AERIALS AND EARTHS

Nelson Evening Mail, Volume LXXII, 14 April 1939, Page 6

AERIALS AND EARTHS

AIDS TO RADIO RECEPTION PRACTICAL ADVICE FROM EXPERTS So much improvement can be effected in radio broadcasting reception br listeners providing efficient aerial and earth systems that Post Office radio inspectors hold the opinion, after investigating thousands of complaint* every year, that quite half the trouble* can usually be cured by attention to these essentials, and the proper maintenance of the radio receiver, particularly its valves.

Based on experience of the radio inspectors, the following information ha* been prepared to assist listeners in maintaining first-class reception. An outdoor aerial is preferable, if it can be provided. This equipment may, however, cause crackling noises m their receiver if it has been erected carelessly. Outside aerials which have poor insulation at the points of suspension, or which make intermittent contact with earthed bodies such a* metal or trees, are a frequent source of trouble.

If two metal stay wires used for supporting a mast cross one another and rub together, interference may be caused even though the aerial Itself is insulated from mast and stays by one or more insulators of the type commonly used.

Where the down-lead to the house j* brought to a lead-in tube which ha* terminals, interference may be caused by a loose contact due to the terminals not being screwed down tightly. This type of trouble would be in evidence mostly on a windy day, and particularly if the down-lead has not been anchored in addition to the lead-in terminal connection.

Corrosion at contacts, loose connections at lightning guard, and broken connections to earth rods or clips are common sources of noise, as are also loose contacts in aerial and earth plugs on the receiver itself.

House wiring faults may consist of loose or corroded connections and broken springs in electric light switches, loose connections at fure boxes, etc. These faults are fairly common.

Where telephone or power installations are carried out in lead-sheathed cable, interference of a severe nature may be caused if the sheathing is not effectively bonded to earth. A bonded cable touching an unbonded one or other earthed object will be very troublesome when vibrated. A case is on record in which the cause of severe interference was traced to an unbonded lead-sheathed cable which ran along an outside wall of a house before entering the building through a corner of a ventilator. A perforated metal grille was fastened over tha opening on the inside, and the vibration caused by passing traffic caused the cable to rub against the grille. The aerial lead-in was also brought in through this ventilator and received an induced charge which was amplified in the receiver.

Domestic electric lamps and street lamps will occasionally cause serious interference to radio reception prior to a complete break-down of the filament. The filament breaks and then makes intermittent contact before the final rupture. Loose connections in electric irons, cookers, radiators, vacuum cleaners, etc., are also possible causes of interference.

Many listeners believe (hat. in these days when supersensitive sets are the rule, an earth connection is unnecessary, and in many cases a disadvantage. "I have never yet investigated a case of radio interference which could not be substantially reduced when a good earth was connected to the set.** reported a Radio Inspector when surveying his official experiences in this connection. "I have come across cases where the joining up of the earth connection has increased the amount of interference received, but in each case I have been able to demonstrate that this particular earth was very inefficient in that the resistance to earth was high, due to the lead to the earth connection being unduly long or too thin, or to the connections being dirty or loose.”

i Reporting on a complaint where n power leak was so bad that only the nearest National station could be heard, an inspector stated that tests of the earth connection showed it to be highly inefficient. The suggestion was made that a sheet of galvanised iron should be buried in a shallow trench, a strip being cut and bent up to be soldered to the earth-lead of the receiving set. A few days later the listener informed the inspector that he tried the effect ! of merely placing two sheets of galvanised iron on the ground, properly connected with Ihe earth-wire of the I sot. and this cleared up the trouble. } Where a long lead to earth is un- | avoidable, it may create high resisti a nee and consequent inefficiency. This trouble can be cured by increasing the I cross section of the earth-lead. Instead ! of one thin copper wire, it might be j necessary on a long lead of. say. 20 | feet or over, to provide a conductor made up of two seven-strand aerial wires fastened together.