WIRELESS NOTES

Evening Star, Issue 19197, 13 March 1926, Page 24

WIRELESS NOTES

RADIO' OH TOUR [By Electro:?.] During a few idle moments a few weeks ago it occurred to me that there might bo a possibility of fitting a single-valve set on a motor car, so that at anv convenient spot (underneath a tree, for instance) a temporary aerial could bo erected- and_ perhaps items from nearby stations intercepted. Collecting a few odds and ends from the radio don, 1 spent a wot Sunday afternoon in assembling them in as compact a form as possible, at the same time taking care not to sacrifice efficiency for space. The set was_ mounted on a panel Win x sJin, this being screwed to a wooden base 10m s iin deep. Everything was ready for a tryout by evening, and, rather to my surprise, the set worked exceptionally well on a small indoor aerial, tuning and regeneration being well under control. Next evening I htted a compartment under the dash board to contain the set, and also fitted the B battery under the seat with flexible leads to tho set. The car battery happened to bo earthed to the frame on the negative side, so there was no obstacle to tho use of the car battery for the valve. Naturally the next thought that occurred was to have tho set permanently fitted in tho car and wired up to the batteries, and from this stage to the installation of an insulated loop aerial round tho hood was an obvious move. On completion of this the phones were inserted', and while the car was standing in Manor place I tried to tune in something. 1 certainly hoped to receive a carrier wave or so, but hardly expected- tho loud carrier that did eventuate, and was agreeably surprised to find that on tuning down quite a loud gramophone record was coming through. In great glee I dashed inside to bring the rest of the family out to hear the music, but on listening we hoard nothing whatever. Seine little time later, however, I tuned in again, find found VLDN coming through with great volume and clarity, so, with the phones on, wo drove slowly in the direction of tho Exhibition, all the time listening to the music. As we neared the Exhibition the music became louder raid louder, until, as we passed through the entrance gate, there was no need to have tho phones on tho head. We drove in and stopped right under the aerial. Here the volume was so groat that the whole set was saturated. Tuning made no difference, and the volume, oven with the valve turned almost out, was too great for the phones. A STAGE FURTHER. Results were so good that I felt the addition of another valve would be worth while,*an on investigation found I had sufficient junk to build up a twovalve amplifier. Tlus_ was mounted on a base about Sin x Sin, and contained two transformers, two valve holders, and one telephone transformer. _ I thought it advisable to use low resistance phonos on account of tho whole car frame being connected to the negative of the A and B batteries,_ there thus being a danger of an accidental short with the frame burning out the phones, or “ shorting ” the B battery. A space was made for the amplifier behind the seat, and a D.P. knife switch used to switch tho valve filaments on, the B battery being permanently connected. The' loud speaker is fastened at the back of the seat, and is automatically connected in circuit when the phone plug is withdrawn. With the set fitted up'and the oar standing still VLDN can be heard with a good loudspeaker strength np to five miles. When the engine is started there is a certain amount of noise from the sparking, which causes a steady patter in the loud speaker. Anywhere in town from Look-out Point to the Brown House the music is sufficiently loud to drown this noise entirely, while within a few blocks of the Exhibition the jnnsio can ho distinguished easily I.ooyds from the car. VARYING STRENGTH.

It is interesting to nolo the shielding effect of buildings, bridges, etc., since as the car passes along the change in strength is readily noticeable. If a person were walking along with a portable set there would be some difficulty in determining the actual change in volume ,ou account of its gradual nature; but with the car travelling at fifteen to twenty miles per hour the changes are rapid and distinct. From tho rough experiments I have done, there is no doubt that many listeners suffer from screening, and in a distance of, perhaps, 50yds the music may _ change from loud to very weak, regaining its original strength as the obstacle is passed. During a trip to Timarn last week I stopped at Herbert on the roadside at 2 o’clock in the afternoon, and fitting in tho car tuned in tho carrier from VLDN on the loud speaker, and, with tho phones, could just distinguish faint music. At Timarn, in the evening, while the car was standing in a small brick garage on a concrete lioor, I tuned in VLDN with great volume on tho phones, and just audible on the loud-speaker. I then ran the car outside under a tree and threw up about 30ft of insulated wire, also attaching the car frame to a nearby water tap. Under these conditions VLDN came in well on the loud speaker, and we heard both Sydney and Melbourne clearly on the phones. One important point in connection noth the car installation is the form of aerial. I don’t think a loop would bo any use on account of the constant change in direction causing change in volume. The method 1 adopted comprised an insulated wire suspended all round the hood inside, and a few inches from tho metal frame to this continuous wire is soldered the lead to the receiver, and from the earth terminal of the receiver another lead goes to earth. With the frame of tho car is used as _a counter. Capacity and change in direction do not appear to make any change in volume. It should be mentioned that the loop round tho hood is practically square, and this factor may be of importance in the determination of directional characteristics. At Waitati wo had a puncture, but the occupants of tho car were quite content to sit in comfort and listen to the music while the wheel was changed. As soon as we reached the brow of tho hill above Dunedin the volume increased several times; in fact, from the moment of passing under the high tension line to Port (at which point the

'music came in with a hurst) a steady increase in volume was noticed right to the brow, where the music was far too loud for the phones to he used at all. Duo to the absence of earth connection and the fact that the car is effectively insulated by the rubber tyres, there is a pleasing absence o 1 many of tbo strange noises that appeal' in radio sets, and the bowling valve trouble is eliminated entirely. It is quite possible to stop the interference from the engine spark if desired, as this has long been accomplished on aeroplanes. Next week I will describe the receiver, so that any of you who desire may try the novel experience of driving along accompanied by pleasant music.