Satgen507 Sat Fingerprints Pt2  by GM4IHJ  (BID SGEN507) 1998-12-12

Before you can begin to assemble a data base of satellite fingerprint
records, you need good omni directional antenna coverage of your
chosen frequency bands. How you do this is very much a matter of
individual choice. At IHJ , the 29 and 200 to 400 MHz frequencies are
covered by crossed dipoles, while the 136 to 150 and the 420 to 450
MHz ranges are covered by quadrifiliar helices. At still higher
frequencies Eg 1500 to 1800 MHz a cavity resonator is used for wide
beam coverage to the north, noting that at 56N almost all the Leo sats
of interest can be caught during that part of their orbit. Once
acquired narrow beam antennas can be deployed. Geosats pose no special
antenna problems.

Commercial receivers covering 28 to 1300 or 28 to 2000 MHz are now
available. With the ICOMPCR1000 being the easiest to use, not least
because of the interesting software which can be used with it.
N4IPs PCRScope software is a perfect accompaniment to the ICOMPCR1000,
covering all its frequencies and formats with a wide variety of search
and scanning modes. But for producing useful fingerprint data you need
to be able to reveal all the characteristics of the satellites signal
not just its frequency , modulation and timing. Here the AF9Y software
is invaluable. It can cover audio bands of 300 to 1500 Hz , or 300 to
2700 Hz, which serves for all but the very wide band digital signals.
So having found the signal using N4IP, the audio is swiched to the
computer programmed for Fast Fourier Transform Digital signal
processing using the AF9Y software.

As mentioned above some signals have very wide bandwidth . These were
a problem, but the recent introduction of HAMVIEW written by I2PHD and
IK2CZL has changed the situation . This FFT program has many features
to appeal to moonbouncers using extremely narrow bandwidth reception.
But it also has a wideband facility ( which needs a fast Pentium II
rated at 200 MHz or more), which can cover roughly any 4300 Hz band in
the range 20 to 12282 Hz. Unfortunately this program (unlike AF9Y )
does not have a facility permiting printing of permanent records of
the fingerprint taken. There are other DSP programs but not all allow
deep analysis of the signal characteristics , and they do not all
provide a printing option.

So whether you have some , all or only a few of these facilities, how
can you start examing satellite signals ? A good start can be made on
our old friend Oscar 10 , and in this case it is often more exciting
when it is not behaving well. A series of records taken over several
hours can show the doppler changes. These can be a surprise if you
have not monitored a Molniya satellite before. Unlike low earth near
circular orbiters, Oscar 10 does not give you a progressively negative
going doppler shift. Indeed over most  of its orbit its beacon
frequency ( 145.812 MHz approx) actually rises as you track it, a
feature which these FFT displays show clearly. Getting to know this
characteristic of Molniya satellites with highly elliptical orbits (Eg
circa 0.6 or greater ), is good practice for identifying sats in
geostationary transfer orbit or modestly elliptical orbits like Fo20
eccentricity 0.054 (ie very different from say RS12 .0028 ).