Manager - AB7RG
Manager Notes

AMTOR: The 'forgotten' digital mode.

Created by on 2002-09-16

AMTOR, the forgotten digital mode.

What is AMTOR? It's a near error free digital mode that uses error detection and correction. This mode has been around so long that all the multimode terminal node controllers (TNC's) have this mode in them even if they have never been upgraded to later update chips. This mode is fun and provides almost perfect copy with poor band conditions. With just a little effort you can get an all mode TNC and explore this digital mode. Dig that old TNC out of the dust pile and have fun with it again. You can also buy them cheap if they do not have Pactor mode, even on ebay they are selling for less that the cost of a "Store bought" PSK-31 interface! The TNC of my choice is the PK-232 or later model PK-232MBX. Even Heathkit supplied the PK-232 under the Heathkit label in kit form as the HK-232. Best of all Timewave still supports this family of TNC's. Timewave, Kantronics and MFJ still sell new all mode TNC's but they cost a lot more than a PSK-31 interface or a used TNC. If you do buy a used TNC make sure it works first or has some kind of DOA warranty. Also get the manual, you WILL need it!

There are two distinct modes in AMTOR. Mode-A which is ARQ (Automatic Reception ReQuest) and Mode-B is FEC (Forward Error Correction). Mode-A requires precise timing between the linked stations and so you can not use a computer sound card and program to operate this mode, you must have a TNC with this mode programmed into it. Mode-B however is like RTTY and some sound card programs allow you to operate in AMTOR Mode-B. Mode-A operation links two stations with each of the stations taking turns being a sending station and a receiving station. AMTOR Mode-A stations linked will produce a distinct rapid chirp...chirp sound. The sending station will send a chirp and then the receiving station will respond with a chirp telling the sending station to resend the data if there was an error detected or to send the next chirp of data. This process continues until the sending station has sent all it's data. At this point the change over of sending and receiving stations is required. To make the change from being the sending station to the receiving station only requires that the sending station sends a plus sign followed by a question mark like this +? .

Linking in AMTOR ARQ mode requires a 4 character station call or Selcal and is made up using your FCC call sign. No numbers are allowed in your Selcal so as an example my FCC call sign is N4ZOU and so my Selcal is NZOU. If you are using a PK-232 TNC the software will simply select your Selcal by entering your full call sign at the MYSELCAL command. Example cmd:MYSELCAL N4ZOU. Then if you enter MYSELCAL at the cmd: prompt it will show as cmd:MYSELCAL NZOU. Another example of a Selcal for a 2 X 3 call sign is KC4UYS would become KUYS and a 1 X 2 or 2 X 1 call sign N0AB would be NNAB. If your using another type of TNC then you will need to read your manual on how to enter your Selcal. NOTE: You CAN NOT use your Selcal as a proper station ID while in AMTOR! You must send your full call in the text of your transmissions. Using a PK-232 TNC to start an ARQ AMTOR contact is simple. First find a station calling CQ or Make a CQ call yourself. An example would be....






A few years ago this CQ would have been done in AMTOR FEC mode and you would expect a quick return. This is no longer possible as there is almost no AMTOR activity.

What I do is to give the CQ call in RTTY (Baudot) mode. This allows making contacts with simple RTTY terminals and stations using sound card modems and software. They can give you a call in the mode they can operate in. However, if a station using an all mode TNC copy's your CQ text and has AMTOR mode they will see the four character Selcal in the CQ text and can switch to AMTOR mode and attempt to link. At this point you would switch to AMTOR mode after hearing the distinctive chirp....chirp of an AMTOR station trying to link to you. With a PK-232 the command would be cmd:OPMODE AMTOR. If everything is setup properly your transceiver will start to key and unkey quickly and the linking station will be the sending station and start sending you text. If on the other hand you find a station calling CQ with AMTOR information in the CQ text simply switch to AMTOR mode and enter there Selcal ID.

With a PK-232 TNC and a dumb terminal program you would enter cmd:OPMODE AMTOR. Now enter the command ARQ NZOU if you were calling N4ZOU or the Selcal of the station your trying to link with. If your using a different type of TNC and software you will need to read your manual. Again the software change over command is +? . Example..BTU KC4UYS DE N4ZOU K +?

Ending an ARQ contact with a PK-232 is easy. The sending station at the end of the contact would send both stations calls and instead of the change over sign of +? . Example THANKS FOR THE NICE AMTOR CONTACT. HOPE TO LINK AGAIN. 73 KC4UYS DE N4ZOU SK . At this point both stations will shutdown.

Where to operate. When AMTOR was still active you could hear them on 20 meters between 14.065 and 14.085. Today I would give PSK-31 operators a break on 14.070 and not get too close to them. RTTY (Baudot) starts at around 14.080 up to around 14.090. I normally call CQ in RTTY mode on 14.079 with AMTOR link information in the text.

Using both a PK-232 and sound card PSK-31 interface on one RS-232 comport.

Yes, you can use just one RS-232 port for both your PK-232 TNC and your RS-232 keying circuit PSK-31 interface. The PK-232 needs only three wires connected to the RS-232 port. Just make sure the TNC and software is setup for XON/XOFF flow control.

SO you can make up a cable with only three wires connected between the computer RS-232 port and TNC. RX data, TX data, and signal ground. Now DTR, RTS and signal ground on the same RS-232 comport are available for use with your Sound card interface.

I used a Radio Shack RS 232 Shielded Jumper Box 276-1403A between the serial cable from the computer and the back of the PK-232MBX. Pins 2,3, and 7 were connected through and then I used a 2 wire with shield cable connected to the computer side of pins 4 and 20 with the shield soldered to pin 7. I drilled a small hole in the side of the plastic case of the jumper box just large enough for the cable to pass through it. I used both RTS and DTR just to make sure I would not have a problem with any of the software available for use with the sound card modes that use RTS or DTR for transmitter keying. This setup works fine and I have no problem with either the PK-232 or sound card interface using the same comport.

Software, There is some good software and some bad software available for use with the PK-232 and other TNC's. In Windows 3.1 and up you can load Hyper Terminal and it will work just fine. Procomm is also a good terminal program if you can still find a copy of it and you don't mind working in DOS mode. My choice of software is PC-Pakratt II for DOS with a PK-232 and will operate under Windows 95 and 98, I don't think it will operate under Windows XP. Also PC-Pakratt for Windows works very good with the PK-232MBX. I just found a very good Windows PK-232MBX terminal program that I downloaded for free that works great! Will take you to the home page and from there you can download This program works only with the PK-232 and PK-900 TNC's.

Good luck with your AMTOR project and hope to link with you soon!

Scott N4ZOU

VE2RWG 2007-08-15
RE: Gurgling water
I used to think those were digital phone transitions. I have no idea really. But talk about MAJOR interference, that would be just it!
VE2RWG 2007-08-15
RE: Gurgling water
Hi guys,

Being a CW enthousiast, I'd much rather hear an AMTOR station next to me than any of the so-called new modes! PSK31 is a real nice thing for what it does but it causes so much interference it's unreal. I wouldn't want to hear this anywhere a CW signal, even on or near a 599. It's very distracting.
AMTOR is almost soothing to hear.

I also have an old Kantronics UTU original model and would love to give it a shot but I can't find a manual for it.

I also like to hear the sound of the other AMTOR or PACTOR broadcast mode.

As for the switching time, we used to have no problem way back when we operated a separate Rcvr and Tmtr. All we had to do was to control the ALC.

I like the idea of adopting a frequency for each of the legacy modes.

On another note I am very thankful that PSK operator stick to their standard frequencies like glue, otherwise the QRM on our bands would be ridiculous.

That's the beauty of PSK. You can have numerous station s on one frequency separated only by a few hertz and it still works fine. Beautiful!

Should we start local nets?
I monitored the RATTS net tonight on 80 mtrs on my IC-7000's little display.

I would love to read about ham radio news or broadcasts of the sort on Amtor. Anybody interested in starting a regular QST sched?

Pete, VE2RWG/W7
Seattle, WA
EI5DS 2002-10-08
RE: Gurgling water
Hi All,

Amtor is alive and well on this side of the pond (Atlantic).

Activity is mostly on 40m around 7035 mark.

Worked DK2JH today. He was using a FT817, 5W, Kam and LW. Excellent copy in poor conditions.

Amtor hangs in there when most modes give up.

Except CW of course!

73's de Ned/EI5DS

NB6Z 2002-10-01
RE: Gurgling water
You ask "On another topic, where is everybody on AMTOR? I have been listening on 20 with no luck...."
The Amtor signals are still on 20 meters, but you have to be 10 light years from earth to receive them. ;-)
K2JX 2002-09-26
AMTOR: The 'forgotten' digital mode.

Just because there are newer modes for Digital Comms does not mean we cannot go back to the future once in a while ! I operate RTTY,MFSK, PSK 31 and CW, been on RTTY since and before the computers. How about some ASCII ? You bring up a good point Scott !

VE2FK 2002-09-20
AMTOR: The 'forgotten' digital mode.
Amtor is sure a nice Keyboard mode and we should still use it, I do... Maybe we should vote for a calling channel to meet. My PBBS is scanning 14079 and more.

73 de Claude VE2FK
KE4MOB 2002-09-20
RE: Gurgling water
I heard it was military spread spectrum over about 150 kHz. On another topic, where is everybody on AMTOR? I have been listening on 20 with no luck....

Steve, KE4MOB
WA6DTX 2002-09-19
RE: Gurgling water
Are we sure those aren't stations running VOX for psk31 control that have let that swimming fishes screen saver come on? Just a thought...has happened more than once<G>

KD1SQ 2002-09-19
Gurgling water
That's Automatic Link Establishment or ALE that you're hearing.

Used to profile circuit conditions on various frequencies.

NT9E 2002-09-17
AMTOR: The 'forgotten' digital mode.
PSK-31 is OK I guess but no substitute for my PK-900 (dual port multi-mode controller)generated RTTY, AMTOR, and PACTOR fun.
KA0MR 2002-09-16
RE: AMTOR: The 'forgotten' digital mode.
The "gurgling water " sound I once read, I ain't making this up, is the sound of the planet Jupiter. I read this story several years ago or at least I have this inbedded in my brain so if I am way off frequency on this please you guys out there be gentle with me because I am serious but will entertain any and all other explanations.
But was wondering when we would revisit the TNC generated modes and not forget about them as the sound card modes are ok for thier intended purpose but I have yet to find a soundcard digital that can "really compare" to AMTOR and TNC generated RTTY.

NB6Z 2002-09-16
AMTOR: The 'obsolete' digital mode.
I keep my KAM+ TNC connected so I can operate it from the MixW sound card program. This makes operating all the digi modes real quick and easy. I still enjoy a Pactor link when I can find one, but Amtor seems to be completely out of the picture these days.
When you have experimented with all of the popular sound card generated modes, you will understand why Amtor is obsolete. ARQ for error free ASCII and binary transfer as accomplished by Pactor is useful, but not really that practicle for simple text messages. These days, text and extended ASCII charactors are sent in near real time with MFSK16. The FEC and interleave techniques that MFSK16 uses make this a nearly error free mode. Bandwidth is approximately the same as Amtor. My point would be... the state of the art has moved ahead and so have 99% of the active digi ops.
K9IUQ 2002-09-16
AMTOR: The 'forgotten' digital mode.
Yes, Amtor WAS a great mode. I used to work it daily. But then along came the soundcard digital modes and all of a sudden everybody was on PSK31. Couldnt buy a contact on Amtor even on 20 mtrs. Finally sold my TNC. You want error correction? Give MFSK a try. No TNC hassle and much better copy on weak sigs than PSK31.

I think Amtor (along with Packet) will stay forgotten in this shack....

K2WH 2002-09-16
AMTOR: The 'forgotten' digital mode.
Sounds like crickets! Now I know what that noise is. Been wondering about that for some time. Does anyone know what mode makes the sound of gurgling water? Been hearing that alot lately, even on the military air frequencies.

KE4MOB 2002-09-16
AMTOR: The 'forgotten' digital mode.
Good Article, Scott!

It's nice to see someone promoting the error correcting modes!! I spend most of my time running PACTOR around 14.078, but actually prefer AMTOR most of all. It seems more "free flowing" and although not perfect, does an admirable job.

To the un-initiated, AMTOR mode A sounds like crickets chirping, and is much like (if not identical) to the SITOR stations still heard in the maritime service. Not every radio is capable of running mode A, because of the rapid TX/RX requirements (usually on the order of 25-30 mS is required).

I would urge every digital op to get and old TNC and give AMTOR a try! Once again, thanks for shedding some light on this really neat mode.

Steve, KE4MOB
VK2GWK 2002-09-16
I still have one of those dedicated thingies... a TONO Theta. Recently came across the manual when I was looking for something else..... Will dig the thing out and tie it to the FT1000MP. See if it is still working.... Might be fun!
AI2Q 2002-09-16
Yup, AMTOR is one of the niftiest ways to "connect" to another station. In the mid-1980s, when I was a cliff dweller, I relied on AMTOR for many FB QSOs---always running my QRP Ten-Tec Argonaut at a few watts into a hidden end-fed wire. It never ceased to amaze me how solid the links were---even in the face of QSB. There were times when the other station faded into the noise, and off the 'scope's CRT, but the link kept chirping away. It was like being linked by wire!

Yes, AMTOR uses a limited upper case character set, but its beauty is its simplicity. The forward error correcting (FEC) mode is incredible unto itself, but the full handshake (ARQ) is a treat. I'll be firing up my old Kantronics UTU soon, and hope to hear others doing similarly. PSK31 is FB too, and its low bandwidth soundcard signal is great in terms of spectrum utilization, but PSK's lack of error correction can ruin a QSO.

The tradeoff is that you (and the other AMTOR station) need reasonably fast-QSK rigs. To me, that's a small price to pay.

--- Vy 73, AI2Q, Alex in southern Maine .-.-.