Further tests on the FM transmitter being developed at this laboratory showed that the deviation was likewise a function of the applied plate supply voltage. This problem will have to be solved by improved circuit design before a suitable FM transmitter can be evolved.
In addition to the AM transmitter model already constructed, a second unit was built. This duplicate was installed in a cardboard container which also houses the storage battery supply and a blocking oscillator to supply an audio-frequency which modulates the carrier at 50 c.p.s. Plans and arrangements were made for testing this unit on a captive balloon.
d. APPARATUS
A battery box containing a metered circuit for constant monitoring of transmitter currents were constructed for field or blimp transmission tests.
An antenna approximately 150 ft. in length was erected on poles twenty feet above the roof of the Electrical Engineering Building for use in receiving signals during test flights.
e. FUTURE WORK
In view of the excellent characteristics of the automatic frequency control of the Radio Receiver R-2a/ARR-5, an attempt will be made to secure the circuit diagram of this equipment and employ its use in any FM receiver which might be used.
Further circuit investigation will be carried out to develop an FM transmitter which is free of the undesirable effects introduced by input voltage variations.
Field tests will be carried out on the AM transmitter using a tethered balloon and a blimp, if available. It is desired to obtain information about the operating range and difficulties which might develop with this transmitter.
Philip Greenstein
Project Director
2.