Note on a Multifrequency Automatic Recorder of Ionosphere Heights

A system is described which gives a curve of virtual heights of the layers of the ionosphere against frequency. The pulse method of Breit and Tuve is employed with modifications. Short pulses of radio-frequency energy are transmitted, and the time required for the energy to go up and return is recorded automatically by a galvanometer oscillograph of the type previously used for fixed frequency work. The transmitting and receiving sets are shifted in frequency from 2500 to 4400 kilocycles at the uniform rate of 200 kilocycles per minute. Records are presented which show the characteristics for different times of day and night. In the daytime, during the period of these tests, three strata were usually indicated. For the lower range of frequencies, reflections come from the E layer with a virtual height of around 120 kilometers. As frequency is increased the waves pass through the E layer and are returned from the F
1
layer with virtual heights of the order of 200 kilometers. The frequency for which this transition takes place varies with time of day and with season. In the middle of the day, during these tests, this critical frequency was in the neighborhood of 3000 kilocycles, while the critical frequency for passing through the F
1
to the F
2
layer was usually between 3800 and 4100 kilocycles. The F
2
layer shows virtual heights of 280 kilometers or more.