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TH78A.MOD
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1992-06-26
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FILENAME:TH-78A.MOD June 25,1992
Modifications for the Kenwood TH-78A Dual Band Micro-HT.
By Rich Garcia N2CZF. Packet Via N2CZF@WT3V.NJ.USA
Owner assumes all responsibility for modifying or using these
modifications!.
The following mods will provide for Crossband Repeat andextended
receive and transmit on the Kenwood TH-78A HT.
I believe other functions are also enabled by these mods. which I
have not found yet but I will update the file as news progresses.
Diode #4- Crossband Repeat
Diode #5- Extended Receive and out of band Transmit.
Remove all screws and open radio as explained in the Kenwood manual
for installing the memory expansion module.
On the back cover half you will find the memory expansion module
socket and a copper shield to the upper left corner of it.
Under this shield their will be a row of SMC diodes which are
unmarked in a vertical configuration to the lower right portion
covered by the shield.
#1 Remove the shield at it's four corners with a solder sucker and
SMALL! iron.
#2 Carefully count down from the 1st diode in the row to the fourth
one and remove for crossband repeat.
HINT: I found if you BRIEFLY touch the iron to the right side lead
while gently pulling up on the SMC diode it should completely come
off without needing to apply heat to the other side and further
risk board damage.
I used a pair of right angle surgical tweezers for this.
#3 Just as above you may remove the fifth diode to preform the
extended receive and transmit modification.
#4 Reset the CPU (yes you will loose all of your programed
memories! argh!) by pressing Function for more than one second and
then "0".
YOU HAVE NOW COMPLETED THE MODIFICATIONS!
#5 For 800Mhz go to the UHF band with the band switch and press
Function for more than one second quickly following with a press of
the Band switch again. 8---.-- will appear.
MY observations... All original functions have maintained the
same which is great. Aircraft band which was accessible before the
mod remains with the same characteristics. It seems that VHF-High
band has improved a bit on sensivity where it was dead as a dog
before the mod (above 155.000MHz) but the 162.000 MHz band where
weather radio is is still a bit deaf for reception at any distance
but about 20 Miles. This depends on your (or my) terrain and
transmitter output power.
On UHF all public safety frequencies up to about 500 MHz seem to
come in well but sensivity greatly drops from there (we really
can't ask for more).
Frequencies can be programed in up to the 920MHz ham band but I
have no way of measuring sensivity and any 800MHz signals are weak
here if at all on a good scanner so I have yet a chance to try
hearing signals up there.
Transmit is enabled up to and incl. 500MHz but aftertesting this on
a frequency counter I find that a signal is only generated to about
490 MHz, even though the trans. LED shows output in the higher
frequencies.
Crossband repeat seems to work fine but BE AWARE the radio get's
HOT! Prolonged use or use on a busy frequency would be
recommended. Also remember this is a dual band HT please use a
proper antenna while in this mode to avoid a high SWR, we should
all know better... Right?
After first booting up the CPU in the mod I found that the message
screen showed "Cloning" so it seems that this radio now has cloning
capabilities but I have not found the keystrokes or a way of
transferring the data yet. This leads me to believe that this HT
may have some more "Hidden" features that I am trying to find some
may be useful. If you have any more information, modifications, or
comments in general on the radio please let me know and I will
update this file as needed.
Rich Garcia N2CZF@WT3V.NJ.USA
73's De Rich N2CZF Southern New Jersey