# Measurements

## Power meters

The 'Monimatch' SWR meter shown in Fig 10.7 is a simple and reasonably satisfactory instrument. The main disadvantage is that the maximum meter deflection is directly proportional to the frequency at which it is being used.

Fig 10.7. Basic reflectometer circuit (Monimatch)

A more effective circuit uses a broad-band current transformer as a sensor. The secondary winding of this is a few turns of wire wound on a small toroidal ferrite core. The single-turn primary is a short length of coaxial cable through the toroidal core. This device can be easily made at home.

The advantage of this circuit is that the deflection produced is independent of the frequency at which it is used. Such a meter can also be calibrated to read power (forward and reverse) and, by the inclusion of a long-time-constant circuit, peak envelope power (PEP) as well.

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