Been playing with a very simple radio controlled car (Tyco Canned Heat) that
as standard does not have proportional control (office races at lunch
time!).  After finding some schemticas for the receiver on the net, I have
found it uses a very simple receiver consisting of a 1 transistor
super-regen stage, followed by a single IC that (I think) is a tone decoder
which drives a couple of H bridges.

In a quest to improve my chances, I have been working on a PIC conversion
that will accept the Pulse Posistion Modulation from standard RC
transmitter, and output two high speed PWM streams to control steering and
motor with somewhat more finesse.  All is going well so far, but I have a
couple of questions:

1)Is it possible to increase the selectivity of a simple regen using e.g. a
crystal? (obviously don't want to  start building a superhet!).  It would be
nice to be able to reliably use at least a couple of the 27MHz channels at
the same time.  My experience with receiver design is somewhat limited to be
honest.  I could spend a huge amount of money on a micro RC receiver, but
that isn't really the point (my car cost me 5UKP from a "bargain bin" in a
department store.  At 31 I still can't resist cheap electronic toys :o)  The
schematic can be found at
http://homepages.paradise.net.nz/bhabbott/tyco.html

2) All the information I have found on PPM radio control has shown a frame
using all 8 channels, the frame typcically taking about 22ms.  In a
transmitter with just two channels, does the fram still take the same length
of time, but with a huge sync pulse, or is the entire frame shortened to
around 8-9 ms?

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