FM Receiving System for Endoradiosonde Techniques

The receiver detects FM signals with frequency deviations up to 30 kc in the 300-400-kc band. The drift is less than ±20 cps per day. The receiver operates satisfactorily with field strength variations of 1:30,000. To prevent erroneous recordings when the signal strength varies abruptly with changes in the mutual direction of the transmitting and receiving antennas, a nondirectional receiving antenna circuit has been developed. Also, an output clamp circuit prevents the recorded values from changing during occasionally low field strength periods.