Front Panel controls of the HAL ST-8000A

              The ST-8000A was designed for the military and as such, the controls are simple to use and robust in construction.  There is a single toggle switch that powers the unit on, and the rest of the controls are membrane buttons.  There is a “2^nd” key that allows for most buttons to be used for two purposes.  There are also LED’s used for tuning, status indicators, and data output for settings such as tone and baud rate that have been selected.  Once quirk of the controls is that once the selection has been typed in, a green LED will blink until the enter key is selected to finalize the input.

              The 8000A is a complex modem that can be configured for a wide variety of inputs.  However, I use it only as an audio filter between the radio and the decoding modem, currently a HAL DSP-4100.  In this case, the important settings for operation are the setting up the filters so that the signal gets processed, and ensuring that the audio path is correct.

              There are two methods to tune the filters of the 8000A, both get to the same place, varying only in the parameters that are being utilized.  The traditional way to set the filters is to have the unit display the mark and space frequencies along with the baud rate.  First select the M/S display and enter each frequency in turn.  The difference between the mark and space will be the shift and the average of the two numbers will be the center frequency.  Since I am feeding a DSP-4100, I set the M/S at the standard Amateur RTTY tones of 2125 and 2295 at 45 baud.  This gives the standard shift of 170 Hz.  Since I am feeding the audio to a DSP-4100 that has it’s RTTY filters set at these tones, it is easy to match the settings.  The Radio RTTY mode outputs are also set at these tones, so the M/S display and setting method makes tuning amateur RTTY easy.

              The second method is to have the 8000A display the center frequency, shift, and baud.  This method is more used when monitoring commercial or military RTTY that use alternative shift and baud rates.  Since commercial and military stations are not as worried about bandwidth, the shift is often around 850 Hz, even with a relatively slow baud rate of 50.  In this case, the radio will be set to USB and to more easily utilize the radio passbands, the 8000A and DSP-4100 tone selections need to be changed.  To make things simple, I change the Cf to 1500 Hz, and select the shift  to the appropriate amount and change the baud rate, all by direct entry.  I then switch the display to M/S where the tone frequency are automatically displayed.   I then go to the terminal software and use the configuration commands to align the DSP-4100 to the same M/S settings.

              For an example of copying commercial RTTY over the air, German weather station DDK broadcasts weather over RTTY using a 425 Hz shift and 50 baud.  I dial in the frequency on the radio set to USB to 10.099.315.  This centers the tones at 1500Hz in the passband.  I can then use the various radio filters to reduce noise and interference.  I set the 8000A to 1500 Cf, 425 Shift, and 50 baud.  Switching to M/S display, I see the tones at 1287.5 Hz for Mark and 1712.5 Hz for Space.  I then go into the Hal Software and adjust the baud on the front panel, and go to the configuration page to change the M/S frequencies.  Using these settings, audio passes through the radio filters into the 8000A where it is filtered and then passed to the 4100 where the audio passes through the DSP board and finally to the decoder where it is converted to serial data for display on the screen.

              Traditional RTTY is sent on LSB but new amateur convention, which is nearly all soundcard modems now, uses USB for digital work.  To correct for this problem when using legacy equipment, everything has to be set to Reverse.  Since I am using FSK settings on the radio, the 8000A is set to REV as well.  I keep this setting for commercial RTTY and reverse it again in the software rather than change the modems around.

              There are some articles on the internet about using the HAL ST-8000 and ST-8000A as regeneration units to supply audio to a second decoder for conversion to serial data that is fed to a computer for display.  This is known as regeneration.  Basically, audio from the radio is filtered and decoded by the primary modem.  Instead of outputting serial date, the modem generates high quality Mark and Space audio tones that are fed to a second decoder for conversion to serial data.  The second decoder can be pedestrian in performance because the quality of the output from the regenerating modem is extremely high, even if that output is full of errors.  In effect the signal is decoded twice, but any errors in the first decoding are carried through to the input of the second decoder.  This is a stop-gap method to use the older TU with newer equipment.  My setup does not work like this.  In my system, the regeneration is on, but the pin that has the output signal is not connected to anything.  In my set up, the audio is filtered in the 8000A but never decoded.  The filtered audio is extracted before the demodulator and fed to the DSP-4100, where it is further processed and then decoded using higher end computers rather than just the analog decoders in the 8000A.  I have a ST-8000 in line that directly decodes the same audio that is fed to the 8000A.  The decoding of the 8000A/DSP-4100 is superior by a significant margin than the old “gold standard” that was the ST-8000.

              The final article in this series will see how radio teletype is utilized at N1ZZZ, and it certainly is, if not unique, at least highly unusual.

HAL ST-8000A Wiring and Pin-out

              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 21^st 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.

HAL ST-8000A Powering up and Internal Testing

Before you purchase a HAL ST-8000A, it would be best for you or the seller to run the internal test procedures to check your firmware and to ensure that everything is still running correctly.  These units are over 20 years old now, and the electronics could start to fail if they have been sitting in storage for too long.  The good news is that this testing is very easy, and only takes the power cable to complete.  So even a NOS unit can be powered up and tested with no technical knowledge about the unit.

              Check on the back panel to make sure that the frequency and voltage match your power mains.  Unlike most TNC’s, the 8000A uses about 30W of AC power and not 13.8 VDC.  In the US this would be 115V and 50/60 Hz.  Europe and Asia require it to be set to 220V and 50/60 Hz.  The frequency switch can also be set to 400Hz for aircraft use in accordance with MIL-STD-704.  If your 8000A has the accessory package, you should be supplied with two power cables, one that is a standard desktop computer cable, and a short adapter that allows the unit to be plugged into military power systems.  The male plug is for the US standard, but adaptors or other cables with the proper female socket will work.

              Once the unit is plugged in, flip the front power switch and the 8000A will go through the first diagnostic check.  During this check the firmware version will be displayed.  The newest firmware is version 1.9.  Once the start up has ended, the unit will show mark and space frequency as well as baud rate, and you should get a slight flicker in the LED bar graphs.  A few of the display LED’s might also be illuminated, depending on the settings.  This is the first test, and the one most ignorant sellers will claim is all they can do.

              The second test is called the BIT test, and this tests the internals of the ST-8000A by routing the modulator through the demodulator to check that the circuits are working correctly.  To perform this test, turn the unit it on, and upon completion of the start up test, hit the “2^nd” key, then hit “BIT” and finally “Enter.”  This will run the machine through a 13 step self-diagnostics test, including testing all the LED’s and testing the demodulator at several audio levels.  If all is well, the unit will end the test by putting “Pass” on the LED display and finally returning to standby mode.  If there is a failure at any point, it will display the step of failure and say “FAIL” on the screen.  The test will not proceed beyond the failure point.

              Once the ST-8000A is verified to be functioning correctly by these tests, it is time to move onto the wiring to be able to get audio into the unit from the source, and then intelligence back out.

HAL Communications ST-8000A Overview

              This will be the first of a series of blog posts on the HAL ST-8000A.  I have had quite an adventure getting one of these terminal units working in my station and there is very little information on the internet to help with the process.  I hope to provide an overview as well as some hints and tricks I learned, or discovered that helped me along the way.  If someone else wants to use this unit in their station, I hope that they can use this information to make the process more painless than mine was.

              The HAL ST-8000A is a teletype modem that was designed for the military to provide a drop-in replacement to the Frederick Electronic 1280A modem.  It can be used in both radio and hardline applications and converts FSK Teletype at a wide range of baud rates to/from either RS-232 or MIL-188 protocols.  Since it was designed for the US Air Force, it uses US Department of Defense Bendix plugs and is built to military specifications.  This means that it is very well build, EMP hardened, and subsequently very costly.  This was HAL Communication’s last terminal unit that did not have a DSP circuit.

              The flow diagram of the unit is as follows: audio is fed through a balanced line into the unit where it passes through a series of filters.  The filters are automatically selected based on the programed front-end settings.  Filter width varies directly with the selected tones and baud rate.  The unit can handle tones from 300 Hz to 3000 Hz, which will handle most radio SSB bandwidths.  There are a series of low pass filters that cut out noise and then the audio is routed both the I/O port (more on this later), and one of two individual discriminators. The first discriminator is used at baud between 30 and 600 baud, and the second for baud rates from 601 to 1200.  The discriminators decode the audio input and uses a microprocessor to convert it to one of three digital signal outputs: 1) RS-232 data, 2) MIL-188 data, or 3) audio tones (Regeneration).

              On the transmit side, the ST-8000A will take data input (RS-232 or MIL-188) and convert it to AFSK tones which will drive the SSB radio or pass it over hard lines.  This is very similar to how most sound card and many TNC’s are utilized to send RTTY.  The unfortunately part of this is that you cannot use the FSK mode on the radio which is disadvantage on many radios due to the filter limitations while in SSB mode instead of RTTY mode.

              Using the ST-8000A as designed will require the appropriate software to decode the RS-232 or MIL-188 data streams in to text.  Given the age of these units, the terminal programs will be difficult to find, and will need to use older operating system emulators to run the software.  Add to this the lack of DSP and the use of AFSK on the transmit side, you may wonder why you would bother to use an ST-8000A in the first place.  The answer to this is the front-end filters.

              When people still used the ST-8000A, or it’s civilian cousin the ST-8000, the operators were looking for a way to use the superior decoders on the ST-8000’s while using their favorite software, which often did not interface with the terminal units.  The stop gap measure was to use the “regeneration” feature of the 8000’s.  This had the 8000 decode the audio with it’s superior filters and discriminators, and then convert them to pure, high S/N ratio audio signals to be converted to data by a secondary TNC which fed data to the software.  Any TNC was able handle the high-quality signals from the regenerator, and then the secondary TNC could be wired to send FSK signals to the rig, overcoming the second issue of the 8000’s.

              With the utilization of DSP, this stop-gap use of terminal units was rendered obsolete.  While some newer TNC’s use DSP, it was pointless to input regenerated tones into them, as the regenerated audio did not need further processing.  In standard soundcard interfaces, software was able to take audio directly from the radio and DSP algorithms were superior to the discriminators to the 8000’s.  Some software and interfaces could even overcome the FSK keying issue and software took over from the terminal units in most applications.  The use of external TNC’s and expensive terminal units essentially stopped.

              My idea in getting the 8000A was to see if I could use the TU as an audio filter and then feed the processed audio into a DSP TNC to take advantage of the filtering of the ST-8000A and then use a secondary TNC to use DSP on the signals, and decode them.  This also allows the secondary TNC to use FSK keying.  This plan could also have audio sent to a sound card interface and so the same thing, but onboard the computer.  This was the challenge that the internet had not seemed to meet as I rooted around for information on the HAL ST-8000A.

              The 8000A was never as popular as the 8000.  A few reasons for this are the fact that the 8000 used standard 25 and 9 pin serial connectors which were easily and cheaply available.  The 8000A uses Bendix 37-pin plugs that are harder to find, and far more expensive.  The other big issue for hams was the lack of dials and the replacement of an analogue tuning oscilloscope with the less popular MARK/SPACE LED bars.  The fact that the Mil-spec 8000A was also considerably more expensive sealed the deal.  Today you can find 8000A’s inexpensively, but the 8000’s are quite rare.  While the interface issue is a matter of preference, there is a way to pull filter audio out of the 8000A and feed it into an oscilloscope for a similar display.  The plugs, while expensive, can be bypassed and refitted because the jumpers between the plugs and the board go into a Molex plug.  Just be sure if you go this way, to ground all of the unused pins or you will get errors. 

                I was able to find a ST-8000A online for a price that I could justify, and had it shipped to me.  The unit had never been wired up, so all the original accessories including the Bendix plugs and pins were included.  Unfortunately, the instruction manual was not in the box.  Fortunately for me, the customer service at HAL is excellent and I had a pdf version of the manual in my Dropbox account which was worth it’s weight in gold.  Now that I had the ST-8000A, I had to research to see if it could do what I wanted it to do, and if it could, how I needed to set it up.  Once I had the ST-8000A in my shack, the real adventure could begin.