Specifications

Receive: Detected
FM direct from the receiver
discriminator
is
available from the RX UNIT at the
iunction
of
R91
and C83.
These
components are shown in the top, righrhand corner of the schematic.
Proceed
as
follows:
1
. Disconnect
power
and all cables fiom the FT136 for safety.
2. Remove
the top cover only.
3.
The RX
unit is the vertical module on the left.
4. Locate R9l
which is about 25mm from the top, and
50mrr
from the rear of the radio; the resistor
is
"on-end"
and near a couple of
glass
diodes.
5.
Scrape any
paint
off R91's free end and wet with solder.
6. Your RX
audio
lead
should be a fine, shielded cable
(such
as RG-174); connect the inner conductor
to R91 and the
outer shield wire to a
ground point
(e.g.,
"can"
of
TO-09).
7.
Route
the cable out through any convenient opening in the case.
8. The discriminator
sensitivitv
(FM
Normal) is about 6 KH/volt.
Norn:
Some FT736 receivers
are
fitted
with an LFHI2-S IF
fllterfor
FM.
(CF01
at the top
front
of
the RX Unit.)
This is a I2 KHz
bandwklthfilter which is
cL
little narrow
for
9600
bps operotion.
It's recomm.en.cled
you
change
this to
l5 KHz,
or better still
for
UOSAT-D
use,
a
20 KHz
bandwidth which
will
alLow
more toler-
ance
for
Doppler
shift and
gives
a
far
better
"
eye." Suitable
ftlters
are: LFH- I55 or CFW455E, and
LFH-
205
or CFW455D. The
first
set
of
these
is a
Yaesu
spcLre
port
and is ojlen already
fined.
Try the standard
first
and see what happens-these
ftlters
have moderate
part
to
part
variations.
Transmit: Inject
transmit audio at the
jr"rnction
ol R32 and
C29
on
the
TX
Unit.
The signal lcvel at this
point
should be 800 mV*n and will
give
+3
KHz deviation-don't exceed this leveL. Set the Mic
gain
on
the fiont
panel
to
its
minimum setting.
Proceed as lbllows:
1.
Disconnect
power
and
all cables from the FT136 for safety.
2. Remove the top
cover only.
3.
The
TX Unit is the module flat on the left
(not
the one
tucked down the side vertically).
4. R32 is
just
to the left of the rectangular shielded enclosure. The resistor is
"on
end." Scrape off any
paint
from
the free leg and wet with
solder.
5. The transmit audio lead
should be a fine, shielded cable
(such
as RG- 174); connect the inner conduc-
tor to R32
and the outer braid to the adiacent
enclosure.
Route the cable out through
any convenient opening
in
the case.
9600 bps FSK modem: Adjust transmit audio level with VR- L
6.
1.
Packet Parameters
The
AX.25
parameters
we all know and love at 1200
bps don't
work very well at
9600
bps. These are
whal
we've
found work well at 9600:
TXDelay Set between 8 and 15 for
best throughput.
RESPtime 100mS seems to have better results
than
0"
FRack
8 seconds on a busv channel: but never less than 5 seconds.