2ZM, GISBORNE

Radio Record, Volume II, Issue 5, 17 August 1928, Page 11

2ZM, GISBORNE

ate A CORRESPONDENT last week wrote complaining that 2ZM was received anywhere on his dial. He has raised quite an interesting point which will no doubt be appreciated by others who, being in a similar position, are inclined, and quite natur- — ally to blame the broadeasting station rather than their own sets. Our correspondent may be interested to learn that in Wellington, and in the neighbourhood of any powerful broadcasting station, the local station will interfere with the reception of other stations over a considerable portion of the condenser range. It will be observed that at one particular dial reading, the volume is at a maximum. This signifies that the condenser is sét to the frequency of that particular station. . The range over which interference is experienced depends on:- ~ ; (1) The selectivity of the receiver. (2) The power of the transmitting station. . (3) The proximity of the receiver thereto.

Q correspondent should satisly himself that his complaint is not due to the properties of th receiver he is using before laying the blame on the Broadeasting station. By using a wave trap or a more selective receiver it might be found that 2ZM keeps on its wave-length i.. fact it is almost impossible for a station to send out more than a limited band of frequencies. In practice, this.band is approximately 20 kilocycles wide and its width is produced by the modulations of the carrier wave. A moment’s reflection regarding the statement that 27M could be received from 0 to 180 (a 1000 kilo-cycles) would suggest that something is at fault and it is most probable that the broadness jis that .of his receiver eg. the single valve feceiver or erystal set is capable of the reception of quite a wide band of frequencies when the condenser is left on a fixed setting, or over a considerable range of the condenser setting when it is adjustable.

, An indication of the constancy and the sharpness of the carrier wave of a broadeasting station may be obtained by listening to the purity and: constancy of the characteristic whistle heard in the ’phones or in the loudspeaker. The pitch of this whistle will depend on the difference between the frequency of the wave emitted from the broadeasting station and that generated in the receiving set. os If a pure note is produced, only one frequency is being received and not a band of frequencies, which would produce anything but a pure whistle in the ’phones.