A Further Analysis of Fading Reports

Radio Record, Volume I, Issue 14, 21 October 1927, Page 12

A Further Analysis of Fading Reports

In a further review of the valuable data secured from listeners in connection with the fading investigation, "Megohm’"’ ‘discusses some of the features noticed, and presents an interesting set of graphs from four different points. :

‘This week, in connection with the fading test, we publish four graplis from different parts of the VominionPort Waikato, Te Aroha, an island in the Hauraki Gulf, and Invercargill. These graphs were prepared by the set owners with a view to being of assistance in the test, and they prove to be of great interest. The first graph is given just as originally set out on squared paper, but the next two, mot being fo the same scale, have been carefuliy redrawn in order to make compariscn easier, The last one, from Invercargill, is given as originally set out, tre length being correct, though the amplitude, or movement up and down, is on a maller | scale. ‘The main point to notice is the position of groups of, irregularity of reception in each one, also making a slight time allowance of up to a minute either way, owing to quite possible discrepancies in timing. It should be noted that at preseut only the first day of test, September 26. is being dealt with. THE GRAPHS COMPARED. It was unfortunate for the station that during the first few minutes transmission ‘"‘went to the pack,’’ and fading was evideut here in Wellington just prior to the second break. Many listeners making records had not tuned in at this time, anG so did not. record the breaks, whilst others have only regarded ‘them as fades. In. three of the graphs printed herewith the breaks are clearly shown. It will be noticed that the graphs are fairly unanimous in noting excessive volume, which seems to have occurred in bursts during the evening, and if controls could have been used this could have been made normal, although in excess of that at the commencement of the session. Volume was greater, and fading less, during the second half of ftfie programme, generally speaking, as is shown by a) great many reports. Whilst graphs @tand 4 show a fade at &8, this is unnoted in 1 and 2. Reception apears to have been generally bad or indifferent until after 8.11, when matters improved Around 8.25 was a bad period, and appears as such in a large number of reports. There is -a deep sag here on all four graphs, but Invercargill, being further away by nearly two hundred miles, felt it sooner than the otters, apparently feeling the first sign of weakening. The curves are, with the exception of No. 8, unanimous in a _ general steadying-up just before 8.50, and with a great many distant listeners this steadier and stronger reception continued until 10 o’clock. From the general survey of reports already made it is probable that graph No. 1 represents a fairly average curvé for distant reception of 2YA on this particuJar night. Graphs 8 and 4 show eonsiderable fluctuation from 9,0 to 10.0, but they are probably quite correct chartings of reception at the pos:tion they represent. It is quite possible that these two receivers are rather more selective than os. 1 and 4, and would, therefore, be more susceptible to any interference with the transmitted wave that had any ftendency to cause alteration in freunency. A good graph was sent in from Napier, but as it only gives the first half of session on the 26th, it was not included with those illustrated, but will, no doubt prove usefn] for comparison. ‘The first half, as recorded, shows the first break to inandibility at §&.64, &.154, bad modulation, at 8.22 a drop m volume, as shown in No. 4, at 8.25 shown on Nos. 1 and 2. At 8.35 there is a drop to about half voiuime, as on No, 1, and a similar drop at 8.389}, as on_No. 4; then at 8.473 a sudden drop, as in

No. 1, returning to normal one minute before 9 o’clock. HOW RECEPTION VARIES. A survey of the charts received certainly gives an impression that distant reception in the same locality may be either good or bad. A settler, say, 550 miles from 2¥A, may be getting enjoyable concert marred by very little fading, while his neighbour, only a few miles away, gets results that are at best nothing more than indifferent. in such cases distance gives no advantage to the one over the other. Then one begins to seek for possible other differences, height and direction of acrial, its insulation, the efficiency of the receiver itself, and possible difference in operating. ‘Then local geogtaphy, the position of hills, their composition, areas of bush, may all be potential contributors to the general disturbance of uninterrupted reception. In connection with the foregoing remarks, the following « sentence contained in a report from the Far North shows a typical example. Enclosing a chart showing only a few fades, all slight, the report states: "I do not attribute fading to the stations, as a listener friend of mine a couple of miles away rately suffers fading."’ ‘This i :

"ee from a place 160 miles north of Auckland, where the person reporting 1s troubled with fading to a certain extent from all stations, LYA in particular. Reception of 2YA in the lar North 1s on the whole good, and tading comparatively slight, and on looking at the map we sce an apparent reason for this. Yaking an. air-line from 2YA to Daergaville, the wireless waves travel the] whole of the distance, 360 miles, over water, with the exception of about 60 miles across Taranaki. Going southward, the position is very much the same, so far as southern coast towns are concerned, for waves froin 2YA to Dunedin have cnly to cross a few miles of land on the Banks Peninsula, the remainder of the route being all over water. There are set owners in Nelson district troubled with more fading than are others two or three lundred miles: further away in either island. One of the objects of this test is to endeavFour to find out whether or not there are certain zones were fading is more prevalent than in others, but it will take some little time to arrive at a conclusion of this kind. Te whole matter is one for calm thinking and continual comparison of reports. Further diagrams will be published next weck, showing other aspects of the question.

LOCAL INTERFERENCE. Some of the reports from populated districts contain a gircat number of slight fades indicated, much more than the average for that place. In such a case one of two causes will probably be responsible. ‘The receiver is either ultraselective, but possibly not very sensitive, and so responds to slight differences of frequency that would be unnoticed in a broadly-tuning set, or else reception is being marred by a nearby radiating set. ‘There are’ may contributory causes of radiation from receivers which, however, it is not necessary to more than mention here. Reports show that the five-valve neutrodyne is an extremely popular cireuit, and if such a set is propetly neutralised, reasonable handling will‘cause no trouble or interference. Some types of neutralised circuit require reneutralisation when a new radio-frequency valve is put in, and unless this is attended to, radiation will occur Owners of small sets without a proper knowledge of tuning-in may cause much trouble if they persist in attempting to bring in a station that 1s beyond the capabilities of the set. Such | attempts are generally accompanied by violent oscillation, which has a varying effect upon the reception by othe sets

on the same wave-length. Howlisg and distortion of signals is the tsual result, but it is often accompanied by a "‘blanketing"’ effect upon neighbouring sets which is equivalent to fading, and miay reduce the volume in other receivers to half, or cut out strong signals altogether. Experienced listeners can usually tell when fading is caused by locat interference, but mot so the novice. Quite likely steps will have to be taken to suppress undue or continued radiation, which at times is apt to be au imtolerable nuisance. , DAYLIGHT RECEPTION. There 1s not very much mention of daylight reception in the reports, but where reference is made, it is .stated to be better than evening reception, and usually free trom fading. The reason for this is that the wireless waves can only travel effectually near the earth in the day-time, so that they are not distorted by meeting waves reflected from the heaviside layer, such reflected. waves frequently not synchronising with the ground waves on rejoining them, and ‘thus complicated blurring and distor ‘tion is caused. A report from Helens» ville states that good speaker reception is chtained im the afternoons with a three-valve set. ‘This appears to . be good reception for a distance of 320 \ miles in daylight, and speaks well for the carrying power of 2YA apart from the fading trouble. At this stage any ideas ‘expressed must not be taken as final conclusions, as they may have to be modified as the investigation continues.