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4*4
Radio Broadcast
FIG. 5
This is the most convenient form of wavemeter oscillator or calibrated oscillator. This instrument covers a wave band of
from 200-20,000 meters. The output may be as great as one or two watts depending on the frequency. The condenser
shown is a large laboratory condenser, but any good condenser may be used
be constructed is a question of personal taste. The leads from the coils to the condenser should preferably be as short as possible; but there is no great objection to having the leads long if it is absolutely necessary. Where long leads are used, always use the same wires. Duo-lateral coils may be mounted directly on the condenser or may be mounted on a panel with the condenser underneath the panel. Three wavemeters are illustrated, showing satisfactory types of construction. The wavemeters shown using duo-lateral coils are the ones recommended, as they are most easily constructed and as all the parts necessary for their construction may be obtained from practically any good electrical or radio supply house. The manufacturers of duo-lateral coils have compiled a table showing the wavelength range covered by each coil when used as shown in either Fig. i or 2. A copy of this table is given. A wavemeter, such as that shown in Fig. 6, when once built up can be used to cover the entire wavelength range with good accuracy at a minimum expense.
MAKING YOUR WAVEMETER MODERN
A GREAT many wavemeters have been described in different periodicals showing a crystal detector and a telephone headset as an indication of the resonance point. A great
many other meters have been shown with a high frequency buzzer as a driver or source of energy. The first wavemeter corresponds to that shown in Fig. i and the second to that shown in Fig. 2. Present day radio does not permit this rather crude method of detection and generation. It is recommended that by all means a vacuum tube be used in either of the manners described.
For the owner of a regenerative receiver and transmitting set the wavemeter described in Fig. i, will perhaps, be the most useful. For the owner of a receiving set only, the wavemeter shown in Fig. 2 will be the best. Either or both of these two instruments will be of great value to the owner of a modern receiving or transmitting station, as they permit him to know definitely how his receiving set is operating and what wavelength he is transmitting on.
Modern amateur communication is carried on at wavelengths from 1 50 to 220 meters. Very few standard wavemeters are supplied to operate at these short wavelengths, particularly if they are also intended for use at higher waves. The method of calibration by means of harmonics outlined above is of particular value in the calibration of wavemeters designed for short wave use. The amateur and operator of a transmitting station will find this method the best he can use to calibrate his wavemeter.