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From: lfry@mindspring.com
Subject: Re: My Spread Spectrum Letter to FCC
Date: Tue, 03 Dec 1996 06:13:49 -0500
At 03:07 PM 12/2/96 CST, KA5WSS wrote:


>All the more reason for weak signal ops to participate. There can
>be a meaningful investigation of this if the weak signal use their
>equipment to test whether SS signals will adversely affect their
>performance.
>

I'm wondering if SS is already there on 6M, 2M, and other bands and we just don't know it.

The military has tens of thousands of SINCGARS radios which operate from 30MHz to 88MHz and are capable of voice and data in frequency hopping SS mode. We suspect the military sometimes uses their ability to operate in the 6m ham bands even if "policy" says no - last summer's "War Games" reports on this reflector are possible evidence of that. So how much are they doing in modes that we don't hear?

Another equipment example is the AN/PRC-117 which has FHSS on 30 - 90, 116 - 174, and 225 - 420 MHz. Don't know how many of those are around, but probably a lot more than there will be stations on those bands under the TAPR STA.


>As an example. An SS transmitter is turned on and a long sequence
>sent (or not) every time slice. The choice of transmit or not
>is random and not known to the WS listener. The WS listener
>listens to the WS calling freq and attempts to determine when
>the SS transmitter is actually sending. Will the WS station be
>able to tell the difference? Maybe. Maybe it all depends on
>the antenna positioning, power, proximity, etc.

So how would you recognize that a FHSS or DSSS system is sharing spectrum with you? There is a picture from a spectrum analyzer at http://www.lxe.com/radio.htm showing 900MHz showing DSSS and FHSS on the same display. If we were going to look for the presence of uncooperating (uncooperating meaning we don't know for sure they are there or what frequencies they are on) military emitters on 2M, 220, or 440 how would we go about it? I don't suppose that SS is called low probability of detection for nothing.


>
>Actually one can do this type of testing without an STA just
>by using Part 15 devices that are available to everyone. Has
>anyone else ever tried this?

Keep in mind that Part 15.247 only allows unlicensed SS devices on 900, 2400, and 5700 MHz.

For an audio example of a part 15 network device interfering with a part 15 wireless mike listen to the RealAudio recording of Steve Bible's Introduction to Spread Spectrum, at http://www.tapr.org/tapr/ra/dcc.96.n7hpr.intro.ram
>


>I don't want to see the WS segments "ruined" but fighting the STA
>(especially at this point) is wasted effort. Better to take part in
>the investigation and really learn what all of this will mean to
>Amateur Radio.
> Agree. As has been pointed out, we'll most likely see SS on the bands, whether we do it, or the spectrum is sold to others

Lee W. Fry AA0JP lfry@mindspring.com See my Part 15 Spread Spectrum Device Compendium at: http://www.mindspring.com/~lfry/part15.htm

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