Is it possible to build a mobile linear amp for a walkie talkie?

[rocket100]

So, my goal is to be able to take two walkie talkies and put one of them on a near space balloon and have a microcontroller send data through the walkie talkie on the balloon down to the one on earth. I'm not sure it would reach all the way back to earth so I thought of putting a small linear amplifier on the balloon walkie talkie to increase the range. But I have no idea how to build one that would work with a walkie talkie. Any ideas on how I could build one?

Here is the walkie talkies incase it helps: Amazon.com: Motorola MH230R 23-Mile Range 22-Channel FRS/GMRS Two-Way Radio (Pair): Electronics

 

[JimB]

Building an amplifier for 450Mhz (ish) is not a trivial task, and by the way for FM the amplifier does not have to be "linear".
Also consider that the amplifier will need a power supply, I guess a battery. Batteries are heavy, weight is something you dont want when building a balloon payload.

A better scheme would be to replace the antenna on the airborn radio with a full sized quarter wave with a groundplane, and for the ground radio, use an antenna with some gain such as a yagi which you can aim at the balloon as it rises and drifts away.
This will result in very little extra weight in the balloon, and an easy 10db gain at the receiving end, equivalent to a 10 times increase in the transmitter power.

JimB

 

[rocket100]

Building an amplifier for 450Mhz (ish) is not a trivial task, and by the way for FM the amplifier does not have to be "linear".
Also consider that the amplifier will need a power supply, I guess a battery. Batteries are heavy, weight is something you dont want when building a balloon payload.

A better scheme would be to replace the antenna on the airborn radio with a full sized quarter wave with a groundplane, and for the ground radio, use an antenna with some gain such as a yagi which you can aim at the balloon as it rises and drifts away.
This will result in very little extra weight in the balloon, and an easy 10db gain at the receiving end, equivalent to a 10 times increase in the transmitter power.

JimB

Thank you! What sort of a yagi antenna could I use?
Also, it still sounds interesting to build a RF amplifier, where could I find out how to build one?

 

[tytower]

Sounds like you will need to read up on yagi antennas -just google .
Same with amplifiers
The battery might be a LiPo which is not so heavy

 

[cobra1]

Why do you need to transmit audio?? any particular reason??

 

[davenn]

Why do you need to transmit audio?? any particular reason??

he said he wants to transmit data not audio

Dave

 

[trash]

I'm not sure why you'd want to use a linear. 1.5 watts ! This is heaps for a balloon.
You might see I mentioned using FRS in the other thread. This is much the same as our UHF CB.
These little transmitters are more than capable of being heard from over 100,000ft and higher if you can get your balloon up there.

Strip them down, throw away the plastic case, and use lithium batteries and reduce the TX duty cycle.
The antenna is ok for the task, but I prefer to make my own. A quarter wave inverted is best for balloons with a 45 degree radiation pattern.

Now, why you'd want to use a linear I have no idea. Building a linear is VERY easy. JimB has said it's 'not trivial' for UHF. But he's thinking of doing it ... the hard way First is that it really depends on how much TX power you want. Second is that the amplifier doesn't need to be 'linear'. It's FM, so a class C will get the most bang for your buck. But if it must be linear... then there are dirt cheap module which do the task so simply even a moron can make them work.
Any of the Motorola black chip modules will do the job, but a Motorola MHW710-2 http://www.chinaicmart.com/uploadfile/ic-circuit/200971415639747.gif
This circuit will work with a fraction of the components shown, it's that tollerant. They typically have about 20dB gain, but I've had some modules with up to 25dB.
So with this circuit, you'll have to attenuate the output from the FRS radio (~10dB) to get an overall gain of +10db and an output of ~15watts which is massive overkill for a balloon payload. You'll have more trouble trying to power it and the heatsink is going to blow your weight budget.

We've tested these modules to destruction and up to 25 watts can be squeezed out of them.

 

[trash]

Actually making a UHF amplifier can be as easy or as hard as you want to make it. JimB is thinking of ... the hard way

The first thing that has been mentioned is that you're thinking of using it for a balloon transmitter on FRS.
The FRS radio already being 1.5W which is heaps of power already.

Next is that the amplifier doesn't need to be linear. Since FRS is FM, you can get away with a Class C amp which is much smaller, simpler, lighter and uses less power for the same gain.

But lets just say you want some specific reason for linear and simple. Then a MHW710-2 will do the job giving you 20dB gain without much effort.
Though with 1.5W, you'll have to settle for 10dB with a 10dB attenuation.

This example has many more components on it that is actually required, but it's simple enough as it is.
http://www.chinaicmart.com/uploadfile/ic-circuit/200971415639747.gif

 

[davenn]

Hey trash

nice to see you on this forum welcome

cheers
Dave
VK2TDN

 

[trash]

Hey dave ... yes much mischief to be found here.

 

[PatM]

If you are located in the United states, using a higher power or different antenna will violate the FCC rules concerning FRS radio's.
I would caution against doing this as the FCC could assess fines for unlawful operation.

https://en.wikipedia.org/wiki/Family_Radio_Service

 

[trash]

Of course, but I'm not the good guys, I'm one of the bad guys.
Don't forget all the aviation laws one might violate.

I fix electronic issues, not legal issues.