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 buy the variable transformer off the shelf?
-Would having long leads from the microphone to the circuit (15cm+) be a major issue?
As has already been explained in the other thread, it's a completely useless circuit, and will only work poorly (if at all?).
But to answer your questions:
1) Yes, about 4 metres long for correct operation (quarter wave whip) - the 22uH coil feeding it is probably an effort to make better use of a much shorter whip.
2) No.
3) No, as long as you use a suitable screened lead.
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 and found that I can use a 27cm whip with 1mm wire with only 12uH loading coil. Would this work better?
Why not Define the link? The worst design is one with few specs.
What latency is needed? How many channels? Transponder time? Voice and data channels.
Collision avoidance? Std Code burst communication for watch your back etc jammers hehe
In the other thread I said the "receiver" is a Mickey Mouse super-regen. Mickey Mouse circuits are too simple to work properly.
The original article said to buy the cheap kid's walkie-talkies or cheap child's toy remote controlled car and use their parts.
Half-duplex does not work in a noisy environment (paint ball shootings?).
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 a powerpoint and I would talk about each of the sections in detail. I hope it provides the necessary information. if not, let me know and I will add it to the spec.
In the other thread I said the "receiver" is a Mickey Mouse super-regen. Mickey Mouse circuits are too simple to work properly.
The original article said to buy the cheap kid's walkie-talkies or cheap child's toy remote controlled car and use their parts.
Half-duplex does not work in a noisy environment (paint ball shootings?).
I most likely will do exactly that and buy some kids walkie talkies, I had a pair a few months ago but i harvested the transistors and 4PDT switches from them for another project - doh!
Bare minimum functionality is all that I care about. Paintball isn't that noisy when everyones using electromechanical guns and pumps. But old style mech guns are hideously loud, I agree.
You don't need a licence, but you have to meet the fairly strict requirements needed - that appalling 'circuit' is going to radiate all over the place, and has no accurate frequency anyway.
Licence free does not mean a free for all to use whatever equipment you like.
There are specifications issued by the licencing authorities, (OFCOM in the UK) which specify the frequencies to be used, the modulation type and the limits on output power and spectral purity.