"Doug McDonald" <mcdonald@SnPoAM_scs.uiuc.edu> wrote in message news:dilv1a$4h3$1@news.ks.uiuc.edu...
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greg

An interesting point. Digital TV (8VSB) signals are ideal for
moonbounce IF you don't want to decode, just receive. Since they
are mostly random sequences (with some pseudorandom parts) with
a flat frequency spectrum they are ideal for doing autocorrelation
analysis. The minimum period is about 80 nsec and the maximum is infinite. The powers are very high. OF course, you would want
transmitter and receiver to be far enough apart that the
moon was near the horizon at the transmitter and near the zenith at
the receiver.

Doug McDonald

Hi Doug,

Well, but what is the bandwidth of this signal ? Most be like 5-10 MHz or so right ?
So, the total power per Hz is spread out over this bandwidth.
This makes the signal very hard to detect when compared to the CW analog TV carriers.
The CW carrier of TV signal contains a considerable (10-20%?) amount of transmission power,
and it is concentrated in a very narrow bandwidth (0.1 Hz or less).
So digital TV signals will be a factor of a million less power per Hz of bandwidth, and
are thus much harder to detect than the analog TV carrier.

I think there is a factor of SQRT(BW) that you can win with spectral integration,
but it still means that digital TV signals should be a factor 1000 harder to detect than analog.

(I am talking about only detecting, not decoding, which is even harder to recover).

This is the basic problem we also face in SETI : If ET is smart, they do not use CW carriers
for their own communication signals, and thus we have very little chance of detecting 'radio leakage'
from ETs.

Rob