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Author Topic: Attempting to add DTMF TONES to old 2 meter rigs for IRLP ACCESS.  (Read 11486 times)
K0YNE
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« on: August 26, 2009, 08:46:00 PM »

I say, attempting to add DTMF tone  to old fm 2 meter radios via the microphone.
. Maybe this is a non issue, but i own a very old 2 meter rig and would like to be able
to use it for IRLP NODE  access. There are tons of old tone telephones on garage sales
for practically nothing.  Usually the red and green wires denote the wires to use and
the are in the center of the modular plug. you can wire a  9 volt battery to these two leads
and can test it for useability and should be able to talk into the phone and hear your
voice in the receiver of the hand set. Other well filtered power supplies such as the
wall warts as they are called, will work  as long as they don't exceed 20 volts for safty.
Although your local phone system still works on 48volts DC. Don't worry about polarity.
The tone could be introduced to a mic connection thru a capacitor of say 10mf at a voltage
greater than the power supply you are using. From the red and green wire on the
telephone cord, is connected to the power supply. Using one connection as a ground to the
radio, and the remaining red wire for example as the tone source, coupled thru a capacitor and
a 10K ohm resistor in series into a mic connection. I will post further circuitry on this subject
swhen time permits, PAUL K0YNE
 
« Last Edit: September 23, 2009, 06:43:42 PM by K0YNE » Logged
K0YNE
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« Reply #1 on: September 09, 2009, 08:55:06 PM »

This is just another comment about the DTMF add on to old radios.
I never bothered to see the amplitude of the tones output, but would think they are very small indeed.
I believe that an outboard audio amplifier might be needed to give the tones a boost into the microphone jack for example. A simplified two transistor arrangement could be used incorporating a output adjustment. My Icom 2200H has a very loud  tone output and is just a little too much. But still using the old telephone touch tone pad is ideal, because it is cheap and just a little engineering on
a transistor arrangement may be enough to drive a small speaker that could be placed near the microphone to couple the tones needed to access a IRLP node or reflector. I know that not everyone could build this contraption, but I believe it could breath new life in some of our older 2 meter radios and including the UHF radios. More data will follow when I can take time to experiment with the tone pads and the outboard audio amplifiers. Maybe you have a preamp somewhere that would fill in this gap.
paul, K0YNE
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K0YNE
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« Reply #2 on: September 18, 2009, 08:31:10 PM »

Just another idea I just stumbled across while using Multipsk version 4.15 having DTMF TONES...
The Program has the DTMF button half way down and to the left of center among the modes
next to throb... since i don't know how fast the tones can be entered, I put six spaces between
each of the four numbers of the reflector or node. This seems to slow down the tones enough to be
similar to how fast you can enter four digits by hand. I believe this can work when the microphone is
placed near  the computers speaker. It is worth trying. Let me know if this will work?.
Just use the tx button at the bottom of screen and then to rx.
Paul  K0YNE
« Last Edit: September 18, 2009, 08:35:54 PM by K0YNE » Logged
K0YNE
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« Reply #3 on: September 18, 2009, 09:01:26 PM »

The Multipsk DTMF worked fine for me the first time. There may be some factors that could limit the
generated tones when transmitted. Microphone quality, speaker quality and maybe too little or too much
output. Some computer speakers are really tinny sounding , but they may work. I transmitted from my speaker to the microphone, not too loud and still brought the node I was calling up the first time.
So, this may be a really cheap and easy way to use old 2 meter rigs and sort of add DTMF.
May be other circuity following this string, but for now, this may solve your problems as well. It did mine.
Paul K0YNE 
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