Abstract :
A fruitful procedure for the study of the ionosphere by wireless methods is the automatic registration of equivalent heights on one or more frequencies, together with frequent determinations, made as rapidly as possible, of the variation of equivalent height and echo intensity with frequency. Theoretically, the echo and frequency-change methods should measure the same quantity, the equivalent height of reflection for the waves being used, and this is experimentally confirmed. The echo method, however, is the more useful since the interpretation of the records is much simpler, automatic registration is quite feasible, and the general operation is much more convenient. Some improvements in receiving apparatus for the frequency-change procedure are described which greatly facilitate these experiments. For the echo work it is shown that a simple squegger oscillator is adequate as a self-modulating device for producing the short pulses of radio-frequency energy. Several thyratron circuits are described which are applicable if the recurrence frequency of the pulses must be rigidly controlled for the method of recording adopted. A suitable receiver has been developed, using linear-law rectification, and a simple valve amplifier can be added to obtain a logarithmic relation between the signal input and output amplitudes. For registration of the pulse signals a string oscillograph may be used, but photography, with a simple camera, of the synchronized patterns on a cathode-ray oscillograph is preferable for adaptation to automatic recording, as this method minimizes the effects of interference and makes for speed and ease of operation. Linear time-scales with a scale value of 1.5 cm per millisecond are found most useful. Automatic records can be made by photographing the stationary echo pattern each minute or by making a continuous ?strip? record on moving paper of the time-base itself, departures from the base line due to the signal deflections being seen on the record as w- hite lines on a black background. The ?snapshot? method is preferable for detailed examination of echo amplitudes and delay times, but the strip registrations are more economical where it is required to obtain records of equivalent heights over long periods. In the manual operation of the apparatus a schedule procedure has been developed for obtaining records of equivalent heights and echo amplitudes on a predetermined series of frequencies at an average rate of about three frequencies per minute. The Appendix describes the distortion, observed in the course of the echo experiments, of transient-modulated radio-frequency energy in tuned circuits, and shows how the trouble may be overcome in the various cases.
