SEEKING GOOD RECEPTION

Radio Record, Volume I, Issue 19, 25 November 1927, Page 12

SEEKING GOOD RECEPTION

THE VALUE OF AERIAL INSULATORS

Starting at the aerial, good insulators are perhaps the first consideration. The porcelain pulley pattern answers well in fine weather with, gay, three in series at each end, and ja ‘wet weather they may be effective if the rain is not very heavy. But there will be occasions. on which heavy rain will cause frequent leakage, giving an effect similar to fading. Such leakage is caused by rain reaching the insulators more quickly than it can ‘run. off, and a good method of reducing this leakage is to give the insulators an occasional wipe over with oil or vaseline. A better method is to purchase a pair of pyrex insulators, costing 5/- the pair, ‘and include one of these at each end of the aerial. The special glass of which these are constructed has a repellent effect upon water, and minimises any loss of signal strength caused by leakage. LEAD-IN AND HALYARDS. The best insulators to use for lead-in wires requiring support are the post-office or ‘"‘petticoat" pattern, as these give practically perfect insulation in all weathers. Attention should be given to the aerial halyards when necessary in order to kecp the wire at a reasonable tautness. To prevent halyards making an irritating noise by flapping against the pole during a wind, a crosspiece of wood can be nailed to the pole a tew feet above the ground, and the halyards passed through a notch in the end before fastening them to the pole. This should keep the halyards clear of the pole for their whole length. } Then there is the old slogan about having a good earth-many listeners are still handicapping their reception by not testing other earth connections than the water-pipe, which is sometimes quite good, but not always. A true constructor is always testing, altering, improvirs, but the set-owner who is not a constructor should not let things rest until he is getting the best reception possible with the apparatus in his possession, and improvements of aerial and earth circuits are within the capabilities of most people. The Browning-Drake four-valve set, made exactly as described in this column, with a Ferranti A.F. 3 transformer in the second audio stage is capable of giving reproduction of a thoroughly high-class order, with full mellow tone, big volume, and not a '¢race of harshness or distortion. But the loud-speaker, also, must Le equal to the task of handling the tone, pas.sed on from the transformers. And this quality and volume is maintained, apart from interference, on reception of all main New Zealand and Australian stations. With a high-

ae | grade of cone speaker the soprano notes are there, the low humming double-bass of the orchestra, the double-diapason of the organ, are there too. "Megohm" would like to be able to hear the ‘tone obtained from each set that has been constructed from his description. Probably few would come near to the tone of the original, and yet by patient adjustment any constructor should be able eventually to bring his set to give reproduction as nearly perfect as is possible. . Ready-made sets are built to sell at a competitive price in most cases, and as 2 natural consequence purchasers cannot expect to get more ‘than they are paying for. The inexperienced person is generally the buyer of a set, and consequently is unable to judge properly the merits of one set against another. A person not used to listening-in has no standard against which to judge quality of reception, and is liable to be carried away by the novelty of the situation and buy almost the first set demonstrated. If this is a set of good design, all may be well, and tone may be good and pleasing. If the set is a low-grade affair, with. trashy components, tone will be raspy, all the emphasised notes will blur and blast, unless volume is kept down almost to inaudibility, and general dissatisfaction with reception will soon creep over the unwary purchaser and his family. These remarks apply from a crystal with one amplifier upwards, — , READY-MADE SETS. A large proportion of bought sets are fitted with audio transformers, and if the set is not giving satisfactory tone, and these transformers are small in size and of poor design, then it would be worth while to have at least the second one replaced by one of modern type. The writer is getting to feel tired of emphasising this point, but from the large amount of information lately received on the question it is evident that there are far too many sets and loud speakers that are unable to handle a little extra volume without distortion. Then there is the last audio valve. In a ready-made set it is a simple matter to put this in where an ordinary valve is in use. If the provision of grid bias is any difficulty, then a power valve should be chosen that does not require too great a C battery voltage. The PM 254 and 256 at 100 volts (12) and 125 volts (17) high tension require grid bias as shown in. parenthesis, Radiotron UX 112 at high tension voltage of 90 (6) and at H.T. 135 (9), whilst Radiotron UX 171 requires grid bias as shown after the high-tension vol- _ -E

aeeieiemienesmaimemmaten tite ire enmeennememattamet nen ennai eines tage in parenthesis-90 (16%) and 185 (27). The C battery is chiefly utilised to improve tone, whilst also increasing volume, and no amplifier should be run without it, Listeners: who live in the country and are dependant upon dry cells for current are more limited in choice of valves, and tor them the Radiotron UX 120 or PM 2 are suitable, requiring at 100 volts HT, 16 and 10 volts grid bias respectively. THE CHOKE, FILTER Every set with four or more valves should be provided with an efficient choke filter at the output. This arrangement has already been described, and is included in the fourvalve Browning-Drake circuit already published in this column. The choke filter improves tone, prevents distortion by overloading of the speaker, and protects ’phone and speaker magnets from demagnetisation. These filters can be bought readymade as one component and connected to the set. These should be tried out, if possible, because some makes may not improve the tone of the set as much as they should, THE LOUD SPEAKER. The choke filter, already mentioned, will make matters much easier for the loud speaker, but the ideal way of getting good volume without overloading the speaker is to have both a cone and a horn speaker connected in parallel. This is the best method of reproduction possible at the present time, and has already been dealt with in this column. Probably there will soon be a speaker combining horn and cone in one unit, both operated by the same armature, but until this is available, two speakers are best. They should be placed two or three feet apart. These notes are really a resume of previous articles in order to give readers in concise form a few outstanding improvements that may be made in many receiving outfits with ereat gain in quality of reception.