How the Empire Broadcasts Are Received

Radio Record, Volume VI, Issue 25, 30 December 1932, Page 7

How the Empire Broadcasts Are Received

A description of the P. & T. Department’s receiving station, with its giant 24 valve receiving set, pictured above.

HE new Empire Station, GSD, ' which was officially inaugurated,on Monday evening, December 19, is now. on a-regular schedule, and the past week’s transmissions have shown that on the technical side, at least, the service will be a

success. The‘relays by 2YA of these transmissions have throughou! \ béen of high quality, and are, in fact, almost indistinguishable- from direct reception.: Signals are strong, with very little fading or gushing, and the noise level is: low. For ‘the success of these relays, thanks are due largely to the P. and T. Depattment, who have loaned their commercial telephony receiver for the reception of the broadcasts. A brief description of this huge set, which employs no less than twenty-four valves, might be of interest. . It is located in a hut on the summit of Mount Crawford, Wellinguite handy to the city, there are no tramway or electric light power lines nearby to cause interference. In the vicinity of the hut is an The site is almost an ideal one for reception as, although it is . elaborate aerial system running roughly north and south, and suspended on three pairs of poles. ' __ The greater portion of the hut’s interior is taken up by the gigantic receiver shown in the photograph. A portion of the bank of batteries

ad employed for operating the set may. be seen on shelves against the reat wall, Batteries have been employed for power supply rather than the electric mains, chiefly because, should the mains supply fail, the receiver would be put out of action

and the service disrupted. This would be serious at any time, Dut especially so in the case of national emergency. The use,of so many valves has resulted in a certain amount ofvalve noise which, though scarcely noticeable, is still there. In an effort to reduce this to an absolute minimum, and to incorporate several more modern features, another set, using indirectly heated a.c. valves operated, from the same power supply, is at present being built. : The system of "floating" batteries is used, or, in other words, while the set is in operation,-the batteries are being charged from the mains. The charging rate can be adjusted to equal the drain taken by the valves, and so there is no load on the batteries. That this system is necessary can easily be seen when it is known that the filament current is just under, 3 amps, while the plate current is about 70 milliamps. Should the charger be put out of action with the failure of the mains, however, there would be sufficient electricity stored in the batteries to keep the set operating for some hours. The "B" supply is taken from 72 two-volt accumulators connected. in series, giving when fully charged a total (Continued on page 24.)

The Empire Broadcasts

(Continued from page 7.) voltage in the neighbourhood of 150. The filament eurrent is drawn from two high-capacity six-volt accumulators. The panel on the extreme left is the power supply panel, with various meters to show the condition of both sets of batteries and for adjusting charging rate. The next panel is perhaps the most interesting, At the bottom may he seen the twenty-four rheostats which control the filament voltages of each of the twenty-four valves, Above these

are three rows of switches for throwing valves in and out of circuit and for making quick tests. The black box at the top houses the alarm relay, while just underneath it may be seen two rows of white panel lights twelve in each row. Bach is labelled with the name of the valve with which it is associated. Should a valve burn out, the alarm sounds and one of the panel lights shows red. Thus a valve which has broken down can be located at a glance, Defects in any of the anode circuits are also revealed by the 130-volt lamps, which may be seen in rows along the top of the main panel. These also afford protection to the batteries and the rest of the circuit, for should a short-circuit occur, the "B" supply is not shorted, but the lamp in the faulty circuit takes the load and lights wp. Thus these lamps do double duty as protectors and fault indicators. On the main panel are mounted the controls of the receiver itself, which is a superheterodyne specially designed by the Post and Telegraph engineers. A signal frequency oscillator and an intermediate frequency oscillator are also included for testing or lining up the set. The receiver covers from approximately 22-38 metres, two sets of plugin coils being used. Many will no doubt think that the set would he almost impossible to tune, but it really Was just a matter of a little experimentation when the set was first placed into operation. A calibrated oscil-

lator operating on the frequency of the desired station is placed into operation, and the set tuned to this. Of course, once the reading of several stations are known, any others are fairly easily located. A special aerial system is employed which is very effective in cutting out unwanted transmissions, Its efficacy was strikingly proved to the engineers while experimenting one day. As Wellington readers know, Mount Crawford is on a point jutting out into the harbour. One day a motor-boat circled the point, travelling from the eastward, round the point to the westward. While on the eastward side the interference from the ignition system was quite clearly picked up, but when the boat had rounded the point toward the westward side, however, no trace of interference could be detected. The signals picked up by this aerial pass through the receiver, are detected and amplified, and then travel by landline to the terminal equipment in the Stout Street Telephone Exchange Building. The programme is then plugged through on a landline to 2YA’s studio and then by special cable to the transmitter on Mount Victoria,