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

by tackyattack
Tags: build, linear, mobile, talkie, walkie
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tackyattack
#1
Apr21-11, 06:41 PM
P: 51
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: http://www.amazon.com/Motorola-MH230...4&sr=8-1-fkmr0
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dlgoff
#2
Apr21-11, 08:28 PM
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You might want to look into Amateur Radio. You can legally do this as this club has:

Amateur Radio High Altitude Ballooning
Mike_In_Plano
#3
Apr21-11, 09:09 PM
P: 560
Instead, I'd optimize the antenna situation. Having line-of-site communications is a great advantage, but you'll likely have all manner of tossing and rotation. Thus, I'd be tempted to attempt circular polarization.
On the ground, a quad helix would give you considerable gain without becoming a pencil beam. From what I've read, they're fairly simple to build and can feed the 50 ohms or so that you'll likely need. You might look under "wi fi quad helix" for ideas.
Oh yes, don't forget to insulate it. The top of the world can be a chilly place.

- Mike

skeptic2
#4
Apr21-11, 09:21 PM
P: 1,810
Is it possible to build a mobile linear amp for a walkie talkie?

Before you get too far along with your plans you should review the FCC Rules for GMRS radios. http://ecfr.gpoaccess.gov/cgi/t/text...47:5.0.1.1.5.1

Here are some excerpts:
95.3 License required.
Before any station transmits on any channel authorized in the GMRS from any point (a geographical location) within or over the territorial limits of any area where radio services are regulated by the FCC, the responsible party must obtain a license (a written authorization from the FCC for a GMRS system).

95.101 What the license authorizes.
(a) A GMRS license authorizes a GMRS station to transmit messages to other GMRS stations at any geographical location within or over the territorial limits of any area where radio services are regulated by the FCC.
This means that if the balloon drifts over Canada or Mexico, or any other country, you must stop transmitting and that means having a means of turning off the balloon transmitter.

95.183 Prohibited communications.
(a) A station operator must not communicate:
(4) Coded messages or messages with hidden meanings (“10 codes” are permissible);
This means that the meaning of your transmissions must be easily understandable to anyone listening on an ordinary receiver. The FCC wants to be sure your transmission is not being used for any illegal activity. You can't just send data.

dlgoff is correct, ham radio is your best bet and it's not that hard to get a license (even I have one).
skeptic2
#5
Apr21-11, 10:02 PM
P: 1,810
Oh and if you believe you can just do it without a license and without getting caught, this is interesting reading.

http://www.fcc.gov/Daily_Releases/Da...C-305523A1.txt
Xarren
#6
Apr21-11, 11:20 PM
P: 8
Have a read through this - My school achieved a ridiculous range, I'm pretty sure it details radio comms somewhere there: http://www.hexoc.com/pages/apex/apex-ii.php

Edit: Here is the technical document specifying data transmissions: http://balloon.hexoc.com/media/apextech.pdf


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