Nick VA3NNW's KWARC CDMA talk

In Jan 2010, I gave a talk to KWARC about CDMA - Code Division Multiple Access. In September 2019 I updated and extended it a bit for Elmira Radio Club's Ham Tech Seminar.

The talk is © Copyright 2010-2019 "Nosey" Nick Waterman VA3NNW but is free for radio hams to present to other radio hams. Please let me know if you DO use it for this purpose (because I'm nosey and like to know who uses my stuff), or please ask my permission if you wish to use it for any other purpose (because that's the point of the copyright).

It can be downloaded here:

CDMA.odp (1MB LibreOffice/OpenOffice Presentation) - the actual presentation
CDMA.ppt (1.8MB Micro$oft Office PowerPoint) - but might not be properly converted, and c'mon, seriously, look at the file size, who still uses M$ Office?!?
CDMA.pdf (1MB Portable Document Format) - without animation/sound but contains all the content
CDMA_WS.ods (38KB Libre/OpenOffice Spreadsheet) - the worksheets used by each side of the room to "transmit" CDMA to be "received" by the other side of the room. Also contains a sheet of graphs, and has a few hidden calculations if you want to play with CDMA signals yourself.
CDMA_WS.xls (70KB Micro$oft Excel Spreadsheet) - but seriously, see above

Some other files I used to make the presentation

You're unlikely to want these unless you wanted to rewrite the presentation yourself, but they can be downloaded subject to the same copyright as above

CDMA1.ods - another spreadsheet to play with CDMA
CDMA2.ods - another spreadsheet to play with CDMA
Makefile - runs the programs below to create some of the charts and graphs
cp.pl - to make the code plots
qso.pl - helps to make example QSOs used in ftdma2.gnuplot
cp.gnuplot fp.gnuplot ft.gnuplot head.gnuplot - used to create many of the diagrams below
vis-example.pl - to make the images used by...
demo.html - a live interactive demo added for the 2019 version of the talk, where you can "tune" over the codes looking for the right codes and timing!

To use the demo...

There are at least 3 vertical copies and 2 horizontal copies of "the band" to be received/decoded. Choose "s" at the top, and demonstrate that you can drag the "secret decoder ring" across the band and use it to pull the already almost-visible "sync pulses" (squares) out of the noise.
Now turn "s" off and select "sync", and demonstrate how you can see 2 sets of sync pulses. Your job is to line them us as best you can to be perfectly synchronised with the code.
Next, leave "sync" on, and also choose "a". When "sync" and "a" are lined up, or even in several other places, you should be able to see my callsign VA3NNW in the "second decoder".
Leave "sync" and "a" on, but also add "b". Effectively using 3 receivers now, you should be able to "tune" my callsign and also see a pattern of blocks. In this pattern is another secret message, but only the person with the correct "long code" - c - can decode it.
Turn off "b". Leave "sync" and "a" on, but also turn on "bc". This is a combination of "spreading code" b and "long code" c to make bc. It's going to be quite tricky to perfectly line the signals up this time, but having done so, by trying to make the "sync pulse" squares vanish, you should see my callsign, and the special secret doubly-encoded message that provides the grand finale for the presentation!