Walkie talkie with LM386

[ariaboy18]

Hi
I'm trying to build this circuit but i don't know the parameters of the transformer such as the type of core and etc.

**broken link removed**

 

[JimB]

It is not so much a transformer as a tuned circuit with an iron dust or ferrite core.

What frequency is this intended to work at?

JimB

 

[4pyros]

Where did you find that circuit?

 

[wookie]

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 slug inductor with two seperate coils wound over one another? I believe that the coils are supposed to be coupled, in order for the LM386 to be provided with an audio signal upon reception.

I would like to build this circuit but the only thing stopping me is the wierd component in the top left.

If possible, could someone provide information on the component with images for reference.

Thank you!

 

[audioguru]

The article says the very simple circuits are used in a 27MHz remote controlled car or in a child's walkie-talkie. They work at 27MHz and the modulation is AM and picks up all kinds of interference making noises.
The receiver circuit is a Mickey Mouse super-regen.

The article says "why re-invent the wheel?". It says to buy a cheap remote controlled car or walkie talkie and use its parts.

 

[JimB]

The receiver circuit is a Mickey Mouse super-regen.

The whole circuit is based upon a plethora of Disney characters!

JimB

 

[Willen]

If anyone really want to make the device, we need minimum a couple (two transceivers) to communicate to each another. Then I guessed frequency of both transceiver need to be same, isn't it? Then we can use any same turns and any same cores in both circuit (if we want any one frequency like between few hundred KHz to tens of MHz any one), Am I right?

In the places like mine, I never have seen such even a toy transceiver around markets! I love such interesting machines too!

 

[wookie]

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 range of frequencies.

 

[Tony Stewart]

THis may be helpful in looking at 10MHz ( or 27MHz) impedance for C L R, Z and impedance ratios , Q
where gain is Q or Xc(f) / Re,, where a bypassed 22R becomes the Rbe resistance which drops for rising bias current.

You can scale this to any decade.

If you pick the wrong ferrite with high permeability, resize it. This would be a mid high permeability type of which there are many

Look at Tokin or Murata or TDK specs or easier buy from Kemet/NEc Tokin or a good distributor like Digikey.