G'day Neil,

I'm also experimenting with 433 MHz modules at the moment; not serial
modules, but radio modules.

Techniques to suggest;

1.  make sure the receiver module power supply is clean and well
filtered,

2.  capture the receiver data waveform and compare it to the
transmitter data waveform, in case you have some source of noise,

3.  mount the transmitter module to the base of the antenna and keep
the transmission line under one sixth of the wavelength, and if
possible do away with connectors,

4.  use a frequency counter or other instrument to verify the
transmitter frequency; at least to get some more significant digits,

5.  try a slim jim or j-pole antenna [A] at 433 MHz using television
ribbon cable (balanced feeder), then tune it, (for me, this can give
about 500 metres range in the open),

6.  try a yagi [B].

I've also had some problems with 151 MHz modules that turned out to be
my misread of datasheet; data input needed a series resistor to ensure
FM deviation was in spec.

I've also had spurious transmitters nearby at 433 MHz.  In one case a
weather station outside transmitter that was continually transmitting,
bringing range of other devices down to a metre or so.  A Spectrum
Analyser can help with this.

Got references for those modules?

References:

A.  calculator for lengths and cut points,
    https://m0ukd.com/calculators/slim-jim-and-j-pole-calculator/

B.  calculator for three element yagi,
    http://www.csgnetwork.com/antennae3ycalc.html

--=20
James Cameron
http://quozl.netrek.org/
--=20
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