"dykesc" wrote in message
...
On Jun 4, 2:10 am, Ian Wade G3NRW wrote:

Is this any help?

http://www.wy2u.com/

Scroll down to "Electrical / Electronic Engineering Links" and click on
"L/C Impedance Matching Design Tool"

--
73
Ian, G3NRW

Thanks Ian. That is the type of calculator I am looking for. However,
this one requires both source and load impedance as input. I am
looking for one that will allow you to specify the source impedance
(50+j0), fill in the capacitor and inductor values, and then tell you
what the matched load side impedance is.

Hi dykesc

I may be missing something. But, if the objective it to learn if the
local 105 MHz signal is actually introducing error into your impedance
measurement, only a few Smith Chart Polts are needed. You know the path (on
the Chart) the shunt reactance will have taken while being adjusted to make
a "match". You also know the path the series reactance took. Start from
the Chart center and move the impedance along the circles of constant
resistance for the series reactor. Move along the circles of constant
admittance for the shunt reactance. When the Xc and Xl are both known, and
you know which is closest to the "transmitter", it seems that a "program" is
unnecessary. What am I mising?

Jerry KD6JDJ

Jerry wrote:
"dykesc" wrote in message
...
On Jun 4, 2:10 am, Ian Wade G3NRW wrote:

Is this any help?

http://www.wy2u.com/

Scroll down to "Electrical / Electronic Engineering Links" and click on
"L/C Impedance Matching Design Tool"

--
73
Ian, G3NRW

Thanks Ian. That is the type of calculator I am looking for. However,
this one requires both source and load impedance as input. I am
looking for one that will allow you to specify the source impedance
(50+j0), fill in the capacitor and inductor values, and then tell you
what the matched load side impedance is.

Hi dykesc

I may be missing something. But, if the objective it to learn if the
local 105 MHz signal is actually introducing error into your impedance
measurement, only a few Smith Chart Polts are needed. You know the path (on
the Chart) the shunt reactance will have taken while being adjusted to make
a "match". You also know the path the series reactance took. Start from
the Chart center and move the impedance along the circles of constant
resistance for the series reactor. Move along the circles of constant
admittance for the shunt reactance. When the Xc and Xl are both known, and
you know which is closest to the "transmitter", it seems that a "program" is
unnecessary. What am I mising?


Fine, for doing a couple or three. Now do it for a dozen measurements
at different frequencies, especially if you have to convert L and C into
Z for each measurement. A program or spreadsheet is nice to have,
because it automates the tedious calculation.

Heck, if you have a RS-232 interface to the antenna tuner, you can
automate the whole process. Quod fecit.

By the way, the assumption that the run of the mill ham rig has a 50 ohm
resistive output impedance is not necessarily valid. In practice,
nobody cares.. they just adjust until the reflected power is minimized.
But if you're trying to use the tuner as a measuring instrument
(essentially, the variable part of an impedance bridge), it's important.

On Thu, 04 Jun 2009 11:47:31 -0700, Jim Lux
wrote:

By the way, the assumption that the run of the mill ham rig has a 50 ohm
resistive output impedance is not necessarily valid.

By the way, this comment above is another assumption in that it lacks
a quantifiable. I find it offered quite often as a negative assertion
to which the several many posters who offer them never provide an
actual value to prove what the run of the mill ham rig is, much less
is "not." Rarer, indeed, is any effort put forward by those posters
to show they have attempted to quantify their own equipment.

As there are posters here who have performed this work, shown their
data, and such data follows conventional design considerations (which
is easily revealed within the page cited at http://www.wy2u.com/);
then these assumptions dressed in denial are rather unprofound proofs.
As this topic has been visited many times, and as it quickly descends
into equally unsupported claims (although often annotated with vague
references and citations that are quickly demolished); I doubt
anything said here is going to sway those assumptions.

As an amusing exercise (I anticipate none will tread down this path),
the page at http://www.wy2u.com/ offers a means to test your own rig's
Source Z - if, in fact, you can cope with translating your tuner's
settings into picofarads and nanohenries, and if you can obtain a
known mismatch. These impediments are Herculean to most,
unfortunately.

73's
Richard Clark, KB7QHC

"Jim Lux" wrote in message
...
Jerry wrote:
"dykesc" wrote in message
...
On Jun 4, 2:10 am, Ian Wade G3NRW wrote:

Is this any help?

http://www.wy2u.com/

Scroll down to "Electrical / Electronic Engineering Links" and click on
"L/C Impedance Matching Design Tool"

--
73
Ian, G3NRW

Thanks Ian. That is the type of calculator I am looking for. However,
this one requires both source and load impedance as input. I am
looking for one that will allow you to specify the source impedance
(50+j0), fill in the capacitor and inductor values, and then tell you
what the matched load side impedance is.

Hi dykesc

I may be missing something. But, if the objective it to learn if the
local 105 MHz signal is actually introducing error into your impedance
measurement, only a few Smith Chart Polts are needed. You know the path
(on the Chart) the shunt reactance will have taken while being adjusted
to make a "match". You also know the path the series reactance took.
Start from the Chart center and move the impedance along the circles of
constant resistance for the series reactor. Move along the circles of
constant admittance for the shunt reactance. When the Xc and Xl are
both known, and you know which is closest to the "transmitter", it seems
that a "program" is unnecessary. What am I mising?


Fine, for doing a couple or three. Now do it for a dozen measurements at
different frequencies, especially if you have to convert L and C into Z
for each measurement. A program or spreadsheet is nice to have, because it
automates the tedious calculation.

Heck, if you have a RS-232 interface to the antenna tuner, you can
automate the whole process. Quod fecit.

By the way, the assumption that the run of the mill ham rig has a 50 ohm
resistive output impedance is not necessarily valid. In practice, nobody
cares.. they just adjust until the reflected power is minimized. But if
you're trying to use the tuner as a measuring instrument (essentially, the
variable part of an impedance bridge), it's important.

Hi Jim

As you can see, this plan to 'double check" antenna impedance by relating
the impedance to that which the tuner produces, is very limited in its
accuracy. One might say *why bother*. My thought was/is, the original
poster asked for an online calculator. When that calculator was given, and
he still asked for more, I thought it would be helpful to point out how easy
it is to use the Smith Chart to get some insight into evaluating his
impedance meter. It is my opinion that extensive calculations with a
computer program are not able to provide any exact answer to the question
about actual antenna impedance when only the tuner Xl and Xc are known. The
Smith Chart is a great tool for estimating how impedance matching can be
realized. I assummed that the OP could possibly benefit from knowing how
easy it is to estimate antenna impedance using the Smith Chart if it can be
assummed that the LC circuit is known and that the resultant impedance is 50
ohms. Shunt reactances move the impedance along the circles of constant
1/R and series reactances along the circles of constant R.

Jerry KD6JDJ

On Jun 4, 12:29*pm, "Jerry" wrote:

* I may be missing something. *But, if the objective it to learn if the
local 105 MHz signal is actually introducing error into your impedance
measurement, only a few Smith Chart Polts are needed. *You know the path (on
the Chart) the shunt reactance will have taken while being adjusted to make
a "match". * You also know the path the series reactance took. * Start from
the Chart center and move the impedance along the circles of constant
resistance for the series reactor. *Move along the circles of constant
admittance for the shunt reactance. * When the Xc and Xl are both known, and
you know which is closest to the "transmitter", it seems that a "program" is
unnecessary. *What am I mising?

* * * * * * * *Jerry * KD6JDJ

Thanks Jerry. No you aren't missing anything other than the fact that
my familiarity with Smith Chart analysis is limited to working through
a few exercises in the last chapter of the ARRL Antenna book. I will
be looking for more Smith Chart tutorial info on the web and am
certain I can get myself up to speed enough to start working with
conductance, suseptance, admittance, etc.

Thanks again. From your post it appears it will be a straight forward
exercise once I get my head around it.

73
Dykes AD5VS

"dykesc" wrote in message
...
On Jun 4, 12:29 pm, "Jerry" wrote:

I may be missing something. But, if the objective it to learn if the
local 105 MHz signal is actually introducing error into your impedance
measurement, only a few Smith Chart Polts are needed. You know the path
(on
the Chart) the shunt reactance will have taken while being adjusted to
make
a "match". You also know the path the series reactance took. Start from
the Chart center and move the impedance along the circles of constant
resistance for the series reactor. Move along the circles of constant
admittance for the shunt reactance. When the Xc and Xl are both known, and
you know which is closest to the "transmitter", it seems that a "program"
is
unnecessary. What am I mising?

Jerry KD6JDJ

Thanks Jerry. No you aren't missing anything other than the fact that
my familiarity with Smith Chart analysis is limited to working through
a few exercises in the last chapter of the ARRL Antenna book. I will
be looking for more Smith Chart tutorial info on the web and am
certain I can get myself up to speed enough to start working with
conductance, suseptance, admittance, etc.

Thanks again. From your post it appears it will be a straight forward
exercise once I get my head around it.

73
Dykes AD5VS

Hi Dykes

As you may already know, the Smith Chart is simply a plot that shows *all*
impedances with a real resistance. Smith displays the impedances so the
user can quickly see how any given impedance can be adjusted by adding any
series or parallel resistances and/or reactances. Series inductance moves
the impedance "upward" along the circles of constant Resistance. Shunt
inductance will move an impedance along the circles of constant conductance.

Jerry KD6JDJ

dykesc wrote in news:0dec42e0-48ab-44f0-8c1a-
:

....
this one requires both source and load impedance as input. I am
looking for one that will allow you to specify the source impedance
(50+j0), fill in the capacitor and inductor values, and then tell you
what the matched load side impedance is.

You want to specify the ATU input impedance which is independent of the
source, not the source impedance (which you don't know or care about).
Hams often confuse the source impedance of a transmitter and its required
load impedance.

Do you intend treating the ATU as a simple two or three component network
using ideal components (no loss, no stray capacitance)? Will that
approach give accuracy either adequate or comparable with the many other
techniques used?

I have thought about this in the past, mainly the prospect of a relay
switched autotuner that reported a calculated load Z based on the found
matching solution, but I concluded that it was not likely to be of
reasonable accuracy over the tuner range.

If you want to measure Z using an instrument based on a broadband
detector, you need to use sufficient power that the broadband detector is
dominated by the test signal. There is at least one instrument for the
ham market that purports to make such measurements at normal transmitter
power. IIRC, R&S used make a commercial product, but it wouldn't have
come cheap.

There is at least one other low level antenna analyser that represents
that it is less affected by interference than the '259B.

If I were looking for an instrument, I would desire one that could refer
the measurements to a point closer to the antenna (eg the feedpoint)
given the characteristics of the transmission line between the
measurement point and the desired reference plane.

VNAs will peform this calculation, but most low cost VNAs use a broadband
detector and low power, so they are susceptible to interference when used
on antenna systems.

Owen

On Thu, 04 Jun 2009 21:33:41 GMT, Owen Duffy wrote:

Hams often confuse the source impedance of a transmitter and its required
load impedance.

sigh....

On Jun 4, 4:33*pm, Owen Duffy wrote:

I have thought about this in the past, mainly the prospect of a relay
switched autotuner that reported a calculated load Z based on the found
matching solution, but I concluded that it was not likely to be of
reasonable accuracy over the tuner range.

Probably would be as accurate as any other gear we can afford Owen.
I'm going to suggest that MFJ make that a feature on an auto tuner. I
don't live to far from their headquarters in Starkville, MS. I have a
son going to Mississipi State there and have never been to their
facility. This will make a good topic of conversation.


There is at least one instrument for the
ham market that purports to make such measurements at normal transmitter
power. IIRC, R&S used make a commercial product, but it wouldn't have
come cheap.

I looked on the R&S site. The only thing I found was a "Field Fox"
analyzer selling for $7,599.00. It is the cat's meow, but guess I'll
have to stick with my 259B.


There is at least one other low level antenna analyser that represents
that it is less affected by interference than the '259B.

Which one Owen.

If I were looking for an instrument, I would desire one that could refer
the measurements to a point closer to the antenna (eg the feedpoint)
given the characteristics of the transmission line between the
measurement point and the desired reference plane.

Now that would be a great feature. Input your line type and physical
length and the analyzer does the transform. Lots of programs available
on the web for that, but would be nice to have at your fingertips.

VNAs will peform this calculation, but most low cost VNAs use a broadband
detector and low power, so they are susceptible to interference when used
on antenna systems.

That has become very obvious to me.

"dykesc" wrote in message
...
On Jun 4, 4:33 pm, Owen Duffy wrote:

I have thought about this in the past, mainly the prospect of a relay
switched autotuner that reported a calculated load Z based on the found
matching solution, but I concluded that it was not likely to be of
reasonable accuracy over the tuner range.

Probably would be as accurate as any other gear we can afford Owen.
I'm going to suggest that MFJ make that a feature on an auto tuner. I
don't live to far from their headquarters in Starkville, MS. I have a
son going to Mississipi State there and have never been to their
facility. This will make a good topic of conversation.

Unless they can find someone elses to copy, it won't happen.

Dale W4OP