How does a forward and reverse power meter work?

In summary, the conversation discusses the use of a diode in a Bird Wattmeter to measure forward and reverse power and VSWR. The diode responds to the direction of the energy being measured, and this is achieved through a sensing loop parallel to the coaxial line. Depending on the mode employed, the energy in the coupling loop may appear to be coupled in the opposite direction to the transmission line. This information can be further explored in the provided links.
  • #1
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I know they have a diode that gets reversed to see forward V reverse power but how does that diode just respond to the one direction of energy? I have a bird wattmeter and it uses two slugs, one pointed in the other out to get simultaneous forward and reverse power and VSWR and such but why does reversing the diode change the response from forward to reverse? I have a hard time visualizing the process. Thanks. AI3N (All In 3 Nights)
 
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  • #2
hi there

this schematic of a Bird Wattmeter may help you

bird_sch.jpg


all the labelled parts in the middle are within the slug
Note the sensing loop parallel to the coaxial line and the diode. The induced current into the loop is rectified by the diode.
When it is orientated one way .. .say as shown it will "see" current induced that is flowing on one direction in the coaxial line.
Rotate the slug and it will "see" and rectify induced current flowing the opposite direction in the coax line

( not the best wording, but hopefully you will get the idea :smile: )cheers
Dave
 
  • #3
A small proportion of the energy propagating along the transmission line is directionally coupled into the coupling loop. One way to think of it is that depending on the direction of the coupled energy, it will either be absorbed in the termination resistor or detected at the opposite end of the loop by the diode.
You should be aware that tricky things often happen in couplers. Depending on the mode employed, the energy in the coupling loop may appear to be coupled in the opposite direction to the transmission line.

http://en.wikipedia.org/wiki/SWR_meter
http://en.wikipedia.org/wiki/Power_dividers_and_directional_couplers
 
  • #4
Baluncore said:
You should be aware that tricky things often happen in couplers.
Truer words were never spoken!
 

1. How does a forward and reverse power meter measure power?

A forward and reverse power meter works by measuring the magnitude and direction of power flow in a circuit. It uses a directional coupler to split the signal into two parts - one for forward power and one for reverse power. The forward power is measured by a detector and displayed on the meter, while the reverse power is measured by another detector and displayed with a negative sign to indicate the direction of power flow.

2. What is the principle behind a forward and reverse power meter?

The principle behind a forward and reverse power meter is based on the properties of directional couplers and power detectors. Directional couplers allow for the separation of forward and reverse power signals, while power detectors convert the RF signal into a DC voltage that can be measured by the meter. By combining these two components, the meter can accurately measure both the magnitude and direction of power flow in a circuit.

3. How accurate is a forward and reverse power meter?

The accuracy of a forward and reverse power meter depends on several factors such as the quality of the components used, the frequency range it can measure, and the calibration of the meter. Generally, a well-made meter can have an accuracy of up to 0.2% for power measurements and 0.5% for SWR measurements.

4. Can a forward and reverse power meter be used for all types of circuits?

Yes, a forward and reverse power meter can be used for all types of circuits as long as they operate within the frequency range of the meter and have power levels within its measurement capabilities. However, it is important to note that some meters may have specific features or settings for certain types of circuits, such as impedance matching for transmission lines.

5. How can I use a forward and reverse power meter to troubleshoot my circuit?

A forward and reverse power meter can be a valuable tool for troubleshooting circuits. By measuring the forward and reverse power, you can determine the direction and magnitude of any power losses or reflections in the circuit. This can help identify faulty components or incorrectly installed equipment. Additionally, the SWR measurement can indicate if there are any impedance mismatches in the circuit, which can also cause power losses and signal distortions.

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