Sorry everyone, but I just retested with no cable and the results I obtain are
precisely the same. The coax cable was only 26" long anyway.
So forget about that transmission line stuff. It's irrelevant here. What I
want to know is why the VSWR indications are the way they are.

If anyone's interested, I can email a small spreadsheet that deals with this
simple circuit (V0-R-jX-r-jx) and allows you to set
a) R,X and r, and vary x
b) R,X and x, and vary r.
I plot side by side on the two corresponding graphs
- modulus of total load voltage
- modulus of load resistor voltage
- modulus of load reactance voltage
- power dissipated in load resistor
- VSWR between source and load
- "conjugate VSWR" between source and load.

One more time with feeling -
What I want to know is why the VSWR indications are the way they are.

Best,
Andrew

"Cecil Moore" wrote in message
...
Dave wrote:
nope, all done. reg is here and cecil can't be far behind. i've had my
fun, time to do other more productive things than watch them re-hash
conjugal matches for the next month or two.

I guess I need to say this again. My take on discussions of conjugate
matching in ham antenna systems is that it is a waste of time. If reflected
energy is not allowed to reach the source, e.g. typical ham Z0-matched
systems, the source impedance is irrelevant and doesn't affect anything
in the system except for efficiency.
--
73, Cecil http://www.qsl.net/w5dxp



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probably because the meter is not measuring what you think it is. remember,
vswr meters are meant to be showing what the vswr is in a transmission line
of a given characteristic impedance. they are not impedance meters, nor are
they proper power meters even though they are often calibrated in watts...
they are only accurate in the specific characteristic impedance system they
were 'calibrated' for... and then only roughly in most cases. if you want
to make proper measurements give up on the vswr meter and measure the
voltage or current with an oscilloscope or properly calibrated rf voltmeter.

"Lord Snooty" wrote in message
nk.net...
Sorry everyone, but I just retested with no cable and the results I obtain
are
precisely the same. The coax cable was only 26" long anyway.
So forget about that transmission line stuff. It's irrelevant here. What I
want to know is why the VSWR indications are the way they are.

If anyone's interested, I can email a small spreadsheet that deals with
this
simple circuit (V0-R-jX-r-jx) and allows you to set
a) R,X and r, and vary x
b) R,X and x, and vary r.
I plot side by side on the two corresponding graphs
- modulus of total load voltage
- modulus of load resistor voltage
- modulus of load reactance voltage
- power dissipated in load resistor
- VSWR between source and load
- "conjugate VSWR" between source and load.

One more time with feeling -
What I want to know is why the VSWR indications are the way they are.

Best,
Andrew

"Cecil Moore" wrote in message
...
Dave wrote:
nope, all done. reg is here and cecil can't be far behind. i've had
my
fun, time to do other more productive things than watch them re-hash
conjugal matches for the next month or two.

I guess I need to say this again. My take on discussions of conjugate
matching in ham antenna systems is that it is a waste of time. If
reflected
energy is not allowed to reach the source, e.g. typical ham Z0-matched
systems, the source impedance is irrelevant and doesn't affect anything
in the system except for efficiency.
--
73, Cecil http://www.qsl.net/w5dxp



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On Sun, 23 May 2004 20:42:59 GMT, "Lord Snooty" wrote:


The amp is single-ended out of an MRF136, so I presume it's Class A. The amp's
designation is H-10 (I bought it surplus). It's rated at around 15W, 0.1 - 30
MHz. The circuit diagram shows no hint of current limiting circuitry.

If one is serious about proper design of a matching network - a network, I
might add, which attaches *directly* (near as dammit) to the Tx output - then
one is all at sea without a proper knowledge of source impedance. See my
comments in the other thread about this.

Hi Andrew.

Specification sheets respond to these issues quite well. The MRF136
is a 400MHz device, normally offering 15W max with about 16dB gain at
28Vdc (although rated higher) in a class A configuration (showing
about 60% efficiency).

As would be expected, it covers a lot of turf. In the HF, the output
Z runs easily near 50 Ohms in push-pull circuit configurations;
otherwise it is simpler to describe it in the teens to tens of Ohms
across any number of variables you do not disclose (like frequency,
the actual configuration, additional interface components). 1 - 10
MHz does not bode well towards the best implementation of an UHF
device.

Load pulling is vastly simpler than S-parameters (also specified in
the data sheets for this device, down to 1MHz), why you want to marry
the two is a mystery.

73's
Richard Clark, KB7QHC

Richard Clark wrote:
Load pulling is vastly simpler than S-parameters (also specified in
the data sheets for this device, down to 1MHz), why you want to marry
the two is a mystery.

A laboratory bench setup is simpler than a calculator and a couple
of sheets of paper? Egads Richard, s-parameter analysis was invented
in order to make things "vastly simpler" - and it does!
--
73, Cecil http://www.qsl.net/w5dxp



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On Sun, 23 May 2004 21:19:23 GMT, Richard Clark
wrote:

[snip

|in a class A configuration (showing
|about 60% efficiency).

Huh?

Cecil wrote,

Richard Clark wrote:
Load pulling is vastly simpler than S-parameters (also specified in
the data sheets for this device, down to 1MHz), why you want to marry
the two is a mystery.

A laboratory bench setup is simpler than a calculator and a couple
of sheets of paper? Egads Richard, s-parameter analysis was invented
in order to make things "vastly simpler" - and it does!
--
73, Cecil http://www.qsl.net/w5dxp



S-parameters are supposed to work best on small-signal analysis, where
everything is fairly linear. In this case, the MRF 136 is a power fet and
Motorola
says you can use s-parameters as a first approximation. In the data sheet, they
provide a list
of common source scattering parameters from 2.0 Mhz up to 800 Mhz. I suppose
that's useful to someone familiar with s-parameter techniques.
73,
KA6RUH

Wes wrote,

On Sun, 23 May 2004 21:19:23 GMT, Richard Clark
wrote:

[snip

|in a class A configuration (showing
|about 60% efficiency).

Huh?


The data sheet doesn't say it gets 60% efficiency in a class A
configuration. It just says, under one bullet, that "Efficiency = 60%."
Further down the column it says, "Ideally Suited For Class A
Operation."
73,
Tom Donaly, KA6RUH

Tdonaly wrote:
S-parameters are supposed to work best on small-signal analysis, where
everything is fairly linear.

Therefore, should work well on transmission-line analysis, where
everything is linear.
--
73, Cecil http://www.qsl.net/w5dxp



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On 24 May 2004 00:04:50 GMT, (Tdonaly) wrote:

Wes wrote,

On Sun, 23 May 2004 21:19:23 GMT, Richard Clark
wrote:

[snip

|in a class A configuration (showing
|about 60% efficiency).

Huh?


The data sheet doesn't say it gets 60% efficiency in a class A
configuration. It just says, under one bullet, that "Efficiency = 60%."
Further down the column it says, "Ideally Suited For Class A
Operation."
73,
Tom Donaly, KA6RUH


Hi Guys,

I trust both of you appreciate the difference between a vaguely
described system and trying to fit a spec sheet to it. Far easier to
proceed direct from one or the other, but making a fit between the two
is like stepping from one boat to another with a high chance of
standing on neither.

73's
Richard Clark, KB7QHC

On 23 May 2004 23:50:02 GMT, (Tdonaly) wrote:

S-parameters are supposed to work best on small-signal analysis, where
everything is fairly linear.

Hi All,

Tom's implication (S-parameters don't fit to power amps) is supported
by a simple comparison of another UHF transistor, 2N3948:
by S-param as measured
input R 9 Ohms 38 Ohms
input X 12nH 21pF
output R 199 Ohms 92 Ohms
output X 4.6pF 5pF

S-params may be useful for comparing devices, but are inadequate for
power application design - unless, of course, you can tolerate 400%
error and inverted reactances.

73's
Richard Clark, KB7QHC