The Birmingham age-herald., 1922-07-16

large duo-latsrai coils iA and 1B must be in an inductive relationship to each other. It will be found that this relationship Is very critical. and the greatest possible care must be exercised in adjusting this relation ship. as well as obtaining the correct amount of capacity In the two con- densers IS and 1a.
 ' Although those two aondenseRs are shown as variable in the diagram. they do not necessarily have to be of tho regulation variable air oondens- CT typo. They can be made up of a number of fixed condensers con neoted in parallel with each other and so arranged to muiti-point switches that any one of them can be brought into or taken out of ths circuit. In other words they can be made variable in steps.
 The loop aerial can be constructed on a square frame three feet long on each of the four sides. The wire can be wound around this frame either in solenoid or spiral fashion. If the former there should be 10 turns, each spaced quarter of an Inch apart, and if ip the latter form, there should be 12 turns, each spaced a quarter of an inch apart Number IS cotton recovered bell wire can be used.
 The loop is connected across the primary of the vario coupler, which Is shown in the diagram as coils and 2. respectively. The tuning to the wave
 length of the incoming f.gnal Is done
 by means of the condenser No. f. The secondary of the varin- coupler 1 should have about twice the number of turns 1t normally has when used for ordinary purposes.
 err4A I.f utxr. L. fftA gram as No. consists of two pocket | flashllght cells joined fin series, giv- | ing 6 total of approximately four volts. The negative terminal of this small battery must be joined to the grid. The filter system is the same as that recently shown in these col umns with the three tube super- regenerative circuit.
 l Resistance and Choke Standard The 12,000 ohm resistances and the 100 milli-henry iron core choke coll are standard instruments used for filter purposes in telephone repeater circuits and they can be obtaintd from stores handling telephone supplies. They will undoubtedly be on the mar ket in quantities in the near future Condenser No. can b0 built up or fixed units in the manner described for condensers 13 and 1B.
 l In this particular circuit 1t must be remembered that there are seven crit teal adjustments to be made. This Is the price that has to be paid in get
 ting one ,uum tube to perform four
 separate and distince functions sue cessfully. This fact Is not stated to discourage the experimenter, but to impress upon him the importance or very delicate and careful adjustment. It will also serve to remind him that in the event of failure at the first time that success can only be ob- l tained from complete mastery of the adjustable parts of the circuit. The subsequent results will amply repay 1 the trouble.
 | For experimenters who are some distance from the broadcasting sta ton a single stage of audio fre- uuency amplification can be added to this circuit in the manner shown In the diagram printed in this paper on July 2, when the three tube super lregenerative circuit was given. The leads to the simplifying transformer primary. will be placed where the telephones are shown in the present diagram.