WIRELESS NOTES

Evening Star, Issue 19062, 3 October 1925, Page 22

WIRELESS NOTES

[By Electron.] INTERFERENCE. I mentioned last week that there was a certain kind of interference causing a pulsation of the carrier wave from distant stations. During the last few nights a new effect has been noticed. .When tuning to distant stations with the valve near oscillation, a loud buzzing just like the A.C. buzz may be heard. This sound is very persistent, and, though it stops at irregular intervals, is generally maintained consistently throughout the evening._ Any suggestions from listeners regarding the cause and elimination of this interference will bo welcomed by all. Static also has been particularly bad of late, and “ clicks, hisses, and gripders” have caused many spoilt evenings in distant reception. Static is generally divided into these three ' classes, and each has a distinctive sound. Clicks are due to sudden disruptive charges of electricity being dissipated. The clouds become electrically charged and discharged between themselves or earth. Hisses are due to steady discharges of 'electricity from the ionised layers of the air, the potential of which may reach several hundred volts even a short distance above the earth. Grinders are due to electro-magnetic disturbances propagated horizontally. NATURE’S POWER STATION. When water is boiled, steam _ rises from the surface, this steam consisting of minute particles of the water. The action of liberating the steam impresses a. negative potential on the particles, and as these rise and collect in masses a cloud of steam holding a negative charge of no mean quantity is produced. This is the action that occurs every day when the sun’s rays fall on the sea, lakes, etc. The water is evaporated in great quantities, and thus we find present in the atmosphere masses of electrically-charged vapor. The action of the sun’s rays not only evaporates the water, but as the masses of vapor rise causes the minute particles to combine into larger particles. This action, however, is not duo to the heat rays, but to the ultra-violet radiation in the sun’s rays. The action continues until finally the minute particles grow so large and concentrated that they fall to the earth in the form of rain. Before this stage is reached the drops of moisture are collected in the form of clouds, and it is easy to realise that the amount of electrical charge held by clouds will differ very greatly. We may thus have a cloud charged to a negative potential _of 100.000 volts, while a neighboring cloud might possess a potential of 600.000 volts. The potential difference would then be 400,000 volts, and if the resistance of tho air between the clouds becomes diminished a discharge will take place from cloud to cloud. Tin's is often observed in the form of sheetlightning. When the clouds become very concentrated and the drops large they hang nearer to the earth, and sufficient potential may be built up to cause a discharge from tho cloud to the earth. This' usually takes the form of a violent spark discharge, and is commonly termed lightning. The potential may easily reach several million volts, and the widespread disturbance in radio receivers can bo imagined. In some of tho large American power stations in great cities the lighting load may reach as much as 100,000 kilowatts, and on a fine day this load will not be on. If a sudden thunderstorm comes over the city these lamps may all be switched on together and. the load built up to immense proportions in a few hours. Since it takes time to get up steam and have extra generators in operation, it will be seen that a sudden thunderstorm may cause tho shut-down of the power station through tho load becoming too great for it to carry without notice. It is here that Nature sounds her own Radio receivers are installed at the station, and the operator on duty can hear the disturbances caused by violent lightning discharges hundreds of miles away. He can then listen, and if the sounds become louder and more frequent lie knows that the storm is approaching, and can even tell roughly how far it is away. Once ho has this information ho can instruct the engineers to get up steam and have additional generators running ready to take the load as soon as it comes on.

LIGHTNING PROTECTION

While talking about lightning it may he mentioned that tho Fire Underwriters’ regulations require the installation of lightning arrestors on every receiving installation. An old sparkplug may be utilised for this, and the points sot fairly close. If a dist irbance excites the aerial sufficiently the discharge will take place across the points to earth. The plug must therefore he connected between the aerial and earth terminals of the receiver, and ns near the point of entry to tho building as can be arranged. A direct flash or lightning is of such power that no lightning arrester can hope to guard against it, and when it is realised that the power in a flash of lightning may reach several hundred or even thousand horse-power it will he obvious that this power cannot ho dissipated by any arrester. The chance or a direct (lash in tho town is so remote as to ho safely termed negligible; but in Iho open country the risk is certainly there, more especially with a high aerial standing alone. .Tn these cases the best safeguard is to use heavy aerial wire, heavy lead-in wire, specially heavy earth wire, with an earthing switch of at least 100 amp. capacity, and an earth connection covering a fair area—an old copper boiler buried in tho ground, for example. All connections should he soldered, and with tho earthing switch in, the aerial, instead of being a danger, will he an ideal protection for the house and surrounding buildings.