2          WHAT DOES IT REQUIRE

   Alright, Mike - I'm sold!  What do I need?

2.1  MODEM

9600 baud packet requires a modem.  The 2 most common varieties are the 
K9NG and G3RUH, but DSP modems will also do K9NG-protocol 9600 baud.  Due to 
the high cost of DSP modems, we will limit our discussion here to G3RUH and 
k9ng modems.

There are 2 flavors of 9600 baud modem: K9NG and G3RUH.  Both are compatible 
and will work with the same TNC's.

The G3RUH is a very nice 9600 modem.  It works with all radios we've tried 
so far.  It's full-duplex capable, and has a lot of test points.

The K9NG is a low cost means of getting into 9600 baud.  It works with a lot 
of radios, but is a little less forgiving of group delay, a form of phase 
distortion inherent in filters when approaching passband edges.  Voice 
tolerates phase delays; data doesn't.  If necessary, this can be minimized 
by widening the receive filter, by reducing C-13 (4000 pf) and C-16 (2000 pf)
to half value (2000 and 1000 respectively).
   
The Kantronics D-410 radio has a data slicer, and has been tested 
successfully with raw data (without a modem).  However, this configuration is
not compatible with other formats, such as K9NG/G3RUH, but could certainly be
used in a point to point service, such as trunking.

2.2  TNC

   Most TNC's are capable of 9600 baud.  Notable exceptions are the
Kantronics KAM/KPC line. (The Data Engine will do 9600 baud and much higher) 
If your TNC has a "9600 baud _radio_" option or setting (as opposed to 9600
baud RS-232), it will likely work with K9NG/G3RUH modems.

2.3  RADIO

   You can _N_O_T_ use the radios microphone and speaker jacks for K9NG or 
G3RUH format 9600 baud packet.  PERIOD!  So don't ask!  

   Why, you ask?  (wise guy...)  Well, the normal receiver signal path is 
designed for voice.  Data doesn't make it through.  The transmitter
microphone and receiver "speaker" audio is pre-emphasized and de-emphasized. 
This boosts and cuts higher audio frequencies, and helps with voice and
music.  HOWEVER, like all filters, it also SHIFTS the PHASE, which is
verboten with data.  Why? (Hoo boy!  You shore ask a lotta ferschlugginner 
questions!)  Your former digital 1 in the 112th position in the wave train is
now delayed to where the 113th position _should_ be, etc., and your data is
corrupt!  (Hey, I didn't know data could be bribed :-) (How much does it cost
to bribe binary data? 2 bits, of course.)

   Besides, both of these 9600 baud modems use "FSK" (shifts between 2 RF 
frequencies, id est 145.009850 and 145.010150 MHz for a nominal operating 
frequency of 145.01), whereas Bell 202 1200 baud AFSK modems, like your TNC 
has, uses 1200 and 2200 Hz AUDIO tones FM'd onto a carrier.

   Translated into simple English, this means you need direct connection to 
the FM modulator varactor and FM detector.