Hi James

My first thought is to use one of those (no license needed) low power HF
frequencies set aside for telemetry, garage doors etc. The allowed power
output varies from place to place. From memory I think around the 1-50mW
range.

There is a fairly common world wide allocation for example around 13.555
Mhz. My thought would be to setup a xtal oscillator on the right
frequency and use very narrow band modulation techiques to continually
transmit the wind numbers (say) every minute or so. How much data you
are sending will govern the intervals and modulation bandwidth. You
might even like to do initial trials with PSK31 but it may not be narrow
enough for the power limitation.

At the receive end a sound card DSP demodulator attached to a receiver.
Not sure what sotware is already available. It would probably be very
easy though to modify existing source code at higher rates to what you
need. The demodulated data could be dropped into a database/file to be
read by your web engine.

Keep in mind that this technique would probably need forward error
correction on the data, or at least some kind of checksum so you could
ignore bad data.

The price? Assuming no transmitter already exists as a kit/off the shelf
you are looking at maybe AUD20 of components, the xtal being the single
most expensive part. The power consumption would be very low.

In case you arent involved in radio generally, the rule is that the
narrower the bandwidth of the signal, the better signal to noise ratio
you will get for a given output power. ie noise is a function of
bandwidth. For example CW (morse code) is often easier to hear at low
signal levels than a persons voice on SSB. There is however a penalty in
using a narrow bandwidth in that the rate of data you can send is
limited. Voice for example generally requires at least 2.4Khz and
"normal" morse code around 500Hz. I think PSK31 needs about 100Hz but
dont quote me.

Funny you shd mention this as I have a long term project to one day send
GPS signals (from a car) on 144Mhz using very narrow band techniques.
The average 30km range base to mobile for a voice circuit will probably
do about 200km using this mode.

Cheers Bob W5/VK2YQA

Coyoteboy wrote:

Hi all,

I've been trying to solve a data transfer problem for about a year now
and i cant find a cheap solution to what i need. I'm basically
transmitting data (average and gust wind speed) once a minute over a
distance of about 20 miles, over small hills and towns (small hills
being 3-400ft) from a beach location. This location has no power source
and no other means of connectivity. My current method is to chirp the
speeds into a mobile phone continuously and set it to auto-answer so
all i have to do is ring it to find out speeds. However I'd like to
WWW-ize it and so cant get the PC to listen to the beeps all the time,
plus this would cost a fortune call-wise if i could lol.

Can anyone suggest a solution that doesnt draw huge amounts of current
or require loads of space - this is a remote location but still close
enough to towns to have things that look like electronics stolen.

Any hints would be great, this is a personal project so budgets are
small lol.

Many thanks.
James