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How to Record Radio Signals
THERE are many occasions when it is desirable to make records of wireless reception. Figs, i, 2, and 3 illustrate a system of recording that is comparatively simple and yet quite effective. The apparatus described was installed as a check on fading phenomena during the total eclipse of the sun on January 24th, 1925.
The apparatus consists of three primary parts, the tuner — which may be any convenient set — the amplifier, and the recording dictaphones. Two stages of amplification are sufficient, although
three steps of resistance-coupled intensification with volume control were used in this laboratory. It is advisable to have some volume regulation in order to lower the maximum intensity below the blasting point of the recording diaphragms.
Standard office dictaphones were prepared by affixing telephone receivers to the throats of the speaking tubes. The soft rubber fixtures intended for adapting head sets to horns, are convenient for the purpose. Two dictaphones are not required but were employed in the Radio Broadcast tests to insure an unbroken record.
The machines should be located at least five feet from the receiver and more if convenient, to eliminate motor induction. Grounding the frames of the machines will also reduce interference from this source.
It is generally desirable to monitor recording on a loud speaker. This is most easily
In the R. B. Lab. This Month
A Complete Article — Radio Recording with a variety of applications, such as tracing oscillating receiver interference, learning the radio code, and others.
Shooting Trouble— How ive go about it. This article is the first of a series that will help the reader to solve difficulties in his receiver systematically and swiftly.
Notes on Wiring Your Own Lab.
accomplished by connecting the telephone receivers (clamped to the recording instruments) in series with the loud speaker. A shunt variable resistance, 200 to 5000 ohms, across the phones, provides the recommended volume adjustment, without greatly affecting the loud speaker. If more convenient, any other satisfactory form of speaker unit may be substituted for the phones.
In recording fading, it is advisable to keep the receiver oscillating and record the beat note or squeal of the distant stations. I n addition to the greater intensity and sensitivity of this arrangement, signal variations will be much more noticeable due to the fact that the sound will vary approximately as the square of the signal variations.
OTHER USES
As
kSIDE from the recording of fading and swinging, this apparatus may be put to many other interesting and useful purposes.
It will immediately suggest itself for recording programs of special or historical interest, such as the inaugural address of the President of the United States. Reception is affected in the manner described, except, of course, that no beat note is produced.
LEARNING CODE
DICTAPHONES have been used for some time in the reception of high speed (80 to 100 words per minute) radio telegraph code signals. For transcription, the machine is