Wireless Broadcast

Star (Christchurch), Issue 16943, 18 January 1923, Page 3

Wireless Broadcast

Contributed by

“Aerial.”

During the last three years or so l have visited a large number of amateur wireless stations, and have seen many different types of receiving outfits, ranging from the humble single slidetuner. crystal detector seyt, to the modern valve receiver, using several steps of amplification, of both radio and audio frequency. In no station in or around this city, however, have 1 ever come across an instrument which comprises both a separate heterodyne and wavemeter. It seems as though its usefulness is not realised by the majority of experimenters in radio. This is somewhat surprising, as it is quite easily constructed, and is very simple to use. Continuous wave signals

are received as a rule, by causing the receiving circuits to oscillate at nearly the same frequency as the incoming wave. These two frequencies, so close together, cause beats of an audible frequency to be set up in the receiver, which, when rectified by the detector, produce sounds in the telephone receivers. Now. to receive continuous wave signals of say 1000 metres wavelength, our receiver must be tuned to nearly the same wave to produce the beats. Obviously, to hour anything, the set must remain out of tune. Suppose we were dead in tune with the incoming wave, and beats were still set up bv some means, signal strength would be much improved, and inter-

our wave-meter until its signals are heard, and read from the chart, the wave-length corresponding to the condenser setting. To measure outgoing waves, hold the instrument somewhere near the transmitting helix, and turn ; the variable condenser until the lamp lights up. Maximum glow from the lamp indicates the resonance p*unt. Read this from the chart again as in the'other case. For this operation the valve need not be lighted. The parts necessary to make a lieterdoyne wave meter, with a range of 130 to 100 metres aporoximately, arc as follows:—A variable condenser of .001 rat'd. max., about fifty feet of No. 20 d.c.c wire, a small flashlight bulb, i throe electrode valve, preferably n Y 24, a few inches of resistance wire, and a “B ’* battery of about 20 volts. These parts can be mounted on a panel of in-

times have a nasty knack of causing ‘ trouble. • A good cure for bodv capacity effects is to shield all tlie gear. Shellac some tinfoil to the back of the panel, and over this a layer of brown paper. Cut the foil away where studs, shafts, etc. come through the panel, but leave tli * foil connected to the earth terminal. If vou cannot get your single circuit tuner (primary and tickler) to oscillate, trv putting a series variable condenser in the aerial <«• earth lead, also try shunting the “ B ’* battery and ‘phones with a large condenser, either variable or fixed. KEY TO FIG. 2. C 7 0005 mid max. A.F.T. Audio Frequency Trausf R.F.T. Radio Frequency Transf. Y2 Det. tube. Y 3- t VI amplifier tubes.

ANSWERS TO CORRESPONDENTS K.W Ki. St Albans. (1) Diagram number 2 should suit quite well. (2 Signal strength would he increased I.n another stage of audio frequency amplification. (3) I should advise two Iranformers to cover tlie range you want The first transformer to rover .i range of/aay, from 3-50 to 175 metro, am! (he second from 170 to 700 metres !•’<.. (he first transformer wind 45 turns No.

——— 10 s.s.c. on a former (cardboard tube-) 2 5 inches in diameter This i«, I<• j„ a single Liver. The second;,rv to have SO turns of the same wire, wound directly* , over the primary. Eo, (he second trails- ’ primary .-ui'l ICO ‘to turns',m‘ ondarv. Same size former to bo used. - winder would 'take"!,., teal'mV.ch"spare t*. deal with here Several amateurs n ' Christ church have these ~ • no doubt they would bo pJea- d to help . 1 HAVE Now in Stock Browns Phones * Type A. adjnstabje diaphmem S'. 19 s 6d. Abo. Radio Sets from S 7 u'-?. which will be installed free of charge*. A. -T. DA COMBE AND ' Radio Expert*. 8. Smollett Street. Syden. «"*.n. Now Showing at Exhibition, -iere -et» and Parts can be obtained.