MFJ259 conversion help
 

On 12/4/2013 6:14 AM, Helmut Wabnig wrote:
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.

I haven't started with SWR yet.
I'm reading the voltage across the meter that displays the R of the
load. The analog meter is fairly accurate, but the distance between 0
and 50 is the same as the distance between 50 and 500. It makes reading
an R of 275 ohms difficult. I was just hoping I could put a digital
meter on the unit and be able to get a bit more detailed numbers. But,
alas, now that I have the voltage readings, the only way I know how to
make sense of them is a conversion chart.
If 50mv = 50 ohms and 100mv = 100 ohms this would make sense but the
voltage vs resistance is non linear.
Thanks, Mikek
chart.

MFJ259 conversion help
 

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 0.1000 volts
365 0.1060 volts
498 0.1090 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.

Thanks, I'll learn about that and see if I can make it work for me.

Mikek

MFJ259 conversion help
 

On 12/4/2013 8:48 AM, amdx wrote:
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 0.1000 volts
365 0.1060 volts
498 0.1090 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.

Thanks, I'll learn about that and see if I can make it work for me.

Mikek

Good. I can tell you how I accomplished it if you are interested.

MFJ259 conversion help
 

"amdx" wrote in message
...
Is that because you think MFJ is junk, or because
there is no easy relationship?


No it is not that I think the MFJ is junk, just there is no easy
relationship.

You did not mention if the volts were AC or DC or RF that I recall.

If DC there is no relationship at all. You do not use DC to measure the
inpedance of an antenna. If AC that most voltmeters will show, the
frequency range is too low to get a meaningful showing. If RF, you most
likely loose too much in the length of the leads.

What you are doing is sort of like sticking the probes in the side of a
tree and trying to see how tall that tree is. You see something on the
meter, but it does not help to tell how tall that tree is.

What you are doing while a learning experiance , is just a negative one.
One that does not work for anything. Like Tom Edison and the light bulb.
When he had tried about 60 differant things for the filiment of the bulb, he
said I now know 60 things that do not work.

MFJ259 conversion help
 

On Wed, 04 Dec 2013 08:39:56 -0600, amdx wrote:

On 12/4/2013 6:14 AM, Helmut Wabnig wrote:
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.

I haven't started with SWR yet.
I'm reading the voltage across the meter that displays the R of the
load. The analog meter is fairly accurate, but the distance between 0
and 50 is the same as the distance between 50 and 500. It makes reading
an R of 275 ohms difficult. I was just hoping I could put a digital
meter on the unit and be able to get a bit more detailed numbers. But,
alas, now that I have the voltage readings, the only way I know how to
make sense of them is a conversion chart.
If 50mv = 50 ohms and 100mv = 100 ohms this would make sense but the
voltage vs resistance is non linear.
Thanks, Mikek
chart.


Ah..now I think I understand

It looks like this:
http://img203.imageshack.us/img203/4766/863l.gif


w.

MFJ259 conversion help
 

On 12/4/2013 9:14 AM, John S wrote:
On 12/4/2013 8:48 AM, amdx wrote:
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 0.1000 volts
365 0.1060 volts
498 0.1090 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.

Thanks, I'll learn about that and see if I can make it work for me.

Mikek

Good. I can tell you how I accomplished it if you are interested.

Hi John S,
Please don't let me work you if your not interested, this is now
probably more of a curiosity than a way to make the MFJ259 more useful.
I ran all the numbers with the formula, it is not accurate enough to
me usable. I don't know if that is a calibration error, resistor error,
(I used 1% resistors) a me error, or the wrong formula.


I don't think it correlates very well with my measurements.
Might need to use fixed font to read this.

My Measurements.

Real R Calculated R Measured Voltage


7.5 ohms 11.4 0.0388 volts
15 15.3 0.0444 volts
25.5 18.3 0.0478 volts
39 30.7 0.0577 volts
50 37.3 0.0614 volts
100 102 0.0807 volts
140 158.9 0.0891 volts
174 200 0.0935 volts
221 253 0.0980 volts
249 284 0.1000 volts
365 384.6 0.1060 volts
498 457.4 0.1090 volts

This is really only usable at 100 ohms. Only 2% error.
52% error low end and 8.1% top end
Is there a better formula.
I'm trying to use a digital meter in place of basically a hand drawn
dial that is very nonlinear.
I'm wondering if I calibrated 50 ohms to read a bit lower
or higher voltage it might help

Anyone's helpful thoughts,
Thanks, Mike

MFJ259 conversion help
 

On 12/5/2013 4:13 AM, Helmut Wabnig wrote:
On Wed, 04 Dec 2013 08:39:56 -0600, amdx wrote:

On 12/4/2013 6:14 AM, Helmut Wabnig wrote:
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.

I haven't started with SWR yet.
I'm reading the voltage across the meter that displays the R of the
load. The analog meter is fairly accurate, but the distance between 0
and 50 is the same as the distance between 50 and 500. It makes reading
an R of 275 ohms difficult. I was just hoping I could put a digital
meter on the unit and be able to get a bit more detailed numbers. But,
alas, now that I have the voltage readings, the only way I know how to
make sense of them is a conversion chart.
If 50mv = 50 ohms and 100mv = 100 ohms this would make sense but the
voltage vs resistance is non linear.
Thanks, Mikek
chart.


Ah..now I think I understand

It looks like this:
http://img203.imageshack.us/img203/4766/863l.gif


w.

Yes! and this is one way I could handle this is to add more grid lines
and just use the graph to find R by finding were V crosses.
I posted new info using the formula John S developed, as you may read
the formula does not come out as accurate as I'd like, I'm not sure why.
Thanks for the interest, Mikek

MFJ259 conversion help
 

On 12/5/2013 10:26 AM, amdx wrote:
On 12/4/2013 9:14 AM, John S wrote:
On 12/4/2013 8:48 AM, amdx wrote:
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 0.1000 volts
365 0.1060 volts
498 0.1090 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.

Thanks, I'll learn about that and see if I can make it work for me.

Mikek

Good. I can tell you how I accomplished it if you are interested.

Hi John S,
Please don't let me work you if your not interested, this is now
probably more of a curiosity than a way to make the MFJ259 more useful.
I ran all the numbers with the formula, it is not accurate enough to
me usable. I don't know if that is a calibration error, resistor error,
(I used 1% resistors) a me error, or the wrong formula.


I don't think it correlates very well with my measurements.
Might need to use fixed font to read this.

My Measurements.

Real R Calculated R Measured Voltage


7.5 ohms 11.4 0.0388 volts
15 15.3 0.0444 volts
25.5 18.3 0.0478 volts
39 30.7 0.0577 volts
50 37.3 0.0614 volts
100 102 0.0807 volts
140 158.9 0.0891 volts
174 200 0.0935 volts
221 253 0.0980 volts
249 284 0.1000 volts
365 384.6 0.1060 volts
498 457.4 0.1090 volts

This is really only usable at 100 ohms. Only 2% error.
52% error low end and 8.1% top end
Is there a better formula.
I'm trying to use a digital meter in place of basically a hand drawn
dial that is very nonlinear.
I'm wondering if I calibrated 50 ohms to read a bit lower
or higher voltage it might help

Anyone's helpful thoughts,
Thanks, Mike

I was going to suggest you try the polynomial, but I just discovered
that Excel has lied grossly to me. The trend line shows it to match very
well. However, I used the equation Excel produces to calculate using the
original values and saw a 34% error at the high end not shown by the
trend line. This has nothing to do with your data. I will see if I can
determine the cause of this.

Cheers,
John

MFJ259 conversion help
 

On Thu, 05 Dec 2013 10:26:33 -0600, amdx wrote:

On 12/4/2013 9:14 AM, John S wrote:
On 12/4/2013 8:48 AM, amdx wrote:
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 0.1000 volts
365 0.1060 volts
498 0.1090 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.

Thanks, I'll learn about that and see if I can make it work for me.

Mikek

Good. I can tell you how I accomplished it if you are interested.

Hi John S,
Please don't let me work you if your not interested, this is now
probably more of a curiosity than a way to make the MFJ259 more useful.
I ran all the numbers with the formula, it is not accurate enough to
me usable. I don't know if that is a calibration error, resistor error,
(I used 1% resistors) a me error, or the wrong formula.


I don't think it correlates very well with my measurements.
Might need to use fixed font to read this.

My Measurements.

Real R Calculated R Measured Voltage


7.5 ohms 11.4 0.0388 volts
15 15.3 0.0444 volts
25.5 18.3 0.0478 volts
39 30.7 0.0577 volts
50 37.3 0.0614 volts
100 102 0.0807 volts
140 158.9 0.0891 volts
174 200 0.0935 volts
221 253 0.0980 volts
249 284 0.1000 volts
365 384.6 0.1060 volts
498 457.4 0.1090 volts

This is really only usable at 100 ohms. Only 2% error.
52% error low end and 8.1% top end
Is there a better formula.
I'm trying to use a digital meter in place of basically a hand drawn
dial that is very nonlinear.
I'm wondering if I calibrated 50 ohms to read a bit lower
or higher voltage it might help

Anyone's helpful thoughts,
Thanks, Mike



Well I did it using an old dirty trick:
adding one fake data point at the end to bend the curve.

http://img560.imageshack.us/img560/1845/yi2.gif

You must then not use the values
which are above the last valid data point.

You may program this formula into an Arduino .-)

w.

MFJ259 conversion help
 

On 12/5/2013 11:31 AM, Helmut Wabnig wrote:
On Thu, 05 Dec 2013 10:26:33 -0600, amdx wrote:

On 12/4/2013 9:14 AM, John S wrote:
On 12/4/2013 8:48 AM, amdx wrote:
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 0.1000 volts
365 0.1060 volts
498 0.1090 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.

Thanks, I'll learn about that and see if I can make it work for me.

Mikek

Good. I can tell you how I accomplished it if you are interested.

Hi John S,
Please don't let me work you if your not interested, this is now
probably more of a curiosity than a way to make the MFJ259 more useful.
I ran all the numbers with the formula, it is not accurate enough to
me usable. I don't know if that is a calibration error, resistor error,
(I used 1% resistors) a me error, or the wrong formula.


I don't think it correlates very well with my measurements.
Might need to use fixed font to read this.

My Measurements.

Real R Calculated R Measured Voltage


7.5 ohms 11.4 0.0388 volts
15 15.3 0.0444 volts
25.5 18.3 0.0478 volts
39 30.7 0.0577 volts
50 37.3 0.0614 volts
100 102 0.0807 volts
140 158.9 0.0891 volts
174 200 0.0935 volts
221 253 0.0980 volts
249 284 0.1000 volts
365 384.6 0.1060 volts
498 457.4 0.1090 volts

This is really only usable at 100 ohms. Only 2% error.
52% error low end and 8.1% top end
Is there a better formula.
I'm trying to use a digital meter in place of basically a hand drawn
dial that is very nonlinear.
I'm wondering if I calibrated 50 ohms to read a bit lower
or higher voltage it might help

Anyone's helpful thoughts,
Thanks, Mike



Well I did it using an old dirty trick:
adding one fake data point at the end to bend the curve.

http://img560.imageshack.us/img560/1845/yi2.gif

You must then not use the values
which are above the last valid data point.

You may program this formula into an Arduino .-)

w.

Yes, the trend line is very close. But, please perform a calculation on
the 498R value using the equation and let me know if it agrees. If yours
does, then something is wrong here.

Thanks,
John