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Modification 1 for Icom 04at Handheld
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IC04AT.4
Subject: ICOM 02/03/04 & Vox Unit
The ICOM Family of Hand-Held Radios (02/03/04 AT) are well suited
for packet radio given the many available power supply options.
The big problem is getting the PTT to operate " CLEANLY " while
not compromising the audio level from the TNC when using the resistor
or resistor/capacitor interfaces suggested in some manuals.
I am using the ICOM HS10-SA Vox unit to interface the ICOM 02/04 AT
here.It has worked somewhat well for some time but I was always plagued with
a MINIMUM 200 msec transmit "hang " delay until I tore it apart for
examination and correction.
The small " delay " pot on the front of the unit is in series with a
2.2 Megohm resistor (R-19 on the board). The adjustable pot is also
about 2 megohms as well. This combination allows a MINIMUM VOX "hang" transmit
delay of 200 msec.
By identifiying the solder connections for R-19 on the back of the PC board
and placing a low value resistor ( or jumper ) in parallel....I was able to
achieve a ZERO "hang" transmit delay time with the delay pot in the FULL
COUNTER-CLOCKWISE position. The minimum 200 msec delay has been defeated.
73 Harold - N4KWB @ W4NVU
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