A: Small radiosondes, like our AnaSonde-E, -M, -R, and -3M, use small radio transmitters operating at nominally 433.92 MHz. Devices using this frequency can fall under FCC regulations (US Title 47, Code of Federal Regulations) at two points. One is unlicensed operation under FCC Part 15 regulations. The other is licensed operation under FCC Part 97 regulations (Amateur Radio).
The following discussion is intended to summarize the regulations and their practical interpretation as they pertain to the AnaSonde and other related devices (such as CricketSats popularized by student ballooning programs) which use similar transmitters.
With respect to unlicensed operation, 47CFR15.231 applies, and more specifically paragraph (e). Paragraph (a) is narrowly defined and excludes operation of devices such as the AnaSonde. Paragraph (e) allows anything, including the AnaSonde. Both of these paragraphs address the use of periodic, pulsed operation. However, for AnaSonde operation, the more restrictive field strength limits found under paragraph (e) apply.
It is easiest to translate these field strength numbers into a corresponding transmitter power by referring to an application note from Radiometrix, a company which makes transmitters of the same general type and power as used in the AnaSonde and similar devices. Here is the link:
http://www.radiometrix.co.uk/apps/apnt102.htm
Looking at their table, we find that the FCC field strength limit for 433.92 MHz corresponds to a transmitter power of approximately -22 dBm. Notice that the rest of the world (Europe, at least) allows much more power - up to +10 dBm - at this frequency. That's why these modules are so common and cheap around the world. Unfortunately, this has led to their widespread availability in the U.S. where they far exceed unlicensed transmission power limits.
For reference, the transmitter used in the AnaSonde has a nominal maximum power of +10 dBm. Again referring to the Radiometrix application note, they note that for use in the U.S. transmitters such as these would require about 35 dB of attenuation to be legal. Antenna efficiencies and supply voltages may contribute a few dB of reduction, but are not going to be anywhere near even 15 dB let alone the required 35 dB!
And, if one were to attenuate their transmitter to this level to make it legal as an unlicensed transmitter under Part 15, the range would be so very short as to be useless except as an across-the-room transmission.
The 433.92 MHz frequency also falls within the U.S. Amateur Radio bands. In this case, a licensed amateur radio operator may transmit on this frequency at powers up to 1500 watts - so the power limit is no longer an issue.
However, the transmitter must broadcast a station identification (generally, the callsign of its operator) at least once every 10 minutes per 47CFR97.119. This rule also specifies the formats in which identification may be transmitted.
This is the approach Anasphere has taken with the AnaSonde.