STATION 2ZF

Manawatu Standard, Volume LIII, Issue 313, 2 December 1933, Page 2

STATION 2ZF

MODERNISING OF EQUIPMENT. About a month ago 2ZF raido station was converted to crystal control, and the final step in the process of modernising the transmitter was carried out last night, when 2ZF transmitted with a “linear amplifier’' in use for the first time. This latter piece of equipment has been in the process of building for some months, and comprises four 250-watt Marconi valves with its associated power equipment.

The new crystal control apparatus comprises a master oscillator with its own separate plate supply. This valve and quartz crystal generate the “carrier wave” of 960 k.c., and the output is then amplified by two screen grid valves, similar to those used in a radio set, but they are larger power valves. The object of using two screen grid valves to amplify the carrier from the master oscillator is to prevent the final valves in the transmitter from reacting on the first one, which in turn prevents any chance of the carrier wave shifting in frequency when heavy passages of music are broadcast. The output of this master oscillator and the two buffer stages is then fed into a 100watt valve and until November 30 this valve was coupled to the aerial system and its power radiated to listeners.

In the new equipment which was put into action last night the output of the 100-watt valve is now fed into the final amplifier instead of the aerial as before. This final amplifier, which has a total capacity of 1000 watts in valves, arranged in “push-pull” connection, has its output connected to the aerial system. 2ZF has thus been completely modernised and at the same time its power has been increased considerably. The new method of operation enables the use of what is known as 100 per cent, modulation; that, is the percentage of music, -etc., on the carrier wave is much greater than in the old transmitter. This increases the useful range of the station, but decreases the interference range with other stations overseas.

A considerable amount of adjustment is necessary before everything will be working as it should, as there are now no less than seven circuits in the transmitter that have to be carefully adjusted. The slightest alteration to one of them throws the rest out of “tuning.” On the l completion of Thursday night’s relay of 2YA, the station was altered to the new wavelength by the insertion of a new quartz crystal which had been cut and ground in readiness,, and the station was finally adjusted, giving clear music. When starting up for the first regular transmission on the new wavelength last night, the crystal refused to oscillate after working perfectly on previous tests. An extra coil was hurriedly wound and connected in the circuit to coax the crystal to start, and 2ZF came on the air late. Unfortunately, the various circuits had been thrown out of “tune” in the process, but this was remedied as the transmission proceeded and the officials are concentrating on getting the music clear in tone- before working the transmitter up to the power of which it is capable. The Mahawatu Radio Club is now in the proud position of owning the most powerful private broadcast transmitter in New Zealand outside of those owned by the Broadcasting Board.