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From: steveh@fons.com
Subject: REALITY CHECK!
Date: Thu, 5 Dec 1996 18:04:42 -0500
WHOA, HORSEY! SLOW DOWN....wait a minute! Let's do a reality check here! Methinks that somehow, we've all been led off the original subject hereabouts! Let's backtrack a bit and see where we used to be afore we go wandering into a different meadow, shall we?

The thread on which Phil Karn, KA9Q, and Tom Clark, W3IWI, have been commenting lately on this reflector seems to have begun immediately after Bob Carpenter, W3OTC, posted some quotations from a paper coauthored by Mr. Karn and Dr. Clark titled "EME2000: Signal Coding and Processing for Weak Signal Communications" and presented at the 1996 CSVHFS conference. Mr. Carpenter, in a response to a posting by "Robert", and also in an apparent attempt to inform subscribers of this reflector of the thoughts of several spread-spectrum "gurus" on the potential use of ss for EME communications, quoted several portions of the paper which included indications of the speed, amount of, and error rate of data that could be received by what Mr. Karn and Dr. Clark considered to be a typical amateur station capable of accessing amateur satellites. For example, Mr. Carpenter said:

"Read the paper by KA9Q and W3IWI that they gave at the 1996 Central States VHF Conference. As I read it, ham EME using advanced modulation techniques will likely be rather narrow-band. Most of the following applies to 100-200 W stations and "Oscar" beams."

He then quoted from the paper to make his point. Mr. Carpenter's final comments on the paper were:

"I thank Phil and Tom for letting me post the above without permission,"; and,

"So, if they are right, we won't see 500 kHz wide "SS" EME stations on the ham bands.

The W I D E SS users will be local terrestrial links, just down the street from you,".

In a later posting to this reflector, Mr. Carpenter again quoted from Mr. Karn and Dr. Clark's paper, opening with:

"More quoted from the KA9Q/W3IWI paper,"; and he finishes with:

">From this I conclude that it is only the BIG GUNS who will have enough 'smoke' to use wide SS for EME,".

Personally, I don't see, anywhere in Mr. Carpenter's postings and quotations, any indication that Mr. Carpenter had the intention, whether purposely or not, to indicate that ss is NOT practical, or that it CANNOT be used for weak signal or EME. To the contrary, I read his postings as informing those of us who have not seen Mr. Karn and Dr. Clark's paper that EME two-way ss communications can, indeed, be accomplished by amateur stations.

But Mr. Karn's first reply posting indicates that Mr. Karn completely misunderstood Mr. Carpenter's intention in quoting the paper:

"As usual, Bob Carpenter quotes very selectively and out of context to try to give the impression that our own paper argues against the use of spread spectrum on EME."

Dr. Clark's consequent posting, apparently inspired by a note from Mr. Karn about Mr. Carpenter's quotations from their paper, makes it clear that Dr. Clark, too, believes that Mr. Carpenter posted the quotations in such a manner that a reader would be impressed to believe that even the ss "gurus" do not believe EME communication is practical using ss techniques:

"As the co-author, let me add a few additional comments to Phil's...".

The last posting I've received from Mr. Karn, reprinted below, shows that Mr. Karn is under the impression that somebody, somewhere on this V/UHF Reflector, believes that spread spectrum communications under adverse or weak signal conditions is not practical:

"By the way, just to show you this spread spectrum stuff isn't all theory, I am typing this message from my laptop while sitting indoors at the local food court near work.

I am logged into my office workstation over a Qualcomm CDMA (spread spectrum -- 1.25 MHz bandwidth) cell phone operating in the 1.9 GHz PCS band. The phone is plugged into the serial port on my laptop, and it's carrying TCP/IP/PPP packets from the Linux operating system on my laptop to the company Internet and thence to the outside world.

The cell site is perhaps a mile or two away on a 2-story building, and the phone is just resting on the top of my bag in a horizontal position. The path is not especially strong; I see only one bar on the signal strength meter. Yet thanks to the strong coding and inherent multipath resistance of spread spectrum, the TCP packet loss rate is nil -- even character-at-a-time typing works just fine."


>From Mr. Carpenter's comments and quotations above, the viability of ss as a communications medium for amateurs, even for such exoteric modes as moonbounce, is clearly not in question.

Mr. Karn and Dr. Clark, may we now return to the original question that started this whole string on this reflector: can spread-spectrum and weak-signal enthusiasts co-exist on the same amateur bands without a degradation in either's existing capabilities? Harry Brown, W3IIT, after all of the above had been posted here, has already attempted to bring us back to the original subject by publicly posting a related question which was addressed to Dr. Clark; I have not seen a reply as yet.

Please keep in mind that not all other amateurs are conversant with the theory and applications of ss; concepts such as the various codings, etc., that you, Dr. Clark, have mentioned, are not only alien to our way of thinking, but also of very little interest to most weak signal enthusiasts. All that we REALLY want to know is:

What do you, as an expert on spread-spectrum communications, predict will happen to our noise floor on the various V/UHF amateur bands as heard on our typical narrowband receiver systems when one or more ss stations operate on the same band utilizing whatever transmission parameters might be expected to be considered normal by other ss users?

73, Steve Ko0U/1

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