World
of
Wireless

Because his electrical generator did not only generate electricity but also a lot of noise, his neighbours often complained with the authorities.
Undoubably this has been one of the reasons why he finally was not succesfull.

On April 30th 1921 the next article apears in "The Wireless World".

THE HAGUE CONCERTS

It is probably in no sense an exaggeration to say that the enthusiasm of the average radio amateur or experimenter in wireless telephony far exceeds his interest in all other branches of wireless work. The ability not only to actually speak and carry on conversations with aether waves as the only connecting link, but also pick up complete orchestral concerts and enjoy them in our own home adds to this keenness for radiotelephone work. In the past we have been treated to occasional radiotelephone concerts from one of Marconi's Wireless Telegraph Co. 's stations at Chelmsford, when special experiments and tests have been in progress, while the more regular transmissions from Surbiton in connection with the exhibit of the same firm at the recent Olympia Exhibition were also a source of enjoyment to many For some time past the Nederlandse Radio Industrie have been adding to above and other concert programmes by series of tlephonic transmissions, sent our for periods of two or three hours regularly, at first on one evening a week, and later twice a week. The power used for transmissions was, however, small and the concerts were therefore difficult to pick up. The power used for these transmissions has now been increased to 100 watts, and will shortly be further increased by installation of a 250 watt Mullard valve. In view of the widespread interest taken in these "Dutch Concerts" it may, pehaps be of further interest to illustrate some of the apparatus used for the transmissions.

Fig.1 shows an outside front of the Nederlandse Radio Industrie at the Hague, from which the transmissions take place. The aerial can just be seen over the building. The aerial consists of three wires approximatly 150 metres (500 ft.) long each, and is stretchd across a road. The station earth connection consists of about 24 metres (80 ft.) of iron pipe sunk in a well, but it is thought that probably this connection is not a perfecly uniform one. Receiving stations listning in to the concerts have frequently reported considerable variations in intensity from day to day, and it is considered likely that variations in the eeficacy of the earth connection may be a contribetory cause. Such variations may arise with the height of the tide and consequent changes of the salinity, and therefore of the conductivity, of the well water brought about by the percolation of sea water into the well. This, however, is a question that could fairly easily be investigated, and extended observations of the signal intensity received from this station would therefore be of interest, especially if they showed a periodicity depending upon the moon and tides. The actual transmitting apparatus in which the transmitting valve can be clearly seen at the top of the panel. The valve shown is nominally of 100 watts capacity. But its output is being pushed up to 150 watts by using an anode supply voltage of 1,000 volts. This valve is shortly to be replaced by a 250 watt Mullard valve, when a greater output should be obtained. The phonograph which is used for transmitting some of the musical selections can also be seen in this illustration, the usual horn being replaced by a tube in which the transmitting microphone is mounted, a second microphone being placed on the table near the phonograph. No separate modulating valveis employed, but a special patented form of grid control is used, details of which, however, are, unfortunately, not available for publication. Arrangements have been made by messrs. Burnham & Co. With the Darewski Publicing Co., through the kindness of Mr. H.Darewski, for the supply to the transmitting station at the Hague of phonograph records of all their newest publications, so that selections from the latest English music will be available to all within the radius of the transmitting station. It is expected also that loud-speaking receiving apparatus will be installed so that the British troops in Cologne can be entertained by the same means. The phonographic selections sent out by this station are also interspersed with selections by a small band, and by four mandoline performers; occasionally also some singers take part. The orchestra and singers perform under a large funnel or horn which contains the microphones connected to the transmitting apparatus, so that the voices and music modulate the radiated power in the usual way. Although they may be heard over a range of roughly 500 miles round the Hague, these concerts are addresed primarily to British wireless experimenters, as is evidenced by the introductory C.W. messages addressed to all British amateurs with which they are prefixed. These messages usually also ask for reports of the reception of the concerts to be forwarded to Messrs. Burnham & Co., Deptford, who are the British agents for the Dutch Company. As regards the reception of the concerts, they have been heard satisfactorily over considerable ranges using but a single detecting valve, but such a simple receiver is not recommended for reliable work. Even at Aberdeen, some 500 miles from the transmitting station the signals have been heard on a single valve, but this must be put down more as a freak reception, or as due to some particularly favourable circumstances inherent to the neighbourhood-an assumption that is not altogether unwarranted in the light of other results obtainable in this district. In general it is advisable to use at least one highfrequency amplifying valve in front of the detector valve in order to obtain satisfactory reception, while, of course, one or more stages of low-frequency amplification (i.e., note magnification) may be added after the detector valve when it is required to operate a loud-speaking receiver. A limited amount of reaction may be employed if desired, but the greatest care must be taken in its use to avoid self-oscillation of the set. If this takes place not only is the reception of the speech prevented but its reception by others for many miles around is also seriously interfered with. This point with regard to the avoidance of autodyne receivers cannot be too strongly emphasised, and every effort should be made to discourage their use. Naturally, when first searching for the station, or when listning to the C.W. signals, it is necessary to use the heterodyne method, but unless an entirely non-radiating receiving arrangment is employed with a seperate heterodyne and appropriate couplings to prevent the oscillations reaching the aerial circuit, the use of an oscillating receiver should be restricted to as short a time as possible. As soon as the signals are heard the reaction should be loosend, so as to stop the oscillations. Not until this is done can the speech, etc., be received properly, although in favourable circumstances some of it may be distinguished. It is much preferable, however, to instal an extra amplifying vlave rather than to jam other receivers in the vicinity. As regards possilble receiving arrangements, any good high-frequency amplifier suiteble for the wavelength (1,150 metres) may be used, together with a detecting vlave of the usual type. Such a receiver may be purchased complete or may be built up from the necessary components parts.

The circuit arrangement shown in Fig. 4 is a simple one that gives good results, although not necessarily the best possible one to employ. It consists of an aerial loading coil L1 having an inductance of about 500 - 700 microhenries connected between tha aerial and earth terminals, and having a tuning condenser C1 in parallel with it. This condenser should have a maximum value not exceeding 0.001 mfd., while it should be kept as small as possible consistent with tuning the coil used to the required wavelangth of 1,100 to 1,150 metres. Across the tuning coil are joined the grid and filament leads of the first valve V1 in the anode circuit of which the anode resistance R1 is connected. The reaction coil L2, in series with the second valve, should have at least as large an inductance as L1 and is preferably somewhat larger. The loading and reaction coils may conveniently be of the multilayer type-honeycomb, Duolateral or "Burndept"- but may also, if preferred, be wound up as single layer coils as the wavelength is not high. Convenient dimensions for such windings are as follows:-

For loading coil:
Diameter = 4 in, Wire = No.22 S.W.G., d.c.c. copper
Length of winding:- =about 4 in. (single layer)

For reaction coil:
Diameter = 3 in. Wire = No.30 S.W.G., d.c.c. copper
Length of winding- =4 in. (single layer)

The resistance R1 may be of 50,000 ohms. Resistance or less, depending upon the valve in use and the H.T. battery voltage available, bearing in mind the fact that the higher R1 is made the higher must be the voltage of the H.T. battery, if the vlave is to work at the same point of this characteristic. The intervalve couling condenser C2 should be about 0.0002 mfd. Capacity, while the grid leak R2 may have a resistance of 1 to 2 megohms. The blocking condenser C3 may have any convenient value exceeding about 0.003 mfd. In place of the head telephones the input transformer of a note magnifier may be joined up so as to enable a loud speaker to be used. The use of a note magnifier, in conjunction with the detecting valve alone, is not usually sufficient to ensure good reception without the high frequency amplifying valve as well. In using the receiver the reaction coil L2 may be coupled to the tuning coil L1 until oscillations are set up, and the wave length varied until the whistle of the C.W. note is heard. The reaction should than at once be reduced until oscillations cease, when, by slight careful returning, the telephony should become audible. While describing the above circuit as a possible simple workable arrangement, it should be understood that it is not necessarily recommended as the best possible one. Every experimenter should investigate this point for himself and determine the details that give the most satisfactory results at his station and with the valves that he customarily employs, bearing always in mind the necessity to avoid both heterodyne radiation as much as possible when searcingfor the C.W. signals and the use of any form of heterodyne when listening for the telephony itself. The former may be diminished by coupling the receiver to the aerial circuit and any other means already pointed out in these columns, and the latter by switching off the seperate heterodyne if one is used, or by reducing the reaction of an autodyne until the oscillations stop. Finally, the writer wishes to express his thanks to Mr. W. Burnham, to whom he is indebted for the loan of the photegraphs illustrating this article, and for some of the information contained herein with regard to the Nedelandsche Radio Industrie.