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