TAPR 9600bps Modem
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The TAPR 9600bps modem is a full-duplex baseband modem
compatible with K9NG and G3RUH standards.  The TAPR
9600bps modem, like other 9600bps modems, requires an
interface to your radio other than via the microphone and
speaker jacks.  The modem fits internally into the case of
many popular TNCs and supports a 20-pin modem disconnect
header which allows for a second external modem (such as
the TAPR PSK modem) to optionally be connected.

The 9600bps modem uses a 4-layer PC board for minimum
noise and utilizes a transmit waveform lookup table in ROM
for minimum transmit distortion.  The transmit path
includes an independent watchdog timer.  The modem
selection logic correctly routes the PTT command from the
TNC to prevent, for example, keying your 1200 baud radio
when running 9600bps.  The receive filter includes a
compensation adjustment to tailor the modem to the radio
receiver and AC-coupling to accommodate frequency drift on
the channel.  An improved state machine is used for clock
recovery.  The DCD circuit works on both signal quality
and the presence of a signal.


9600bps Modem Clock Option
--------------------------
The clock option provides the necessary radio port clock
for 9600bps operation.  When you enable the external
9600bps modem on a TNC 1, TNC 2, or clone, your TNC will
automatically be set up for the correct radio port speed.
When you switch back to the TNCUs internal modem, the TNC
will automatically select its normal radio port speed
again.  Thus, you can switch between 1200bps and 9600bps
operation with a single switch.  The clock option is
necessary if you wish to use your modem as part of a
stand-alone full-duplex 9600bps repeater, in conjunction
with the bit regenerator option.  The clock option is also
useful if you wish to operate at a non-standard data rate
(say, 8700 bps) for backbone links that you donUt want
other users on.  Note: You will have to replace the
crystal in the clock option kit if you wish to use a non-
standard rate.


9600bps Modem Bit Regenerator Option
------------------------------------
This option is intended only for use as part of a full-
duplex 9600bps repeater.  It is not suitable for use at a
home station.  The bit regenerator keys the PTT line of
the modem whenever it receives an incoming signal (DCD is
true).  It stores the first 8 bits in a buffer, then
starts sending the bits out again, resynchronizing them
with its own crystal-controller clock to remove jitter and
noise from the received signal.  The buffer is 'elastic'
so it can accommodate a slightly different '9600bps' data
rate from the sending station and its own 9600bps clock.
Full-duplex bit-regenerating repeaters for 9600bps are
starting to be used in more and more locations.  It truly
makes 9600bps operation fast and friendly.


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Tucson Amateur Packet Radio Corp.
8987-309 E Tanque Verde Rd #337 * Tucson, Az * 85749-9399
Phone: (817) 383-0000 * Fax: (817) 566-2544

TAPR is a Non-Profit R & D Corporation
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