[amsat-bb] Re: Yubileiny Digital Fm Signal
domenico.i8cvs at tin.it
Mon May 26 06:48:58 PDT 2008
----- Original Message -----
From: "Robert Turlington" <rob_g8ate at hotmail.com>
To: "Amsat Buleitin Board" <amsat-bb at amsat.org>; "Andy Thomas"
<andythomasmail at yahoo.co.uk>; "John Heath" <g7hia at btinternet.com>
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
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
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