©1996 Hamtronics, Inc.; Hilton NY; USA. All rights reserved. Hamtronics is a registered trademark. Revised: 1/19/00
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CAUTION.
The TD-5 contains
static sensitive ic's, which require nor-
mal static prevention techniques when
handling to avoid damage. Wearing a
grounded wrist strap is a prudent prac-
tice. For wired units, do not remove the
unit from its protective package until
ready to install. For kits, do not open
package with semiconductors until
ready to install on board.
FUNCTIONAL DESCRIPTION.
The TD-5 is a general purpose
CTCSS Encoder and Decoder module
designed with enhanced features to
allow it to be used in repeater control.
It is crystal controlled for precise tone
accuracy and is easily tunable by set-
ting a DIP switch to cover the entire
range of subaudible tone frequencies
from 67 to 254 Hz. Its CMOS cir-
cuitry operates on +7 to 15 Vdc,
drawing only 7 mA!
As a general purpose tone en-
coder,
you can easily adapt your ex-
isting fm transceiver to access all your
favorite closed repeaters. If you only
need one tone, you can select it with
the DIP switch on the module. If you
need several tones, the manual shows
how you can set up a front panel
switch to select between preset tones
for several repeaters. A pot on the
board allows you to set the transmi t-
ter deviation for the tone separately
from your microphone audio.
As a general purpose receiver
decoder,
the same TD-5 can be used
to mute receive audio unless the
proper subaudible tone is present on
the signal. A convenient control line
can be used to manually unmute the
receiver to allow monitoring the chan-
nel when desired, and a high pass fil-
ter gets rid of annoying tone buzz in
the speaker audio. Unlike many such
units, the TD-5 module handles both
encode and decode! When used in a
transceiver, your ptt line can be con-
nected to the unit to switch between
transmit and receive modes.
The TD-5 was designed espe-
cially to have the added features
needed to provide closed access for
your repeater.
To block repeater
transmission unless the user signal
has the proper subaudible tone, an
output transistor grounds the COS
line between the receiver and the
control board to prevent it from re c-
ognizing that the squelch is open. The
TD-5 provides remote on/off capabi l-
ity when used with a DTMF controller.
Whenever you need to defeat the TD-5
and allow anyone to access the re-
peater, simply ground the control line
with any touch tone controller and the
repeater becomes an open repeater.
It can also be used as a repeater
tone encoder.
Most repeaters use
CTCSS only on receive. But if you
need to transmit a subaudible tone as
well, it is a simple matter of connect-
ing the tone output of a second TD-5
module to the modulator input of your
exciter. There is a handy tone output
level control to set the transmitter de-
viation.
CAUTION.
M
The TD-5 kit contains static se n-
sitive ic's, which require normal static
prevention techniques, such as wrist
strap and grounded soldering iron to
avoid damage. Do not remove the ic
from its protective package until so
instructed.
M
The kit also requires soldering a
small surface mount ic to the pc
board. If you don't feel you can do
these operations properly, you may
want to seek help from someone more
experienced or exchange the unit for a
wired/tested module.
THEORY OF OPERATION.
Refer to the schematic diagram.
The heart of the unit is the
MX-465DW ic, which provides en-
coding and decoding of all standard
subaudible tones. Pins 2 and 3 ope r-
ate in a 4 MHz crystal oscillator cir-
cuit. Pins 5-10 are control lines
which select the frequency, and pull
up resistors are provided in the chip.
Frequency selection normally is done
with the DIP switch on board, but it
can also be done with an external cir-
cuit placing grounds on selected lines
using a front panel switch and a diode
matrix arrangement. Pin 17 controls
whether the ic is operating in the
transmit or receive mode at any time.
Pin 24 is the input for the tone
detector. If the audio present con-
tains the proper subaudible tone, RX
Detect line pin 15 goes hi. The output
of this detector is integrated to pr e-
vent bouncing and falsing by C6. The
turn on time constant is set with R4
and R5-D2 in conjunction with C6.
The turn off time is set by R4 and C6.
The integrated signal is applied to a
comparator at pin 14, and the
switched output is the RX Decode sig-
nal at pin 13.
The RX Decode output is used to
turn Q1 on and off, and the transistor
is used to inhibit the COS line going
to a repeater controller, such as our
COR-5 module, thus providing closed
access repeater operation. The Defeat
line at E5 provides a way for a touch
tone control circuit to defeat the COS
Inhibit function when desired.
The RX Decode signal also
switches the audio path between pins
23 and 19. Between these two pins is
a switched capacitor high-pass filter,
which attenuates audio frequencies
below 250 Hz by about 36 dB while
passing frequencies above 300 Hz.
This can filter can be connected in se-
ries with the audio path in a receiver
to remove the buzz associated with
subaudible tones and also to mute the
audio completely if the tone isn't pres-
ent on the rf signal. The Push To
Listen (PTL) line at pin 18 can be used
to defeat the muting action when you
want to monitor the channel to check
for activity before transmitting.
When the RX/TX line at pin 17 is
grounded, the ic changes to the
transmit mode. In this mode, the
switched capacitor high-pass filter can
be used in the transmit audio path to
remove frequencies below 250 Hz from
the signal. This feature normally is
not used in amateur radio applica-
tions, but in transceivers, it can be
used to prevent low frequency speech
components from falsing a CTCSS de-
coder at the receiver hearing the
transmitted signal. When used, the
audio line is run through pins 22 and
20 to the modulator in the transmit-
ter.
ASSEMBLY.
GENERAL NOTES.
Construction is fairly simple. Re-
fer to the parts list and component lo-
cation diagram, and solder all parts in
place, using short leads. Following
are some special points to consider.
a. The ic is static sensitive. Sui t-
able precautions must be taken when
handling, including using a wrist
HAMTRONICS
HAMTRONICS®® TD
TD -5 SUBAUDIBLE TON
-5 SUBAUDIBLE TONE ENCODER/DECODER MODULE:
E ENCODER/DECODER MODULE:
ASSEMBLY, INSTALLATION, AND OPERATION
ASSEMBLY, INSTALLATION, AND OPERATION
