Modifications for the Kenwood TM-431
TM-431A Wide Band Transmit Modification
This modification allows the TM-431A transceiver to transmit and
receive from 420.000 MHz through 444.975 MHz with essentially full
power throughout the band.
Remove top cover
Locate a green jumper wire sticking out of the front panel
assembly (behind VFO switch)
Cut the jumper in half and insulate the ends
This will reset the microprocessor and you will have to
reprogram all channels
9600 mod for TM431A
Connect TX data to MO input at PLL circuit board (X58-3480-00)
through a 100 kohm resistor.
Connect RX data to DET output pin 12 at IC1 (FM IF HIC)
The only problem is that you must mute the TX data when you RX,
because this way you modulate the PLL.
You can find these pins when you open the bottom cover.
Locate the four points where the PLL circuit cover is soldered to.
They are marked with 0 in the drawing.
73 de Wes OH3NWQ @ OH3RBR.#TRE.FIN.EU
PS. I have tried this - it works.
Measure deviation using TM231,431,531
From AA9HX - ON7WP @ ON7RC.BT.BEL.EU
To all technical kenwood freaks,
All people clever enought to know that they have to do something about the
tremendous amount of people constantly overdeviating, mainly all using off
the shelf kenwood equipment, coming straight from the factory adjusted at
6,7 or EVEN 8 KHz Peak deviation !!!!
This article describes how YOU can use your kenwood transceiver TM231, TM431,
TM531 and apparently also the TMX41 range to measure ON THE AIR deviation of
repeaters and all other stations...
The principle of measurement is indeed very simple and DOES NOT NEED ANY MOD
INSIDE YOUR TRANSCEIVER NOR EVEN OPENING IT !!!
Your microphone connector provides at pin 6 an audio output, straight from the
FM detector. As all kenwoods use the same detector chip and coil, all give
the same output voltage for a given deviation. The output at this pin 6 (and
pin 8 as a ground) is linear up to 5 KHz deviation. As the IARU standard for
amateur radio communication is 3 kHz peak deviation, this range from 0-5 KHz
is perfect. Connect your oscilloscope to pin 6 and 8 as ground, 400 mV peak
to peak voltage corresponds to 3 kHz deviation. So 200 mV is 1,5 KHz deviation
and so on.
CTCSS deviation should be around 300 Hz although most kenwood transceivers
only react well from 400 Hz.
Packet should be set to approximately 2 KHz.
And additional an extra tip for improving the modulation quality of your
As the microphone amplifier is quite overdriven, modulation sounds very
rough, due to extreme clipping of the signal, especially a nuisance in
noisy environments, such as when mobiling in a not so luxury car.
This can become much better just by changing or in some cases adding the
input resistor of the microphone amplifier. Differnt types are used depen-
ding on the market the transceiver was designed for. As they still believe
at kenwood that europe uses a 25 kHz raster and the states 20 kHz, europe
types get lesser attenuation before the amplifier then stateside trx's.
Hey You there at the kenwood factory reading this: whole europe is changing
to a 12,5 kHz raster, so will you please stop delivering your transceivers
and portabels with a deviation standard dating from jurassic park time !!!
Deviation potmeter TM231 VR3 and decrease R64
Deviation potmeter TM431 VR2 and decrease R58
Deviation potmeter TM531 VR3 and decrease R60
So remember 3 kHz is the standard, do not discuss wether it is good or not,
IT IS THE STANDARD FOR AMATEUR RADIO.
It is the only way to live peacefully and to prevent wars between adjacent
repeater or simplex channels.
(and by the way, narrowing the receiver bandwidth extends your range...)
Im looking forward to all comments, and I hope that somebody of the kenwood
technical crew also will read this and do something about the adjustment of
the new transceivers...
73 from Pedro M.J. WYNS AA9HX, ON4AWQ, ON7WP,
full licensed transceiver doctor... HI !
ON7WP @ ON7RC.BT.BEL.EU
Go Back To The Kenwood Mods Page
Go Back To The Main Modifications Page
Go Back To The CB / HAM Radio Main Page
Go Back To The Main Home Page
Copyright © The Defpom 1997-2008