The pulsar route to CETI - thoughts about signal detection
The value of working with pulsed signals should not be underestimated.
If we accept the argument in favour of looking directly away from pulsar
Px for signals pulsed at Px's rate, and if we assume that such directed transmissions
might plausibly be at 1.42GHz and some of the overtones, then signal enhancement
comes readily and a target direction can be checked in an hour or less.
The signal enhancement is in two forms. Because of the known pulse
rate the signal from the receiver (tuned to the 1.42GHz channel) can be summed
using a window defined by the pulse rate. An hour will give several
thousand overlays for a ~one second pulse repetition period typical of many
pulsars. If the pulse rate is much shorter then so much the better.
Additionally, the channels for the overtones can have their outputs summed
in the same way. One can select a smallish number - say 8 - of potential
overtone channels.
And the two sets of outputs can be scrutinised separately before combining
(the assumption must be that the phasing of the overtones is coherent with
the 1.42Ghz). Summing the overtone channel signals into the main channel
signal will lift a weak signal out of noise if the overtones are being used
because even if data are being transmitted the statistical properties will
give some overall enhancement (otherwise information theory is being broken!).
Clearly there will be smear/shift because of relative motions and etc., but
appropriate measures can be taken to try different windowing lengths to adjust
for such problems (with different channel frequencies and bandwidths likewise).
Some of these adjustments are required probably standard anyway.
Information updated on 28th February
2003
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The University of Birmingham
School
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