Amps Digest wrote:
To: <amps@contesting.com>
> Date: Fri, 28 Nov 1997 20:17:39 -0800 (PST)
> From: Peter Gerba <pgerba@crl.com>
> Subject: [AMPS] Comm Qtrly Fall
>
> In the mail today was the Fall "Communications Quarterly" containing a
> fine piece: "Source Impedance of HF Tuned Power Amplifiers and the
> Conjugate Match" by Jack Belrose, Walter Maxwell, Tom Rauch.
>
> Good reading !
>
> pete, kn6bi
>
I have a question about p36.....
"He (Tom Rauch, W8JI) repeated Bruene's experiment (see FIGURE 4). Using
Bruene's method, Rauch obtained reflected power measurements similar to
Bruene's."
What exactly was the method.....(I assume) of tuning and loading?
Then the article says......
"However, when Rauch tuned and loaded his PAs in the conventional manner to
obtain maximum output power with any given, fixed amount of drive, there was a
significant difference." .......da di da......"Thus Rauch's experiment
indicates that, when the amplifier is tuned and loaded for operation in the
conventional manner, the output impedance, Zout is close to 50 ohms, and not a
value five times greater."
So at this point I am reading that the difference is in how the amplifiers are
tuned and loaded. This pretty much reduces the whole controversy to an issue of
how to properly tune and load an amplifier. It was my impression in the very
beginning back in '91 or whatever that Bruene was simply making the point that
if you tune and load an amp with regard for the design engineer's intentions of
where to run on the characteristic curves, that many of the amps we know and
love will not be showing a conjugate match to the load. And also that the amp's
internal resistance can be varied all over the place (with feedback, etc.)
without affecting the power output limit of the amp. All of the response to
Bruene's original article seems to say that when an amplifier is tuned and
loaded for maximum power (at a given drive level), then they will exibit a
conjugate match.
Period. That the internal resistance is not the output impedance of the PA. So
much for Bruene's theory basis to explain his results, but how did Bruene get
his results and how did Rauch get similar results and then get different
results with the same expermental setup?. What exactly did Rauch change for the
two sets of results with the same setup?
BUT then the article goes on to say.....
"So why the difference between Bruene's initial measurements and ours? Were the
directional couplers causing the discrepancy?"
And, no reference to these seemingly different ways to tune and load (with a
given drive level), Bruene's "method" and Rauch's "conventional method". Did
Bruene tune and load and then vary the drive from 0 to full output? Is that
it? Does Bruene tune an amp at some certain plate ma with a certain grid ma?
When I tune my L7 the way Drake says to, am I tuning it so that I stick to 1KW
input (the old rule) or am I tuning it for maximum linearity?
Thanks for putting all the time and effort into your article.....just a few
loose ends for me.
Charles (Jack) Hawley
Chuck....Ham Radio KE9UW
AKA "Jack" BMW Motorcycles, MOA #224 K100RS
Wife rides...Viki, MOA #18120 K100RS
President IBMWR
c-hawley@uiuc.edu
Sr. Research Engineer Emeritus
University of Illinois, Urbana-Champaign
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