From:Tony Fonseca 

Subject:TX delay mod for the YAESU MH-27 DTMF microphone



November 4, 1996.



I didn't like to have to depress the PTT switch with one hand and the

DTMF buttons with the other hand especially while driving so, I modified

my mike to automaticly transmit the DTMF code and have a one and one

half (1.5) second TX delay if the DTMF buttons are to be used.  Here is

the mod.



Open the microphone by removing the three screws on the back.

You will have to lay the componants properly under and above the cuircut

board. They fit in there quite nicely. I used longer leads on the 2n2222

transistor so it could be tucked nicely under the cuicut board beside

the up/down buttons.



Parts needed:1 each     2.2K ohm resistor

              1 each     10 Megaohm resistor

              1 each     10 ufd 16 volt electrolytic capacitor  

              1 each     2n2222 NPN transistor (or equivalent)



Solder one end of the 2.2K resistor, one end of the 10 megaohm resistor

and the positive terminal of the 10 ufd 16 volt electrolytic capacitor

to the base of the 2n2222 transistor. Solder the other end of the 2.2K

resistor to the anode side of the LED (D1). Solder the other end of the

10 megaohm resitor, the negative side of the 10 ufd capacitor and the

emitter of the 2n2222 transistor to ground.



The ground terminal is pin 5 of the 8 pin connector. One side of the PPT

switch is also grounded to pin 5.



Solder the collector of the 2n2222 transistor to pin 3 of the 8 pin

connector. Pin 3 is also connected to the other side of the PTT switch.



To vary the time delay, change the value of the 10 megaohm resistor. The

higher the valu, the longer the delay.  



This mod works great. Enjoy easier mobiling.



Tony, VE7ACF @ VE7DRA.#NWBC.BC.CAN.NOAM

      afonseca@sno.net                (email)

      http://www.sno.net/afonseca/    (web page)

Amsterdam



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