Hello!! I'm a newcomer here. I'm from Malaysia and I hope my English is not too bad so that anyone can understand it.

I'm doing my final year project about full duplex walkie talkie. A normal "walkie talkie" style two-way radio will only operate if the radios are within a certain distance of each other and it is half-duplex walkie talkie.

So, what am I gonna do to make it duplex (I mean, how to modify the circuit, what to add to the circuit or whatever, to make the circuit becomes a full-duplex. ) and how to make it operates within more than 100 meters? (150 meters maybe..)

Thank You!!

 

First of all, can you tell us

The frequency
The channel spacing
The modulation type
The licencing, regulations and Type Approval specifications relating to the radios you wish to modify.

JimB

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Experience is directly proportional to the value of the equipment ruined.

 

Hey Missy,
Do you know what you are getting into?

Half-duplex walkie-talkies operate on a single RF frequency. To be full-duplex the 1st one must transmit on the 1st RF frequency and be received by the 2nd walkie-talkie on that RF frequency, and the 2nd walkie-talkie must transmit on a 2nd RF frequency and be received by the 1st walkie-talkie on that RF frequency.

Most half-duplex walkie-talkies use a single speaker/microphone. To be full duplex each walkie-talkie needs a separate speaker and microphone.

What about acousical feedback howling? Sound picked up by the mic in the 1st one is transmitted to the 2nd one where it is reproduced in its speaker. The 2nd one's mic will hear the sound and transmit it back to the 1st one where it is heard by the 1st one's mic. Around and around goes the sound and it will howl or squeal loudly.
You could use sealed earphones to stop the howling or use DSP echo cancellation like on expensive speakerphones.

You must be thinking about modifying cheap toy walkie-talkies that have a range of only 100m. Over here we have FRS or GRS ones that are fairly inexpensive now. They have 38 programmable channels. Their range is up to 10km. Of course they are half-duplex.
I have lots of fun listening to other people and making smart-ass remarks! I use them to find my wifey in large stores but she doesn't like everyone around her to hear my smart-ass remarks about her. :lol:

__________________
Uncle $crooge

 

As Jim says, you need to consider all those things!.

But basically, for full duplex, you need to use two widely seperated frequencies - the old analogue cordless phones used to use something like 49MHz from handset to base, and 1.8MHz from base to handset.

To try and do it in the same sort of band is VERY difficult, and expensive, and even then gives reduced performance.

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Well, I think I had been mistakenly thinking about to do this project. then, I think I should forgot about it and do something else. Well, the point is to add signal reception distance in a transmitter and receiver circuit.

for example, i have an fm transmitter and receiver circuit that can only operates within 10 m distance. what to do to make it can operate within 100 m? maybe, use a longer antenna or whatever.....

the other point is how to make a simplex circuit becomes duplex. i know that for duplex, both side have transmitters and receivers, but both the transmitters and receivers at the both side are similar circuits?

 

Add to the above fun the fact you would likely want to have "sidetone."

Sidetone is the ability to hear your own voice in the transmitters earpiece. It is done to reduce confusion of the person talking, help them regulate their own speaking volume, and makes the process seem more "natural."

This will involve filters, anti-feedback, etc. It is done on telephones, and takes a bit of work to get it right.

A lack of sidetone results in the common phenomenon of people shouting when they are wearing headphones.

 

for this to be 100% legal, you need to be somewhere way out in the middle of the ocean, and have someone else way out in the middle of the ocean 150 meters away from you. At least then if you pick the wrong frequency (like the FM band) to transmit on, no one will hear you because you are too far away from any land.

Walkie talkies can operate on any distance. Once they are far enough away, distortion and eventually no transmitting voice will occur in the receiving end. A walkie talkie works perfectly well in transmission if the two are two inches apart

For full duplex, the BEST way to go is to follow the above methods and use two frequencies. One for transmit and one for receive. The other walkie talkie will use the same frequencies, but the transmit and receive frequency will be inversed.

If you don't want to use two frequencies, you could probably get away with some circuit using a microcontroller, but I haven't done it yet. and if the microcontroller was used, there will be reduced performance due to the amount of processing the uC takes AND if we factor the maximum clock speed in the microcontroller, I can't see a uC being a solution.

Before you begin, find two frequencies that are being used by nobody at all (probably > 500Mhz) then talk to us.

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-=: The best low-priced components to troubleshoot with are the speaker and the LED :=-

 

I made a little FM transmitter when I was a teenager about 45 years ago. It transmitted about 100m and I didn't know anything about RF.
A few months ago I made my 2nd little FM transmitter and it goes about 2km. I know a little about RF now but still not very much. Aren't you learning anything about RF in school?

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Uncle $crooge