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Learn more. Thanks for the write up, interesting to see, the info is really neat! Report comment. Adam: Might want to fix that, or at least clear up the ambiguity. Anyone here knows how to measure RF powers in mW range?
Frequency is 27 MHz. Leave a Reply Cancel reply. Search Search for:. Teardown: Analog Radionic Analyzer 55 Comments. Hackaday Links: November 7, 3 Comments. In the circuit the transmitter and load are connected by a feeder, and this is coupled to two additional short lines within the RF inline power meter.
On each of these coupled lines there is a resistor used for impedance matching, and a diode - the position of these relative to the direction of power flow determines whether forward or reflected power is measured.
The diode acts to rectify the coupled power so that it can be directly read by a meter and the capacitor removes the residual RF. In many inline RF wattmeters, only a single coupled line is used, and the components switched to select the forward and reverse power measurement. The advantage of the inline power meter capability means that the power meter can be kept in circuit whilst the load is active.
This can be particularly useful if the load needs to remain active whilst the power is measured - this cannot be achieved using an absorption wattmeter. Simple directional coupler circuit that could be used for inline power measurements The circuit is a very simple form of directional coupler and illustrates the basic concept. Passing through the rectifier diode, an unmodulated carrier will result in a DC voltage proportional to the peak-to-base value of the RF voltage, which will deflect the meter to a point on the scale that has been marked in watts corresponding to the power being sampled from the main line.
If the modulation frequency is very low, the needle will try to follow and quiver about the center reading. There is one notable exception, namely the measurement of two-toned single side-band transmission.
Since all the correction factors are known, they can be applied to the meter reading as follows: In two-tone modulation of equal magnitude, the true heating power is one-half the peak envelope power. The meter will read the average of the rectified pulsating DC output from the element, or.
Since the dial is calibrated in power, it will indicate. It should be stressed that this conversion factor only applies to measurements of two-toned modulation of equal amplitude of single side-band transmission.
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