radiosonde Vaisala RS92-SGP (by: ANgazu,Rapidbit)

2 November 2017

radiosonde Vaisala RS92-SGP
(by: ANgazu,Rapidbit)

The RS92-SGP has been manufactured and marketed by the Finnish company Vaisala since 2003. It incorporates a Helix Antenna (QFHA=Quadrifilar Helix Antenna) for the reception of GPS satellites.

This type of radiotracer has a GPS receiver to determine its location and allow indirect measurement of wind speed and direction at altitude... The RS92-SGP has a silicon pressure sensor, a heated dual humidity sensor and a small, fast temperature sensor.
The synthesizer-based transmitter is stable and uses narrow bandwidth. The RS92-SGP radio sensor complies with the European ETSI standard for digital radiosondes operating in the 400 MHz band.
The SONDE MONITOR software allows the data transmitted by the RS-92 SGP to be decrypted, in particular the exact position measured with the aid of the GPS receiver on board, which makes it easier to locate it in the field.

Measurements carried out with the aid of a radio-sounder are relative to a specific place and time interval. In order for such data to be truly useful, polls conducted around the world must be synchronised. These polls are usually conducted at 00h and 12h GMT. Some stations carry out polls at 06h and 18h regularly.
More than 850 surveys are conducted, at least twice a day worldwide. The distribution of the radiosonde centres is not regulated on the planet's surface and developed countries in the northern hemisphere (82%) are better covered than deserts and oceans in the southern hemisphere (18%). 820 of these surveys are carried out by fixed stations and some 30 of them are carried out from ships, both merchant and regular lines.
Surveys are mainly carried out by meteorological services, but from time to time we may find ourselves with radio probes launched by:
- Weapons test centres (missile, ammunition and radiosounder testing).
- Scientific missions, atmospheric monitoring services (ozone measurements, radioactivity)
- Special campaigns for the study of regional climatology and meteorology.
- Artillery units, before firing practice.

- Radio sounding training centres (meteorological, military, manufacturers of radio sounders...)

Radiosondes are telemetry devices that measure various atmospheric parameters.
They are usually launched using a weather balloon and, while ascending and moving in the wind, transmit the data in real time. They can reach a considerable height, so reception is possible far away from the launching point.
The signal for this entry , from a Vaisala RS92-SGP, was recorded near an airport somewhere in the south of Europe. Frequency was 403 Mhz.
This signal is a very interesting one since it shows a considerable Doppler effect due to both its ascent speed and its lateral displacement due to the wind (Fig.1).

Fig. 1

The spectrum exhibits a phase modulated signal framed by two unmodulated tones (Fig. 2). Tones are separated 4800 Hz.

Fig. 2

Analyzing the signal as a whole, modulation speed is 4800 sps using a GFSK modulation, but filtering out the outer tones to isolate the internal signal, result is a BPSK with a speed of 2400 sps.(Fig.3)

Fig. 3

Should the signal be demodulated as GFSK, result is a stream of manchester coded bits. Once manchester decoded, the bits are exactly the same as if the inner signal was demodulated as BPSK. Frame ACF is 1 s. There is a second ACF for character of 4,16 ms (Fig. 4)

Fig. 4

Once decoded, frames are 2400 bits long (Fig. 5) using 8N1 characters.

Fig. 5

The combination of vertical and lateral velocity of the probe produces a doppler effect on the signal. In the image, the frequency variation in a tone for about 21 m (Fig. 6)