I may be asking for something that doesn't have an answer.

I connected a voltmeter to the R meter of my MFJ259.
I checked a bunch of resistors and recorded the voltages.
Now I have all these voltage readings vs. Resistance and
don't know how to relate them except for a conversion graph.

Is there a math function that relates these voltages to Resistance?

Load Resistance Voltage reading

7.5 ohms 0.0388 volts
15 0.0444 volts
25.5 0.0478 volts
39 0.0577 volts
50 0.0614 volts
100 0.0807 volts
140 0.0891 volts
174 0.0935 volts
221 0.0980 volts
249 0.0100 volts
365 0.0106 volts
498 0.0109 volts

If you can figure this out, I'll reward you with the
SWR chart :-)

Thanks, Mikek

"amdx" wrote in message
...
I may be asking for something that doesn't have an answer.

I connected a voltmeter to the R meter of my MFJ259.
I checked a bunch of resistors and recorded the voltages.
Now I have all these voltage readings vs. Resistance and
don't know how to relate them except for a conversion graph.

Is there a math function that relates these voltages to Resistance?

Load Resistance Voltage reading

7.5 ohms 0.0388 volts
15 0.0444 volts
25.5 0.0478 volts
39 0.0577 volts
50 0.0614 volts
100 0.0807 volts
140 0.0891 volts
174 0.0935 volts
221 0.0980 volts
249 0.0100 volts
365 0.0106 volts
498 0.0109 volts

If you can figure this out, I'll reward you with the
SWR chart :-)

Thanks, Mikek

Simple answer is you are wasting your time.

On Tue, 03 Dec 2013 21:07:35 -0600, amdx wrote:

I may be asking for something that doesn't have an answer.

I connected a voltmeter to the R meter of my MFJ259.
I checked a bunch of resistors and recorded the voltages.
Now I have all these voltage readings vs. Resistance and
don't know how to relate them except for a conversion graph.

Is there a math function that relates these voltages to Resistance?

Load Resistance Voltage reading

7.5 ohms 0.0388 volts
15 0.0444 volts
25.5 0.0478 volts
39 0.0577 volts
50 0.0614 volts
100 0.0807 volts
140 0.0891 volts
174 0.0935 volts
221 0.0980 volts
249 0.0100 volts
365 0.0106 volts
498 0.0109 volts

If you can figure this out, I'll reward you with the
SWR chart :-)

Thanks, Mikek


Ever heard about OHM'S LAW?


w.

On 12/4/2013 3:07 AM, Helmut Wabnig wrote:
On Tue, 03 Dec 2013 21:07:35 -0600, amdx wrote:

I may be asking for something that doesn't have an answer.

I connected a voltmeter to the R meter of my MFJ259.
I checked a bunch of resistors and recorded the voltages.
Now I have all these voltage readings vs. Resistance and
don't know how to relate them except for a conversion graph.

Is there a math function that relates these voltages to Resistance?

Load Resistance Voltage reading

7.5 ohms 0.0388 volts
15 0.0444 volts
25.5 0.0478 volts
39 0.0577 volts
50 0.0614 volts
100 0.0807 volts
140 0.0891 volts
174 0.0935 volts
221 0.0980 volts
249 0.0100 volts
365 0.0106 volts
498 0.0109 volts

If you can figure this out, I'll reward you with the
SWR chart :-)

Thanks, Mikek


Ever heard about OHM'S LAW?


w.


Yes Helmut I have. Obviously you don't have any understanding
of my question or you wouldn't have ask a smart ass question.
An MFJ259 is an antenna analyzer, it has two analog meters on it,
one displays the resistance of the load and the other the SWR.
Both meters have a non linear scale on the faceplate.

One would normally think a 50 ohm resistor would display a ratio
of 2 to 1 when compared to a 100 ohm resistor. As you can see the ratio
is 1.3 to 1. Also a 500 ohm and a 50 ohm resistor have a ratio of 10.
But the voltage ratio is 3.56.
So, do you have any other ideas?
Mikek

On 12/3/2013 10:30 PM, Ralph Mowery wrote:
"amdx" wrote in message
...
I may be asking for something that doesn't have an answer.

I connected a voltmeter to the R meter of my MFJ259.
I checked a bunch of resistors and recorded the voltages.
Now I have all these voltage readings vs. Resistance and
don't know how to relate them except for a conversion graph.

Is there a math function that relates these voltages to Resistance?

Load Resistance Voltage reading

7.5 ohms 0.0388 volts
15 0.0444 volts
25.5 0.0478 volts
39 0.0577 volts
50 0.0614 volts
100 0.0807 volts
140 0.0891 volts
174 0.0935 volts
221 0.0980 volts
249 0.0100 volts
365 0.0106 volts
498 0.0109 volts

If you can figure this out, I'll reward you with the
SWR chart :-)

Thanks, Mikek

Simple answer is you are wasting your time.



Is that because you think MFJ is junk, or because
there is no easy relationship?

*&^%$# noticed I slipped the decimal point on the last few
measurements.
They should read,

7.5 ohms 0.0388 volts
15 0.0444 volts
25.5 0.0478 volts
39 0.0577 volts
50 0.0614 volts
100 0.0807 volts
140 0.0891 volts
174 0.0935 volts
221 0.0980 volts
249 0.1000 volts
365 0.1060 volts
498 0.1090 volts
Sorry, Mikek

On 12/4/2013 4:25 AM, amdx wrote:
On 12/4/2013 3:07 AM, Helmut Wabnig wrote:
On Tue, 03 Dec 2013 21:07:35 -0600, amdx wrote:

I may be asking for something that doesn't have an answer.

I connected a voltmeter to the R meter of my MFJ259.
I checked a bunch of resistors and recorded the voltages.
Now I have all these voltage readings vs. Resistance and
don't know how to relate them except for a conversion graph.

Is there a math function that relates these voltages to Resistance?

Load Resistance Voltage reading

7.5 ohms 0.0388 volts
15 0.0444 volts
25.5 0.0478 volts
39 0.0577 volts
50 0.0614 volts
100 0.0807 volts
140 0.0891 volts
174 0.0935 volts
221 0.0980 volts
249 0.0100 volts
365 0.0106 volts
498 0.0109 volts

If you can figure this out, I'll reward you with the
SWR chart :-)

Thanks, Mikek


Ever heard about OHM'S LAW?


w.


Yes Helmut I have. Obviously you don't have any understanding
of my question or you wouldn't have ask a smart ass question.
An MFJ259 is an antenna analyzer, it has two analog meters on it,
one displays the resistance of the load and the other the SWR.
Both meters have a non linear scale on the faceplate.

One would normally think a 50 ohm resistor would display a ratio
of 2 to 1 when compared to a 100 ohm resistor. As you can see the ratio
is 1.3 to 1. Also a 500 ohm and a 50 ohm resistor have a ratio of 10.
But the voltage ratio is 3.56.
So, do you have any other ideas?
Mikek

I noticed I slipped a decimal point on the last few measuements.


7.5 ohms 0.0388 volts
15 0.0444 volts
25.5 0.0478 volts
39 0.0577 volts
50 0.0614 volts
100 0.0807 volts
140 0.0891 volts
174 0.0935 volts
221 0.0980 volts
249 0.1000 volts
365 0.1060 volts
498 0.1090 volts
The last Ratio I posted as 3.56 to 1 should be 2.8 to 1.

On 12/3/2013 9:07 PM, amdx wrote:
I may be asking for something that doesn't have an answer.

I connected a voltmeter to the R meter of my MFJ259.
I checked a bunch of resistors and recorded the voltages.
Now I have all these voltage readings vs. Resistance and
don't know how to relate them except for a conversion graph.

Is there a math function that relates these voltages to Resistance?

Load Resistance Voltage reading

7.5 ohms 0.0388 volts
15 0.0444 volts
25.5 0.0478 volts
39 0.0577 volts
50 0.0614 volts
100 0.0807 volts
140 0.0891 volts
174 0.0935 volts
221 0.0980 volts
249 0.0100 volts
365 0.0106 volts
498 0.0109 volts

If you can figure this out, I'll reward you with the
SWR chart :-)

Thanks, Mikek


V = 0.0191*ln(R) - 0.0077

You're welcome.

On 12/4/2013 4:50 AM, John S wrote:
On 12/3/2013 9:07 PM, amdx wrote:
I may be asking for something that doesn't have an answer.

I connected a voltmeter to the R meter of my MFJ259.
I checked a bunch of resistors and recorded the voltages.
Now I have all these voltage readings vs. Resistance and
don't know how to relate them except for a conversion graph.

Is there a math function that relates these voltages to Resistance?

Load Resistance Voltage reading

7.5 ohms 0.0388 volts
15 0.0444 volts
25.5 0.0478 volts
39 0.0577 volts
50 0.0614 volts
100 0.0807 volts
140 0.0891 volts
174 0.0935 volts
221 0.0980 volts
249 0.0100 volts
365 0.0106 volts
498 0.0109 volts

If you can figure this out, I'll reward you with the
SWR chart :-)

Thanks, Mikek


V = 0.0191*ln(R) - 0.0077

You're welcome.

If you want it closer to your data, use the 4th order polynomial...

V = -5E-12*R^4 + 6E-09*R^3 - 3E-06*R^2 + 0.0007*R + 0.0334

amdx wrote:
Is that because you think MFJ is junk, or because
there is no easy relationship?



It's a noise bridge. It works by putting a signal into an unknown tuned
circuit and looking for null points. If the antenna is not connected or
totally nonresonant, all of the signal coming out of the oscillator
goes to the meter. If it is totally resonant, it all goes out the antenna.

Before the MFJ, people used wide range noise generators, and receivers
tuned to the frequency you wanted to measure. You tuned the circut
to get a null in the receiver.

The more sophistocated ones had a variable resistance, you could adjust to
compensate for extra inductance or capacitance in the circuit.

How the impedance meter actually works I don't know, but I will hazzard a
guess. If you were to place a meter at the known resistance, you could get
an indication of impedance, possibly voltage, possibly current flow.

So what they do is calibrate the meter so that it reads 50 ohms at the
center, then place a 25 ohm load and read where the meter is. They do this
at several known resistances, and then make a meter scale. It is not a
precision instrument, so the same scale can be reproduced for the entire
production run.

It's only useful in context of the device it is in, and can't be used
for something else. Again a guess, but mine is that it is less than 10%
accurate (i.e. wider than 45ohms to 55 ohms reads 50 ohms).


Geoff.


--
Geoffrey S. Mendelson, N3OWJ/4X1GM/KBUH7245/KBUW5379

On Wed, 04 Dec 2013 04:25:29 -0600, amdx wrote:


Ever heard about OHM'S LAW?


w.


Yes Helmut I have. Obviously you don't have any understanding
of my question or you wouldn't have ask a smart ass question.
An MFJ259 is an antenna analyzer, it has two analog meters on it,
one displays the resistance of the load and the other the SWR.
Both meters have a non linear scale on the faceplate.

One would normally think a 50 ohm resistor would display a ratio
of 2 to 1 when compared to a 100 ohm resistor. As you can see the ratio
is 1.3 to 1. Also a 500 ohm and a 50 ohm resistor have a ratio of 10.
But the voltage ratio is 3.56.
So, do you have any other ideas?
Mikek

Could it be you don't know how to calculate an SWR?
Then look at this:
https://sites.google.com/site/tapeme...wave-ratio-swr


w.