All receiving sets that receive over a range of wave lengths of from 150 meters to 3,000 meters are called intermediate wave sets and all sets that receive wave lengths over a range of anything more than 3,000 meters are called long wave sets. The range of intermediate wave receptors is such that they will receive amateur, broadcasting, ship and shore Navy, commercial, Arlington's time and all other stations using spark telegraph damped waves or arc or vacuum tube telephone continuous waves but not continuous wave telegraph signals, unless these have been broken up into groups at the transmitting station. To receive continuous wave telegraph signals requires receiving sets of special kind and these will be described in the next chapter.
Intermediate Wave Receiving Sets.--There are two chief schemes employed to increase the range of wave lengths that a set can receive and these are by using: (1) loading coils and shunt condensers, and (2) bank-wound coils and variable condensers. If you have a short-wave set and plan to receive intermediate waves with it then loading coils and fixed condensers shunted around them affords you the way to do it, but if you prefer to buy a new receptor then the better way is to get one with bank-wound coils and variable condensers; this latter way preserves the electrical balance of the oscillation circuits better, the electrical losses are less and the tuning easier and sharper.
Intermediate Wave Set With Loading Coils.--For this intermediate wave set you can use either of the short-wave sets described in the foregoing chapter. For the loading coils use honeycomb coils, or other good compact inductance coils, as shown in [Chapter X] and having a range of whatever wave length you wish to receive. The following table shows the range of wave length of the various sized coils when used with a variable condenser having a .001 microfarad capacitance, the approximate inductance of each coil in millihenries and prices at the present writing:
TABLE OF CHARACTERISTICS OF HONEYCOMB COILS
Approximate Wave
Length in Meters in
Millihenries
Inductance .001 mfd. Variable Mounted
Appx. Air Condenser. on Plug
.040 130-- 375 $1.40
.075 180-- 515 1.40
.15 240-- 730 1.50
.3 330-- 1030 1.50
.6 450-- 1460 1.55
1.3 660-- 2200 1.60
2.3 930-- 2850 1.65
4.5 1300-- 4000 1.70
6.5 1550-- 4800 1.75
11. 2050-- 6300 1.80
20. 3000-- 8500 2.00
40. 4000--12000 2.15
65. 5000--15000 2.35
100. 6200--19000 2.60
125. 7000--21000 3.00
175. 8200--24000 3.50
These and other kinds of compact coils can be bought at electrical supply houses that sell wireless goods. If your aerial is not very high or long you can use loading coils, but to get anything like efficient results with them you must have an aerial of large capacitance and the only way to get this is to put up a high and long one with two or more parallel wires spaced a goodly distance apart.
The Parts and How to Connect Them Up.--Get (1) two honeycomb or other coils of the greatest wave length you want to receive, for in order to properly balance the aerial, or primary oscillation circuit, and the closed, or secondary oscillation circuit, you have to tune them to the same wave length; (2) two .001 mfd. variable condensers, though fixed condensers will do, and (3) two small single-throw double-pole knife switches mounted on porcelain bases.
To use the loading coils all you have to do is to connect one of them in the aerial above the primary coil of the loose coupler, or variocoupler as shown in the wiring diagram in Fig. 57, then shunt one of the condensers around it and connect one of the switches around this; this switch enables you to cut in or out the loading coil at will. Likewise connect the other loading coil in one side of the closed, or secondary circuit between the variable .0007 mfd. condenser and the secondary coil of the loose coupler or variocoupler as shown in Fig. 53. The other connections are exactly the same as shown in Figs. 44 and 45.
An Intermediate Wave Set With Variocoupler Inductance Coils.--By using the coil wound on the rotor of the variocoupler as the tickler the coupling between the detector tube circuits and the aerial wire system increases as the set is tuned for greater wave lengths. This scheme makes the control of the regenerative circuit far more stable than it is where an ordinary loose coupled tuning coil is used.