From: Steve Schear <schear@lvcm.com>
Date: Mon, 14 Sep 1998 01:14:05 +0800
To: "Brian B. Riley" <brianbr@together.net>
Subject: Re: radio net
In-Reply-To: <199809130024.UAA12462@mx02.together.net>
Message-ID: <v04003a03b22162c43eae@[192.168.229.5]>
MIME-Version: 1.0
Content-Type: text/plain



> Spread spectrum would have more promise as many stations could be on the
>air at once on the same frequency thus making life quite confusing for
>the T-hunters.

I investigated this application several years back and see two practical
approaches: one adapt a commercial SSB or Ham transciever to use frequency
hopping spread spectrum, or two build a pirate spread spectrum satellite
ground station.

Until recently most SSB gear didn't have the RF characteristics to use FH.
Now there are a number of inexpensive sets which use direct frequency
synthesis (as opposed to the older, and much slower, phase-locked loop
approach) and can be driven at hundreds or even thousands of hops per
second. FH helps solve two problems: first it provides privacy, second it
can mitigate or eliminate fading (which is highly time-frequency
correlated). Also, the higher the hop rate, the higher the process gain,
jam resistance and the lower the probablity of intecept (all other things
being equal).

It think it was Phil Karn (Qualcomm) who once mused that it would be rather
straightforward to masquarade a high process gain SS signal on a commercial
satellite transponder. To it's owners the SS signal would be almost
invisible, making itself known as only a very slight depression in the
transponder's gain. Effectively, this could offer an inexpensive covert
channel for tunneling packets and thwarting traffic analysis.

After the Captain Midnight episode I discussed this possibility with a very
technically knowledgeable staffer at the FCC and was assured that discovery
of such signals were beyond (at that time) the ability of commercial and
national technical (e.g., Lacrosse) means.

There's much more, but this should give you the general idea.

--Steve

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