TH-27A frequency expansion
                  ==========================

The TH-27A, is an excellent aircraft receiver as well as a fine two metre
transceiver.  It also covers a full 134-174MHz on transceive, but as yet a
mod permitting full transceive and aircraft receive has not been found,
(except for the Asian configuration, described below).

When modified for full 136-174MHz transceive in any of the Western configs,
the aircraft AM is defeated (see chart).  In the Asian config, the rig
becomes a versatile wide band receiver (118-174 & 200-400MHz display only
and will transceive 136-174MHz).  This configuration causes some key
positions to be relocated (see cross-reference).

R334  R335  R337  W301  REMARKS
 O     -     O     O    K,P US STOCK CONFIG
 O     O     O     O    E     144-146 TX/RX  NO AIRCRAFT
 O     O     O     -    E2    136-174 TX/RX  NO AIRCRAFT
 -     -     O     O    M     144-148 TX/RX NO AIRCRAFT
 -     -     O     -    M2    136-174 TX/RX NO AIRCRAFT
 O     O     -     O    X     144-148 TX/RX
 O     -     O     -    US MARS 118-174 RX 142-152 TX
 O     -     -     -    US MARS+136-174 TX/RX NO AIRCRAFT
 -     -     -     O    ASIAN STOCK
 -     O     O     -    ASIAN MOD 118-174,200-400 RX, 136-174 TX
 O     O     -     -              136-174 TX/RX NO AIRCRAFT
 O     -     -     O    NOT TRIED
 -     O     -     O    NOT TRIED
 -     O     O     O    NOT TRIED
 -     -     -     -    ASIAN RECEIVE MOD 118-174 RX, 200-400 RX, 144-148 TX
 -     0     -     -    COMMERCIAL 136-174 TX/RX, 5.7MHZ OFFSET, 150 DEFAULT


"O" MEANS RESISTOR OR JUMPER IN PLACE
"-"  MEANS OPEN
The first six configs are shown on the Kenwood schematic.
W301 is our old friend, the green wire.

TH-27A TO TH-F27 (Asian version) key relocations
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
TH-27A KEY     =  TH-F27 KEY
TONE/TONE SEL  =  CALL/C-SCAN
CALL/C SCAN    =  BELL/STEP
3 TALT         =  3 TONE
SHIFT/REV      =  REV/SHIFT
MHZ/STEP       =  MHZ (NO F FUNCTION)

I have settled on the Asian mod for my TH-27A, and find that the button
differences are easy to live with. All functions on the rig seem to work in
the Asian config except the Auto-dialler doesn't seem to dial a * or #.  It
does, however, send these characters manually, if required.

To repeat, the coverage of the Asian configuration is:

118-136 AM RX (WITH A REAL AM DETECTOR)
136-174 FM TX/RX
200-400 RX

Although 200-400MHz is shown on the display, it doesn't appear able to
receive on these frequencies.

Other button differences not mentioned earlier are:

             TH-27A                     TH-F27
F1SEC,3      TONE ALT SOUND             TONE SELECT
F MHZ        STEP                       BAND SWITCH 118/145/340

OTHER NOTES:
~~~~~~~~~~~
Autopatch works well
CTCSS tones sent OK, DTMF and CTCSS squelch works
Band scanning, etc works OK
Processor reset defaults to 145.000 instead of 144.000
TX/RX no problem on VHF FM
RX aircraft, great! As good as a Bearcat 100/200, better than ICOM 2SAT.
The TH-27A has a "REAL" AM detector/AGC (see schematic).

SENSITIVITY MEASUREMENTS
~~~~~~~~~~~~~~~~~~~~~~~~
TH-27A   12/18/90
USING AN IFR MOD 1000S SERVICE MONITOR
REFERENCE IS 1 LED SEGMENT LIT
1000 HZ TONE

FREQ.   SIGNAL
MHZ     MICROVOLTS

118     1.7     AM
120     1.5
122     0.9
124     0.9
126     0.9
128     0.9
130     0.8
132     0.8
134     0.8
136     0.8
136     0.5     FM
138     0.4
140     0.4
142     0.3
144     0.3
146     0.3
148     0.4
150     0.4
152     0.4
154     0.4
156     0.5
158     0.5
160     0.5
162     0.6
164     0.8
166     0.8
168     0.8
170     1.0
172     1.3
174     1.5
200-400 NO RX

Note: The above gives information enabling transmission outside permitted
bands of operation.  It is illegal to transmit outside permitted bands and
transgressors face heavy penalties for so doing.  Beware!

73 Tom N5OFF @ K5ARH.LA.USA

(Downloaded from GB7SYP)