FAQ: Shareware RTTY/FAX decoding software for the PC

FAQ: Shareware RTTY/FAX decoding software for the PC

Post by David Mois » Sun, 02 May 1993 22:49:23

          Shareware RTTY/FAX Decoding Programs for the IBM PC

                      Frequently Asked Questions

                         by Dave Moisan, N1KGH

                      Last Revised--30 April 1993

Many people have gotten interested in receiving RTTY and FAX
transmissions with their PC's.  Shareware, combined with cheap, easy-
to-build hardware, has put RTTY and FAX reception in reach of anyone
with a good digital portable such as the Radio Shack DX440 or Sony
2010.  

Two programs have become very popular:  Hamcom 2.1, a RTTY terminal
program, and JVFAX 5.1, a full-featured FAX/SSTV receive program.  The
two programs both use an identical basic interface, so one can get
started in FAX and RTTY for almost nothing.  Another program, PKTMON,
lets you monitor HF and VHF packet off the air, using the same
hardware.

This FAQ list is divided into five sections:

        Introduction
        Using HamComm
        Using JVFAX
        Using PKTMON
        General Problems

        Appendix--HamComm Interface Schematic and Parts List

INTRODUCTION
------------

**  Where do I get the software?

  HamComm and JVFAX are available from a number of sources on the
  Internet, including simtel20.army.mil and nic.funet.fi
  (/pub/ham/misc);  look for HAMCOM21.ZIP and JVFAX51.ZIP.  
  PKTMON 1.2 is available from nic.funet.fi and should be on
  Simtel as I post this.  

**  What are the basic system requirements?

  HamComm:  XT or better, 320K RAM, hard disk not required.

  JVFAX:    286 or better, at least 1M RAM;  a hard disk is
            strongly recommended.  Note that JVFAX has its
            own extended memory driver, which may conflict
            with HIMEM.SYS and other memory drivers.

  Pktmon:   286 or better.

**  What are the basic receiver requirements?

  I've successfully received RTTY, fax and Packet with my
  Radio Shack DX400 digital portable, and have had less
  luck with CW.  Receivers like that will work, but table
  top radios (Kenwood, Icom and Yaesu) and ham transceivers
  are much more suited for this application.

**  Where can I find plans for the basic interface?

  The plans are included in the documentation for both Hamcom and
  JVFAX.  JVFAX has schematics for both the basic interface, and
  a more sophisticated interface that also receives GOES/APT
  satellite pictures.

  A complete schematic and parts list is included at the end
  of this FAQ list.

**  I don't want to build it.  Can I buy a interface?

  Yes.  William Nolle is selling his version of the interface,
  called FAXCAP, and it includes all software discussed here.
  Contact him at:

     William Nolle
     122 Phillips Rd
     Hazel Green, AL 35750

  (Disclaimer:  I am not affliated with William, nor am I even
   a customer, but merely a friend and fellow enthusiast.)

  Also, Dieter Dippel is selling an interface (with surface-
  mount components) which includes JVFAX and HamComm.  Contact:

     Dieter Dippel
     Fenitzer Str. 33
     D-8500 Nuernberg
     Germany

**  How does the interface work?

  This is a zero-crossing detection circuit, made up of a 741
  connected in an open-loop configuration.   For every zero-
  crossing (twice a cycle), an interrupt is generated.
  HamComm measures the time between successive interrupts using
  the PC timer chip.

**  How do I connect it to my radio?

  Simply run an audio cable from the interface box to the earphone/
  headset output, record output, or data output of your radio.  The
  Sangean 803A has a record output, and the DX440 can be modified for
  same.  Note that the interface needs 100 mV of audio to work,
  but most rigs can easily supply this.

**  Can you transmit with the interface?

  Depends on the software, and how you construct the interface.
  Hamcomm will send through the speaker or TxD line of the serial
  port;  JVFAX sends through the speaker.  Pktmon doesn't transmit
  at all.  See the appendix for details.  

USING HAMCOMM
-------------

**  How do I set up HamComm?

  There's a sample configuration file in the HamComm archive, HC.CFG
  which explains the numerous parameters required for the program
  to run.  Here are the ones you should set:

  select port com<n>  (Select default com port, <n=1 to 4>)

  Note:  COM1 and COM2 are already defined.  If you need to
  use COM3 or COM4, here are the "define port" statements
  to use:

  define port com3  iobase 0x3e8  irq 4
  define port com4  iobase 0x2e8  irq 3

  You don't need to do this for COM1 or COM2 unless you have
  an unusal setup.

**  Where can I find RTTY on HF and what does it sound like?

  The ham bands are the best place to find decodable RTTY.  I tune
  into CFH, Halifax, Nova Scotia on 4271, 6496.5 and 10536 KHz.
  RTTY is usually sent on the half-hour.  RTTY has a "deedle-
  deedle" sound that you're probably familiar with if you've
  ever randomly tuned shortwave.

  If you want to know what an RTTY signal sounds like, go
  to the RTTY screen (F3) and try control-T (transmit on/off).
  Type in some text and hit ENTER.  You will hear a signal from
  the PC speaker according to the currently selected speed,
  shift and center frequency.

**  How do I tune RTTY?

  First, hit F9 for the tuning screen and, using the arrow keys, set
  the center frequency to 1200 Hz.  For example, if you're trying to
  decode the ARRL bulletins on 3625 KHz,  the tuning screen should
  look like this:

                      Signal Frequency: 01### Hz

    0 . . . .500 . . . .1000 . . . .1500 . . . .2000 . . . .2500 Hz
                  Space ->   |   |  <- Mark
                               |

                      Center Frequency: 01200 Hz

  Using the arrow keys, move the lower tuning bar between the two
  upper tuning bars.  You may need to vary your BFO, RIT or
  clarifier so that the upper bars are centered on the display.

  The difference between the two frequencies, or "distance"
  between the two upper bars is the *shift* of the RTTY signal.
  Hit Alt-K and select the appropriate shift--in this example, 170
  Hz.

  You'll know when the signal's tuned properly, because a train of
  square waves will appear at the bottom of the screen.

  Next, hit Alt-S and select the *speed*;  Ham RTTY is usually 45
  baud.  Outside of the ham bands, 50 and 75 bauds are most common

  (Note:  If you're mathematically adept, you can figure out the
  speed yourself.  Hit F8 to select the Scope and freeze the display
  by hitting Return.  Measure the time interval of the _shortest_
  peak, and calculate Baud rate = 1/t*10**-3, where t is in
  milliseconds.)

  Now, hit F3 (for Baudot), and readable text should scroll forth on
  the screen.  If it doesn't, hit the Tab key to toggle between
  Normal and Inverted keying.  If text is still unreadable, hit Alt-S
  and adjust the speed.

**  How do I log RTTY to a file?

  Hit Alt-F R or Alt-F W;  select the directory or file you want to
  save to and hit Return.  To stop logging, hit Alt-F R.    

  Here's some RTTY recorded off the air on 4271 Khz (at 0230 UTC):

    avalon peninsula
    east coast the bonavista peninsula only.
    freezing rain warning continued for the bonavista peninsula only.
    tonight..overcast. intermittent drizzle or freezing drizzle.
    periods of freezing rainpm yrkwivonavista peninsula ending
    overnight.  winds becoming strong northerly. low zero.
    friday..cloudy. patchy freezing g7+)-01vtov

**  Whenever HamComm is receiving a string of numbers (like
    from CFH or other weather stations), it comes in garbled.

  HamComm has a AutoLetter mode that automatically shifts from
  Figures to Letters after 5 characters have been received.
  Turn this off with Control-L;  the "L" at the bottom right
  of the display should disappear.  This feature is akin to
  the "Unshift On Space" option found on other decoders.

**  I found RTTY, but Hamcom can't decode it.

  A sad fact of life in the shortwave bands is that at least 3/4's
  of all RTTY is encrypted, and alas, much of the unencrypted
  traffic is not sent in plain Baudot.  There still are many
  decodable signals, but you'll need good references to find them.

**  How do I decode CW?

  Decoding CW is similar to decoding RTTY, except that there's only
  one frequency to be concerned with.  While you hear the CW,
  go to the decoding screen, as below:

                      Signal Frequency: 01200 Hz

    0 . . . .500 . . . .1000 . . . .1500 . . . .2000 . . . .2500  Hz
                                 |            
                                 |

                      Center Frequency: 01200 Hz

  Just move the arrows so that the lower line is lined up with the
  upper and hit F2.  

  Here's a sample of CW copied off the air, on 4281 Khz

     vvv vvv vvv cqde vcs vcs vys qsx 4 6 and 8 mhz chnl 3/4/7/8 vvv
     vvv vxv cq de vcs vcs vcs qsx 4 6 and 8 mhz chnl 3/4/7/8 vvv vvv
     vvv cq de vcs vcs vcs qsx 4 6 and 8 mh7 chnl 3/4/7/-.--.. vvv
     vvv vvv cq de vcs vc5 vcs qsx ......- 6 und 8 mhz chnl 3/4/7/8

  Note that HamComm subsitutes dot-dash marks for any character it
  can't decode.                                                          

**  I'm hearing CW, but Hamcom just garbles it.

  There are two different problems encountered with CW decoding in
  HamComm.  Here's what Django, DL5YEC, author of HamComm has to say:

    Problem 1: Tone detection

    For many people it is obvious that an RTTY signal has two states,
    usually called mark/space or high/low tone.  ANY data
    transmission requires at least two states for 1 bit at a time and
    CW is no exception.  So what are the two states for CW?   They
    are the tone and ... NOISE !   You may be surprised to hear that
    a certain amount of noise is REQUIRED to detect that the tone
    has ended.  

    HamComm has an indicator for the tone detector output.  At the
    bottom of the RX window, just to the right of the WPM display,
    is a small white dot that jumps up and down:  up = tone detected,
    down = no tone (noise) detected.  Listen to the signal and watch
    the jumping dot.  It should follow the signal precisely and not
    jump around nervously or stick to one position.

    The input signal is compared to the currently selected mark/space
    tones.  To be regarded a valid tone the signal has to stay in that
    range for a certain amount of time.  So the behaviour of the
    detector mainly depends on the currently selected SHIFT.

    The tone detector output as displayed by the dot is the input to
    the character decoder.  

    Problem 2: Character decoding

    In theory a dash is three times as long as a dot, the gaps within
    a character are dot-sized and the gaps between characters are
    dash-sized. In reality there are short and long tones and gaps
    of variable size because CW is usually 'hand-made.'  The speed
    and length ratios also change during a transmission if the
    operator gets tired.

    HamComm keeps a floating average of the tone duration to adjust
    to speed changes.  Overall decoding quality mainly depends on
    the tone detector.

  As an aside, I should mention that the bouncing-dot display also
  works great for RTTY;  just tune the receiver until the dots bounce
  equally between top and bottom.

USING JVFAX
-----------

**  How do I set up JVFAX?

  Select "Configuration" from the menu, and you should see a Config
  screen.  Options are set using the arrow keys to select, and the
  space bar, - or + to set each option.  Here are the options you
  need to set:

  Demodulator:  Set to "7 bits" and "Comparator/IRQ 4" or
                "Comparator/IRQ 3".  Specify the address according to
                the following table:

           For:   Specify IRQ:  and  Address:
           ----           ---        -------
           COM1             4        03F8
           COM2             3        02F8
           COM3             4        03E8
           COM4             3        02E8

  Graphics and SSTV-Graph:  Set this as appropriate for your system.
  Most users can specify "VGA (640x480)".  A number of Super VGA
  cards are supported, but you'll have to refer to your VGA
  manual for register settings.

  Printer:  Again, set this as appropriate for your system.  Most
  popular dot matrix printers and the HP Laserjet are supported.
  (As an example, for my Panasonic 1124, I selected "Epson 24-pin".)

  Enable scrolling:  This determines whether faxes will scroll
  off the screen when being received.  Set this to "Yes".

  Default Picture Directory:  Enter the disk and directory where
  faxes will be stored, e.g. "C:\WEFAX".

  Store Pictures in GIF 89a:  JVFAX uses the GIF 89a standard to store
  special information on each fax, such as mode, LPM and IOC.  Unless
  you're using other GIF software that can't handle this standard,
  leave this enabled ("Yes").

  Miscellaneous Settings:  Hit Esc to enter yet another configuration
  menu!  There are just two settings you need to make:

      Quicksave:  This feature lets you save the last picture sent;
      it works by continuously capturing faxes to a .GIF file, which
      may become *very* large.  Unless you have lots of hard disk
      space, set this "off".

      Initial RX Mode:  Set to "1--Wefax 576";  this is the mode that
      almost all weather faxes are sent in.

  Hit Ctrl-Enter to leave this menu.  Hit Ctrl-Enter again, and
  you're done!

**  Where do I find fax and what does it sound like?

  A Fax signal will have a "scratchy wheel" sound when sending
  a picture, and a carrier tone when idle.  It can be found
  easily in the maritime bands.  Unlike RTTY, there are few
  variations, and no transmissions are encrypted that I know
  of.

  Two stations I hear regularly on the US East Coast are NAM,
  Norfolk, VA on 3356, 8080 (irregular) and 10865 KHz, and CFH,
  Halifax, NS on 4271, 6496.5 and 10536.  CFH sends faxes on
  the hour,  generally.   I've found press fax on 9244, from
  Buenos Aires, Argentina.

**  What modes are faxes usually sent in?

  Weather faxes are usually sent with an IOC (Index of Correlation--
  the ratio of width to height) of 576, and an LPM (Lines Per Minute)
  of 120.  Press faxes, the few I have found, use an IOC of 288 and
  an LPM of 60.  

**  OK, I'm hearing it.  How do I tune in?

  Using NAM, 10865 KHz as an example, follow these steps:

  1) From the JVFAX main menu, hit F (Fax), and you'll be shown
     a blank screen with a tuning indicator and a menu box on the
     bottom of the screen.

  2) Select the mode by hitting 1 ("Wefax 576").

  3) Set the deviation to 400 by hitting the D key till it comes up.

  4) Using your BFO, RIT or clarifier, tune the signal (in lower
     sideband) until you see a peak on the tuning indicator.  Tune
     this peak towards the W (white) end of the scale (This will
     normally be 1.9 Khz below the center frequency, in this case
     10863.1 Khz.)  The indicator should look like this:

                                                     !  <- Signal
                                                     !     peak
                                                     !     should
                     .    . . ..  .. ..     .    . ##!     be here
             -----------------------------------------
             B                                       W

  5) Hit A (APT);  it should read "Running" and you should start to
     see a fax appear on the screen!  To stop recieving, hit A
     again.

**  I don't get a fax, or I get something garbled.

  Check the mode;  most fax transmissions use "Wefax 576", mode 1
  in the program.  The LPM should be 120.  Check your connections
  to the interface.  If that's in order, you may have an RFI or
  interrupt problem (see questions in "General Problems").

**  I get a fax, but it comes out slanted.

  Hit / and a line will appear;  use the arrow keys to tilt and
  move the line so that it's lined up with a line on the fax
  (such as a border or a chart line).  Hit Return, and the fax
  should now come in straight.  Note that this is a permanent
  adjustment, and you shouldn't need to fix this ever again,
  no matter what faxes you subsequently receive.

**  I get a fax, but it's not aligned with the edge of the screen.

  Hit R (Rotate) and move a line with the arrow keys to the left
  edge of the fax (there'll be a black bar where the fax is
  supposed to start.)  Hit Return and the fax should now be
  properly aligned.

**  My fax is negative!

  You're receiving the fax on the wrong sideband;  try the other
  sideband.  Most faxes will be sent in LSB.  A few press stations
  transmit negative pictures (JVFAX can be set to fix this;  see
  the docs.)

**  My fax is too dark.
    My fax is too light.

  Your receiver is mistuned.  If the fax is too dark, tune towards
  the white end of the tuning scale (peak moves towards W).  If the
  fax is too light (washed out), tune towards the black end of the
  tuning scale (peak moves towards B).  

  Also, make sure the deviation is set correctly, at 400 for most
  faxes.  This is especially important for receiving the GOES
  satellite images that NAM sends.

**  How do I save a fax to disk?

  While you're not receiving a fax (APT "waiting"), the S key will
  toggle the  save-file option on and off.  Faxes will be saved in
  .GIF format to the disk and subdirectory you specified in the
  configuration  screen.

**  How do I print a fax?

  Two ways:

  1) While you're in the fax receive mode and not receiving a fax
     (APT "waiting"), P will enable your printer;  it's a toggle,
     so hit P again to disable printing.  

     NOTE:  You cannot have both Save to File and Print options
     enabled at once.  Also, once the fax is printing, the Rotate
     command will not work on the printout.

  2) Hit H (Show and Send Pictures).  Select the fax you want to
     print.  When it appears on the screen, hit P.  JVFAX will
     ask how much width it will print in (0-100%);  hit Return
     for the default (100%).

**  The GIFs I save are too big!  How do I shrink them?

  It's not uncommon for weather faxes to be very large, especially
  if you regularly pick up 16-shade GOES images over NAM (a recent
  GOES fax from them "weighed in" at 870k!)  

  There are several methods you can use to shrink the size of your
  GIFs:

  1) You can crop them.  From the main menu select H (Show and Send
     Pictures);  from the directory listing, select the file you want
     to crop.  The fax will show up on the screen--select the Z (Zoom)
     option.  Use the arrow keys to move the zoom box (which is about
     the size of a regular 640x480 VGA screen), and the X, Y, + and -
     keys to resize it.  Hit Return and the cropped image will
     fill the screen.  Hit S to save it (under a different name.)

  2) You can reduce the resolution on faxes to be received.  
     Most faxes (of the Wefax 576 variety) have a resolution of 1810x
     1000, which makes for beautiful printouts, but is overkill if
     you're just using a GIF viewer.  

     To fix this, go into the Mode Editor (M from the main menu) and
     select the mode you normally use (e.g. Wefax 576).  Step through
     the options with the arrow keys and select Resolution.  For
     Wefax 576, it'll normally be 1810.  Enter a smaller value (800 is
     OK) and hit Return.

     If you're only interested in charts and not satellite images,
     select the Grays option and set the number of shades to 2
     (B&W only--no gray scale).  Your GIFs should be much smaller,
     though at a significant loss of resolution.  (That being said,
     I once saved some GOES images from NAM for a friend of mine
     in 800x600x4 and they still looked good.)

**  I get an all-white/all-black signal, no matter what signal is
    coming in on the receiver.

  Either your audio cable to the interface is broken, or you have an
  interrupt conflict between serial ports.  If it's the latter
  you may need to move the interface to another port.  Note that
  MSDOS's HIMEM.SYS may conflict with JVFAX.  (At least it does
  on my setup [286, 1M, DOS 5.0])  (See "General Problems" for
  more on this.)

USING PKTMON
------------

Unlike HamComm and JVFAX, Pktmon has few options and is simpler in
scope.  Using the same interface, Pktmon will decode HF and VHF
packet.  Pktmon can log to a file, and will optionally keep track of
packets, assembling them into separate files for you.  Note that the
program is receive-only.  

While it will never approach, let alone replace, Baycom or a TNC, I've
been delighted with its very ingenious attempt at implementing AX.25
in software, and have found it a surprisingly fair performer.  It even
comes with source code (Turbo Pascal) for implementing your own
projects with the interface!

There isn't much to running Pktmon, so here's a quick rundown through
the prompts.

"COM 1 or 2?"      Self-explanatory.  
                   Pktmon doesn't support COM3 or COM4.

"Packet type?"     Enter 1 for HF packet or 2 or 3 for VHF packet.
                   I've never noticed a difference between the latter
                   two options in use.

"Log bad packets?" If you answer Y, packets with CRC errors will
                   printed, otherwise, not.  I usually choose to
                   log them.

"File to log all packets"

                   Self-explanatory.  If you don't specify a file,
                   packets will go on the screen.

"File to log sorted packets"  

                   Enter a filename, _no extension_.  Pktmon will
                   sort packets to the files <n:filename.#>, #=
                   0 to 9.  It also creates a file <n:filename.OTH>
                   for uncategorized packets such as beacons.

That's it.  Pktmon will start decoding packets until you hit Return.
There's a tuning indicator on the top of the screen that indicates
activity.  Here are some sample unsorted packets copied off the air
on 14099 Khz around 2300:

 Started Logging on 1993-04-16 at 18:00:11
 [...]
 18:03:00 => CQ    -0  WA2GGI-0    Ctrl:03 [UnAck Info] Pid:F0
  Data: #0D
 18:03:11 => K4YPE -0  WA2GGI-0R   Ctrl:73
 18:03:13 => K4YPE -0R WA2GGI-0    Ctrl:00 [Data, seq 0] Pid:F0
 Data: **HI BOB IN BOCA RATON FL.BUSY NOW PLEASE LEAVE MESSAGE
 ON MAILBOX TNX.#0D
 18:03:23 => K4YPE -0R WA2GGI-0    Ctrl:04 [Data, seq 2] Pid:F0
 Data: ,RM,S, or Help >#0D
 18:03:35 => K4YPE -0  WA2GGI-0R   Ctrl:73
 18:03:38 => KB7HJM-0  WA2GGI-0    Ctrl:63
 18:03:41 => KB7HJM-0  WA2GGI-0    Ctrl:00 [Data, seq 0] Pid:F0
 Data: **HI BOB IN BOCA RATON FL.BUSY NOW PLEASE LEAVE MESSAGE ON
 MAILBOX TNX.#0D
 [...]
 82 total frames received and 6 good ones + 3 CRC errors
 Stopped logging on 1993-04-16 at 18:20:42

It's rather like reading the news on an RS232 service monitor,
isn't it? :)  Note that control characters are depicted as "#cc".

Now, here are some sorted packets:

 ****** File open at 18:03:16 on 1993-04-16 for
 WA2GGI-0 => K4YPE -0 traffic

 **HI BOB IN BOCA RATON FL.BUSY NOW PLEASE LEAVE MESSAGE ON MAILBOX
 TNX.  [1 lost pkts] ,RM,S, or Help >
 ****** connection inactive for 5 minutes
 ****** File closed at 18:09:02 on 1993-04-16
 ****** File open at 18:13:28 on 1993-04-16
 for KC4FS -0 => W1DXQ -0 traffic

 Phone call Jack. Please wait...

 ****** connection inactive for 5 minutes

Now, the questions:

**  Where do I find packet and what does it sound like?

  On HF, packet can be found mainly at the lower end of 20 meters
  (14090-14150 usually) and in the 30 meter band (10100-10150 Khz).
  VHF packet can be found on 145.01, 145.03, 145.05, 145.07 and
  145.09, among other places.  It has a "braaaap..." sound quite
  unlike RTTY.

**  How do you tune in packets on HF?

  On the upper edge of the screen, there's an "A" scale.  While
  hearing packets, tune VERY carefully until the scale reads 6 or
  higher.  Pktmon expects a tone frequency of about 1000 Hz.

**  I'm logging sorted packets, but they're missing linefeeds.

  You'll have to go into your favorite ASCII word processor and
  have it insert linefeeds.  I usually copy all the <n:filename.#>
  files into a single file and fix it there.

**  I'm getting lots of CRC errors.

  On HF, this is, sadly, normal.  Packet is just not well suited
  to a ever-changing ionosphere, and it's marvelous that it works
  at all.  (When I copied the sample text, the ionosphere was
  *very* quiet, an unusual occurence as I'm writing this.)

  On VHF, on the other hand, CRC errors may be a result of Pktmon
  being unable to keep up with transmission.  1200 baud is near
  the limit for this type of interface.  I've also found that with
  my setup (in an apartment), I seem to be prone to multipath
  and other VHF anomalies that disrupt reception, especially
  of packet.

**  The program locks up on me when receiving lots of packets!

  If there's too much activity on the air, or the receiving tone
  frequency is too high, Pktmon tends to lock up, as it can't
  "follow" the signals fast enough.  This has been reported by
  several users on Fidonet.

  According to the author, Pawel Jalocha, if Pktmon takes a long
  time to terminate upon hitting Return, your machine may be
  too slow.

GENERAL PROBLEMS
----------------

**  Can I use EMM386/QEMM or other memory managers with HC, JVFAX or
    PKTMON?

  Generally, no.  HamComm, JVFAX and PKTMON are interrupt-intensive
  and use up most of the CPU cycles.  That's the price you pay for
  having the demodulation and decoding done in software (rather
  than in a TNC).  JVFAX comes with its own memory manager, anyway.

  Note:  JVFAX may not work with MSDOS's HIMEM.SYS.  You may need to
  remove the "DEVICE=HIMEM.SYS" and "DOS=HIGH" statements from your
  CONFIG.SYS before using JVFAX.  I've not seen any problems with
  HIMEM and HamComm or Pktmon.

  If you regularly use EMM drivers, Windows or Desqview, make
  up a minimal boot disk disabling all such programs, before running
  HamComm, JVFAX or PKTMON.

**  I get noise from my computer--HELP!

  One of the most difficult problems in linking the PC with the radio
  is RFI.  It's beyond the scope of this FAQ list to cover every
  possible contingency, but here are some suggestions:

  1) Keep your computer and your antenna *well* separated from
     each other and use good, well-shielded, coax for the lead-
     in.

  2) The HamComm interface should be *shielded*--use a metal or
     foil-lined box.  Use good shielded cable for both the audio
     and data connections.

  3) Use RFI toroids (available at Radio Shack) on all cables.

  4) Install 0.1 uF capacitors from the DTR and RTS lines to ground.

  5) Install an audio isolation transformer between HamComm and the
     radio.  (Radio Shack #273-1374).

  6) Make sure the monitor, printer and their connecting cables are
     well shielded.  Monitor noise is very common, as is printer
     noise.

  In my case, I had to do all of those steps.  My 286 PC was feeding
  RFI back through the earphone jack of my radio), *desensing* it
  (ouch!)  I never got all the RFI out, but I reduced it considerably
  so that I only get a slight increase in background noise on a few
  frequencies.

APPENDIX -- THE HAMCOMM INTERFACE SCHEMATIC
-------------------------------------------

  Here's a schematic of the HamComm interface, reproduced with
  permission:

                  HamComm 2.0 Receive Circuit
                  Copyright (c) 1990, 1991 by W.F. Schroeder

                                                   RS232 25pin 9pin

                                           D1
                         -------*--------*-I<--*--> DTR   20   4
                         |      |        | D2  |
                    3 |\ |      |      ---->I---
    >------| |--*-----|+ \ 7    |      | |
            C1  |     |    \____|______|_|________> DSR    6   6
           .1 uF|   2 |741 /6   |      | | D3
                |  ---|- /      |      | --I<--
 AF             |  |  |/ |4     |      |   D4  |
 In             |  |     ---*---|------*--->I--*--> RTS    4   7
       R1, R2  [ ][ ]       |   | +            |
        100K    |  |       === ===  C2, C3     |
                |  |       === ===  1 uF       |
                |  |     +  |   |   16V        |
    >-----------*--*--------*---*--------------|---> GND    7   5
                            |                  |
  PTT Circuit             E |                  |
  (omit for receive-only)   ^\      R3         |  D1-D5
                Q1            \I    1K     D5  |  1N914/4148
                2N2222         I----[ ]----I<--|
    PTT                       /I B
    <-----------------------/
                          C

 Transmit Audio Circuit    R2         R3
 (omit for receive-only)   15K        15K
              --------*----[ ]---*----[ ]----*----<  Out
      C1      |       |          |        R4 |          
      .1 uF  [] R1    |          |       220K|
 <----| |--->[] 10K  === C2     === C3      [ ]    PC Speaker
  MIC        [] var. === .022  === .022      |    
  Out         |       |  uf      |  uF       |
 <------------*-------*----------*-----------*----<  +5V

 NOTE:  HamComm sends RTTY through the COM port's TxD line, as well
 as the speaker.  See the HamComm docs for more details.

 If you're just interested in receive, omit the PTT and transmit
 audio circuitry.

 None of the parts are critical, so raid your junkbox!  Prices for
 equivalent Radio Shack parts are given for reference--which you
 can beat by judicious shopping/scrounging.

 Parts List -- Main Circuit
 --------------------------

  Part     Value         Radio Shack #     Price (1993)

  C1       0.1 uF        272-135           $0.59 (for 2)
  C2, C3   1 uF 16 V     272-1434          $0.59 each
  D1-D4    Diode, 1N914  276-1122          $0.99 (for 10)
 *D5       Diode, 1N914  276-1122
  IC1      Op amp, 741   276-007           $0.79
  R1, R2   100K          271-045           $0.29 (for 2)
 *R3       1K            271-023           $0.29
 *Q1       Trans. 2N2222 276-2009          $0.59

* Not needed for receive-only interface

Parts List -- Transmit Audio Filter
-----------------------------------

 Part      Value         Radio Shack #

 C1        .1 uF         272-135           $0.59 (for 2)
 C2        .022uF        272-1066          $0.69 (for 2)
 C3        .022uF        272-1066
 R1        10 K var.     271-282           $0.49
 R2, R3    15 K          271-036           $0.29 (for 2)
 R4        220 K         271-043           $0.29

Miscellaneous:

Enclosure (RS #270-239 recommended, $2.19), PC board (RS #276-170,
$2.79), audio jack (RS #274-316, $2.19 for 4), RFI toroids
(RS #273-104 $7.95 for 2), DB-9 connector (RS #276-1536, $1.29),
audio cable, plug to match radio.

If you buy all Radio Shack parts for the converter, it should cost
$15 for the full circuit (plus transmit portion), not including the
RFI toroids.  Again, the circuit is not really critical--if you have
any parts lying around that fit, use them!  

CLOSING COMMENTS
----------------

This FAQ list was the inspiration of myself and many others on the
Fidonet SHORTWAVE echo, who have been using and experimenting with
HamComm and JVFAX for over six months, trading ideas and hints along
the way.  When more people asked me for help, there and on the
Internet, I thought of the obvious and wrote this! <g>

The following get credit for lending me a hand:

W.F. Schroeder (DL5YEC), Pawel Jalocha (SP9VRC), Reid Kelly,
John Palaima (N1NIG), William Nolle, Tom Carney (WB9RJX),
Ken McKenzie, Derek Buchler and Stephen Lee.

Additions wanted
----------------

1) I'd like a list of "cornerstone" RTTY and FAX frequencies.
In other words, if you're on the US West Coast, in Europe,
Africa, the Mideast or Asia, what stations do *you* hear best?
I'm not looking for an entire Klingenfuss text, just a few good
frequencies for various parts of the world.

2) I've learned of another fax program, HFFAX5 (no, it's NOT
related to SSC's software as far as I can tell..)  The doc
files that come with it are of the "I got this neat program
from a friend-of-a-friend" slant, and I'd like to find out its
status (shareware, freeware or pirateware) before I write about
it further.  Nothing gets my goat like mysterious ZIP files with
no documentation!

2A) And has anyone used FFTMORSE (Soundblaster CW) or TOR117
(AMTOR terminal unit in software)?

3) I'd like to hear from anyone who's tinkering with the interface
or even the Pktmon source.

4) I do intend to update this list with the introduction of new
shareware, updates to existing programs, or (most likely) stuff
everyone else is using but that I never heard of. <g>  (A new
version of HamComm is slated for later this year, BTW.)

More questions?
---------------

If anyone has questions or comments or even flames, drop me a
line!  My address(es):



Snailmail: David Moisan
           86 Essex #204
           Salem, MA 01970

73's and Good Listening, Dave

--


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