WIRELESS NEWS

Press, Volume LXVIII, Issue 20648, 10 September 1932, Page 7

WIRELESS NEWS

(liy "-MAX.''.) Quitu u number of receivers have a distinctly noticeable hum between items, it is not at all comparable I with needle scratch on the old-type gramophone using steel needles, but to the man who takes a special pride in having a silent background it is not. always pleasant. Recently a receiver wa>> built up employing au Aus-truhan-nmdo timed choke. This choko is mude to tune to the fifty cycle A.C. frequency, but when the set was coripleied tJicre was a distinct hum. Tlio addition of a small fixed condenser across the choko cured the trouble, showing that the choke did not tune correctly. Fortunately tho natural ircquency of the choke was slightly above filty cycles, and the added .0001 mid condenser was just sufficient to bring the frequency down to fifty cycles. Had the natural frequency of the choke been below fifty cycles it would have made matters worse by adding a shunted capacity. The u.-o of a filter system timed to the A.C. supply is not a new idea, but does not appear to bo employed to any extent. Filter chokes of generous inductance and largo electrolytic condensers meet with the most favotir. It is possible that the reason is tho use of more than one supply frequency, but if this were the sole reason, then a choke for sixty cycles con hi be made and a small condenser added for fifty cyelo working.

I . "Radi3 News" has been giving a series of articles on small and largo outfits for partially deaf people. A one-valve amplifier complete with a special microphone and oar-piece and batteries contained within a box about tho size of a small box camera is tho design for a single person, the largo outfits are for churehes, etc., where special seats and ear-phones are provided for a number of persons. It appears that in America, where different types of eids for the 'deaf can easily be procured, the cheapest of apparatus, consisting of a .microphone, battery, adjustable resistance, and < n car-piece, costs about £7, and others run up to £25 or more. From a detailed price-list, it seems that a good microphone sells a 6 about £4. These types imported into this country would cost about double, it appears that at least three ranges of >ound frequency have to be provided for and threo varieties of microphones are needed to enable customers to select the one most suitable for them. Sonio persons arc deafer to high frequencies, others to low and still others to medium frequencies.

A one-valve amplifier employing a low consumption of current could bo built at a cost of about one pound, but the microphone transformer (30s), microphone, small cabinet and ear-phone would bring up the price. The writor suggests that the double grid valve similar to the 141 type would be most economic in both "A" and "B" battery consumption, and it would be easy to design an amplifier using a pair ot "C" bias batteries of nine volts for the plate supply and torch cells for the filament, which takes only 60 milliarnps. A reliable microphone is essential so that the background noise, to quote one feature, should be a minimum. Some of the special microphones use polished balls of carbon instead of irregularly shaped granules, and the diaphragm is generally extra thin. Ihe subject is well worth experimentation by any radio dealer who has enquiries for apparatus of this kind.

Two new appointments are announced to the staff of the Broadcasting Board One,is that of Mr J. 11. | Smith, A.M.1.&.E., who will be engineer at 2YA and who was lately in the employ of the Post and Telegraph Department, where he has had considerable experience in radio telegraphy and telephony. Mr W L Harrison, 8.E., B.Sc., etc., ' has been appointed to 3YA. Ever since Station 2ZW came on the a .V*5 Harrison has been responsible for the engineering side and the high quality of transmission is sufficient proof of bis .abilities as a radio engineer. Mr Harrison has the distinction of being the first amateur to secure permission to erect an amateur transmitting station in Wellington after the conclusion of the "World War.

Station 2GB, Sydney, is to have two new studios, on which the sum of £IOOO is to be expended. The control equipment is to be overhauled and brought thoroughly up-to-date, £ISOO covering this portion. When tfle work has been completed it is claimed that this station will have the finest studios and apparatus for controlling purposes in Australia. Very great care has been taken in designing the additional equipment, and judging from the details the claims made will be justified.

"Wireless Weekly," in an article giving complete details, announces that the British Broadcasting Corporation intends to make records of the more important of its programmes, so that these can he put over the air from the newly completed Empire short-wave station. This will overcome the difficulty of the difference iii times in listening-in on the two sides of the globe. The recordings can be used when New Zealanders and Australians are listenirig-in, and the same method can he adopted for relaying to othor parts of the Empire. Besides the direct transmissions, copies will be sent to those stations who join as subscriber to the new service.

In Eussja full use is made of the possibilities of radio for purposes, as well as for entertainment. Orders hare been issued by the Soviet that over thirty-thousand loud-speakers must bet installed in the streets of Leningrad and in the factories and workingnjen's clubs.

We recently had cable news of the altitude breaking records made by Professor Piccard. The object of tli3

Notes From Far and Near

attempts, of which there were two, woro iiiuitiy to ootain ecientinc reg.iraing eosnne rays as well as tho reception ot sbuntl waves and also covering radio transmissions from a height not reachable in the ordinary way. A ■ secondary use for the wireless equipment was as an emergency in the event of a landing in an out of' the way place.

Any Jand with ;i sea front is liable to be a source of smuggling, and the employment of apparatus which is sensitive to a ray of invisible or infrared light can prove very useful. A stretch of water can be covered by a beam, and if any object crosses the ray the interruption will operate a signal. Smugglers naturally work under cover of darkness a great deal, and it is said that along part of Germany's coast this method is adopted to detect smuggling.

A number of Australian set manufacturers are adopting a new method of receiver design, which does away with one valve. American procedure has proretl that the design is a practicable one. The idea is to use a penthode as a combined detector and power output stage. Sufficient volume can be obtained to satisfy the requirements of the average listener. Another feature is that there is no hum as there are no stages of audio amplification, and this allows for cutting down the sizes of the filter chokes and condensers. In fact the speaker field winding will suffice for the purpose of smoothing. With n large range of penthodes, some delivering up to nearly ten watts of undistorted output, there seem to be excellent prospects for the new designs. .

Complexity of design does not necessarily mean a, complicated system of wiring, as a photograph of a recent type of sunerhet is a marvel of simplicity under the baseboard. Hadio engineers are evidently rising to the occasion and reducing assembling costs.