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From: wd5ivd@tapr.org
Subject: Re: My Spread Spectrum Letter to FCC
Date: Fri, 29 Nov 1996 18:54:16 -0600
At 8:25 PM -0600 11/29/96, Robert Carpenter wrote:
>Thanks, Greg, for your messages. I think the fact that they have
>appeared on the VHF Reflector can be a big help.
>
>It seems to me that a six-month STA doesn't give enough time for serious
>work. From my own experience, it would seem very hard to get anything
>non-commercial on the air and well tested in such a short time. I, for
>one, wouldn't want to go all-out to whip up something good, just to have
>the STA run out as the gear was nearing completion. People on 902
>(K5LLL) have already complained about the greatly increased noise floor
>from the commercial SS sharing the band. We need experience with other
>techniques and bands to achieve some sort of completeness.

Yes a short time period does put some strain on the project. But I feel that several tests will be accomplished using different approaches. Frank Perkins, WB5IPM, has just released a DS SS example using the TAPR/AMSAT DSP-93. While it only uses a simple PSK modulation and generates a signal 3khz wide -- it shows how a faster DSP could be used to generate as wide a DS signal as you needed -- only add the RF and we could have a Direct Sequence system on the air quickly as a test. I wouldn't be surprised if the Motorola EVM56303 board would do the trick at about $200. I believe someone will be wanting to possibly do something with a test of this on 219...a good candiate band in many ways, since the primary user on that bands seems to be hesitant to allow any operations of amateur stations on narrow allocation channels. A lost band without something that will not interfere with and also take the interference generated by the primary user. If we don't get something operational on 219 in the next year or so -- that band will be potentially open for a petition for reconsideration from an outside source.

I think that what people call 'SS' on 902-928 has many definitions. While it might be spread, many a Part 15 device does not really have the necessary processing gain or even use any type of spreading codes to make them really interference resistance and non-interferring. One reason I am already using Horz antennas on the 902-928 band was to drop these signals I was seeing on the 17db vertical I was first listening on. Thet are now down 20db using the horz beam, which makes them disappear. I could see many (my guess) SW Freedom phones (since my folks have one to compare aginst) operating across the band and lots of other commercial part 15 devices. The interesting thing about 902-928 is the operating environment. Since we are not primary and everyone else has different degrees of rights in which to operate, well implemented SS can save this band for all amateurs to use as you point out, since more and more and more people will be purchasing devices that will operate on that band. With 3 million devices already sold under Part 15 rules (this should probably double in the next 18 months), we had better begin to explore methods to use the band which co-exists and allows us fair usage at the same time.

As to weak signal operations -- I'll just point to the paper that Phil Karn and Tom Clark wrote for the last Central States VHF/FM convention -- you want to operate weak signals...try SS with some signal processing techniques that Phil has been working on at Qualcomm and you can get down to almost theortcial limits. Want to work EME on an AMSAT satellite station -- it could be possible. No need for great antennas, high-precision radios, and large amounts of power. SS with a little computer power. You can read the pdf file at ftp://ftp.tapr.org/tapr/ss/eme-2000.pdf Why keep using technology from the 50's when new technology that outperforms it a great deal more with little or no additional invesment in equipment -- since that equipment is probably already setting in your shack or at least being used by you now to access the Internet to read this e-mail -- is available.

How people state or define 'Noise floor' seems to be very relative as well. As the conversation you and Phil Karn had several months ago that went into great detail on the subject. What you should do is get Phil on this list and you guys can discuss the pros and cons of the various aspects of Spread Spectrum and Signal Floor levels in detail for everyone to read. I did enjoy the comments and learned a lot. But there is a lot of untold story there, when someone just says 'noise floor increase'.

Cheers - Greg, WD5IVD

----- Greg Jones, WD5IVD Austin, Texas wd5ivd@tapr.org http://www.tapr.org/~wd5ivd -----

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