©1994 Hamtronics, Inc.; Hilton NY; USA. All rights reserved. Hamtronics is a registered trademark. Revised: 11/27/01
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GENERAL INFORMATION.
This sheet provides information on
modifications to the TA901 Transmitter
and the R901 Receiver when used with
the MO-96 Packet Radio Networking
Modem for 9600 baud networking of
TNC's. It is intended to give specific
information on parts changes and
alignment details peculiar to these ver-
sions of the transmitter and receiver,
and it should be used along with infor-
mation in the regular manuals for the
transmitter and receiver. General sys-
tem information, interconnections, etc.
are contained in the MO-96 manual
along with information on construction
and alignment of the MO-96 unit. Re-
fer to TA901-HS and R901-HS dia-
grams attached for locations of connec-
tion points.
PARTS INCLUDED.
If you bought both the transmitter
and receiver, this kit will include parts
to modify both. If just one, then only
the parts for the one are provided.
Transmitter Parts, 1 each:
1 uF electrolytic capacitor
MV2111 varicap diode
47K resistor
socket pin
Receiver Parts, 1 each:
0.15uF polyester capacitor
(red) 30 pf NP0 disc capacitor
47K resistor
MV-2101 varactor diode
10.7MA ceramic filter*
SFH455D ceramic filter*
*Note: The crystal filters and ce-
ramic filter normally used in a receiver
kit are not supplied when this option is
ordered.
TA-901 TRANSMITTER
MODIFICATIONS.
If you are building a kit, please
mark the parts list with the following
changes before beginning construction
and use the attached parts location
view in place of the one which comes
with the kit. If you ordered a wired
unit, these changes have already been
made.
a. Remove C12 and C13 from the
standard unit, and replace C13 with
varicap diode MV2111, orienting with
polarity as shown.
b. Solder one lead of a 47K resistor
to "hot" hole normally used by C59.
Leave the other end free and trim it to
about 1/4 inch to allow a wire to be
soldered to it as a connection from the
MO-96 or other source of data used to
modulate the transmitter.
If an oven will be used, then leave
that end of the 47K resistor free, and
trim it to about 1/4 inch to allow a wire
to be soldered to it as a terminal.
c. Change value of C18 to 1 uF.
Observe polarity.
d. Remove R17 to break the normal
audio path to the modulator.
e. If voice audio will not be used,
set R15 fully clockwise. If you wish to
use voice transmissions occasionally,
for testing, etc., connect output from
C10 to the optional voice audio input
on the MO-96 board.
(See MO-96 in-
structions for method of providing voice
operation.)
f. Because of the high multiplica-
tion factor from the oscillator fre-
quency to 900 MHz, it may be neces-
sary to reduce the deviation adjustment
of R1 on the MO-96 unit more than the
50K pot allows. If necessary to adjust
the deviation to a low enough setting,
change R1 on the MO-96 to a 500K
pot. If you don't have a pot to use, the
value of R2 can be changed to a higher
value instead.
R901 RECEIVER
MODIFICATIONS.
If you are building a kit, please
mark the parts list with the following
changes before beginning construction
and use the attached parts location view
in place of theone which comes with
the kit. If you ordered a wired R901-
HS unit, these changes have already
been made.
a. Remove or do not install regular
i-f filters FL1-FL5 and capacitors C53-
C55.
b. In positions for FL1, FL2, and
FL3, install pieces of #24 bus wire
(lead clippings from some components)
between the two end holes
(don't use
ground hole).
Make the jumpers as
short as possible to minimize induc-
tance.
c. Install "10.7MA" ceramic filter
(small 3 lead device) in position FL4.
You may have to use something like a
dental pick to enlarge the holes slightly.
d. Install SFH455D (5-lead) ceramic
filter in position FL5. This is a special
filter having low group delay charac-
teristics.
e. If not already this value, replace
C60 with 0.15uF metalized mylar (red)
capacitor for quicker squelch action.
(Some R901's already use this value).
f. Remove R28 in the squelch cir-
cuit. The open collector of Q4 which
results is wired to the squelch input of
the TNC to provide carrier detect lock-
out. (This also causes the "DCD" led
on the TNC to illuminate.)
g. Install MV-2101 varactor diode
CR1 in unused holes of board, orient-
ing polarity as shown in component
location diagram.
h. Install 47K resistor R1 in unused
hole of board as shown in component
location diagram. The upper lead
should be trimmed to 1/4 inch to be
used as a terminal for connection of the
"fast AFC" output from the MO-96 unit
to the open end of R1. (The hole just
below the body of R1 is not used.)
i. Change the value of C1 to 30 pf.
This compensates for the added capaci-
tance of varactor diode CR1.
Note that it is necessary to make
tradeoffs to use the special filter system
for high speed data. Since a wider
bandwidth is necessary for high speed
data reception, the receiver is more
prone to interference. The crystal filter
normally adds a considerable amount
of selectivity to the receiver, in addition
to that provided by the ceramic filter.
In this receiver, the normal 100 dB ad-
jacent channel selectivity is reduced to
about 50 dB. This is still adequate in
most amateur installations; since they
usually are located in suburban loca-
tions where interference is less of a
problem.
HAMTRONICS® HS-220 KIT TO MODIFY TA901 & R901
FOR HIGH SPEED DATA
