WIRELESS NOTES

Evening Star, Issue 19044, 12 September 1925, Page 22

WIRELESS NOTES

RADIO in THE CmiBTSY [By Electron.] Last week I bad occasion to spend a few days out of town, and at tiio last minute decided to take a radio receiver with me. Any of the apparatus available was too bulky, so that it became necessary to build a set specially for the job. There was ouiy one evening loft to do it in, so simplicity became an important consideration. An ebonite panel 10 x 8 was used, fitted to a wooden base and supported' by inchsquare sticks mounted in the lorni of two squares. One was litted at each end of the panel, and they were fastened to the base. This bold the panel vertical ami left plenty of room to gel at the apparatus ami wiring. Across the back a strip of ebonite was Listened to hold 15if terminals, seven ol there being Used. Tim anparatus was one .000—-» mid 11 ain menu ml '•oudeuse.r. one mil meg vanouivte:'. o’e grid i-oiiile'ise! 4 and hut. ~;:e by-pass eomi'-m-T. 0,,e Brad-ley-i aI . imc i V ft. i A i:.'ve a.id |>;.scehull !i-> ll l,■ i■. one a ‘l'liil c-'il oi luel'.'C t;;;■ 11 . mu' M"-iul.il'.v I'.el <n mmv Minis, The ::1 end v. is iviiiin'l round a liotiie, i hell slipped mi' and tit < 1 up with a piece oi lap; 1 , ju>t '.round ill a liuiii'h. not Dyer wound. The 'avondarv oil was din in di.i meier, wound in (!;e low I"--. iniiiiiiM' round <■!( veil din nails wiGi I'm bends cut off. The bolder was screwed to the base at the bark, the condenser aud_ variometer mounted on the panel, with the Draclleystat in the bottom right-hand corner. The grid condenser and by-pass condensers were supported in air by the connecting wires. The low loss tuning coil was hold by the connections to the condenser (the coil was wound with 2(l-gauge wire), and the aerial coil was pushed inside the low loss coil to about the centre. No soldered joints were used, and the whole set was wired and assembled in one evening. TUNINC IN. On arrival at the destination a test aerial consisting ol about .'JUIt of copper wire, was strung between two chimney pots and a lead-in taken down to the nearest window. A piece of half-inch iron rod 31't long was driven into the ground for an earth, in the evening we managed to tune in IYA Dunedin. Christchurch, Auckland, Sydney, and Melbourne, but some of the si at ions were rather too laint lor two pairs of phonos, so we added one stage of audio amplification with a breach !1 valve and DU volt B battery. With iho extra valve IYA came in with tremendous volume, and with the phones lying on the table could he hoard in any part of the room. It was no (rouble to tune him out and get on to ilu- other stations, all ol which were quite audible on the phones, Encouraged by these results, we decided to put iiji a better aerial, and since the onlv wire available was a coil of leucine: wire, this was used. One end was attached (u I lie lop of the verandah post, while (be other end was fastened to the top of a hiue, gum tree about KiOft away, and -JUlt, to 50ft high. A piece of motor car tube was used for an insulator at the tree end, while at the other end wo relied on the verandah post. With the big aerial, results wore naturally better, but wo touna that it was not possible to time out 4YA completely, though with the small aerial this presented no difficulty whatever. We heard some very enjoyable band selections from Melbourne on Sunday night, and the set was quite stable. In fact, during the evening I was so tired that I fell asleep with the 'phones on, and when I woke up the hand was still goiim strong. The instrumental and vocal items from 2BL were also good. Gisborne came in with fair volume, and 2YK was surprisingly loud and of better quality I linn usual. The announcer intimared that the station was under the control of the Department of Telegraphs, and would he improved mid remodelled. Evidently tins was the first transmission under the new arrangement, but wheiy I turned_ in lie was in the middle of his concluding address, so that I did not gather tlui ’ full purport of Hie announcement. As 2BL signed off wo heard the an-, nonnceinont that an address would bo cihen at 11 o’clock the next morning (Sunday), but at 12.110 we could not pick up the carrier-wave, even though after sunset this came in well. From the above notes it will be gathered that, provided you use reliable apparatus intelligently, there is no necessity to take elaborate precautions to obtain quite fair results ; but, other hand, with cheap, inefficient apparatus; even the greatest pains cannot achieve even fair results. SHORT-WAVE GENERATOR. I offer the following information to any amateur who cares to make a transmitter suitable for wave-lengths under ten metres, and down even under two metres. Firstly, the Hartley circuit is not effective bclowi _ fifty metres, the Colpitts circuit is limited to about twenty metres, while the circuit described can produce wavelengths of two metres with VT2. 1.6 metros with the VT 12, and 1.4 metres with VT 14. The tuning coil is a rectangle 13 era wide, ami variable in length by a sliding bar from 8 to 21 cm. The condenser consists of two concentric cylinders 3 and 2 cm long, with diameters of 1.8 cm and 2.5 cm. The choke is made by winding eleven double turns of 21-gauge magnet wire on a former 2.2 cm square and 2.2 cm long. The stopping condensers are made of alternate sheets of foil ami mica, each 2.5 cm square. _ Enough arc assembled to make a capacity of about .1)015 mfd. With the base of the .tube removed, the capacity between electrodes was about .000005 mid each. The relative location of the apparatus is most important. Connect the centre of the bottom of the rectangle to earth. From one side of the rectangle connect through the sliding condenser to the centre point; from the centre point through a stopping condenser to the plate; from the grid to the other side of the rectangle; from the plate also connect through a terminal to Hie plate simply. Three terminals are required. The left hand connects to the plate, the centre one to the middle of the bottom side of the rectangle, the right-hand one through one winding of the choke to the filament of the valve. The centre terminal also goes through the other winding of the choke to the remaining filament wire. A stopping condenser is required across the two 'right-hand terminals. Keep the three terminals together, and in the centre below the centre tap _on the bottom side of the rectangle. The current in the, rectangle will he_ greater than four amperes with an input of from 15 to 30 walls. A ihenuo couple galvanometer stems io he necessary lo measure the wave-length, h"t. there is a good field to explo 4 "* ll in detecting the produced waves, Perhaps some of our local amateurs can suggest some means of receiving the short-wave energy and, thong!) it seems an extreme (light of imagination, they might even succeed in modulating the wave by phone.