On Sat, 04 Dec 2004 18:40:20 GMT, Richard Clark
wrote:

On Sat, 04 Dec 2004 05:24:33 GMT, (Robert Lay
W9DMK) wrote:

Just today, I made a careful measurement on an RG-8/U line of 5.33
meters length at 30 MHz and terminated with a 4700 + j 0 load. The
Matched Line Loss of that line at 30 MHz is 0.9 dB per 100 feet, and
its Velocity Factor is between 0.75 and 0.80 The input impedance was
actually measured at 2.45 -j15 ohms for an SWR at the input of 22.25.
The SWR at the load end was 94. Those two SWR's establish a total loss
on the line of 0.15 dB. If one were to blindly apply the formula in
The Antenna Book on page 24-9, the result obtained would be 4.323 dB.

Surprisingly, it was not until today that I finally made a computation
of the input power to the line for the configuration above.
Specifically, I was able to compute the voltage and current at the
input to the line that would produce a 100 volt reference voltage
across the 4700 ohm line. That is the obvious thing that had to be
done in order to establish a reference power for purposes of computing
losses. That calculation resulted in an applied voltage at the line
input of 29.2 volts at angle -171.5 degrees and a current of 1.917
amps at -90.78 degrees. Computing power into the line as E*Icos(theta)
= 9.024 watts. The power delivered to the load is 100 volts squared
divided by 4700 ohms, which is 2.127 watts.

Therefore the efficiency is 23.6% and the losses in the line are 6.275
dB. In all fairness, I did have to change one assumption in the data
above. I had to revise my attenuation value of 0.9 dB per 100 ft.
upwards to a value of 1.72 dB per 100 ft. in order to get my measured
impedance at the line input to be consistent with that line impedance,
length, load value and velocity factor.

Hi Bob,

I notice that true to form, all the response in this thread were not
to your bench results. I trust you will appreciate hard
correspondence rather than the fluff.

The one thing (actually there are several) I noted was your having to
double the presumed line loss to make the numbers come out. Given
this injection (or removal) of 100% (or %50) of error, it stands to
reason that your bench, method or instruments need a attention.

The details as I've sifted from the postings:
Cable type = Columbia's number 1198 - not 9913.
Open circuit stub length = 5.334 meters
Frequency = 10.6 MHz,
Input Z = 0.57 + j 0.3 ohms.

The above details appear to have shifted in mid-stream to:
Cable type = RG-8/U line
stub length = 5.334 meters
Frequency = 30.0 MHz,
Open end termination = 4700 + j 0
Input Z = 2.45 -j15

I will skip the determinations of loss and SWR as being problematic as
you indicate and simply go with your observations noted above, and
summarized he
Open end Vtermination = 100V @ 0°
Open end Itermination = 0.0213A @ 0°
Fed end Vinput = 29.2V @ -171.5°
Fed end Iinput = 1.917A @ -90.78°

I was puzzled to see what was initially a resonant stub now measured
with an extremely high Reactance until I re-scanned the material to
note the tripling of frequency.

What caught my eye was this load and certainly your leap of faith that
it was wholly resistive, especially at HF for its size. This would be
extremely unlikely even in a standards lab.

To make a measurement, the rule of thumb is to have instrumentation
whose precision and accuracy exceeds the goal of measuring an unknown
by 5 to 10 times. For really difficult tests (and RF is classic in
that regard) 3 times is often the best you can achieve.

Let's look at that 4700 Ohm resistance. It demands that any
instrumentation support a paralleling load of no less than 23.5K Ohms
to 47K Ohms, or worst case, 14K Ohms. Let's simply ask about the
family lineage of that 4700 Ohm resistance. It sounds suspiciously
like a common (hopefully) carbon composition resistor.

If so, such beasties are rare if it is of the commercial variety, to
not exhibit reactances due to spiral cut value trimming, or an
end-to-end capacitance. Let's just say that you obtained a remarkable
resistor, but it cannot escape this common parasitic capacitance which
for the garden variety resistor amounts to 1.5pF.

At 30 MHz, this 1.5pF capacitance represents a reactance of 3.5K Ohm.
This rather sweeps aside your specification for the load and replaces
it with 4700 -j3537 Ohms. This is a big time source of error and does
not even come close to the 3X requirement for the lowest accuracy.
Worse yet, you haven't even added the bridging impedance of your
measuring device which is certain to be on par, if not worse (you
haven't identified your instrumentation).

Hope you are still looking forward to more fun. ;-)

73's
Richard Clark, KB7QHC

Dear Richard,

New Measurements -

I created a terminating load consisting of 4 composition resistors in
parallel. That measured 4.3 + j0.65 AT 20 MHz. I then measured the
input impedance of the 5.33 meter length of RG-8/U Foam coax
terminated with the 4.3 +j0.65 ohm load at 20 MHz, and that was 5 -
j7.1 ohms. The SWR at the load is 11.63 and the SWR at the input is
9.88.

Using a velocity factor of 0.745 and an attenuation value of .77, I
calculated the theoretical input impedance of the coax with the above
terminator. That gave a result of 5.17 - j7.3 ohms (theoretical). The
SWR at the load is 11.63, and the SWR at the input to the line is 9.88
(theoretical).

In setting up the simulation, it is necessary to pick an attenuation
and a velocity factor that are not only within the normal distribution
for that particular coax but also give a reasonably good match with
the measured values. In my opinion, the values that I used in the
simulation are well within the normal distribution of values for this
type of line, which has published values of VF=.8 and attenuation =
74 at 20 MHz.

The simulation also predicts the losses, and I used two different
models for that calculation. Both loss models predict a total loss of
0.723 dB, which is 0.589 above the matched line losses based on the
normal attenuation. The two math models used were as follows:

1) ITT Reference Data for Radio Engineers, 5th Edition, pages 22-8 and
22-9.

2) The ARRL Antenna Book, 17th Edition, page 24-9.

Based on the limited tests that I have made so far, the two models
seem to give the same results. However, I am hoping to be able to
conduct measurements on configurations that involve much higher SWR
values. The immediate problem to be overcome is the measurement of
such impedance values as will be encountered.
Bob, W9DMK, Dahlgren, VA
http://www.qsl.net/w9dmk

On Sun, 05 Dec 2004 22:51:03 GMT, (Robert Lay
W9DMK) wrote:

New Measurements -

I created a terminating load consisting of 4 composition resistors in
parallel. That measured 4.3 + j0.65 AT 20 MHz.

I threw together two Allen Bradley 10 Ohm 5% 1/4 Watt resistors and
came up with 5.1 -j0.5 in a quick test at 20 MHz.

I then measured the
input impedance of the 5.33 meter length of RG-8/U Foam coax
terminated with the 4.3 +j0.65 ohm load at 20 MHz, and that was 5 -
j7.1 ohms. The SWR at the load is 11.63 and the SWR at the input is
9.88.

Using a velocity factor of 0.745 and an attenuation value of .77, I
calculated the theoretical input impedance of the coax with the above
terminator. That gave a result of 5.17 - j7.3 ohms (theoretical). The
SWR at the load is 11.63, and the SWR at the input to the line is 9.88
(theoretical).

In setting up the simulation, it is necessary to pick an attenuation
and a velocity factor that are not only within the normal distribution
for that particular coax but also give a reasonably good match with
the measured values. In my opinion, the values that I used in the
simulation are well within the normal distribution of values for this
type of line, which has published values of VF=.8 and attenuation =
74 at 20 MHz.

Hi Bob,

I would say that your data shows a very good correlation to the models
and certainly the presumptions you made are well within the production
variables.

The simulation also predicts the losses, and I used two different
models for that calculation. Both loss models predict a total loss of
0.723 dB, which is 0.589 above the matched line losses based on the
normal attenuation. The two math models used were as follows:

1) ITT Reference Data for Radio Engineers, 5th Edition, pages 22-8 and
22-9.

2) The ARRL Antenna Book, 17th Edition, page 24-9.

Based on the limited tests that I have made so far, the two models
seem to give the same results. However, I am hoping to be able to
conduct measurements on configurations that involve much higher SWR
values. The immediate problem to be overcome is the measurement of
such impedance values as will be encountered.

Measure Q by the BW of the Half Power points.

73's
Richard Clark, KB7QHC

On Mon, 06 Dec 2004 01:05:54 GMT, Richard Clark
wrote:

On Sun, 05 Dec 2004 22:51:03 GMT, (Robert Lay
W9DMK) wrote:

New Measurements -

I created a terminating load consisting of 4 composition resistors in
parallel. That measured 4.3 + j0.65 AT 20 MHz.

I threw together two Allen Bradley 10 Ohm 5% 1/4 Watt resistors and
came up with 5.1 -j0.5 in a quick test at 20 MHz.

I then measured the
input impedance of the 5.33 meter length of RG-8/U Foam coax
terminated with the 4.3 +j0.65 ohm load at 20 MHz, and that was 5 -
j7.1 ohms. The SWR at the load is 11.63 and the SWR at the input is
9.88.

Using a velocity factor of 0.745 and an attenuation value of .77, I
calculated the theoretical input impedance of the coax with the above
terminator. That gave a result of 5.17 - j7.3 ohms (theoretical). The
SWR at the load is 11.63, and the SWR at the input to the line is 9.88
(theoretical).

In setting up the simulation, it is necessary to pick an attenuation
and a velocity factor that are not only within the normal distribution
for that particular coax but also give a reasonably good match with
the measured values. In my opinion, the values that I used in the
simulation are well within the normal distribution of values for this
type of line, which has published values of VF=.8 and attenuation =
74 at 20 MHz.

Hi Bob,

I would say that your data shows a very good correlation to the models
and certainly the presumptions you made are well within the production
variables.

The simulation also predicts the losses, and I used two different
models for that calculation. Both loss models predict a total loss of
0.723 dB, which is 0.589 above the matched line losses based on the
normal attenuation. The two math models used were as follows:

1) ITT Reference Data for Radio Engineers, 5th Edition, pages 22-8 and
22-9.

2) The ARRL Antenna Book, 17th Edition, page 24-9.

Based on the limited tests that I have made so far, the two models
seem to give the same results. However, I am hoping to be able to
conduct measurements on configurations that involve much higher SWR
values. The immediate problem to be overcome is the measurement of
such impedance values as will be encountered.

Measure Q by the BW of the Half Power points.

73's
Richard Clark, KB7QHC

Dear Richard,

I finally created a test load that gives me the higher SWR that I
wanted.
It measures 7.0 - j2008 at 1.8 MHz. I placed that test load at the end
of a 150 foot piece of RG-59/U and measured the input impedance as
38.5 + j 151.6 at 1.8 MHz. The load SWR is 7901 and the input SWR is
10.18.

Solution of the transmission line equations for this particular load
and with coax characteristics of 73 ohms, VF = .646 and an attenuation
of 0.57 dB per 100 feet gives an input impedance of 38.67 + j 149,
which is a very good match to the measured value.

Losses are calculated using the same two methods as reported in my
previous posting, as follows:
1) ITT Reference Data for Radio Engineers, 5th Edition, pages 22-8 and
22-9.

2) The ARRL Antenna Book, 17 th Edition, page 24-9.


Matched line losses = 0.855 dB
Additional losses = 28.087 dB
Total losses = 28.942 dB

I am satisfied that the methods of calculating losses as described in
the two references are in agreement and are valid.

I am also reasonably satisfied that the 1 dB steps that are printed on
Smith Charts as the means of determining matched line losses are
valid, as are the nomograms provided in the ITT Handbook, pages 22-7
and 22-8, above.

73,
Bob, W9DMK, Dahlgren, VA
http://www.qsl.net/w9dmk

On Mon, 06 Dec 2004 18:03:47 GMT, (Robert Lay
W9DMK) wrote:

I finally created a test load that gives me the higher SWR that I
wanted.
It measures 7.0 - j2008 at 1.8 MHz. I placed that test load at the end
of a 150 foot piece of RG-59/U and measured the input impedance as
38.5 + j 151.6 at 1.8 MHz. The load SWR is 7901 and the input SWR is
10.18.

Solution of the transmission line equations for this particular load
and with coax characteristics of 73 ohms, VF = .646 and an attenuation
of 0.57 dB per 100 feet gives an input impedance of 38.67 + j 149,
which is a very good match to the measured value.

Losses are calculated using the same two methods as reported in my
previous posting, as follows:
1) ITT Reference Data for Radio Engineers, 5th Edition, pages 22-8 and
22-9.

2) The ARRL Antenna Book, 17 th Edition, page 24-9.


Matched line losses = 0.855 dB
Additional losses = 28.087 dB
Total losses = 28.942 dB

I am satisfied that the methods of calculating losses as described in
the two references are in agreement and are valid.

I am also reasonably satisfied that the 1 dB steps that are printed on
Smith Charts as the means of determining matched line losses are
valid, as are the nomograms provided in the ITT Handbook, pages 22-7
and 22-8, above.

Hi Bob,

Congratulations are in order for your effort at the bench, regardless
of outcome.

Congratulations are in order for your chain of reasoning, your
attention to detail, and the obvious refinement of technique that is
now agreeing not only with references, but is also consistent from one
test to the next.

I still see some aberration in the data when you have to drive the
cable Z to 73 Ohms to make the formulas work. It shows that the
generality of the references is good, but with the instance of your
data is a forced conclusion. I don't find that particularly upsetting
as the accumulation of error could easily account for some of the
differences.

You might want to revisit some of Bart's offerings in this thread;
especially his discussion of the effect of Low-R loads as a source of
Hi-Z, Hi-SWR.

73's
Richard Clark, KB7QHC

On Mon, 06 Dec 2004 19:57:34 GMT, Richard Clark
wrote:

On Mon, 06 Dec 2004 18:03:47 GMT, (Robert Lay
W9DMK) wrote:

I finally created a test load that gives me the higher SWR that I
wanted.
It measures 7.0 - j2008 at 1.8 MHz. I placed that test load at the end
of a 150 foot piece of RG-59/U and measured the input impedance as
38.5 + j 151.6 at 1.8 MHz. The load SWR is 7901 and the input SWR is
10.18.

Solution of the transmission line equations for this particular load
and with coax characteristics of 73 ohms, VF = .646 and an attenuation
of 0.57 dB per 100 feet gives an input impedance of 38.67 + j 149,
which is a very good match to the measured value.

Losses are calculated using the same two methods as reported in my
previous posting, as follows:
1) ITT Reference Data for Radio Engineers, 5th Edition, pages 22-8 and
22-9.

2) The ARRL Antenna Book, 17 th Edition, page 24-9.


Matched line losses = 0.855 dB
Additional losses = 28.087 dB
Total losses = 28.942 dB

I am satisfied that the methods of calculating losses as described in
the two references are in agreement and are valid.

I am also reasonably satisfied that the 1 dB steps that are printed on
Smith Charts as the means of determining matched line losses are
valid, as are the nomograms provided in the ITT Handbook, pages 22-7
and 22-8, above.

Hi Bob,

Congratulations are in order for your effort at the bench, regardless
of outcome.

Congratulations are in order for your chain of reasoning, your
attention to detail, and the obvious refinement of technique that is
now agreeing not only with references, but is also consistent from one
test to the next.

I still see some aberration in the data when you have to drive the
cable Z to 73 Ohms to make the formulas work. It shows that the
generality of the references is good, but with the instance of your
data is a forced conclusion. I don't find that particularly upsetting
as the accumulation of error could easily account for some of the
differences.

You might want to revisit some of Bart's offerings in this thread;
especially his discussion of the effect of Low-R loads as a source of
Hi-Z, Hi-SWR.

73's
Richard Clark, KB7QHC

Dear Richard,

No - I didn't. That was a surprise to me, too! The specs on RG-59/U
say 73 ohms. There are 2 other RG-59 types - RG-59 Foam (75 ohms) and
RG-59A, also 73 ohms.

C'est la Guerre!

73,

Bob, W9DMK, Dahlgren, VA
http://www.qsl.net/w9dmk

On Mon, 06 Dec 2004 22:25:03 GMT, (Robert Lay
W9DMK) wrote:

No - I didn't. That was a surprise to me, too! The specs on RG-59/U
say 73 ohms. There are 2 other RG-59 types - RG-59 Foam (75 ohms) and
RG-59A, also 73 ohms.

Hi Bob,

You are, in the expression common here in the NW, whipsawing me with
your changes in cable type. I failed to catch that in your post.

Given you are using 73 Ohm line, your results are very remarkable.
I'm glad you've gone the distance. This group, however, exhibits a
very odd ethic that I would call the reverse Little Red Hen story.

Through more than 150 postings they all want to offer advice on how to
cut the grain; they will tell you where to mill it into flour; they
will offer you recipes on what to bake; but none seem to be around to
praise the chef or the cake.

73's
Richard Clark, KB7QHC

On Mon, 06 Dec 2004 23:36:13 GMT, Richard Clark
wrote:

On Mon, 06 Dec 2004 22:25:03 GMT, (Robert Lay
W9DMK) wrote:

No - I didn't. That was a surprise to me, too! The specs on RG-59/U
say 73 ohms. There are 2 other RG-59 types - RG-59 Foam (75 ohms) and
RG-59A, also 73 ohms.

Hi Bob,

You are, in the expression common here in the NW, whipsawing me with
your changes in cable type. I failed to catch that in your post.

Given you are using 73 Ohm line, your results are very remarkable.
I'm glad you've gone the distance. This group, however, exhibits a
very odd ethic that I would call the reverse Little Red Hen story.

Through more than 150 postings they all want to offer advice on how to
cut the grain; they will tell you where to mill it into flour; they
will offer you recipes on what to bake; but none seem to be around to
praise the chef or the cake.

73's
Richard Clark, KB7QHC

Dear Richard,

Well, I only came here to share, so I'm not the least disappointed -
as some say, the pleasure is in the doing!

You might have asked why I changed coax.

I didn't feel that it would be as dramatic with only 17.5 ft of line.
So, I went to the barn and looked for the biggest, cleanest roll of
coax hanging on the wall, and that was it - Hi!

Bob, W9DMK, Dahlgren, VA
http://www.qsl.net/w9dmk

On Tue, 07 Dec 2004 00:14:28 GMT, (Robert Lay
W9DMK) wrote:

You might have asked why I changed coax.

I didn't feel that it would be as dramatic with only 17.5 ft of line.
So, I went to the barn and looked for the biggest, cleanest roll of
coax hanging on the wall, and that was it - Hi!

Hi Bob,

I didn't ask why because it was evident from the drama of results.
May as well force the numbers to expose the theory. I tried that with
my own thread when you started this one - it n'er came out as well as
yours. However, your confirmation of the loss does support my thesis,
even if my thread did not.

73's
Richard Clark, KB7QHC

I never did quite get clear about your thesis. Would you mind restating it?

Roy Lewallen, W7EL

Richard Clark wrote:

Hi Bob,

I didn't ask why because it was evident from the drama of results.
May as well force the numbers to expose the theory. I tried that with
my own thread when you started this one - it n'er came out as well as
yours. However, your confirmation of the loss does support my thesis,
even if my thread did not.

73's
Richard Clark, KB7QHC

On Mon, 06 Dec 2004 19:03:47 -0800, Roy Lewallen
wrote:
I never did quite get clear about your thesis. Would you mind restating it?

Source Z matters.