RADIO TOPICS.

New Zealand Herald, Volume LXIII, Issue 19455, 11 October 1926, Page 16

RADIO TOPICS.

SHORT-WAVE BROADCASTS. AMAZING VOLUME OF SOUND. I A PECULIAR DISTORTION. BY THERMION. Special test transmissions .from tho 'American broadcasting station KDKA, located at Pittsburg, were conducted last week for certain Australian newspapers on a wave length of 63 metres, and New Zealand listeners had an opportunity of hearing these distant broadcasts on simple receiving apparatus. This broadcasting station, KDKA, was the first in the world to commence broadcasting services and has the honour also of being the first to broadcast on a wnvo length below .1.00 metres. At the present time simultaneous broadcasting is conducted at KDKA on a number of different wave lengths and the transmissions on 63 metres are of particular interest to followers of broadcasting progress. Unfortunately conditions of severe static obtained last week and tho test Was considerably interfered with. Listeners to tho broadcasts, however, had an opportunity of noticing the remarkable loudness obtainable with the simplest of receiving apparatus. On a receiving set consisting of a valve detector and two stages of audio-frequency amplification the signals were at good loud speaker strength in spite of the distance of tho broadcasting station. This, of course, is to bo expected when it is remembered that New Zealand amateur transmitters can conduct world-wide communication on low wave longtlis, the receiving sets used having only two valves. The broadcasts had tho usual defects of short wave telephony transmissions in that there was pronounced distortion duo to rapid fading. All listeners are familiar with the effect of fading signals, but the fading of tho low wave length broadcasts is unusual, owing to its rapidity. On a single musical note tho strength of tho signal may vary from loud to weak to loud again in intervals of less than a second giving distortion which is sufficient to considerably mar the musical quality of the broadcasts. THE TESTS REBROADCAST. The test transmissions were picked up and rebroadcast by some of tho Australian broadcasting stations and by 3YA, Christchurch. Through listening direct, to KDKA the writer did not hear the rebroadcasts, but apparetlv they were not very successful owing to the severe static and to the fading, although the attempt must havo interested listeners who have not short wave receiving sots capable of tuning to the original wave length of 63 metres. If the characteristic fading effect of short wave • broadcasts can he eliminated then there would be no difficulty in hearing British and American broadcasts conducted on these wave lengths in New Zealand either direct or as rebroadcast by local stations. It is in this direction that we must look for tho possibility of international broadcasting whereby a speaker in London, say, could be heard by listeners throughout the world on simple and cheap receiving sets. When the present inherent defects are overcome, as they undoubtedly will be, listeners will havo tho broadcast programmes of tho world at their disposal, but it will be a few years before this desirable state of affairs obtains. There is another point of importance In connection with short-wave broadcasting and that is the large number of broadcasting stations which can be accommodated within a comparatively narrow band of wave lengths without interference between them. Between 30 and 60 metres 250 broadcasting stations conld be placed without the slightest interference, while 1000 broadcasting stations could operate between 10 and 30 metres. While applauding tie present efforts of those j pioneering broadcasting on short wave lengths we should therefore hope for their ultimate success in overcoming the existing obstacles.

AUSTRALIAN BROADCASTING. Unfavourable atmospheric conditions marred the pleasure of listening to the Australian broadcasts last week and on Wednesday night there occurred the unusual phenomenon of the broadcasts being practically inaudible due to some freak atmospheric effect. The cause of tho inaudibility could not be stated as there is yet so much to be learned regarding the effects of external conditions on wireless transmission. It is fortunate that such an effect is quite rare. The Sydney station, 2FC, showed a falling-off in the quality of its transmission after its first broadcast on 442 metres, but a steady improvement has been noticeable during the course of the week. On Saturday evening 2FC was the loudest of the Australian stations, but the generator hum is still pronounced. Listeners may expect reception from 2FC in the near future. The Sydney Theosophical Society's broadcasting station, 2BG, operating with a power output of 3000 watts, is easily heard at loud-speaker strength in Auckland, and the programmes are quite good. This station has, in common with the high-powered Anstralian stations, a distinct generator hum. It was understood until recently that a rearrangement of the wave lengths of the Australian broadcasting stations was under consideration, but a Melbourne writer states tho present wavelengths will not be altered. This is a pity as certain modifications would benefit Australian as well as Zealand listeners. OUR STATIC TROUBLES! The excessive amount of static interfering with the reception of distant broadcasting last week has caused manv to wonder why the interference has* not been eliminated. Static has been one of the great obstacles to radio progress and has necessitated the erection of much higher-powered telephonic and telegraphic wireless stations than if static did not exist, or if it could be avoided. High power is used at the transmitter so' that its signals at a distance may be as loud, or louder than, the interfering noises so that the signals may be intelligible at a distance. Static is caused by wireless waves sent out from lightning discharges during electrical storms so that it has always existed, but its presence was not known until the commencement of radio signalling. Static can travel long distances and much of it that wo hear may well have oomo from the other side of the world. Direction-finding observations in Auckland have shown that the greater portion of our static comes from north of Australia. The broadcasting that we hear is sent out by means of wireless waves and the problem is to suppress the static wave without suppressing tho broadcast. Static waves, too. are not of a definite wave length, having nil. wavelengths present in its waves thus making a further complication. The problem is analogous to that of eliminating unwanted noise in a gramophone while leaving the .music audible. So far the best brains of the wireless world have not discovered a successful method of eliminating static. When listening to a local broadcasting station there is, of course, no interference because the broadcast signals aro so loud as to drown out even the loudest static and becatiso tho valves of tho receiving set are not adjusted for maximum sensitivity. So far it would seem that, tho ultimate solution of tho problem lies in the development of broadcasting stations of pernors sufficiently high to oovcr the region kre intended to serve, with a sufficient to be much

Fortunately there are frequently clear conditions when static is almost or entirely absent and those who crave for distant listening must take the bad with the good. A theory _ has been advanced that the amount of static is in some way , conneced with the prevalence of sunspots, and it this is so static disturbances should increase until 1927 and then go through a decreasing cycle for the ensuing eleven years. THE CRYSTAL SET. Since the commencement of broadcasting from tho Auckland and Christchurch stations there has been a rapid increase in the number of listeners and a large proportion of the new listeners are purchasing simple crystal sets. Tho crystal set is cheap and no batteries being required, there are no upkeep expenses. Tho rango of the crystal set is limited to local stations, although under exceptional conditions distant stations are audible where a sensitive crystal and a good aerial arc used. The crystal detector gives a purer reproduction of broadcast music and speech than is obtainable with valves. The loudness of the music can bo increased by the addition of one or two stages of audio-frequency amplification and the writer has heard of a number of cases recently where loud-speaker reception of the major Australian broadcasts is being obtained with a crystal detector and two audio stages. A crystal set, like any other, should be carefully designed and low-loss components used if the best results are to be obtainedListeners who are experimentally inclined and who havo valve receiving sets should try the effect of replacing the grid condenser and leak of the detector valve by a crystal detector when listening to local music. The ordinary detector valve then acts as a low-frequency amplifier so that signal strength will not be impaired, while greater purity of music will result.

NOVEL CLUB MEETING. A recent experiment condncted in America by the West Gulf "Fone" Club, the members of which are amateur transmitters, has attracted no little attention. It was suggested that owing to inclement weather members should hold their meeting " in the air," and a wave length of 190 metres was decided upon. At the appointed time all members were at their sets when the president started up his radiophono and called the meeting to order. The roll was called by the secretary and, as thoir names were spoken, the memhers picked up their microphones and answered "present." The subsequent business was conducted in a similar manner, the session lasting more than two hours and meeting with such general approval that it was voted to hold similar meetings at regular intervals. There are possibilities in this where memhers of any association are widely scattered and further developments will be awaited with interest. HERE AND THERE. There has been a noticeable reduction in the whistling interference due to bowling valves during the past week, but whether tins /was due to excessive static or to broadcast lectures on tho manipulation of sets was not evident. Remarkable, crystal recaption is repoited by a young lad at Ohoka, 13 miles from Christchurch. He says 3YA can be heard 15ft. from his loud speaker, and IYA on the phones without an amplifier pf any kind. The Dnnedin station, 4YA, will in future transmit only on Sunday, Tuesday, Thursday and Saturday nights and on Friday afternoons. The alteration has been made at the request of Dunedin listeners and dealers, to enable them to have moro time to tucfo. in 3YA, Christchurch. There is a rumour current that the authorities are to be petitioned to lower the wave length of the latter station to 270 metres. One of the old grievances of Auckland listeners was the interference to bioadcast reception by the local spark station, VLD. Lately a low-power continuous wave transmitter has been in use during broadcast hours, and last week a new 1500-watt valve equipment was installed and has been interfering to a large extent. This may be regaided as a testing period for the new apparatus, and it is to be hoped the new interference will be eliminated. The classes of instruction in wireless which have just commenced at the Seddon Memorial Technical College have a roll of over 40. The students all desire to learn Morse so that an increase in the number of Auckland amateur transmitters can be expected in the future.