From: "Brian B. Riley" <brianbr@together.net>
Date: Tue, 15 Sep 1998 15:28:24 +0800
To: "Steve Schear" <schear@lvcm.com>
Subject: Re: radio net
Message-ID: <199809152029.QAA03672@mx02.together.net>
MIME-Version: 1.0
Content-Type: text/plain



On 9/6/98 6:20 PM, Steve Schear (schear@lvcm.com)  passed this wisdom:

>> 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.

 I would suppose the T-hunt aspects of a clandestine network would be 
obviated by piggybacking it into a commercial satellite transponder 
channels ... which brings to mind about how expensive one or two of those 
channeles might be. I remeber in the early days of ham packet radio we 
had several 'wormholes' where hams had obtained through their places of 
employemnt temporary use of unused satellite channels where we were given 
essentially RS232 access and we adapted the packet switches to an async 
backchannel in place of another synch RF path. They did make for some 
intersting network improvements. I guess it always comes down to how do 
you fund such things.


Brian B. Riley --> http://members.macconnect.com/~brianbr
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