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Author Topic: Autek WM1 SWR/PWR Computing Meter  (Read 213 times)
W5DXP
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« on: November 10, 2018, 11:35:31 AM »

Does anyone know whether the WM1 reads (forward power) or (forward power minus reflected power) on the PWR meter?
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73, Cecil, w5dxp.com
K7MEM
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« Reply #1 on: November 10, 2018, 01:34:29 PM »

Oddly enough, another question on th WM1 came up this morning.

Here is a link to a old, May 2016, posting on QRZ that contains a Reverse Engineered Schematic.

You can see for yourself.
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Martin - K7MEM
http://www.k7mem.com
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« Reply #2 on: November 10, 2018, 02:25:41 PM »

Thanks very much, Martin. I'm not sure I see a computer.
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73, Cecil, w5dxp.com
K7MEM
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« Reply #3 on: November 10, 2018, 03:21:23 PM »

I'm not sure I see a computer.

Your just not looking hard enough. The whole circuit is a computer.

When the label says "Computing", everyone assumes that there must be a micro controller or micro computer in the design. I guess that's a sign of the time. But long before they computed digitally, they computed with analog circuits. With analog, its fairly simple to do addition and subtraction. But when your trying to do multiplication and division, there is a problem. That is, until you convert the linear voltages to logarithmic voltages.

The Op-Amps (LM348) have much the same characteristics as the old uA741. They are just lower current and have smaller offsets. And there are four of them in the package. The diodes (1N4004) in the Op-Amp feedback, take care of the log conversion. After that it's just adding/subtracting the corrected values. Now, I know you know the equations necessary to calculate VSWR from the Forward and Reverse voltages.
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Martin - K7MEM
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W5DXP
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« Reply #4 on: November 10, 2018, 06:16:11 PM »

Your just not looking hard enough. The whole circuit is a computer.

I guess I basically a digital guy. If it's not a one or zero, it's broke. Smiley
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73, Cecil, w5dxp.com
W9IQ
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« Reply #5 on: November 11, 2018, 03:59:19 AM »

If you would like to see the math that a typical SWR meter performs, take a look at this link:

https://ham.stackexchange.com/q/9778/9493

- Glenn W9IQ
« Last Edit: November 11, 2018, 04:03:37 AM by W9IQ » Logged

- Glenn W9IQ

I never make a mistake. I thought I did once but I was wrong.
W5DXP
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« Reply #6 on: November 11, 2018, 10:08:22 AM »

If you would like to see the math that a typical SWR meter performs, take a look at this link:

Glen, how does someone answer a question on that site? I found an "ask question" button but I can't find an "answer question" button.
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73, Cecil, w5dxp.com
W9IQ
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« Reply #7 on: November 11, 2018, 10:15:39 AM »

After you register and sign in, scroll down below the question and you will find the spot to answer a question. There are also apps for tablets and phones.

It is a nice site where snarkiness, trolling or bragging is not permitted. Formulas and exacting answers are preferred.  You would be a welcomed contributor to the site.

- Glenn W9IQ
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- Glenn W9IQ

I never make a mistake. I thought I did once but I was wrong.
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