WIRELESS NEWS.

Press, Volume LXI, Issue 18461, 15 August 1925, Page 11

WIRELESS NEWS.

0 NOTES FOR THE BEGINNER. CRYSTAL VALVE AND AERIAL. (sfecijllly ■warrrKJ ros "thx psiss.") By "Elcctra." In the crystal set, tho crystal detector is the part that most often gives trouble. Not all of them are sensitive on the entire surface of tho crystal. Most of them are sensitive only on certain spots, which are very difficult to find, unless it is when listening to a local station. A device known as a test buszor is tho thing to find theso sensitivo spots, and not to keep lifting the point from the crystal in an endeavour tr; find a good spot. The test buzzer takes all tho work and worry out of a crystal detector set-. The parts required are a small buzzer, dry cell and a means for making and breaking the circuit of buzzer and dry cell, which may be a push butt-on or switch.

Details are as follows: IVocure an ordinary buzzer and run a wire from each terminal to the ..two terminals on tho dry cell. Now twist a few turns of wire around the earth lead and connect one end of these turns to the terminal that is connected to tho vibrating arm of the buzzer. Tho switch or push-button is connected into one of tho wires running from the battery to buzzer. It is operated thus: The switch is closed which starts the buzzer vibrating, the telephones are on your head and the crystal detector is adjusted until the loudest sound from tho buzzer is heard The louder the sound, the better tho "point" you have.

A valve detector is much more complicated than the simple crystal, but it will brine; in many distant stations, so it is worth the extra expense and adjustments. There aro several typos of valves sold, but it is well to stick to the standard makes that are nationally known and have been for several years. Some of the others are good, but it is distinguishing one from tho otuer where poor results come. Valves vary as to filaments, cifiTCiV* and rheostats. The "VTD will operate' from a single dry cell, because it onlv requires 1.1 volt for operation, and the dry cell gives 1.5 volts. A Cohm rheostat should be used. The w199 type requires 3 volts for operation and two dry celb woul<j supplv this amount, but only temporarily, so three dry cells are necessary and a rheostat of 30ohms. If four drv cells giving 6 volts are used, or a 6 volt storage batterv, the filament rheostat should bo increased to 60 ohms. The large type of valves such as 201 A require 5 volts for tho filament, and this is usually supplied by a 6 volt storage battery. Drv cells may bo used, but they are costly. Like tho w199 type, a high resistance rheostat is used, and it should be about 25ohms. There aro large valves used for nothing but detectors, such as tho vv2COO. This roquiros o volts for filament lighting, but consumes ampere, which is four times that of the other largo valves and draws so much current that a 6v storage batteTy is necessary. A 6ohm vernier rheostat should be used with this valve. The "B" battery or plate potential is critical and runs between. 15 and 22i volts, while the plate voltage of the others, which may also be used for radio or audio frequency amplification, is not critical and will vary between 22i and 60 volts. Radio amplification is when the signal is amplified before detection and audio amplification is after the signal has passed through the detector. If you have not met with success with your first aerial, it may be due to the aerial not being high enough; not being properly insulated or situated between buildings that screen it. | Not • being insulated properly means j loss of energy by the signals leaking from the aerial to,the supports, whether they be masts, chimney, roof or fence. ITEMS OF INTEREST. One type of aerial that has not as yet come in for a great deal of discussion is the vertical rod type, as used by Mr Edwards, 3AO Christchurch. It is the latest fashion, but the idea if by no means new. KOKA. the big U.S.A. broadcasting station, has been using one Tor some time now and many Americans and Australian* use them. It has been almost impossible, however, to obtain reliable as to how it compares with the usual typo of antenna as regards signal strength. This is because the amateur usually dismantles the old aerial 'before erecting the new one. There is only one reliable way to decide this question. Have both aerials np and receive the same station on the same night on both aerials. Mr O. D. Maclurcan, in his notes on this subject in "Radio," states that he has done this when transmitting to English and Yankee "shapis" and thev all reported his strongest on the vertical pipe aerial. I would be pleased to hear of results obtained by anyone using this type of aerial. The construction is as follows:—Five or six 6-foot lengths of ordinary galvanised down pip© joined together and well sweated. Some sort of a ton is fitted so as tokke n the rain water out. The whole is up-ended and slipped over the top of a large swan-neck insulator screwed into the side of the house. The lead-in wire is soldered to the bottom of the tube. Two sets of guys will be wanted and 4 heso should preferably be of some sort of rope that will not shrink. Mr Jack Orbell is doing some good work with his station ZIAX. He is putting out splendid Signals from his 250-watt tube and is one of the loudest Now Zealand stations. A lot of reports are coming m about the variation lately of 3LO's transmissions. This station is using a set more or less of a temporary nature since the drop in wave length. A new set for the higher power is being installed bit by bit, and soon everything will be O.K.

If yon get a kink in your aerial wire, the least strain on it will break it 'Your aerial should also havo more insulators in each end. 3AC are to he complimented on their 8 to 10 concert last Tuesday evening. On Tuesday, 18th. Mrs Gobbe's concert party and others will put on a pood programme from 3AC. On Friday, 21st, the Rua;by street Methodist Church Choir will broadcast from this station, and on Tuesday, 25th, from the same station the Christchurch Banjo Band will again give one of their special concerto. It is also possible that the Woolston Band will be on at this station in the very near future The Radio Society are holding & special radio demonstration to eet funds to keep SAC going. It will be held in the Y.M.C.A., on August 25th, and there will be .various well-known types of Bete op exhibit. The admission will be by silver coin and all interested in radio are advised to be present. The half-yearly general meeting of the R.S.C. will be held on August 27th on? C ' u k room > .St. Asaph street. 2BL. Sydney, is working on a temporary wave-length of 363 metres. It sometimes happens, particularly when finishing off the wiring of a set, one wants to get at a spot which - e soldering iron is too thick to reach. In this case a piece of square tinned busbar wire should be wound several times around the head of the i^on. leading a j rejecting end, either straight or bent, as the circumstances require. The whole U then heated up, and in reasonable expert hands the wire end will be found to retain the heat eufiU cwnuy keg to complete the job