"Roy Lewallen" wrote

- - - - - right answers when the underlying
principles
are too hard for us to understand.

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

Roy, there you go again - blaming the principles.

On Tue, 2 Sep 2003 08:54:45 +0100, "Ian White, G3SEK"
wrote:

Certainly you could come up with a smoking gun couldn't you?

If you can't get it from the key paragraph I quoted, then read all 15
pages of AN1526. If you still can't see that your notion about "device
output impedance" is shot clear through, then neither Motorola and I can
help.

Complete
with an actual, demonstrable specification for the item I offered
(seeing as you still lack any concrete example). What does your new
and updated resource say about the MRF 421.

You know perfectly well that AN1526 won't say anything about your
specific pet device, so what was the point of asking that question?

Quite obvious isn't it? (Speaking of rhetorical questions....) You
fail to offer ANY of your personal knowledge outside of the
cut-and-paste rebuttal that you loath as being inferior to thinking
for oneself. I supplied my experience and thought both with
correlations and supplemental insights that you condemn through
association; and you cannot dredge up any affect your understanding of
AN1526 bears on the literal design application of the MRF 421. In
short, an academic appeal to it being unknowable with the concomitant
ivory tower snub of application (including your own!).

Does it abandon that
discussion entirely to this new-age era of all being unknowable?

And that is an even worse travesty of what Motorola and I are saying.

You AND Motorola? Are you two in a joint partnership? Twice you draw
on this stale illusion where your own original experience offers a
vacuum of discussion.

If you want to measure the *true* output impedance of an MRF 421 - as
distinct from the load impedance given in the data sheet - then go ahead
and do it. After all, you're the one who claims it is an important
design parameter.

This merely underlines you having ignored my having posted both
commentary AND data to that effect, and you remain silent in regard to
your own efforts that could prove insightful to the meaning imparted
by AN1526 to you. To this point, and through my prodding you have yet
to offer any substance of its importance aside from snippets that are
drawn from an unknown context that you challenge me to review. And to
what end if I were to; and offer your understanding lacked in its
regard? More denial and little detail of substantiation? Who does
your thinking for you? You toss that in my face and then abandon the
field when I put it to you to explain how it bore to the application
you built under your own hands. Was this piece-de-resistance a
Heathkit? Why does its detail of implementation remain cloaked from
your discussion?

I'm the one who says it is (a) not what you think it is; and (b) not
important anyway.

Is there any doubt? (a) remains deliberately vague and (b) is,
frankly, contradicted by the hew and cry that attends your
considerably extended fulmination.


Now it's up to other people to judge the technical truth of the matter.

Ah Ian,

The TRUTH. As if there is only one answer and its altar is not to be
approached. Appeals to educating the lurker is vanity. I enjoy that
game as much as the rest of you, especially when you guys, like
wallflowers, come up so stylistically drab and technically
un-prepared. :-)

Too many mix Truth with explicit admission that this discussion is
not important anyway.
The quality of your rebuttal already proves your sentiment.

Now, your offering any further discussion that relates to your
experience; the role of this AN1526 to it; and some, even if plagued,
specification for any source you designed to, if that follows; then we
may actually get around to a dialog over the topic. Anything less
will be repetition and would again belie your closing sentiment.

73's
Richard Clark, KB7QHC

"Richard Clark" wrote in message
Hi Tam,

You missed the point. 100 Watts PEP is not 100 Watts continuous (such
as your computation leads to).
............................................

Hi Richard,

The voltage swing at the collector can only go between roughly ground a
2*VCC. For a continuous wave it does that for every cycle of the RF signal.
For SSB, it only reaches that on voice peaks, but it can get no larger.
Although you will be on the ragged edge, you can tune up a pi network linear
on a constant tone, and operate with speech.

BTW, did you notice the 174 Ohm Zo of the MRF450. Clearly, you can't
conjugate match that. I am convinced that is a real number, and not a
conjugate of load number. They do not give any min or max limits on this. I
looked at some small signal transistors, and found that Ro can vary by more
than an order of magnitude from unit to unit.

I think that virtually all current HF ham transmitters are push pull, and
use feedback. That will affect the output impedance.


We have all been quoting Motorola literature. I am going to look at what
Philips, and the Japanese have to say on this.

Tam/WB2TT

On Tue, 2 Sep 2003 21:18:03 -0400, "Tarmo Tammaru"
wrote:


"Richard Clark" wrote in message
Hi Tam,

You missed the point. 100 Watts PEP is not 100 Watts continuous (such
as your computation leads to).
............................................

Hi Richard,

The voltage swing at the collector can only go between roughly ground a
2*VCC.

You've got the cart before the horse. Your computation converted to a
PEP valuation is on par and excursions of 2*VCC is not suggested by
anyone.

For a continuous wave it does that for every cycle of the RF signal.
For SSB, it only reaches that on voice peaks, but it can get no larger.

Why voice peaks? What confines PEP to voice? What defines PEP as
voice modulated signals characterizing Z? Two-tone tests are
sprinkled through the literature when it comes to modulation - I don't
think they mean duo-tonic renditions of whistling dixie.


Although you will be on the ragged edge, you can tune up a pi network linear
on a constant tone, and operate with speech.

Where in the specification with an equivalent circuit is there a pi
network? You are probably looking at power decoupling.

BTW, did you notice the 174 Ohm Zo of the MRF450. Clearly, you can't
conjugate match that. I am convinced that is a real number, and not a
conjugate of load number. They do not give any min or max limits on this. I
looked at some small signal transistors, and found that Ro can vary by more
than an order of magnitude from unit to unit.

Small signal characterization? Other than being two orders of
magnitude off, you should stick with large signal characteristics.
Seems like this exact discussion has been gone through before.


I think that virtually all current HF ham transmitters are push pull, and
use feedback. That will affect the output impedance.

Making an appeal to "modern" equipment? Look at the schematic for
your own rig and describe the negative feedback path and its
magnitude. What you are looking at is neutralization. That may be
feedback, but it is far from the gain determination characteristic in
the classic sense defined by Bode. If you didn't have it, you would
be in trouble stability-wise.


We have all been quoting Motorola literature. I am going to look at what
Philips, and the Japanese have to say on this.

Tam/WB2TT


Hi Tam,

Look at
http://www.semelab.com/
which offers to allow you to select FETs by specifying Z (how about
that? 10 years after Motorola gave up in confusion - by some accounts)

http://www.polyfet.com/Dsheet%5CSM724.pdf
or
http://www.polyfet.com/dsheet%5CSR341.pdf
chosen at random, another outlet that foolishly treads where Motorola
gave up in confusion - by some accounts

http://www.semiconductors.philips.co...F145_CNV_2.pdf
about the only HF Power transistor in their repertoire (I could be
wrong as they too offer input and output Z where Motorola gave up in
confusion - by some accounts)

Hi All,

You know fellas, this goes far afield from a simple bench test to
perform against 2 resistors and a hank of transmission line. As no
one handles these "advanced" topics of schematic reading and parts
specification, don't you think you might want to prove you can turn on
a transmitter and read a meter?

If you cannot accept a figure clearly displaying the Z characteristics
of your output finals, how do you think you are going to argue
something simpler such as line loss? It requires no advanced degree,
only proof of performing a task suitable to an amateur. Surely you
can manage that little.

Too much breezing on in place of work. The chorus of appeals of
"doing it for the lurker" must have them rolling in the aisles. :-)

73's
Richard Clark, KB7QHC

Richard Clark wrote:
Does it abandon that
discussion entirely to this new-age era of all being unknowable?

And that is an even worse travesty of what Motorola and I are saying.

You AND Motorola? Are you two in a joint partnership?

I and the Motorola technical reference that I quoted.

Recall what happened: I gave my technical point of view. You challenged
it, asking if I'd ever read any Motorola literature. I quoted a
reference from Motorola, supporting my point of view. Now you attempt to
smear me and Motorola both.

Twice you draw on this stale illusion where your own original
experience offers a vacuum of discussion.

When you quote Motorola AN282A, it is a reference. When I quote AN1526,
it is a "stale illusion."

Along with the "new-age... unknowable" stuff, these are cheap smears
that discredit only you.


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

Reg Edwards wrote:

Now it's up to other people to judge the technical
truth of the matter.

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

Justice from 'peers' on THIS newsgroup ??????


I wasn't feeling in need of justice - it's more about encouraging people
to think for themselves.


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

Ian, G3SEK wrote:
"..It`s more about encouraging people to think for themselves."

Why shoulld people worry with reflection coefficients or SWR?

Terman says:
SWR is important because it is easily measured, and SWR directly
indicates reflection in a system.

Reflection coefficient is defined in my dictionary as:
The vector ratio between the electric fields associated with the
reflected and incident waves, at the junction of a uniform transmission
line and a mismatched terminating impedancee.

Other planes and junctions producing an impedance discontinuity are also
cited as producing a reflection and thus a reflection coeficient.

The dictionary quantifies the reflection coefficient as:
(Z2 - Z1) / (Z2 + Z1)
where Z1 = source Z
and Z2 = load Z.

Absolute values are used above for the reflection coefficient when
relating it to SWR.
This is the voltage divider fraction.

Terman says on page 97 of his 1955 opus:
"Reflection coefficient (rho) = (VSWR-1) / (VSWR + 1).
"S" ---sometimes called (VSWR) to distinguish it from the standing-wave
ratio expressed as a power ratio, which is (Emax / Emin) squared.

best regards, Richard Harrison, KB5WZI

Richard Harrison wrote:
The dictionary quantifies the reflection coefficient as:
(Z2 - Z1) / (Z2 + Z1)

Terman says on page 97 of his 1955 opus:
"Reflection coefficient (rho) = (VSWR-1) / (VSWR + 1).

Please note that if Z1 and Z2 are characteristic impedances of
transmission lines at an impedance discontinuity point, these
two equations yield different results.
--
73, Cecil http://www.qsl.net/w5dxp



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Richard,

Do yourself a favor and try to get a copy of Motorola ap note AN762. It
describes several amplifiers, including a version with the MRF421. It is
clearly stated that the MRF has an output rating of 100W, PEP OR CW. Also,
the amplifier has negative feedback.

Tam/WB2TT

On Thu, 4 Sep 2003 20:25:01 -0400, "Tarmo Tammaru"
wrote:

Richard,

Do yourself a favor and try to get a copy of Motorola ap note AN762. It
describes several amplifiers, including a version with the MRF421. It is
clearly stated that the MRF has an output rating of 100W, PEP OR CW. Also,
the amplifier has negative feedback.

Tam/WB2TT


Hi Atm,

"Continuous collector current could go as high as 21.3 A at
13.6 V operated into any load."

By Ohm's law, and variations, P = 289.68W and with a collector
efficiency 55% (however, only spec'd at 180W) results in 159W in RF
products (not all within band) over a full cycle. This spec is for
the tandem configuration common to most finals' decks found in amateur
equipment, not a single transistor and not at 12V. Further, the
current is shared by each transistor through alternation as the two
are in series feed to the primary of T3. At the drive levels offered,
the transistors each offer ballpark 1.2 Ohms T3 is specified at 1:5
(again, just as I described in past messages) and offers a 25:1
impedance transform would at a first pass evaluation offers exactly
what I said it would.

Motorola (in their confusion) offers:
"For example, in the 180 Watt version the input
transformer is of 16:1 impedance ratio, making
the secondary impedance 3.13 Ohm with a 50 Ohm
interface."
...
"It should be noted that in the lower power versions
[common to the experience and quality of gear found
in amateur application - rwc] the input and output
impedances are higher...."

At the end of AN762 they offer a design for low pass filtering (to
remove some of those out of band RF products) which specifically
includes the source specification of (-gasp!-) 50 Ohms, and a load of
50 Ohms. Of course, this all occurred prior to some accounts of the
great Motorola confusion of the early 90's that rendered all such
advice - um, well, who knows?

As for the negative feedback. Again, this is exactly what I said it
was "The Input Frequency Correction Network." This hardly qualifies
in the classic Bode sense of Z stabilization so commonly found in AF
amplifiers.

Now I did you a favor by reading it to you.

73's
Richard Clark, KB7QHC