|7680 kHz||7690 kHz||7700 kHz||9185 kHz|
|9310 kHz||9332 kHz||10120 kHz||13430 kHz|
This set of frequencies was frequented for many weeks around the end of 1996, by a sweeping carrier operating on a regular cycle.
The signal took the form of a slow sweeping carrier, which operated on a four minute cycle, at thirty second intervals. Each frequency was swept in turn, and always in the same order.
The sweeping carrier seemed to display an unusual use of frequencies, and for no apparent reason.
Once the signal was picked up on one frequency, it could be followed through the above chart, returning to its original frequency after four minutes before repeating the cycle.
Harv (K2PI) tells me that this sounds like a propagation checking system known as "Chirpsounder".
Propagation sweepers transmit signals on various frequencies, and by using multiple receivers to track the signal can provide useful information about the conditions and suitability of those frequencies for communication.
Sweepers are well known on the short wave, but are usually heard as a rapid "Swish" as the transmitter sweeps across the band.
Although this is their usual mode, it is possible to program the Chirpsounders to settle on specific frequencies. This may be because the whole spectrum is not available to the user, or where only a small range of frequencies may be of interest.
Not heard since 1996. Nor have these frequencies since been occupied by a specific user.