Probably
the toughest part of using the HAL ST-8000A is wiring up the unit in the
configuration that you want to use it.
As mentioned in the introduction article, you have four options to run
the unit. The first is to use it as
designed, where audio is fed into the unit, demodulated, and exported as RS-232. The second option is similar, but uses
MIL-188 data output. The third option is
for the terminal unit to “regenerate” the audio and output Mark and Space tones
for further decoding. The fourth is one
that isn’t clearly documented, and has the ST-8000A filter the input audio, and
then output the audio to the Data I/O connector before it is demodulated at
all. Of the four modes, the last holds
the most promise for effectively using the ST-8000A in the 21st
century.
In this
article, I will review the pin outs for using the unit as a regenerator and as
a filter, as both can be done simultaneously.
To use the rig to output serial data, the number one port needs to be configured
away from regeneration, so I have not pursued those options.
The first
step is to open the 8000A and set some of the jumpers. Just remember to have the unit turned off and
unplugged. It is also advisable to take
proper static precautions when reaching into the interior. There are quite a few options, most of them
dealing with the remote control and RS-232 parameters. Details of these are in the manual, but since
I was not using these functions, I did not adjust them from factory defaults. The first jumper I set was the input impedance
jumper (A1J6) in the upper left corner of the unit. Since my Icom 746 has an audio out impedance
of 4.7 kilo-ohms, it made for less of a mis-match to set it to 10 kilo ohms
rather than the default of 600 ohms. The
second jumper I set was for the tones mute (A1J8). To use this unit in regeneration mode, this
jumper must be changed from the factory default so that the tones are always
on. This fact was confirmed in an email
from HAL Communications. Once these two
jumpers are set, then you can re-install the top cover and get the soldering
iron ready.
There are
three sockets in the back of the ST-8000A.
They are marked Audio I/O J2, Data I/O J1, and Remote. I do not use the remote socket, as I change
all parameters from the front panel. The
Audio I/O port is a MS27508E14F35SA connector which is female. You will need a MS2743E14F35PA Male connector
to mate with it. These are available for
about $40 online if you are missing the original. The socket has 37 pin possibilities, but
fortunately we won’t be using most of them.
Soldering them is pretty easy, as you solder the pin to the control
cable, and then insert the pin into the socket using a special tool which comes
in the accessory pack. The audio in and
out are via balanced lines. Ground pins
3 and 12 if you are feeding an unbalanced line, which is what you are normally
going to do. The manual states to ground
them at the radio.
The Audio I/O Jack has the
following pinouts: (if a pin isn’t listed, it’s not connected)
Pin 1 Modulator FSK
Audio Output (AFSK out) rated -30 to 0 DBm 600 ohm
Pin 3 Modulator FSK Audio Output (AFSK out) rated -30 to 0
DBm 600 ohm (ground this if you are feeding an unbalanced system)
Pin 5 Keyline relay
contact (PTT) +50V, 0.2A max
Pin 6 Keyline relay contact (PTT) +50V, 0.2A max
Pin 8 jumper wire to J1 Pin 8, 200V 5A max
Pin 10 Demodulator FSK Audio input (Audio In from line) -45
to 6dBm, 600 or 10K ohms
Pin 12 Demodulator FSK Audio input (Audio In from line) -45
to 6dBm, 600 or 10K ohms (ground this if you are feeding an unbalanced system)
Pin 37 Shield (ground)
For my
setup, I ran two sets of XLR balanced audio lines from the plug that then
allows me to use adapters for various audio inputs. I am generally using HAL DSP controllers
which use RCA plugs, so I have XLR to RCA adapters for most of the work. I only utilized Pins 1, 3, 10, 12, and 37 for
my setup. Running the PTT via Pin 5/6
would be required for normal operation, but not regeneration or filter mode, as
the 8000A isn’t used to transmit anything in these latter modes.
The second socket is Data I/O J1. The socket is type MS27508E14F35SB and the
male plug required is a MS27473E14F35PB.
The Data
I/O jack has the following pinouts:
Pin 7 Demodulator undetected Mark, 0 dBm Mark audio (this is
the filtered audio output)
Pin 8 Jumper wire to J2 Pin 8
Pin 9 Demodulator undetected Space, 0 dBm Space Audio (this
is the filtered audio output)
Pin 10 is the carrier detect output (+/-6 VDC selected by
jumper A1J9)
Pin 12 Demodulator Analog Ground (use this as the ground
return when using pin 7 and/or 9)
Pin 13/14 ground
Pin 15/16 Keyline Relay contacts +/-50 V, 0.2A max
Pin 17 Data I/O RTS Input +/-18 V RS-232
Pin 18 Data I/O CTS output +/-6 V RS-232
Pin 19 Transmitter clock output +/-6 V
Pin 20 Modulator Digital Data Input +/-18 V RS-232/MIL-188
(Jumper to Pin 22 for Regeneration Mode)
Pin 21 Demodulator Mid-BIT clock output +/-6 V RS-232
Pin 22 Demodulator Digital Data Out (RS) +/-6 V RS-232
Pin 23 Demodulator Digital Data Out (MIL) +/-6 V MIL-188
Pin 24/36 Modulator Analog Ground
Pin 25/26 Ground
Pin 37 Shield (Ground)
The Data I/O port has more
connections, but we use very few of them in Regeneration or filter mode. Getting REGEN audio out of the ST-8000A
proved to be a big stumbling block for me.
I resorted to emailing HAL, and they told me to be sure to jump pins 20
to 22 in this plug to route demodulated audio back into the modulator to get it
to loop effectively. This is in addition
to turning on the REGEN function on the front panel. Once this jumper was installed, I was in
business.
I was
intrigued by pins 7 and 9 when I read the manual, especially this passage:
“The
demodulator undetected outputs signals (MARK = Pin 7, SPACE = Pin 9) are
usually not connected to data terminals.
These are filtered audio signals recovered from the demodulator input
signal. These signals may be used for further
data processing or for connection to an external tuning display (oscilloscope)…
The external load to ground on Pin 7 or 9 should be 10K ohms or higher.”
This
passage got me thinking. Can I extract audio from the ST-8000A and
run it through a DSP box and have the DSP box do the decoding? Better yet, can I split the audio and have it run to and external tuning unit AND
have it run to a DSP decoding box as well? I posed the question to HAL and the response
was “I hadn’t thought of using Pins 7 and 9 in this
way. I can’t think of any reason that it won’t work. It is a pretty high level output so I don’t
think it will cause any problems.” The
short answer is, yes you can, and it does work.
As a caveat, I did use audio isolation transformers to isolate all the
various hardware components.
The
plug wiring is pins 7 and 9 are run through an XLR plug via shielded audio cable;
Pin 7 on the 8000 is Pin 1 on XLR, pin 9 is Pin 2, and Pin 12 is Pin 3. This then runs one of two pigtails. One pigtail converts the XLR to RCA by wiring
both data pins (1&2) to the tip, and ground (3) to the ring. This runs through a Y-adapter and then each
leg run through a 1:1 isolation transformer.
The audio feeds a HAL DSP-4100
for DSP processing and decoding, and the second leg goes to a HAL DXP-38 for
tuning indication. I also have a pigtail
that sends each audio signal via coax to BNC connectors for an X-Y display
oscilloscope. The use of the scope would
currently require me to use the unit in Regeneration mode, as the audio signals
are never joined. I have also
successfully run the audio solely to the DXP-38 for tuning indication and decoding.
I used a
simple wire jumper in the plug to connect Pins 20 and 22.
The
audio in section I saved for last. I run
two audio cables to the ST-8000A. The
first is audio from my ICom 746 using the ACC(1) port pin 5. This has a fixed impedance of 4.7K ohms and
level of 100-300 mV. This is more than
enough to drive the unit. I use an audio
isolation transformer to block any DC. I
also have a cable running from my computer headphone jack to the ST-8000A. I checked with my scope to make sure that the
audio drive was under 300 mV (a volume setting of <30 on my computer) and
the system worked well. I used this to
copy RTTY newswires from www.RTTY.com
I
use the DSP-4100 or DXP-38 for all transmitting work and this is done with the
standard FSK keying line into the Icom.
The 8000A is really used only in the receive side of the radio
system.
That
is the wiring of the unit. The next task
will be to set up the front end to get the unit to decode.
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