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 perimeters. 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.