# SWR Measurement Watt Meter

1. ## SWR Measurement Watt Meter

I am working on a new project using a PIC16F877A, I want to calculated A Watt Meter (SWR Measurement), refer on formula I think is :
Power = Volt X Amp

but I try this I got wrong value.

My reference volt on RA0 is XX mVolt and then convert to Watt.

Can anyone guide me to given some information how to do this.

Anyway....., I am using MikroC.

Thanks.
JR in Bandung.

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2. ## Re: SWR Measurement Watt Meter

PIC can't process SWR meter RF voltages directly. There must be a circuit converting RF quantities in DC voltage. The units have to be scaled respectively.

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3. ## Re: SWR Measurement Watt Meter

Are you making a FM Power Transmitter ? I have done a few FM Transmitter projects and have SWR power measurement circuit.

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4. ## Re: SWR Measurement Watt Meter

SWR and power have little correlation. Are you trying to measure power or ratio of forward and reflected power?
SWR doesnt care if it's AM, FM or any other kind of modulation.

Brian.

5. ## Re: SWR Measurement Watt Meter

Yes, I am making a SWR Power Meter for my tranceiver 144Mhz & 440Mhz Band http://www.kenwood.com/usa/com/amateur/tm-v71a/
FVM : I'm not put PIC standalone, but I've to put a AD8307, LF355 or LM358 before in to RA0 & RA1.
I just want to know, how to calculated it to convert from Milivolt to Watt in PIC16F877A.
Okada : Can you explain me how to calculate for your FM Transmitter.
Betwixt : Yes, exacly I want to measure Forward and Reflected power.

I hope someone can help me.

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6. ## Re: SWR Measurement Watt Meter

For SWR all you need is the forward and reflected voltages. Look at Wikipaedia for the formulas to convert then to the VSWR.

Power is simply a voltage measurement at the antenna but it assumes you know the antenna impedance. W = (V^2)/Z. It is best done with a dummy load (SWR = 1:1) but if you really want to go to the effort, you can monitor the antenna voltage and current then multiply them, that makes it independent of load impedance. Monitoring RF currents can be tricky!

Brian.

7. ## Re: SWR Measurement Watt Meter

A SWR meter is essentially a directional coupler plus rectifier circuit. The coupling factor and rectifier conversion gain defines the millivolt to watt relation. Particularly the coupling factor can vary over a wide range and is set by the coupler design.

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