The HAL RTTY-1 Tuning Display

              The RTTY Tune is a device marketed by HAL Communications to displays standard split teletype tones in a traditional cross display that mimics the “Crossed banana” displays of oscilloscopes.  In its standard configuration, the RTTY-1 takes raw audio from the receiver or other source and filters out all but signals near the 2125 Mark and 2295 Space tones used for old school baudot teletype.  Of course, ASCII and AMTOR/SITOR tones near these same frequency pairs will also be indicated.  The RTTY-1 does not decode anything, but rather just indicates the amplitude of the signal found within its passbands.

              When properly tuned, the arms of the cross will be equal length and the stronger the signal, the longer the arms.  They will alternate back and forth at the baud rate indicating proper reception of the signal.  If the signal is not centered on the standard tones, the arms will be of differing lengths and a slow, but sure alteration of the receive frequency should bring the arms into alignment and decoding should begin.

              The RTTY-1 is small and a far easier display to use than its predecessor the RS2100 oscilloscope.  The solid state RTTY-1 is much smaller and more power efficient while giving a much larger display as well.  The RS2100 was an actual CRT oscilloscope requiring 120V input in a large cabinet and substantial current draw.  The RTTY-1 is about an inch thick and runs off 12-13V DC.  The RTTY-1 also only requires a single audio feed via a phono plug, while the RS2100 requires decoded mark and space inputs from a terminal unit, a feature missing from most modern equipment, and difficult to pull from a DB25 port on other units.

              The standard RTTY high tones are the default of the RTTY-1.  However, if you change certain resistors, alternative audio frequencies can be selected.  Unfortunately, this is more of a permanent modification and does not allow for rapid changes.  The idea is to be able to use the indicator with marine radios or other equipment that uses lower frequency pairs.  This limitation makes the unit less useful for modern amateur RTTY operation where signal selection is usually made on a waterfall display by clicking the mouse and the tones can be anywhere from 500 Hz to 2500 Hz. 

              Where the unit holds the most promise is older hardware that relied on small LED indicators of various quality.  I can see this unit being very helpful for PK-232 or older KAM and SCS units that used bouncing LED’s to indicate tuning.  Of course, old terminal units such as the HAL ST-6 would benefit greatly from this display if a vintage RS2100 isn’t available.   For display purposes, it also makes a nice light show for when you are listening to RTTY.

              Typical of most HAL products, the power connector isn’t standard so if you get one missing the HAL specific coaxial power plug, it is worth a note to Urbana to acquire a new one.

              HAL did publish a paper on how to modify the tones of the RTTY-1 to either Low tones or Marine tones.  The former centers at 1,360 Hz (1275/1445) and the latter around 1,700 Hz (1615/1785).  Unfortunately, both modified tones still don’t help with most waterfall displays which like to center around 1500 Hz.  Still, the low tones are far closer to the center of the audio passband than the standard high tones.  I have not modified mine, since I tend to listen to internet teletype which is still sent on the high tones and all the scopes in my shack are calibrated to these tones.  However, if you would like to modify an RTTY-1 to the low tones you must replace some resisters.  The following is the table


Low Tones


Change     from   to

R1         6,980    11,000

R2         6,490    10,500

R12       7,500    12,400

R13       6,980    11,820

R6 adj 2295 Hz to 1445 Hz

R20 adj 2125 Hz to 1275 Hz



Marine Tones


R1         6,980    8,870

R2         6,490    8,450

R12       7,500    10,000

R13       6,980    9,310

 R6 adj 2295 Hz to 1785 Hz

R20 adj 2125 Hz to 1615 Hz


              Of course, my mind always goes to the place where you could add 6 potentiometers and have a variable resistance for the six resistors and then you can adjust the tones to whatever you’d like.  Of course, you’d have to mark each control to ensure that each is at the proper value for the tone set you’d like to see.  You would also be able to adjust it so that you can have different tone spreads for commercial/military teletype.  This would take some engineering of course as well as a plan to wire up a control panel with the new controls.



                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                      

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.

Pactor II verses Clover II

In the early 1990's DSP chips finally became financially feasible and two DSP based, phase-shifted modulation modes became available to hams.  Ham developers in the USA and Germany separately developed two HF digital modes that combined high data transfer speeds while remaining fairly robust and capable of maintaining point-to-point links over the HF radio spectrum.

The two modes were Clover and Pactor II.  Implementation of the phase shift modulation was slightly, different, but these two modes were generally the same speed and claimed nearly equal robustness in the face of low S/N ratios.

I have always been a big fan of both of these modes and have used both since about 2003.  These modes have be upgraded over the years, but the version two of these modes have always been very good for keyboard links. 

Recently I was on the air with Pactor II with VE1XL.  Conditions were poor with large fades in the path.  Even the robust Pactor II was having some trouble moving data.  It was still good enough for keyboard work, but the fades caused several error messages going back and forth as the data packets did not make it.  Given that these were adverse conditions, I suggested to VE1XL that it would be a nice opportunity to test Clover and Pactor head to head. 

We ended our Pactor link and switched to our DXP-38 Clover modems.  These are the latest of the Hal Clover II modems and gave the mode the best chance at keeping a link.

We were able to establish the link, but we had trouble with the data blocks.  Unlike Pactor, Clover uses what it calls Clover Control Blocks.  These are sent at a modulation scheme that is the most robust it can muster.  Unfortunately the CCB's modulation is not available for data packets.  This proved to be the deal breaker on this link.  Despite some error packets, the CCB's managed to get through, but as soon as the data packet tried to make it through, it was not able to get there.

Sadly eventually the link failed and we had to go back to Pactor.

So what shall we make of this?  While I still find Clover more fun to operate due primarily to the fact that it has a more effective semi-duplex paradigm, and the ability to exchange station data on both ends of the link, it still needs more power to keep the S/N ratios up to the point where data can make it through.  Pactor is a superior poor link mode, and this is a common consensus.

73
N1ZZZ

Welcome to the N1ZZZ blog. This will also be the home of my DX callsigns and other operating locations. Since a vast majority of my radio activity takes place outside of my home, it may take us far afield.

I've been licensed since 1997 when I swept through and aquired my amateur call as well as the first of three commercial radio licenses. Currently I hold an amateur extra call, General radiotelephone operators license, Global Marine Distress and Safety System operator (GMDSS-O), and GMDSS maintainer's license. I also hold the radar endorsement. In addition to these FCC licenses in the US, I have also held radio licenses issued by the BIOT (VQ9JA and VQ9ZZ) and Ascension Island (ZD8JA). Through reciprocal agreements I have also operated in EA8 (Canary Islands). Lastly I operated KH0 in Saipan, CNMI; and KH6 from the island of Maui, HI.

I tend to go off the beaten path with most of my operating. While I love being the DX and working the pileups on RTTY and SSB, at home I take a much more laid back approach and perfer the digital modes. On HF I work quite a bit of PSK31 and some of the lesser used soundcard modes. I am particularly fond of MFSK16 and Feld-Hell. Still, I really love using the TOR modes and I have TNC's to operate most of them. My favorite is Hal Communications Clover which I find great to use both to access BBS' and to work keyboard QSOs. I also like to use Pactor, and operate at levels I, II, and III through my PTC-IIe controller. Most of my pactor work is on the Winlink 2000 system at sea for email, but I also enjoy keyboard QSO's. I am also capable of GTOR and AMTOR, but since I can't find anyone to work with me on those modes, I tend not to use them. The only TOR mode I don't use is 300 Baud HF packet. There are so many better options out there, that I just don't like to use it.

On the VHF side, I have the ability to use from the 6 meter to the 70 cm bands inclusive. Most of my VHF activity is mobile or on foot. I use FM voice to a limited extent, but most of my transmissions arein the form of APRS packet on 2 meters. I have a transponder in the car and a portable unit. The car is usually N1ZZZ-9 and pedestrian mobile is N1ZZZ-7.

My day job is a merchant Mariner. That is to say that I work as an officer on cargo ships in the US Merchant Marine. I usually work HF from the ship where I bring a tuned long wire and a small HF rig. As I mentioned, I use WL2K for email, but also get on the digital modes or SSB to work various stations from odd water grids. I usually send position reports via WL2K so it's pretty easy to track me across the oceans.

I do QSL both with paper and electronically. I always answer my cards, but it may take awhile due to my schedule. LoTW and eQSL.cc cards are uploaded fairly soon after I return home, and then I try to answer all direct QSL cards. Buro cards are answered on a secondary basis and are usually mailed to the ARRL right before I return to the ship.

73
Jeremy N1ZZZ