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None of these coils is variable; all are wound to receive waves up to 360 meters in length when used with a variable condenser of .001 mfd. capacitance. In other words you slide the coils in and out to get the right amount of coupling and you tune by adjusting the variable condenser to get the exact wave length you want. With Compact Coils.

They have a capacitance of 1 mfd. and will stand 750 volts. These condensers cost about $2.00 each. The Filter Reactance Coil. It consists of a coil of wire wound on a soft iron core and has a large inductance, hence the capacitance of the filter condensers are proportionately smaller than where a small inductance is used which has been the general practice.

This switch and fuse block is the same as that used in the experimental set. The Protective Condenser. This is a fixed condenser having a capacitance of 1 mfd. and will stand 750 volts. It costs $2.00. Connecting Up the Transmitting Apparatus. From all that has gone before you have seen that each piece of apparatus is fitted with terminal, wires, taps or binding posts.

All of the apparatus for this C. W. telegraph transmitting set is the same as that described for the 100 and 200 mile sets but you will need: one or two 50 watt oscillator tubes with sockets; one key condenser that has a capacitance of 1 mfd., and a rated potential of 1,750 volts; one 0 to 500 milli-ammeter; one aerial ammeter reading to 5 amperes, and an A. C. power transformer for one or two 50 watt tubes.

This is made to take care of a 10 volt current and it costs $10.00. The Filament Storage Battery. This must develop 12 volts and one having an output of 40 ampere-hours costs about $25.00. The Protective Condenser. This condenser has a capacitance of 1 mfd. and costs $2.00. The Motor-Generator.

If you are using a condenser having a capacitance of .007 microfarad, which is the largest capacity value that the Government will allow an amateur to use, then if you have a hot wire ammeter in your aerial and tune the inductance coil or coils until the ammeter shows the largest amount of energy flowing through it you will know that your transmitter is tuned and that the aerial is sending out waves whose length is 200 meters.

As the capacitance and the inductance of the circuit, which may be made of any value, that is amount, you wish, determines the time period, that is, the length of time for a current to make one complete oscillation, it must be clear that by varying the values of the condenser and the inductance coil you can make the high frequency current oscillate as fast or as slow as you wish within certain limits.

Where this type of interrupter is employed the condenser that is usually shunted around the break is not necessary as the interrupter itself has a certain inherent capacitance, due to electrolytic action, and which is called its electrolytic capacitance, and this is large enough to balance the self-induction of the circuit since the greater the number of breaks per minute the smaller the capacitance required.

The condenser used in the secondary coil circuit has 14 plates and this is equal to a capacitance of .0004 mfd. There are a number of inductance coils and these are arranged so that they can be connected in or cut out and combinations are thus formed which give a high efficiency and yet allow them to be compactly mounted.

All of the apparatus for this C. W. telegraph transmitting set is the same as that described for the 100 and 200 mile sets but you will need: one or two 50 watt oscillator tubes with sockets; one key condenser that has a capacitance of 1 mfd., and a rated potential of 1,750 volts; one 0 to 500 milli-ammeter; one aerial ammeter reading to 5 amperes, and an A. C. power transformer for one or two 50 watt tubes.