THE COUNTRY RECEIVER

Hawke's Bay Tribune, Volume XIX, Issue 282, 13 November 1929, Page 9

THE COUNTRY RECEIVER

EFFECT OF WEATHER ON RECEPTION.

We see everywhere signs of spring, which will be quickly followed’ by summer. The warmer weather usually has considerable effect on reception at distances which are outside the normal range of the broadcast transmitter, writes on Australian contemporary. Fading usually becomes more pronounced as tho period of daylight leng thens. Electrical storms which frequently make their appearance during summer months increase static and atmospheric noises. In the winter time it quite frequently happens that stations are comparatively easy to tune in, and for this reason possibly not a great deal of attention is given to the receiver when conditions are good. With the increase of static and fading effect it is advisable to look over tho receiver with a view to increasing its ability to reach out. Reach out by any receiver largely depends on the amplifying ability of its radio frequency amplifier and tho sensitivity of the detector. "A” BATTERIES. Every typo of valve in order to function correctly must be fed with batteries of suitable pressure. A poor A battery which is starving the filaments of the valve will not permit their being worked to full capacity. The accumulator typo of A battery seldom lasts more than approximately two years, after this time it losses its punch; and tho renewal of this unit will frequently show a marked increase in the efficiency of the receiver. "B” BATTERIES. Where plate supply is taken from dry cell batteries, which are usually termed B batteries, tho efficiency of tho receiver will very often gradually fall. It falls so slowly that it is not noticed until the old battery is replaced by a new one. A 22J-volt B battery block will frequently fall as low as 17 volts and still work without making noise. It must bo remembered that if the pressure goes down this much that in all probability the C battery presure, which was adjusted originally for the full plate pressure, will be incorrect. In this way volume is frequently sacrificed. If the B battery is suspected it should be renewed, and the pressure adjusted on both B and C batteries to give maximum results. "C” BATTERIES. A great number of operators overlook tho fact that a C battery will run down just as a B battery docs. This can only result in loss of efficiency. As the pressure of a C battery falls owing .to the using up of tho chemical energy within the cell, its resistance rapidly increases. This results in not only a fall duo to incorrect pressure on the grid of the valves, but also inefficiency due to the added resistance in the grid circuit. Tho presence of this high resistance frequently makes its appearance in the form of a highpitched audio-frequency whistle. This whistle will continue during the wnole time that the valves are lit, and can very often be heard quite loudly during the reception of even the most powerful station. The changing of the C battery for a new ono is almost cer tain to overcome this disadvantage, and will result in quiet and better reception. VALVES. Valves do not always terminate their useful life by a burn out of the filament. The modern valve has what is termed a coated filament. This means that the filament has deposited on it a coating of some chemical, usually an oxide, to increase the electron emission from tho filament while it is heated. It is not uncommon for a valvo to exhaust this coating and loose its emission although the filament continues to light. When a valve reaches this condition it is said to be tired. If tho radio-frequency amplifying valve. Is approaching this condition its ability to amplify will fall off considerably. This moans, then, that the signal level being impressed on the detector grid is considerably less thaan is possible with a new valve. With altered weather conditions this may prove just the dif ference between good reception from a distant station and very indifferent reception. THE DETECTOR VALVE. The above remarks apply to the detector valve, and ns a consequence of its loss of electron emission is is likely to become insensitive, and as a con sequence will not pass on the same amount of audio frequency output as would be tho case with a new vnlve. This results in the loss of volume from tho reproducer. AUDIO-FREQUENCY VALVES. Tho loss of emission is more likely to happen first in the audio-frequency valves, as these are called upon as a rule to handle much more current than the preceding valves. The adjustment of C battery should never be undertaken with the plate pressure on, as the temporary opening of the grid circuit for C battery adjustment will cause immediate overload of the electron stream far in excess of the total load for which tho tube was designed. In this way it is possible to destroy a perfectlj' good valve in a few seconds. If valves are replaced in any portion of the receiver tho adjustment of A. B, nnd C pressures should be completely revised so that best results may bo obtained from the receiver.