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Old Jan 25, 2012, 06:13 PM
Registered User
Romania, Bucuresti, IF
Joined Mar 2011
33 Posts
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DIY 27Mhz RX/TX

Hi there,
Because is winter and cold outside i started to build a homemade TX/RX.
I had 2 old walkie-talkies with some missing components but with some nice Xtals on 27Mhz. So, after more than 7 years since i did not burn my fingers, and because 12 years ago i loved playing with RF and now i have some free time, i decided to reverse engineering thouse.
I know i am reinventing the weel, but i am having fun.
Also, Ivan (http://translate.google.com/translat...n%2Findex.html) inspired me and i will like to thank him.
Right now i moved the TX part (FM modulated) to a test board, with success (i can reach third harmonic on my cheap radio - around 81Mhz).
Check the pictures attached.
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Old Jan 26, 2012, 09:36 AM
RC beginner
New York
Joined Oct 2008
6,054 Posts
i am very interested in 27mhz. it is my favorite band because of low cost and further range than 72mhz or 2.4ghz. i have dozens of toy plane and car radios in addition to old walkie-talkies. but i think you are just using the parts to build 81mhz for fm radio?
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Old Feb 04, 2012, 06:06 AM
Registered User
Romania, Bucuresti, IF
Joined Mar 2011
33 Posts
Quote:
Originally Posted by dave1993 View Post
i am very interested in 27mhz. it is my favorite band because of low cost and further range than 72mhz or 2.4ghz. i have dozens of toy plane and car radios in addition to old walkie-talkies. but i think you are just using the parts to build 81mhz for fm radio?
Hi,
I am building a 27Mhz RX / TX by modifying an old walkie-talkie (single conversion).
Is true MC3361 can be used at higher frequency, but this design / or at least the old walkie talkie design is on 27Mhz, but using frequency modulation (FM) - which i believe is more reliable than AM.
Because first i buit the TX (and have no 27Mhz receiver yet) to test it i used a conventional multiband FM receiver (which can receive both FM bands 64-108Mhz ), tuned on the third harmonic 27Mhzx3 (81Mhz) and removing the TX final PI filter (which remove harmonics).
So far i finished the TX, i had a problem with modulating this high Q oscillator, but i modified a little bit the original circuit by inserting a coil in series with the crystal and lowering it's Q factor so i can obtain a nice modulation. Is true i lost some power by doing this.
Is working fine, next step is to rebuild it to a dual side copper board.
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Last edited by MrBadNewS; Feb 04, 2012 at 06:29 AM.
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