From: ericj@hwcae.Honeywell.COM (Eric Jacobsen)
Subject: Re: Radio dreams
Organization: Honeywell, Air Transport Division; Phoenix, AZ
	<ERICJ.92Sep9124702@calcutta.cfsat.Honeywell.COM>
	<1992Sep10.103654.756@csc.canterbury.ac.nz>
Date: Thu, 10 Sep 1992 00:32:14 GMT

In article <1992Sep10.103654.756@csc.canterbury.ac.nz> kaiser@elec.canterbury.ac.nz (Chris Kaiser) writes:

...stuff deleted...

   This is essentially the method that ethernet uses. For low traffic volumes (i.e.
   few users in the RC scenario) it works well, however for large amounts of traffic
   its performance drops off fast, and delays become rather long. Another problem is
   that it is statistical packet system, which means that information is transmitted
   in discrete packets, and each packet can take a different amount of time before its
   succesfully received. This isn't a problem for most data communication applications,
   however RC stuff can be quite sensitive to time delays :-)

That was my point. Murphy says that when you misjudge the wind on short final and your
bird heads for the ground your correction signals are gonna be the ones that get
delayed... :(

   > Another method, though is to use a spread spectrum technique where you don't
   > really care (as much, anyway) about how much radios are interfering with
   > each other. This also complicates ($$$$ again) the transmitter and receiver.

   Add to that that eash flier would have to have their own unique code, and there are
   only a finite number of codes. Therefore you'd still have to have a control pegboard,
   although it'd be a code control board rather than a frequency control board. Also, its
   much easier (more idiot-proof?) to change a crystal than a spreading code.

Actually, I kinda thought you could use the garage-door-opener approach and just have
a dip switch that lets you select a new code. This could be made much easier than a
crystal change and wouldn't require a re-alignment or anything.

   These three techniques (frequency division multiplexing, time division mux'ing, and code
   division mux'ing) are the major methods of allocating an available frequency spectrum
   between multiple users. Each has advantages and disadvantages for different applications.
   For RC applications, frequency division mux'ing (our current system) is currently the
   best system in terms of cost, time delay, ease of use, control of clashs, etc.

Plus, r/c receivers these days are sooooo small and light and low-powered that adding
the additional complexity would come with a significant cost in power budget plus
a bit of extra weight. For the average modeller this would probably be a noticeable
disadvantage.


--
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* Eric Jacobsen        Honeywell Inc.                           *
|     1-602-436-3941   Commercial Flight Systems, Air Transport |
* HVN       436-3941   US Mail: P.O. Box 21111, MS 2Q34C1       *
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* The opinions expressed are my own and therefore better        *
| thought out than my employer's.                               |
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