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From: hbrown@voicenet.com
Subject: SS Testing/Analysis, Etc.
Date: Sun, 1 Dec 1996 08:19:10 -0500 (EST)
I work for a very large aerospace company that is very involved with communications. Like any large company that is involved with communications systems whose costs are in the billions, they use analytical techniques to determine the capability of the systems before they invest big bucks. Like antenna analysis programs that are in use today, they are accurate enough to determind the performance of the system in a "near" real world situation. This includes propagation and interference from all possible sources. The programs they use allow them to do all sorts of "what if" testing so that their billion dollar investment does not go down the tubes because they did not account for interferance from an downlink amateur satellite relay in a frequency band that they want to use for their proposed new communication system (SS or whatever). They also look into lots of interfering signals simultaneously. They are aware that their analysis is not perfect but like NEC used for antenna analysis, it's close enough for them to make decisions as to the technical performance of their system before moving on with spendng the dollars.

What I'm leading up to is a question for this group on what they may be aware of that has been done in this area for SS, FM, etc. system affects on each other's performance. I am sure that a some of you work for companies that are doing similiar work in SS and may be aware of studies that have been done and published. To the learned professional in this area, there must be some studies indicating the effects of many SS signals at various spreading bandwidths on other services that are in adjacent or in the same shared bands. Likewise, there must be studies on the impact on SS by interfering signals using non-spread narrow bandwidths.

These studies must exist and I would think that they must be referenced in applications to the FCC for frequency allocations when companies apply for the use of new modulations in existing frequency bands. Who knows about them?

Another more detailed question for the group concerns the sharing of a band by SS and narrow band signalw. Last spring when the ARRL requested that SS be allowed on some VHF bands, there were several comments to the FCC that interference from SS signals can be reduced by following the band plan - by not transmitting the SS signals in the weak signal portions of a band. Does this mean that a SS transmitter would spread it's signal with gaps covering perhaps the satellite 2 meter downlinks used by Oscar satellites and also have gaps in it's output spectrum so that it does not transmit in 144.2 MHz range? Doesn't seem like an easy thing to do to me. How do you create an algorithm that accomplishes this in real like? Can someone that knows more about real SS signals tell us more on how this is accomplished?

Hope that this makes sense. I can't beleive that there are not analytical tools out there that will answer a lot of these questions. No one expects analytical studies to be perfect but they would provide a benchmark for comparing the SS test results that TAPR is sponsoring to be compared to. It does not seem like a reasonable approach to run a study of a limited number of signals on the air and if little or no interference is noted by others to declare that there is no problem. I'm sure that TAPR and the study partisipants(sp?) are not planning to do this but the approach being taken has not appeared on this reflector and I would like to know what is being planned. If anyone knows where the detailed plans and approach are posted or where they are available, please let us all know.

73, Harry, W3IIT

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