Tech Arsenal 1/Tech Arsenal (Arsenal Computer).ISO/tek-20/96man.zip/96MAN.TXT

Text File | 1991-12-08 | 30KB | 717 lines

        *************************
        9600 BAUD PACKET HANDBOOK
        *************************

    A handbook of helpful information for those
    wanting to implement K9NG/G3RUH format packet

version 1.1a

11/19/91

by Mike Curtis wd6ehr
7921 Wilkinson Avenue
North Hollywood CA 91605-2210
[phone]
wd6ehr@n6yn.#socal.ca.usa
internet wd6ehr.ampr.org![e-mail]

c 1991 by Mike Curtis, except as otherwise noted
permission to copy in whole and/or in part for non-commercial purposes is
given provided that proper credit is given and context is maintained.

        CONTENTS


1        9600 BAUD PACKET - WHY?
1.1        DEFINING PACKET RADIO'S SHORTCOMINGS
1.2        THE CURE

2        WHAT DOES IT REQUIRE
2.1        MODEM
2.2        TNC
2.3        RADIO

3        HOW 9600 BAUD PACKET IS DONE
3.1        MODEM
3.2        TNC
3.3        RADIO
3.3.1        CRYSTAL CONTROLLED PHASE MODULATED RADIOS

4        MODIFICATIONS
4.1        RADIO MODS
4.1.1        TXA CUTOFF
4.1.2        FT736 MODS
4.1.3        CRYSTAL CONTROLLED RADIO MODS
4.2        TNC MODS
4.3        MODEM MODS
4.3.1        K9NG MODS
4.3.2        G3RUH MODS
4.3.2.1        G3RUH "GARBAGE" MOD

5        9600 BAUD PARAMETERS

6        HELP


1        9600 BAUD PACKET - WHY?

   An often heard quote on packet:  "My TNC works fine at 1200 baud.  Why
bother with 9600?  I can only type with 2 fingers."

   This is true, but only if we assume the following:
1. you're the only one typing with 2 fingers on "your" channel;
2. typing with 2 fingers is the ultimate goal of packet;
3. what we're presently doing is all we ever want to do, and;
4. packet in fact _is_ working perfectly.

   However, this is far from the case.  The present packet system is in
desperate need of improvement.  Packet is capable of far more than what we
see it doing today.

1.1        DEFINING PACKET RADIO'S SHORTCOMINGS

   First, let's analyze the situation:
1. Short hop simplex works well, but only if the hop is a clean, line of sight
   path and the channel is not very busy.  If you live in L.A., you're already
   rolling on the floor with hysterical laughter.
2. NETROM/TheNET/ROSE, and other networking protocols work poorly with multi-
   hop 1200 baud trunking.
3. Mail requires days/weeks to reach its destination, IF it ever gets there!
4. Ruling out HF packet (which isn't such a bad idea anyway :-), we're limited
   to NETROM over radio paths of a few hundred miles or so.
5. Other areas, like Europe, have far more sophisticated and efficient packet
   trunking systems and user access channels that work.
6. Urban packet channels are overcrowded to the extent that many have thrown
   in the towel.

1.2        THE CURE

   Now let's dream a bit:

   NEWS FLASH!  WD6EHR's faerie godmother grants Mike several wishes.  After
the obvious wishes have been carried out, a slip of the tongue grants us a
super-duper packet system. (HEY!! I wanted a new pair of socks instead! My
old ones are gettin' kinda gamey!!)

   When I wake up in the afternoon, I work FR0CK in France, TR0PIC in Gabon,
L0RRY (Moe) and CU2LY (Joe) (and SH3MP breaks into our roundtable, too), doing
all of this via our high-speed packet multi-megabit world-wide trunking system.

   I receive packet mail at my station within seconds of its being posted.  We
have conferences with 50 to 100 packeteers on a single 2 meter frequency.  Wow,
are my eyes buggin' out!  A lot of us are involuntarily learning to speed read!

Todays TIMES headline: EVELYN WOOD DECLARES BANKRUPTCY!

   Large files are being transferred between local stations, and are coming in
via the high speed trunk.  I decide to get a copy of the newest PD version of
"Super Italian Brothers", which was just finished 30 minutes ago in Japan, so
I connect to our _L_O_C_A_L_ fileserver (he got it automagically off the
master trunk) and download a copy of this 400K file.  This takes me all of
10 minutes on our 9600 baud end user channel, while I chat with a few of the
locals (W1MPY in Baastin, Mass; and K0OKY in Dayton, OH) on the conference
bridge.  While in QSO, I open another session and look up these guys in the
central nameserver data base, and find that W1MPY used to be a shipmate of
Popeye Doyle, went to school with Dan Quayle, and was originally licensed
in the '60's as H1PPY.

   I want to use my little T-1000 laptop XT to do some super-autoCAD (which
requires a full blown 486), so I remote execute on another machine via high
speed packet, and receive the results on my printer.

                -=-

   Packet has capabilities far beyond simple text applications, such as file
transfer, remote execution (allowing you to use my computer to run software,
and then send the results back to yours), nameservers (callbook on a CD is an
example of this), remote printing, and even linking several smaller computers
to undertake a much larger task than any of these would be capable of alone.

                -=-

   What would make all of this possible?  Higher speed packet.  A 10 megabit
world-wide trunking system would tie all the metropolitan areas together, and
these would be served by metropolitan area networks, with efficient 2 meter
9600 baud local access channels. (and higher speed, i.e. 56 kB, on higher
frequencies.)

   Am I dreaming?  Too many brewski's?  Not at all - this is all done using
EXISTING, INEXPENSIVE technology!  We don't need any magic - just a small fire
under certain easy chairs - YOURS!  And do you know who I'm talking about?  All
of you who think I'm talking about someone else!  Yes - with POPULAR support,
this isn't just possible - it's easily accomplished!

   2 meters is a logical place for end users.  The band is amateur-only and is
one of our most consistent and predictable bands.  9600 baud packet is a
"natural".  It is "top speed" on 2 meters.  It's a lot more efficient than
1200 baud, and therefore a much better use of our precious radio spectrum.
Being FSK, it requires slightly LESS bandwidth than 1200 baud AFSK packet, or
voice, in spite of its greater baud rate.

   We're going to have 9600 baud elsewhere, of course; but many feel that
two meters should be the primary thrust for end user 9600 baud packet.


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.


3        HOW 9600 BAUD PACKET IS DONE

With mirrors, of course :-)

3.1        MODEM

   The PacComm NB96 g3ruh modem board plugs inside many TNC,s, such as TNC2
clones (MFJ 1270B, etc).  There is a special modem available for the MFJ
1278T (and maybe it'll work with other MFJ's, too???), from MFJ.  It takes
the place of the 2400 baud modem.

   The k9ng modem kit is cheaper than the g3ruh modem, but is a little fussier
about receivers.  If the radio you want to use has a pretty broad receiver
passband, it'll work almost as well as the g3ruh.  If the receiver is tight,
the k9ng will be _very_ noticeably poorer.  However, this can be somewhat
ameliorated by widening the k9ng's receive filter, as detailed below.

   If you need to externally mount your modem and use a ribbon cable, mount
the modem header on the opposite side of the PCB, or use a second short
ribbon cable.  Ribbon cables "flop" the pins, i.e.:

    1 3 5 7 9  ___________________________ 2 4 6 8 10
    2 4 6 8 10                             1 3 5 7 9

By placing the connector on top rather than underneath, the flop is reversed.

   Normally, you'll want to use the TNC's keying circuit.  With the g3ruh,
you have no choice.

3.2        TNC

   PacComm, Kantronics, Gracillis, MFJ and probably others have TNC's with
9600 baud G3RUH modems built in.  Check the ham mags, call the manufacturers,
or contact your local dealer for information.

   Many of us will take the route of installing our own modems.  These may
often be installed internally.  Sometimes it may be necessary or desireable
to install these externally.

   As with all RF environment installations, shielding is important.  If an
external box is desired, it really should be a metal one.  Shielded cable
to the radio is mandatory - it will not work without it.  Some kind of RFI-
proofing of the modem disconnect cable is needed as well.  This should be
kept as short and unexposed as possible.

   The G3RUH modem requires you to use the TNC's keying circuitry, and this is
recommended for the k9ng as well.  If you do this, don't cut the PTT line on
the modem disconnect.

3.3    RADIO

   Many modern rigs are true FM, and it's very simple to add a 9600 baud port.
You need only a couple of internal connections and decoupling components to
bring out the "raw" transceiver: the direct detector output and direct FM
modulator input.

   Most modern rigs use receiver chips, such as TA7761F/P, LA5006M, LC7532M,
TK10420, TK10424, MC3357P, and others.  Note: ALL of the chips mentioned here
use pin 9 for the detector output.  Others may or may not, so check first!

   Transmit "audio" is injected through a 5 to 10 uF non-polarized capacitor
through a 5K resistor into the modulator.  This is typically a varactor diode
in a transmit oscillator stage, and is pretty simple to find, by simply
tracing forward from the microphone.  If this is "over your head", see the
free offer at the end of this manual.

3.3.1        CRYSTAL CONTROLLED PHASE MODULATED RADIOS

   We have found that synthesized, true FM multimode rigs using varactor
modulation in a crystal oscillator stage tend to work best.  They tend to have
a tad wider IF filter (i.e. CFW455E) and pass data with less distortion.  Most
synthesized rigs can be made to work, most with extremely simple mods.

   However, if your rig is crystal controlled, it can be made to work.  If
it's a true FM rig, it's simply a matter of connecting directly to the FM
modulator.  This will always be in a crystal oscillator stage.


4        MODIFICATIONS

   There are some 9600 baud ready radios, like the TEKK KS-900, Kantronics
DVR 2-2 (not recommended), and D410, but most of us will be using our existing
radios for 9600 baud packet.  Here are some specific "mods" and tips.

    Radios known to be used at 9600:
Alinco: DR-1200 DataRadio, ALR-72, ALR 709; Kantronics DVR 2-2 Data Radio;
Icom IC series: 25,38,228,271,290,471; Kenwood TR series: 7500, 7700;
TM series: 211,212,221,231,431, TS series: 700 and 770
Standard C58, C140; Yaesu FT series: 212,221,230

4.1        RADIO

4.1.1        TEKK KS-900

   For the TEKK KS-900, a TXAudio attenuator is necessary to swamp the modem's
4 volts peak to peak down to the 50 mV range.

   This is simply a 470 ohm resistor in series, and a 39 ohm resistor across
the TEKK's transmit input and ground.

4.1.2        OTHER RIGS

   It's almost embarassing to call these "mods".  We're only bringing out
terminations of existing signals.

   These mods are non-destructive unless you QSLF (solder with your left
foot :-) - your rig still does whatever it did before.

   Icom IC290H/V: RXA may be obtained at IC12, pin 9, on the main board;
TXA may be injected at D-3 cathode on the main board  (This one is my
personal 2 meter 9600 rig, and is a top performer!)

   Icom IC28A/E/H : RXA may be obtained at IC1, pin 9, on the RF unit;
TXA may be injected at R-45, at the end NOT connected to trimpot R-100

   Icom IC3200A/E: RXA may be obtained at IC1 pin 9 (main board) - this is a
common receiver chip for both bands; TXA may be injected at D3 cathode (VHF)
and D1 cathode (UHF).

   Kenwood TM221, TM321A, TM421: RXA may be obtained at IC1, pin 9 (IF board);
TXA may be injected at connection #7 on the VCO assembly on the TX/RX unit.

   TR751: RXA may be obtained at IC2,pin 9 on the RX unit;
TXA may be injected at D21 cathode on RX unit.

   Use the following circuit to couple the modem to the radio.

MODEM                    RADIO
      5 - 10 MF non-polarized
RXA ----||----------------------------- RXA
      5 - 10 MF non-polarized
TXA ----||------o-------o---/\/\/\----- TXA
        |    |    10K (approx - adjust for 3 KHz dev
        |    \         with modem's TXA pot about 75%)
      .001 ===    / 500 ohms
        |    \
        |    /
        |    |
           _|_     _|_
          ////    ////


4.1.1        TXA CUTOFF

   If you want to leave your 9600 connected and use the rig for other stuff,
use the following relay circuit:

+ 12 VDC----------------o     o--->|<------------- Radio PTT
                        |     |   N.O.
                       _|_    |
                      |   |  _|_
                    |RY1| ////
                      |   |
                      |___|   o--->|<------------ Radio TXA
                        |     |   N.O.
TNC PTT ----------------o     |
                              |
Modem TXA --------------------o

RY1 is a double pole 12 volt relay.  Use the normally open contacts

   This removes the modems TXAudio line from the radio's modulator when you're
not keying from the 9600 baud TNC.  If you're using the same TNC for 1200 and
9600, make sure you remove the PTT signal from the relay!  Otherwise you'll
pick up a nice 4800 Hz "tone" from the 9600 band modem.


4.1.2        FT736 MODS

                    FT736 & 9600 Baud Operation
                    ---------------------------
                       by James Miller G3RUH

These notes tell you where to get FM RX audio direct from the
discriminator, and where to modulate the FM TX varactor directly.  These
mods are non-destructive and take no more than a few minutes.  The signals
bypass the "DATA SOCKET" for high grade FM operations.

The RX mod is suitable for:

 *  UOSAT-D 9600 baud downlink and terrestrial links
 *  1200 baud AFSK/FM Standard Packet - BUT IT'S UNSQUELCHED.

The TX mod is suitable for:

 *  FO-20/PACSAT uplink (1200 bps Manchester FM)
 *  UOSAT-D 9600 baud uplink direct FSK and terrestrial links
 *  1200 baud AFSK/FM Standard Packet.

                            ---****---

FT736 -  FM Direct from Discriminator
-------------------------------------
Detected FM direct from the receiver discriminator is available from the
RX UNIT at the junction of R91 and C83.  These components are shown in the
top right-hand corner of the schematic.

Proceed thus:
 1. Disconnect FT736 from the mains electricity. (Safety).
 2. Remove top cover only.
 3. RX Unit is the vertical module on the left.
 4. Locate R91 which is about 25mm from the top, 50mm from the radio rear.
    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 RXaudio lead should be a fine screened cable;  connect the inner
    to R91, and the outer braid to a ground point (e.g. can of TO09)
 7. Route the cable out though any convenient aperture in the case.
 8. The discriminator sensitivity (FM Normal) as about 6 kHz/volt.

Important note on 9600 Baud Use
-------------------------------
Most FT736 receivers are fitted with an LFH12-S IF filter for FM. (CF01 at
the top front of the RX Unit).  This is a 12 kHz bandwidth filter which is
a little narrow for 9600 bps FSK operation.  It is recommended you change
this to 15 kHz or better still for UOSAT-D use, 20 kHz bandwidth which
will allow more tolerance for doppler shift, and give a far better "eye".
Suitable filters are: LFH-15S or CFW455E, and LFH-20S or CFW455D.  The
first of these is a Yaesu spare part, and is often already fitted.  Try
the standard first and see what happens;  these filters have moderate part
to part variations.



FT736  DIRECT VARACTOR FM MODULATION
------------------------------------
Refer to the circuit diagram; inject your TXaudio at the junction of
R32/C29 on the TX Unit.  The signal level at this point should be 800 mV
peak-peak, and will give +/- 3 kHz deviation.  DO NOT EXCEED THIS LEVEL.
Set Mic Gain to min.

Modulating the FM transmitter this way you get an LF response down to 18
Hz (at which point the associated synthesiser PLL begins to track the
modulation), and an HF response which is flat to some 10 kHz.

Proceed thus:
 1. Disconnect FT736 from the mains electricity. (Safety).
 2. Remove top cover only.
 3. 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 any paint off the free leg.
 5. Your TXaudio lead should be a fine screened cable;  connect the inner
    to R32, and the outer braid to the adjacent enclosure.
 6. Route the cable out though any convenient aperture in the case.

 7a. 1200 BAUD G3RUH PSK MODEM: TXAudio of 800 mV pk-pk can be obtained by
     adjusting the components C9= 1uf, R3=47k, R5=infinity (i.e. remove).
     C10 stays at 10nf (0.01uf).

 7b. 9600 BAUD FSK MODEM: Adjust TXAudio level with VR1

 Notes compiled by G3RUH @ GB7SPV 1990 Mar 16

4.1.3        CRYSTAL CONTROLLED RADIO MODS

   If your crystal-controlled rig is true FM (varactor modulator in an
OSCILLATOR stage), inject TXA through a 5 mF cap into the varactor cathode.

   However, a lot of crystal controlled rigs are phase modulated and need a
varactor modulator added to the transmit crystal oscillator.

   Use an abrupt junction type, such as the MV2105 (available from Kantronics),
and adjust the capacitance in the crystal circuit to compensate for the
additional C of the varactor.  If there are fixed caps, remove or pad them.
If not, change the trimmer to one of a lower minimum value.

   You'll need to bias the varactor.  I've used the transmit oscillator Vcc
and a 20K trimpot to ground, feeding bias through 2 10 to 47k fixed resistors,
feeding the modem TXA thru a 5 to 10 uF cap to the center junction of these,
and feeding the free end to the cathode of the varactor.  The bias needs to
be adjusted for best received eye pattern on a service monitor or receiver.

TRANSMIT MODS

Transmit oscillator
       +Vcc         Modem TXA
    o        o
    |        |
    1        |
    0        |
    0        |
    K           === 5 uF non-polarized (required for k9ng)
    |        |
    \ 20K        |            MV2105  4-20 pF
    / <----- 47K ---o---- 47K ------o-------o----- to TXCO crystal
    \        |        |    | ^
    /        |        |    |/
    \           === .001           ===     ===
    /        |           /_\     /|
    |        |        |    |
    o---------------o---------------o-------o----- to TXCO ground
       _|_
      ////


        Modifying the IC22A for 9600 baud operation

by Mike Curtis, wd6ehr and Dave Shalita, w6mik

This is one of the more difficult rigs to modify - most are even simpler!

This mod will make your IC22A into a dedicated 9600 baud packet radio.
Components with * are added to the crystal board.

   Remove the trimmer capacitor for the transmit crystal socket you'll be
using for 9600 baud.  Replace with the above circuit.  The 4-20 pF trimcap
should be a good quality ceramic or other low-drift trimmer.  (Sorry - Radio
Shack doesn't have anything suitable.)

   Connect 2 10K resistors to C-53 (both sides) and tie the other ends
together.  This junction is where you'll pick off your RXA.

   Turn R-67 (dev control next to P-1 and P-2) completely counterclockwise.
This kills signals that may get into the phase modulator.

   Using a service monitor, or oscilloscope connected to the detector of a
receiver, adjust the varactor bias for the best eye pattern.
Alternate bias adjustment:
Use the k9ng's 4800 Hz "idle" tone to adjust your modulator for best linearity.
Using a service monitor, or a receiver with a fairly wide passband, adjust
varactor bias for the "best" sine wave.  Thanks to Brian Kantor wb6cyt for
this tip.

4.2        TNC MODS

   Your TNC will work better at 9600 baud if you speed it up.  For TNC2
clones, change the Z-80 and Z-80 SIO to 10 MHz types, and change the clock
speed by changing the jumper on JP1.  Older ones use the 2 OUTER pins, and
newer ones use the center and (other) outer pin.

4.3        MODEM MODS

   Most rigs require a lot less TXA than the modem outputs, and a resistive
swamping network may be needed.  For example, the TEKK KS900 wants 50 mV.

   On the TEKK KS900/PacComm NB96 combo, I use 470 ohms series, and 39 ohms
across the TEKK's input terminal to ground.

4.3.1        K9NG MODS

   The k9ng modem's keying circuit can be omitted if you use the TNC's
existing PTT circuit.  If you do this, remember to leave the PTT connections
uncut on the TNC modem disconnect.

   The k9ng modem's DCD circuit is terrible, and can be vastly improved by
shorting R-31 and changing C-18 to 0.1 mF.

   You may find it helpful to widen the k9ng's receive filter.  Change C-13
to 2000 pF and C-16 to 1000 pF (half their present value for 9600 baud).
This will widen the passband, and in the process will minimize group delay.

   Use the PTT from the TNC instead of the k9ng modem.  This  lets  you use
the TNC's watchdog timer, and makes things a lot  simpler.  Make sure to cut
only the following traces between pads on  your  TNC-2's modem disconnect J4:

1/2     DCD
11/12   transmit clock
13/14   receive clock
17/18   receive data

   The TNC-2 manual tells you to cut other traces, but by doing it this way,
you'll be able to use the TNC's PTT circuit.  The k9ng's keying circuit, which
doesn't work all that well without modification (it's designed for the
Hamtronics FM-5), may now be omitted from the pcb, if you like. This is most
of the stuff on the lower edge of the pcb.

The g3ruh modem from PacComm already does this.

4.3.2        G3RUH MODS

              PacComm NB96 MODS

by Mike Curtis wd6ehr

The PacComm NB96 g3ruh modem has a jumper-selectable "defeat", JPS.  When
a jumper is in position here, the modem disconnect is normalled through.

I've installed a DPDT slide switch on the front of my MFJ 1274 to make radio
baud rate changes simple.  The first pole is used to make the connection to
JPS.The second pole is used to change the radio baud rate selection normally
made by the rear apron DIP switch.

A quick and dirty DCD LED can be easily added to PacComm's NB96 9600 baud
modem board.  Pin 13 on U-10 supplies a DCD signal.  Connect a 680 ohm
resistor and LED between this and +5 volts, obtainable on pin 24 of S-1
or S-1a, both 26 pin connector positions on the PCB.  Only one is used.
Solder your +5 volt wire into the unused hole of the other.  Tack the
other lead to U-10 pin 13, or if you do the "garbage" mod below, to pins
8 and 9 of the 74HC00.

You may also use the DCD LED in your TNC by lifting the cathode of the LED,
inserting a diode in series, tacking a second diode to the LED cathode, and
running the cathode of this to modem U-13 pin 10.

4.3.2.1        G3RUH "GARBAGE" MOD

by Steve King kd7ro
Gets rid of random garbage "calls" in MHeard
(edited)
Here is the modification I made to my PAC-COMM NB-9600 modem.  This mod got
rid of all the garbage calls in my mheard list both when using the TNC in
standard mode as well as while using net/nos software packages. This
modification makes sure that the modem will send all zeros to the TNC until
the modems PLL is locked on a signal.  This means that the TNC will not be
reading garbage coming in to the UART all the time.

1. Remove socket for U11 (74HC14).
2. Insert the 74HC14 directly into the PC board.
3. Lift all the pins of a 74HC00 except 7, 12 and 14.
4. Bend pins so they are pointing straight out.
5. Cut back the bent pins so the 74HC00 can be piggybacked on the 74HC14.
   Without removing the socket on  U11, I would not have ben able to slide
   the modem and Tiny-2 back into the box (you may not have this problem).
6. Cut the trace from U11 pin 12 to U20 (74HC157) pin 13.
7. Solder the 74HC00 on top of U11 (soldering pins 7, 12 and 14).
8. Wire U10 pin 13 (LM339) to the 74HC00 pins 9 and 10.
9. Wire 74HC00 pin 8 to pin 13.
10. Connect pin 11 of the 74HC00 to pin 1 and 2 of the 74HC00.
11. Connect pin 3 of the 74HC00 to pin 13 of U20 (74HC157).
12. Put a piece of tape over the top of the 74CH00 to insulate from the case.
  The DCD signal coming from U10 (LM389) is low true so I invert it using
one of the nand gates (pins 8, 9 and 10).  This is used to qualify the
RXD signal from the 74HC14 (pin 12). Pin 11 of the 74HC00 is the RXD signal
(low true) qualified by the DCD signal which is LOCK DETECT.  One more
inversion of this signal (74HC00 pins 1, 2 and 3) and I have the qualified
RX DATA signal which is connected to U20 (74HC157) pin 13.
  RX DATA is always zero until the PLL is locked to the data.  Then RX DATA
will be the true data comming from the unscrambler or zeros if we are not
locked.

Steve King   (KD7RO) [e-mail]
             Hewlett Packard
             Boise, Idaho


5        9600 BAUD PARAMETERS

   As you'd expect, the parameters we all know and love at 1200 baud don't
work very well at 9600 baud.  These are what we've found work well at 9600.

5.1        AX.25 PARAMETERS

TXDelay        between 8 and 15 - set for best throughput
RESPtime    100 mS seems to have better results than 0
FRack        8 seconds on a busy channel; but never less than 5 seconds
PERSIST        128/users; if it's a pretty clean channel, 64 is nice; if it's
        busy, guesstimate the average number of users and divide 128
        by this number, i.e. 4 users = 128/4 = 32
SLOTTIME     20
MAXFrame    If the channel is great, 7; average, 3; rough, 1
RETry        15
CHeck        300 seconds

5.2        TCP/IP PARAMETERS

   My 9600 baud interface is called "96"; here are params from my files.

par 96 1 8
par 96 2 64
par 96 3 20
par 96 4 2
ax25 maxframe 3
ax25 paclen 256
ax25 pthresh 64
ax25 retry 15
ax25 t1 8000
ax25 t2 1000
ax25 t3 300000
ax25 t4 900000
mode 96 datagram
ax25 persist 96 256 5 128 15 60

   Some of these parameters are specific to pe1chl NET, so don't get an
ulcer if your version barfs on them.


6        HELP

   If you have a radio you'd like to use for 9600 baud, but don't know where
to find the "magic points", send me 2 copies of the schematics - one for me,
and one for you (block diagrams are nice but not absolutely required), and
a stamped, addressed return mailer.  I'll get out my red "test grading" marker
and mark the points where you'll find raw RXA and TXA.

   Some of these mods are tested, and some aren't, but should work fine.
These are non-destructive (yup - you can still use it for whatever it was used
for before), and are generally a simple matter of tacking 2 caps to easily
accessible spots on the PCB, adding the 2 resistors, attaching 2 pieces of
mini shielded cable, and bringing the 2 connections out.

 Yours,
  _ _ _             __
 ' ) ) )   /       /  )        _/_
  / / / o /_  _   /    . . __  /  o _
 / ' (_<_/ <_(/_ (__/ (_/_/ (_<__<_/_)_

 Packet: wd6ehr@n6yn.#soca.ca.usa    [e-mail] [44.16.0.21]
 Internet: wd6ehr.ampr.org![e-mail]      Compu$erve 73240,3523
 wd6ehr-3 netrom switch   wd6ehr-6 conference bridge  wd6ehr-8 mbox/info
 145.36- 1200/9600 baud duplex repeater <----> 439.025 - both @9600 baud
 7921 Wilkinson Avenue; North Hollywood CA USA 91605-2210 [phone]
/ex
b