Any available circuit diagrams of good basic walkie talkie licence free India

[aruneshdutta]

Hello all

I wanted a basic and good circuit diagram for walkie talkie that can be designed and made into ready use.Have attached image.Thanks all

 

[rjenkinsgb]

There are lots of DIY radio schematics available, for many different frequencies and power levels.

However, unless you have an appropriate level Amateur Radio licence in whatever country you live in, it's generally illegal to use any home-built radio equipment.
(Or any with sufficient power top work over more than a couple of metres, anyway).

Mass produced "consumer grade" pre-approved ones are available very cheaply in many countries.

 

[aruneshdutta]

There are lots of DIY radio schematics available, for many different frequencies and power levels.

However, unless you have an appropriate level Amateur Radio licence in whatever country you live in, it's generally illegal to use any home-built radio equipment.
(Or any with sufficient power top work over more than a couple of metres, anyway).

Mass produced "consumer grade" pre-approved ones are available very cheaply in many countries.

Thanks I wanted to use it for free spectrum which are available in India and I know there are have attached the licenced free band in India

 

[rjenkinsgb]

OK; out of those bands, the only really practical ones are 26.957 - 27.285 and 865 - 867 MHz.

The others are either too low power, use restricted or too high frequency for simple construction.

This is a fairly simple design that could easily be modified for 27MHz operation (it's for 49MHz as drawn).
https://www.qsl.net/va3iul/Homebrew_RF_Circuit_Design_Ideas/49MHz_Walkie-Talkie.gif

The four-pole switch marked a - v is the receive / transmit switch.

You will need to work out the inductor values to resonate on 27MHz.

Two more designs specifically for 27MHz:
https://www.qsl.net/va3iul/Homebrew_RF_Circuit_Design_Ideas/27MHz_4-BJTs_Walkie_Talkie.gif
https://www.qsl.net/va3iul/Homebrew_RF_Circuit_Design_Ideas/27MHz_3-BJTs_Walkie_Talkie.gif


And a serious, high quality design - use the general values from the "10" table, but the crystal frequencies (X1 etc.) need adjusting so it works on 27MHz rather than 29MHz. It's for CW (morse code) as shown and will need some changes for voice use, but gives you an example of higher quality RF design.
https://www.qsl.net/va3iul/Homebrew_RF_Circuit_Design_Ideas/10m_1Watter_TRX_W8DIZ.gif

 

[unclejed613]

the 27Mhz band will probably be the best for home-built equipment. while the 866Mhz band is practical for walkie talkies, making homebrew equipment for that band requires attention to detail that most hobbyists (at least starting out) haven't developed. wires and PCB traces need to be kept very short, and proper PCB layout is critical (even the width of PCB traces can "make or break" the radio).

for figuring out changing coil parameters from 49 to 27Mhz, multiply the number of turns by 1.8 which will at least get it close.

i found this with a google search: http://electronics-diy.com/27mhz-walkie-talkie.php

 

[unclejed613]

be aware some of the walkie talkie circuits have a widebanded receiver, which means you can hear radios that aren't always on the same channel you are using.

 

[JimB]

Note that just because a frequency is listed as "Licence Free", it does no mean that you can use any old radio which you have made on the kitchen table, to talk to your mate down the road.

You will notice that in the table you showed, the Applications/Specifications column defines what that freqyency may be used for.

JimB

 

[unclejed613]

that's one of the reasons to choose either 27Mhz or 866Mhz, the power and usage restrictions are what you would expect for a two-way local radio system.

 

[Ramussons]

Also be aware of spurious outputs...... Harmonics and Intermods. The 3rd harmonic of 27 MHz band falls plumb in the Police Wireless.

 

[unclejed613]

yeah, you don't want harmonics interfering with anything important...
harmonics of 27Mhz:
2nd 54Mhz amateur 6 meter band
3rd 81Mhz land mobile, FM broadcast in some countries
4th 108Mhz harmonic will be in the FM broadcast band if using frequencies of 26.xxx, and aeronautical band if above 27.000Mhz
5th 135Mhz aeronautical

so, you may need to use a low pass filter to get rid of these harmonics. you can use an RTL-SDR radio to detect any of these harmonics (connect RTL-SDR to a separate antenna, don't connect it directly to the walkie-talkie).