Re: Range and low power draw mutually exclusive?
- From: Bob Bob <bob3bob3@xxxxxxx>
- Date: Thu, 15 Sep 2005 12:11:39 -0500
Well strictly speaking such a low power transmission shouldnt be a huge problem in design and build. You might get away with a simple xtal oscillator and maybe a "power stage". You'll find lots of designs for that all over the web. Look for CW transmitter designs for QRP use.
Your first step though is to find out what the rules and regs on unlicensed low power HF devices is in your country.
The next biggest problem is how you modulate that oscillator in a very narrow band mode. FSK (freq shift keying) and PSK (phase shift keying) are relatively easy to do. Likewise you'll find lots of designs for that on the web. I should also point out that oscillator stability and "bad" noise/sideband generation also needs to be closely looked at for extreme narrow band modes. Your power supply also needs to be as noise free as possible and things like hanging TTL switching etc off the same supply might be problematic.
What you didnt mention is what is the actual output of the wind speed device. Is it a uP device with lots of options or does it just send out pulses? If it just does pulses you'll probably need a counter in TTL etc. I'd be interested to hear how you already have that working and interfacing to the phone.
The receive side is pretty simple in a sense. Assuming you have a reasonably stable SSB receiver you then only need a soundcard connection. (ie radio speaker to sound card line in) You'll need to decouple the computer from the radio (like through a transformer) to reduce noise pickup. Antennas of course are another "problem" to be solved and how much time you spend on them depends on how good a signal you get on first tests. PSK31 might actually be a good starting point because there have been lots of programs written for it that are GPL. Hence you can modify at will.
Hey I use to write assembler and do prototypes etc for the old 8085's uP's.. That was a long time ago!
Cheers Bob
Coyoteboy wrote:
I was thinking along this line too but having no experience with RF transmissions or methods of doing so I've just realised i'm going to need to sit back and read for a while! Coding im OK with, electronics I can deal with (though I mainly do microprocessor stuff) but RF is less in my area lol. Thanks for the hints, I'm currently running through google pages like never before :) so I'll get back to you when i feel more on a level to understand the information presented.
Thanks again! James
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