WIRELESS NEWS.
RADIO RECEIVERS.
ECONOMICAL CONSTRUCTION AND UPKEEP.
From Christchurch Press, Volume LXII, Issue 18639, 13 March 1926, Page 10.
(Specially written for “The Press.”) (By “Electra.”)
The various methods of effecting economy in receiver design and operation have been exceedingly neglected by most radio writers, so the writer feels that it is incumbent for him to dwell on this subject in detail and present a comprehensive explanation regarding the phases of radio economy to which the average reader may advantageously give his attention.
Many manufacturers have evidently given little consideration to the maintenance expense of the sets which they produce. This is proven by the fact that the total upkeep cost of a set is often (when the set has been used one or two years) greater than the price which was fixed for it. The reader will therefore, appreciate, that the factors influencing this maintenance cost should be given careful consideration.
There are conditions outside the set which also require attention, when striving for economy. The efficiency of the antennae has great influence on the range and volume of the receiver. Thus, a more expensive set will be needed to obtain the same results with an indoor antenna which could be obtained with an outdoor one. This statement applies to all sets with the possible exception of the super-heterodyne, which has sufficient sensitivity to overcome to a large extent the disadvantages of an inefficient antenna. This is one of the reasons that it is generally used with a loop. The types of antenna, in the order of desirability when considering their efficiency are: (1) Outdoor antenna; (2) indoor antenna, and (3) loop.
The most economical way of increasing the audibility of sound volume of the broadcasts is to lengthen the antenna There is, however, a maximum limit to the length. The antenna, which includes lead-in, plus the length of the ground wire, should not exceed 200 ft in length. To attain better reception of distant stations with the least expenditure, increase the height of the antenna, though a high antenna will not make the reception of DX a certainty. A crystal set, for instance, will seldom receive broadcasts from distant points, no matter how efficient the antenna.
As we are striving for maximum efficiency with minimum expenditure, No. 14 or 7.20 copper wire should be used for the antenna and the ground wire.
Insulate the antenna well, especially, the lead-in. Keep this wire at least three feet from the wall, excepting, of course, at the point where it enters the house. Here it should pass through a porcelain lead-in insulator. It pays to insulate the lead-in well. Lead-in strips which fit between the window and the sash are not always satisfactory. This is generally a copper strip, covered with thin insulating material and provided with a binding post or clip at each end. The antenna is brought in by this means without drilling a hole, but there is apt to be considerable leakage of the weak radio energy, especially in rainy weather. The volume will be practically as great, but a lead-in device of this kind is quite detrimental to DX reception.
If the landlord objects to drilling a hole for the lead-in insulator, you may easily surmount thus difficulty by inserting a board several inches in width with the proper size hole in it between the window and sash.
The crystal set costs less than any other type of receiver. As it has practically no maintenance expense, it is the ideal set for the man of limited means.
If a vacuum tube receiver is desired, the most economical are those which employ reflex.
When a reflex set is designed for a loop, however, the increase in efficiency resulting from reflexing is counteracted by the inefficiency of the loop. The radio frequency energy collected by the loop of average size is but a small fraction of that obtainable with outdoor antenna. There are many kinds of reflex sets on the market, und the prospective purchaser may best ascertain their relative merits by having the sets demonstrated.
The regenerative set is a close second to the reflex in economy.
There are many makes of these sets, most of which will give satisfactory results. It must be emphasised, however, that a single circuit regenerative receiver should not be used. It radiates and causes interference to neighbours. It also lacks selectivity. (To be Continued.)
Practically all the distant stations have been subjected to pronounced fading this last week, 2BL and 3LO in particular. These two stations fade both together proving that the trouble is in the atmospheric conditions and not at the stations.
A Poor Recorder.
Few persons realise the enormous range of the human ear. In pitch a good youthful ear can hear all tones from as low as 16 vibration’s a second to as high as 40,000. The range of intensity is likewise enormous. If we take as the strength of the weakest sound we can hear, then the strength of the ordinary talking voice will be 1,000,000. In estimating the relative strength of signals our ears deceive us; for instance, when asking persons about the comparative strength of two radio sets, one often hears them say that one was twice as loud as the other. When they say that they do not understand the peculiarities of the ear. On being questioned, they agree that the stronger set behaves as if it had one more stage of amplification than the weaker one. Now one more stage of amplification represents 200 times the power output, yet it seems only twice as loud. In other words our ears are very poor at gauging the intensity of sound. This is a very necessary condition. If our ears were sensitive to changes in intensity, they would either be insensitive to weak sounds or moderately loud noises would become unbearable.
The degree of the ear’s insensitiveness to loudness can be well illustrated by the fact that it is difficult to distinguish between two sounds, one of which is twice as strong as the other.
To successfully make the differentiation, it is necessary that both sounds have the same pitch, the same quality or timbre, and that the comparison be rapid. If as much as 30 seconds are allowed to elapse between listening to the two sounds, no conclusion as to relative strength could be relied upon.
A while ago a test was conducted on 108 sailors. They had to listen to two telegraph signals and tell which was the louder. One signal was adjusted to have twice the power of the other, and a switch was provided for throughing from one signal to the other. Each man put on headphones and listened once to one signal and then immediately to the other. After that he wrote down his choice. Some men said the signals had equal strength, some said the weaker signal was the stronger. Only 56 out of the 108 determined correctly.
2YK Wellington seems to be a very poor station so far as reception in this City is concerned. With the average set. YLDN is the only New Zealand station from which one can get good loud-speaker strength.
