Wettersonde E084 (Radiosonde)
|Frequency Range||403.05 MHz - 403.05 MHz|
|Short Description||The E084 is a radiosonde designed in 1990 by Deutsche Wetterdienst. It broadcasts a temperature reading at 403.05 MHz via a FM-modulated tone which changes pitch depending on the temperature.|
|I/Q Raw Recording||Download file|
The E084 is a radiosonde designed in 1990 by Deutsche Wetterdienst. These radiosondes are fairly common and cheap as surplus items, and it is possible to adjust the frequency to transmit in the 70cm ham band.
A temperature sensor controls the frequency of a sawtooth generator. The prescaler divides the transmit frequency by a factor of 64. The signal generated then modulates a UHFUltra High Frequency (300-3000 MHz) transmitter, which transmits the measurement data in frequency modulation with a deviation of ± 2.8 kHzKiloHertz (kHz) 10^3 Hz. A 74HC4066 is configured as a phase detector and now tries to adjust the divided transmission frequency to the quartz frequency using a control voltage (VCO). Both the tone generator and the UHFUltra High Frequency (300-3000 MHz) transmitter are built in SMD on 0.8mm thick FR4 for reasons of space and weight, the whole circuit is encased in a lightweight expanded polystyrene shell.
A frequency meter on the demodulated audio is sufficient to recover the temperature information. At 0 °C the audio frequency will be 300 HzHertz (Hz), unit of frequency, defined as one cycle per second (1 Hz)., at 26 °C 375 HzHertz (Hz), unit of frequency, defined as one cycle per second (1 Hz)..
Based on the official documents, the formula for the conversion is: temperature = 0.33 × frequency - 105
With a frequency of 396 HzHertz (Hz), unit of frequency, defined as one cycle per second (1 Hz)., the temperature is 0.33×396-105 = about 25.6 °C.
This temperature needs to be corrected by the correction factors stated on the label attached to the radiosonde itself.