WIRELESS ON THE HOLIDAYS - LISTENING to wireless transmissions is a
. companionable and " all. weathers " hobby. This summer- wireless will o
hold its own in popular favour as a result of programme adaptation and the introduction of novelties in the way of portable sets and appliances. Holiday makers " week-ending " in a suburban garden, resting, between sets by the tennis-lawn, will have wireless installations suited to their needs, while the more adventurous who seek diversion picnicking, yachting, punting or motoring, will be able to carry both headphones and loud speaker equipment with them, and they shall have music wherever they go.
' In order to enjoy wireless in the garden, on the river, or on motor trips, it is necessary to obtain a special licence for portable and transportable reception in addition to the ordinary licence required for a wireless installation at home. If a loud 'speaker is to be employed it is nearly always necessary to have two low frequency valves, but one valve is ample for :3 or 4 • telephones. Of course, if out-of-door listeners wish to receive transmissions from high power and relatively long wave stations, they should remember to make provision for extra coils. In general when assembling a portable set compactness and lightness are the main objects of endeavour. It is easy to attain lightness if one is going to travel in a motor car, because one can always make use of the lighting or starter battery for the filaments and it is very easy to tap on to a special high tension battery carried in the ear. Without a car, listeners will be well advised to make use of valves of the D.E.R. or D.3 type.
To secure the best reception in the open air, one must guard against vibration, and ensure that the microphonic effect of the valves shall not interfere. For the same reason it is a good plan to provide for very positive control of the installation even to the point of gearing, in order not to disturb timing positions. As frame reception in most cases requires at least 4 valves, which would mean very great. bulk for purposes of transport, a temporary aerial together with a copper earth mat or earth pin will he preferable. For the erection of such an aerial experience shows that it is best to use rubber covered flexible aerial wire. It may often be found that part of this is snapped off in the attempt to fix the wire over a branch, and to avoid this calamity an attr c!i- ment to the end of the wire connected by a piece of thin string will act as a mechanical fuse which parts upon tuggingh so that the wire comes away without breaking. With such an open aerial, the minimum number of valves required for multiple telephone reception is, generally speaking, one high .frequency, one detector valire. with .reaction and one low frequency added if..more than 30-40 miles from the station. Where a frame aerial is used, two high frequency detectors and two low frequency will be required. If the earth is very dry better results are likely to be obtained by running another piece of insulated aerial wire along the ground parallel with the elevated aerial. if three dull emitter valves are used they should take rather less than 1 ampere. Where a power valve is incorporated, however, of the D.E.5. type, another .25 ampere is indicated (5 volts, .25 Amps. 30-120 on H.T. and grid bias of from 4 to 5 volts when using 120 volts on anode).
Coils in parallel . Tuned React ion Wavelength. with aerial. Secondary. Anode. on Anode. 300-490 m. .001 .0005 .0003 — Burndept SI 84 85 83
Gambrell A C C A
Igranic C2 or 35 C3 or 00 • C4 or 73 C3 or 100 Met, Vickers 35 40 59 . 40 Longer aerials than 100 feet, 1 size smaller. • Shorter aerials than 100 feet, 1 size Larder. Coils in parallel Wavelength. with aerial.
1500-1750 — Secondary.
— Tuned Anode.
— React:c a on Anode.
— Burndept 150 200 300 150 Gambrell D G G
A Jeanie
150 250 300 200 Met. Vickers 150 300 300 200
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