SETI Ultra Wideband Radio Interference Threat?


David Woolley (david@djwhome.demon.co.uk)
Sat, 31 Jul 1999 12:18:07 +0100 (BST)


This article was in response to someone who appeared to have seen the
marketing hype without having been aware that digital and, in particular,
spread spectrum, already posed a threat to the detectability of the earth,
by leakage radiation.

However, the point of interest is that the centre frequency for this
system can be anything from 650MHz to several GHz and it is very broad.
The spectrum from 650MHz has largely tailed off at 1420MHz, but other
frequencies would put power into the hydrogen line. I think they can
get away with this, because the power from any single transmitter is
below the noise, at much more than a few metres, but, if the system can
support a significant number of users the cumulative power could become
significant (they suggest 1,000 user, i.e. +30dB, per cell).

From: david@djwhome.demon.co.uk (David Woolley)
Newsgroups: alt.sci.seti
Subject: Re: Is seti analyzing the data for Ultra Wide Band signals?
Date: Fri, 30 Jul 1999 00:02:28 +0100
Message-ID: <T933288994@djwhome.demon.co.uk>
References: <7nijrc$t3$1@nnrp1.deja.com> <T933111394@djwhome.demon.co.uk>

In article <T933111394@djwhome.demon.co.uk>,
david@djwhome.demon.co.uk (David Woolley) wrote:
> In article <7nijrc$t3$1@nnrp1.deja.com>, smileyface4688@my-deja.com wrote:
>
> > There is a new technology that may revolutionize wireless communication.
> > The technique is called pulse technology or ultra wide band. Since this

> > For more info on the invention go to:
> > http://www.time-domain.com/index.html
>
> I haven't read this, but your summary indicates that, at least for the

I've now had a quick look at the site and it is a code division multiple
access spread spectrum system, but not the traditional direct sequence
method (although one could consider that it is equivalent to taking
it to the limit of an extremely small chip size).

I note that they carefully avoid mentioning existing spread spectrum
methods on their technical overview web page; it would compromise several
of their selling points and at least one diagram. They do mention it
in the white paper.

It will have the same problems as conventional spread spectrum from
the point of view of being difficult to detect by SETI searches. In
fact, if you take the sales pitch at face value, it is impossible to
detect. (NB even relatively narrow spectrum digital transmissions
are difficult to detect; can you tell modem noise from white noise?)

They seem to be targetting only the local communications market.
Possibly because the number of channels is limited by the number of codes
available and possibly because of conflicts with existing technology.

However, if it was adopted for satellite and other global communication,
it would compromise radio astronomy, in general, and SETI because it
would raise the general RF noise level in the reserved frequency bands;
although any one transmitter may not increase signals appreciably above
the noise, as you get close to saturating the capacity of the method
they would all add up to produce wideband noise from 0MHz to well into
the waterhole frequency range.

I suspect a higher power tranmitter would be rather effective at
disrupting nearby electronics - the signal is almost a series of
EMPs, but of low amplitude in the local communications application.
:



This archive was generated by hypermail 2.0b3 on Sun Aug 01 1999 - 16:28:48 PDT