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- MARCH NEWS LETTER


ISOTRON 20/15/10
Time for some DXing.
 
THE BEST WAY TO OPERATE HF
 
EASY INSTALLATION
EXCELLENT PERFORMANCE
DURABLE CONSTRUCTION
CC&R FRIENDLY (XYL ALSO) 

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A LITTLE ABOUT DTMF
 
This technology has been with us for over 50 years. It must be good, because we are still using it. You will see it on many of our VHF and UHF transceivers. It is used to control repeaters and many other remote devices.
 
What is it?
 
Dual Tone Multi-Frequency, or DTMF. Also know as "Touch-Tone". The later term was given by Bell Labs back in the 1960's.
 
Before this was developed, remote equipment normally was hard wired to control it. This technology allowed the elimination of the wires. The tones could be transmitted over the radio to control devices.
 
To start, the tones are produced by an "Encoder". During the early start of this technology, it took a fairly complicated circuit. However, now, one small integrated circuit does it all.
 
What does the circuit do?
 
It produces two audio tones for each number, 0 - 9. As well as the # and * key. By using two tones together, the reliability or accuracy is excellent.
 
Two tones are sent at the same time. One high tone and one lower tone. A chart of the tones per its number is below.
 
So, how do you differentiate the tones in respect to the number?
 
With a "Decoder". Again, in the early stages, it took a circuit for each pair of tones. Now an integrated circuit does it all. Normally the IC will produce a hexadecimal output for each number. This reduces the amount of outputs you need for all 12 combinations.
 
Here are the tones for 0 - 9 and * and #.
 
LOW (VERTICALLY) HIGH TONE (HORIZONTALLY)
 
                  1290 HZ    1336 HZ    1477 HZ
 
697 HZ              1          2          3
770 HZ              4          5          6
852 HZ              7          8          9
941 HZ              *          0          #
 
Experimenting with DTMF is within the scope of the average hobbyist. At least you have an idea of what is happening every time you push that button.
 
73,
Ralph WD0EJA
 
10-17
 
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