----- Original Message ----- From: "Robert Turlington" [email protected] To: "Amsat Buleitin Board" [email protected]; "Andy Thomas" [email protected]; "John Heath" [email protected] Sent: Monday, May 26, 2008 12:32 PM Subject: [amsat-bb] Yubileiny Digital Fm Signal
Hi All using Spectogram I analysed the audio signal from Yubileiny as follows:- main carrier 2400hz the bandwidth being 120hz wide so far as could tell. I estimate that the central carrier was pulsing at 4 times/sec, if these figures sound familiar to anybody please let me know! Regards Robert G8ATE
Hi Robert, G8ATE
The early APT satellites ESSA-8, TIROS and ITOS during 1972 were transmitting in FM at 136 MHz and after discrimination a continuous subcarrier of 2400 Hz was extracted. This subcarrier was AM modulated by the video signal at a rate of 4 pulses /second The 2400 Hz subcarrier transmitted by the satellite was used by the ground station as a reference signal to lock in frequency and in phase a 2400 Hz local oscillator This generated 2400 Hz signal was then divided by 40 to get a 60 Hz signal to rotate upon amplification the drum of a Faximile at a syncronized speed of 4 turns / seconds i.e. at 4 picture lines / second Alternatively the 2400 Hz signal was divided by 600 to get 4 pulses per second to syncronize the X axis of an oscilloscope to get the horizontal scanning at a rate of 4 lines / second and develope the picture directly on screen using a camera in a dark room. I still have this equipments in the shak just to remember the early APT time when the computer was not currently available for the amateur radio.
In a separate email I have sent to you some pictures received from ESSA-8 and ITOS at 4 lines/second.
I hope this helps
73" de
i8CVS Domenico