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27MHz is the CB band and you don't need a license. Is there something else that makes this circuit illegal apart from "appalling[ly] poor circuit[ry]"
Below is my spec, copied from my specification powerpoint:
this list is noticeably more concise than a normal spec, due to the fact it was for...
Okay great, I can conduct some field testing and add it to my report- good idea :)
What improvements could be made to the circuit to optimize it? Can't be all bad surely?
Hi Nigel,
I read the other thread (infact I revived it) but didnt see any claims that the circuit would be useless.
4 metres is a hell of a whip. I was hoping for much less than that.
Yes I believe that the 22uH is a loading coil to make use of an electrically short whip.
I used this calc...
Hi Ethan,
I still use Circuit Wizard from my school days, its great at simulating circuits and playing around with components - you learn a lot.
I would recommend a push-to-make switch that feeds into a decade counter's input. You will see on the software (use the Voltage Levels view) that...
Hi everyone,
I am working on a college project to design and build a 27MHz half-duplex walkie talkie for a paintballer and his teammates.
The circuit I would like to use is the one below:
I have some questions however:
-Can I use a whip antenna, and how long should it be?
-Can you...
Hi Willen,
Unfortunately I do not think it is that simple. The reciever (and possibly the transmitter) contains components specifically selected for 27MHz (the advertised frequency).
I hope I am wrong about this, because I would like to make the circuit to function across the Citizens Band...
Sorry to revive an ancient thread but I am looking to build this exact circuit.
Found at the bottom of THIS PAGE, the writer offers the LM386 based solution as a variant of a discrete walkie talkie further up the page.
I too have questions about the transformer - is it in fact a variable...
The delay over propagation distance is exactly what I am looking to determine, as it is the key to calculating distance traveled :)
How I actually compute that is a whole other kettle of fish... We'll cross that bridge when we come to it :)
Thank you steveB!
You can try to convert the image to a vector and then upscale without worry of distortions.
There are various online tools that can convert black/white images to vectors for you, have a google and find which one suits your needs :)
Hi Steve,
The plan is to measure the beat frequency of the light by comparing the outgoing sawtooth to the incoming sawtooth (reflected off the target).
I have discovered that to do this, a sawtooth waveform is not ideal, as the rise/fall times are uneven. a perfect triangle wave is now the...
Okay, I think I understand. My chirp signal is not a true FM transmission, it is a hybrid of FM and AM, due to the nature of lasers in general - correct?
No info on that, the laser light frequency is fixed.
Hmmm..... you can't change the frequency of the laser light, but can you use the frequency as a carrier for the "chirp" signal? more investigation needed
I HAVE MADE A MISTAKE.
There is no "frequency modulation stage". I got confused with my own design. The laser driver is driven by the VCO output. The VCO is to operate linearly from 55MHz to 130MHz.
Still learning here :)
Correct, I would need to find a diode without inbuilt current regulation, and design my own to drive it.
I know this can be done, because there is a similar circuit here.
Edit1: Also, I may be getting confused with FM terminology. I included the 433MHz carrier wave as I thought it would be...
Why do you say that?
Just to give you an idea of my project, it goes like this:
Clock -> Rampwave Gen -> VCO -> Freq. Modulator -> Laser
The clock generates a 2kHz baseline for the system.
The Rampwave gen makes a sawtooth waveform, making the VCO "chirp" between 4-60kHz.
This chirp signal...
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