FELDNEW8... a Program for Feldhell Tx/Rx using a Soundcard
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History
*******
This program has been developed to fill a real need for those wishing to use
this most interesting mode without the need to construct any interface
hardware. After many efforts to derive timing from the soundcard itself
which came close to success I have had to resort to the use of the PC timer
which means that this is very much a DOS program and Windows will refuse
to run it. It is necessary, therefore to close Windows and restart in DOS
mode. IT WILL NOT RUN IN WINDOWS.....NOT EVEN IN A DOS BOX.


Soundcard compatibility is a real problem. I started with 16 bit DMA sampling
which meant that SB16 compatibility was vital and many soundcard clones
failed. This version uses the FM generator for output and 8 bit direct access
for the input so it should be compatible back to the opiginal SB cards, but
clones....well you will have to suck it and see. If the soundcard gain comtrols
do not work then you will have to make your gain adjustments off-line.

On receive the program uses a 100 element FIR DSP filter  at 900 Hz which
makes for good selectivity, however there is a price to be paid in the speed
requirement of the computer. For this reason also, I have set the sampling
rate at 2450 Hz, which means that the Nyquist frequency is 1225 Hz and
therefore you can see signals at 1800 Hz as an "alias". With my IC735 this is
no problem as I set the pass band tuning to give a low pass function.

There is much for me to do to make the program more user friendly.

Versions
********

Version 1.0    Not formally numbered.

Version 1.1    Dynamic range of white to black widened.

               Error in Hellschreiber plotting method corrected.
               (Thanks to Pier Haringsma for spotting this)

Version 1.2    Changed the detection mechanism to a squared function for better
               sensitivity.

               Removed FSK facility.... this was not widely used.

               Added facility to change display sensitivity.

Running the Program
*******************

Unzip the program into a directory of its own. Connect the audio from the RX
to the mic input or possibly to line. AGC is only available on the mic input
of the SB16 and onwards. Connect the SSB TX audio input to the Line output
of the soundcard. If you have true SB16 compatibility then you will have
control of these parameters from within the program otherwise you will have to
externally switch the parameters in and set levels via a program such as
sb16set.exe or the equivalent or possibly a Windows mixer control panel
before leaving Windows. The output level from the FM generator is controlled
via the midi control and then the master.

On first running the program you will be prompted to enter your callsign.
Do this and a file called CALLSIGN.TXT will be generated to hold it.

Apply audio.

If all is well, you will clearly see detected output peak at about 900Hz
in the mini 'scope display at the top LHS of the screen. Note that soundcards
do not limit in the way that an op-amps do and it is VITAL that you set input
levels so that you remain within the display area and do not overload.
Ideally, use a recording program such as that issued with your soundcard
software package to establish that your input is at the correct level.

Left and right arrows lower/raise the mic gain (if you are SB16 compatible)

F2 toggles the speed between normal Feldhell and a mode whereby each vertical
line of pixels in the character is sent twice thus making the character
twice as wide when received normally. This mode could be of great help under
poor conditions.

F3/F4 raise and lower the display sensitivity in 6 steps. Default value is 3.
This is alters a mathematical constant operating on the decoded data and
does not affect the input to the soundcard.


F5 toggles the AGC on the mic gain on and off (if you are SB16 compatible)
The benefit of using AGC is debatable, experiment and see. Overloading the
input may be even more catastrophic if this facility is used.


F6 toggles the display between 16 colours and 16 greys according to
preference.

F7/F8 raise and lower a threshold value which is subtracted from the detected
signal. This will be of help under noisy conditions.

There is a type-ahead buffer available which allows the entry of up to four
lines of text with backspace allowing the deletion of characters one at a
time.



F10 takes you to TX.

Transmission uses the FM generator of the sound card to generate keyed
audio for use with an SSB TX. The attack and decay time of the keyed audio
has been selected to avoid key clicks. I have not incorporated a direct
keying facility although this could be done via, say, a parallel port
if required later.

A transmit switching facility that raises the RTS line on a chosen COM port
is available. If you inspect the CALLSIGN.TXT file that is generated on
first activating the program you will find a second line that has the word
"NONE". Edit this to read "COM1" or "COM2" depending which port you wish to
use.

The transmit buffer is displayed in magenta across the screen. Type ahead
is via the keyboard buffer and back arrow allows you to delete single
characters. Any characters in excess of the visible buffer (320 characters)
will be lost. On entry to the transmit screen any characters in the receive
type-ahead buffer are transferred to to the transmit buffer and sending will
commence.

There is a facility for sending pre-edited text messages such as CQ or
station details. These must be simple text files in the same directory as
the program, shorter than 320 characters in number and bearing the suffix
.MSG. There can be up to six of these and the transmit screen will list those
available. To send one hit F2 followed by the message number.

F3 gives you a tune up level setting facility (If you are SB16 compatible).

F6 allows you to clear the transmit buffer immediately.

Esc gets you back to receive.


Setting up Sound Card
*********************

Pier Haringsma has kindly provided a routine to help with this.
You will find it in the file FELDRUN.ZIP

As a last resort, the author may be contacted on lionel@lsear.freeserve.co.uk


