From    : G1YYH @ G1YYH.GB7CRG.NW.GBR.EU
To      : MODS @ GBR
Date    : 891214/2039
Msgid   : BF 207@G1YYH, 14567@GB7YHF $THX5AT.PT4
Subject : Kenwood TH-x5at Mods - 4/4
Path    : GB7YAX!GB7CHS!GB7CRG!G1YYH

R18exact function unknown.
installed:as delivered in USA.
removed:TX disabled from 146-148.

The RX and TX frequency range based on R22 and R28 are
unknown if R18 is removed.

On the TH-45AT:

R18,28select RX and TX frequency range.

R18R28RX rangeTX range
-------- ------- -----
inout440-450440-450
inin438-450438-450(USA default)
outout200-500200-500(only where
your PLL
locks up.)
outin215-230215-230?(PLL won't
lock up.)

R22TX offset selection
installed:1.6 MHz offset (perhaps for 220, or Europe)
removed:5   MHz offset (USA default)

---------------------------------------------------------------------

PLL adjustment
--- ----------

I have found a quick and easy way to retune your PLL (in the
TH45-AT) with a minimum of test equipment.  All you need is a scope
and a small tuning tool.  First, take off the battery pack holder
plate.  Then, remove the silvery sticker covering the tuning pot
access holes.  If the radio is positioned on its back, with the top
folded over so that the touch tone pad is also facing down, the test
point you want 
(TP1) is on the bottom half of the rad
io, near the
center (left to right), and close to the battery; the tuning pot you
want (TC1) is on the bottom, and closest to the PTT switch.  Under no
circumstances change the tuning of TC51.  This is used to calibrate
the output of the radio with the display the radio is giving; you
don't want to mess with it.  Once again, the Service Manual makes it
very clear where these points are, if you are having trouble with my
descriptions.  On with retuning the PLL.  With the radio on, and
receiving, monitor the voltage and the waveform on test point TC1.
Tune the radio DOWNWARDS in frequency until the PLL unlocks.  Note
that the radio will beep when this happens, and the waveform on TP1
will change.  Tune the radio about 1 MHz higher so that the PLL locks
up again, and note the voltage on the testpoint, TP1.  Now, tune the
radio to the LOWEST frequency that you want to be able to receive.
(Be very careful when you adjust TC1.  If you are not careful, you
could break TC1 loose.  This will cause your radio to have
microphonics.  Mechanical vibrations will change the value of this
capacitor, and thus change the tuning on the PLL.  If you encounter
this problem, you can repair it by dripping wax through the small
hole onto TC1, or by replacing TC1.  It is of course better not to
break it in the first place.)  Adjust TC1 until the voltage on the
test point TP1 is the same as what was noted earlier.  Button the
radio back up, and you're done. You will not be able to tune the PLL
to any range you want.  There are limits.  On my radio, I have been
able to retune the radio so that I can recieve from 439.2-468.6 MHz
with a set of batteries fresh out of the charger.  The tuning range
will probably diminish as the battery voltage decreases.  I have not
retuned the PLL on my 2m HT, but I'd imagine the same technique will
prove fruitful.

---------------------------------------------------------------------

In the rare case that original ideas   Kenneth J. Hendrickson    N8DGN
are found here, I am responsible.      Owen W328, E. Lansing, MI 48825
Internet: kjh@pollux.usc.edu           UUCP: ...!uunet!pollux!kjh