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Have you ever been listening to a frequency in SSB and heard periodic “tweeps” vip through the audio? Ever wonder what it was? In a ham band you might be hearing someone spin the dial on the VFO while the TX is keyed down. But, the more likely culprit is a “Chirpsounder”, something similar to the AN/TRQ-35 family of Chirpsounders. Information on this family of sounders can be found in “FM 24-18 Appendix B Ionospheric Sounder AN/TRQ-35(V)”. Link to PDF here: http://www.fas.org/irp/doddir/army/fm24-18.pdf
A Chirpsounder is also called an Ionosonde. This is a sounder that looks at the propagation characteristics of the atmosphere as a plot against frequency using multiple sources and receivers around the World. Using the data from a Chirspounder network you can predict the current paths that exist for any frequency and any distance. The military, various government agencies, and educational facilities are tied into these Sounder networks.
Video of 3 Chirpsounders vipping through the ham 20 meter band here:
Sounder, Chirpsounder in ham 20M band, May 27, 2012, 1456 UTC - YouTube
Video of 2 Chirpsounders vipping through the ham 17 meter band here:
Sounder, Chirpsounder in ham 17M band, May 27, 2012, 1421 UTC - YouTube
Wideband image of a Chirpsounder sweeping from below 6600 kHz to about 28000 kHz:
http://www.pbase.com/token/image/127146098/original.jpg
When listening in USB mode most Chirpsounders “tweep” through from low pitched sound to high pitched sound very quickly. This is because most of these sounders sweep low to high and at rates on theorder of 100 kHz per second, meaning they zip through your sub 3 kHz SSB filter bandwidth in something under 1/30 of a second. And in LSB mode these will make a sound sweeping from high pitched to low pitched, also very fast. In AM they will only make a change in background noise unless there is an AM carrier in your receiver pass band, and then you will actually hear the signal go form high to low, and then low to high, very fast, as it beats against the AM carrier in the passband.
There is software available to decode the source of a sounder you hear. It takes the time you hear it on a given freq and the chirp rate. This gives a start time at the low end of the band and that yields who it was sent from as each station has specific start times. There are a few web pages describing techniques to plot and receive the signals and there used to be a Yahoo Group dedicated to it, but that group has not been active for a while.
T!
A Chirpsounder is also called an Ionosonde. This is a sounder that looks at the propagation characteristics of the atmosphere as a plot against frequency using multiple sources and receivers around the World. Using the data from a Chirspounder network you can predict the current paths that exist for any frequency and any distance. The military, various government agencies, and educational facilities are tied into these Sounder networks.
Video of 3 Chirpsounders vipping through the ham 20 meter band here:
Sounder, Chirpsounder in ham 20M band, May 27, 2012, 1456 UTC - YouTube
Video of 2 Chirpsounders vipping through the ham 17 meter band here:
Sounder, Chirpsounder in ham 17M band, May 27, 2012, 1421 UTC - YouTube
Wideband image of a Chirpsounder sweeping from below 6600 kHz to about 28000 kHz:
http://www.pbase.com/token/image/127146098/original.jpg
When listening in USB mode most Chirpsounders “tweep” through from low pitched sound to high pitched sound very quickly. This is because most of these sounders sweep low to high and at rates on theorder of 100 kHz per second, meaning they zip through your sub 3 kHz SSB filter bandwidth in something under 1/30 of a second. And in LSB mode these will make a sound sweeping from high pitched to low pitched, also very fast. In AM they will only make a change in background noise unless there is an AM carrier in your receiver pass band, and then you will actually hear the signal go form high to low, and then low to high, very fast, as it beats against the AM carrier in the passband.
There is software available to decode the source of a sounder you hear. It takes the time you hear it on a given freq and the chirp rate. This gives a start time at the low end of the band and that yields who it was sent from as each station has specific start times. There are a few web pages describing techniques to plot and receive the signals and there used to be a Yahoo Group dedicated to it, but that group has not been active for a while.
T!
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