On Tue, 07 Oct 2003 14:25:26 -0500, Cecil Moore
wrote:
Shorting out the coil will leave the load at 50-j442 ohms, a very high SWR.

Hi Cecil,

That's the point....

73's
Richard Clark, KB7QHC

"Cecil Moore" wrote in message
...
Tarmo Tammaru wrote:
Very interesting. Can you take one more reading. Leave the meter between
the
coil and cap, and then short out the coil. If shorting out the coil
makes
any difference, you are seeing the imperfection due to the meter. This
is
what I was alluding to in my response to Walter.

Shorting out the coil will leave the load at 50-j442 ohms, a very high
SWR.
--
73, Cecil http://www.qsl.net/w5dxp
Hi Cecil,

I think what you did was to force the current to be in phase with the
voltage and fooled the meter into thinking it was all forward power. That is
sort of the experiment I was going to do, but you beat me to it. Note that
in the case where you moved the meter, you actually changed the load, but
you know that.

Tam/WB2TT

Richard Clark wrote:
The long of it: You have merely
demonstrated your own invention of two conjugated reactances and one
resistor - not the same thing at all, not even conceptually.

But it is what Chipman discusses.
--
73, Cecil http://www.qsl.net/w5dxp



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Tarmo Tammaru wrote:
I think what you did was to force the current to be in phase with the
voltage and fooled the meter into thinking it was all forward power. That is
sort of the experiment I was going to do, but you beat me to it. Note that
in the case where you moved the meter, you actually changed the load, but
you know that.

I didn't appreciably change the load on the transmitter. All I did was
change the position of the SWR meter in the serial component chain.
This is essentially what Chipman discusses in his book. Now comes the
big question. Does the same thing happen on a line with reflections
when the impedance looking one direction is 100+j100 ohms and the
impedance looking the other direction is 100-j100 ohms? Is there a
localized energy exchange between that +j100 ohms and that -j100 ohms
that affects the SWR meter?
--
73, Cecil http://www.qsl.net/w5dxp



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On Tue, 07 Oct 2003 20:27:58 -0500, Cecil Moore
wrote:

Richard Clark wrote:
The long of it: You have merely
demonstrated your own invention of two conjugated reactances and one
resistor - not the same thing at all, not even conceptually.

But it is what Chipman discusses.

Hi Cecil,

OK, so you are not up to the issues I am discussing. I'm not
interested in debating the single page you have xeroxed. You asked
for any reference that bore upon the Source Z and I noted it was on
the page facing the first page you xeroxed for other discussion. If
you find some interest in it, that's fine, but you are operating under
a very slim lead of a single citation I offered to answer your
question that covers far more territory. Chipman offers many pages of
discussion (basically an entire chapter that goes unread by his
"disciples" here) describing the action of the Source upon the
system's SWR and that one page you inappropriately treasure as an icon
is hardly the beginning and certainly not the end.

73's
Richard Clark, KB7QHC

However, if you have coax with good dielectric (polyethylene or
Teflon), at HF and below the loss is strongly dominated by the R term.
You can verify through measurements, if you are careful, that G can
be assumed zero unless you've done something to degrade your line's
dielectric. BUT...it's much easier to measure the line's attenuation
directly than to measure (accurately) the impedance's real and
imaginary parts anyway, so why would one try to do it that way?

Cheers,
Tom

(Example: RG174 at f=30MHz will have a bit more than 3.4dB/100 feet
loss because of R, and probably well under .025dB/100 feet loss
because of G. See Roy's suggested reading for the source of those
numbers.)

"David Robbins" wrote in message ...
"Cecil Moore" wrote in message
...
David Robbins wrote:

"Cecil Moore" wrote:
Does (R+jXL)/(G+jXC) really equal 2500 for RG-174 on 12m? The specs
say the Z0 of RG-174 is a nominal 50 ohms.

of course its not exactly 2500, otherwise there would be no loss. but
its
close, maybe 2500+j10 or something like that. and even the resistive
part
may not be exact, the nominal 50 ohms could be 45 to 55 depending on the
tolerances of the manufacturer.

Comparing the 6dB loss of RG-174 to the 0.14 dB loss for hardline -
is all that extra loss accounted for in the +j10 term?

no, its more complicated than that.

the attenuation constant (usually alpha) = Re(gamma) where gamma is
sqrt((R+jwL)(G+jwC)) Zo is sqrt((R+jwL)/(G+jwC)) so there is not a simple
way to relate the characterisitic impedance to loss. for a low loss line
the approximation for alpha is (R/2Zo)+(GZo/2) which can probalby be applied
for most normal cases, but again, you have to get the R and G values of the
line which can not be directly calculated from Zo.

Cecil,

You changed the load the SWR meter saw. In the first instance it was 50
Ohms. Then you changed it to 50 - j442. I think what you want to calculate
is the phase of the current flowing through the SWR meter relative to the
phase of the voltage. I wonder if anybody on this newsgroup has a contact at
Bird who could shed additional light on this.

Tam/WB2TT
"Cecil Moore" wrote in message
...
Tarmo Tammaru wrote:
I think what you did was to force the current to be in phase with the
voltage and fooled the meter into thinking it was all forward power.
That is
sort of the experiment I was going to do, but you beat me to it. Note
that
in the case where you moved the meter, you actually changed the load,
but
you know that.

I didn't appreciably change the load on the transmitter. All I did was
change the position of the SWR meter in the serial component chain.
This is essentially what Chipman discusses in his book. Now comes the
big question. Does the same thing happen on a line with reflections
when the impedance looking one direction is 100+j100 ohms and the
impedance looking the other direction is 100-j100 ohms? Is there a
localized energy exchange between that +j100 ohms and that -j100 ohms
that affects the SWR meter?
--
73, Cecil http://www.qsl.net/w5dxp



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Tarmo Tammaru wrote:
You changed the load the SWR meter saw.

Exactly! Now the question is: In a conjugately matched system where
100+j100 is seen looking back toward the source and 100-j100 is seen
looking toward the load, have we "changed the load the SWR meter sees"
by installing it at a 100 +/- j100 point?
--
73, Cecil http://www.qsl.net/w5dxp



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I guess I'm not surprised by the 150W fwd power reading, but there
should be a correspondingly large ref power and a high SWR, if the
meter is accurate. Assuming a perfect 50-j442 load and a meter
calibrated perfectly to 50 ohms and perfectly accurate, I'd expect to
see 102.7W going out and 97.7W coming back. But I also do NOT expect
a typical meter to read very accurately at high SWR.

Another thing to remember: the meter will disturb the resonance
significantly, when inserted between the cap and coil. The capacitor
is only about 50pF, and the meter is likely going to look like more
than 5pF at that high impedance point between the inductor and
capacitor. It's easy enough to look at in RFSim99, for example. When
you move the SWR meter, the load on the transmitter does NOT stay the
same! I simulated the meter as 7cm of 50 ohm air-dielectric line, and
the return loss seen at the transmitter (at 7.2MHz) went from very
high (theoretically infinite) without the line/meter inserted, to only
8.14dB (~2.3:1 SWR) with the line/meter between the coil and cap.

It's important to understand the limitations of your test equipment,
and also to realize how that equipment may affect operating conditions
of the circuit.

(Tam: my recommendation is to do the test yourself. It will be a lot
easier to play with "what-ifs" and to check out things that don't at
first make sense if you have direct control of the experiment.)

Cheers,
Tom

"Tarmo Tammaru" wrote in message ...
Cecil,

You changed the load the SWR meter saw. In the first instance it was 50
Ohms. Then you changed it to 50 - j442. I think what you want to calculate
is the phase of the current flowing through the SWR meter relative to the
phase of the voltage. I wonder if anybody on this newsgroup has a contact at
Bird who could shed additional light on this.

Tam/WB2TT
"Cecil Moore" wrote in message
...
Tarmo Tammaru wrote:
I think what you did was to force the current to be in phase with the
voltage and fooled the meter into thinking it was all forward power.
That is
sort of the experiment I was going to do, but you beat me to it. Note
that
in the case where you moved the meter, you actually changed the load,
but
you know that.

I didn't appreciably change the load on the transmitter. All I did was
change the position of the SWR meter in the serial component chain.
This is essentially what Chipman discusses in his book. Now comes the
big question. Does the same thing happen on a line with reflections
when the impedance looking one direction is 100+j100 ohms and the
impedance looking the other direction is 100-j100 ohms? Is there a
localized energy exchange between that +j100 ohms and that -j100 ohms
that affects the SWR meter?
--
73, Cecil http://www.qsl.net/w5dxp



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"Tom Bruhns" wrote in message
m...

(Tam: my recommendation is to do the test yourself. It will be a lot
easier to play with "what-ifs" and to check out things that don't at
first make sense if you have direct control of the experiment.)

Cheers,
Tom
Tom,

I read you, but first I have to paint the kitchen. I was going to use 50
+/& -j50. I also want to get inside the meter and look at the voltage and
current separately. It's a Kenwood, no sealed slugs. Good point about the
meter changing the reactance; 160 m might be a good place to do this, or I
might use a variable capacitor.


Tam/WB2TT