Ohm line is terminated with a load of 200+ j0 Ohms. The normal
attenuation of the line is 2.00 decibels. What is the loss of the line?"

The ARRL Antenna Book is a reference designed for radio amateurs and
available to many..

(Eq 13) on page 24-9 gives: SWR = R/Zo, or 4 in Richard Clark`s
question.

(Fig 13) on page 24-10 gives a reflected power of 36 W from a 4:1
mismatch when 100 W is applied.

(Fig 14) on page 24-11 gives an additional 1.2 dB loss when an SWR of 4
applies to a cable with a matched loss of 2 dB. Total is 3.2 dB loss.

The 19th edition of the "ARRL Antenna Book" eliminates most of the
arithmetic needed to calculate loss added by SWR. Just use the
convenient figures on pages 24-10 and 24-11.

Next to Terman`s "Radio Engineering", I think the ARRL`s "Antenna Book"
is the best reference you can have on your shelf.

Best regards, Richard Harrison, KB5WZI