PACTOR II-III using the WinLink system. The AirMail application provides full Internet e-mail access via radio, plus direct mailbox to mailbox service. This combination is eminently suitable for emergency traffic - when zero errors, high speed and reliability are essential characteristics.
CW, RTTY, AMTOR, PACTOR I-II-III, PSK, NAVTEX. You name it. With a suitable client software the PTC-IIpro can handle it.
To stay in contact with a sailing vessel en route between Stockholm and Greenland, we selected the WinLink-compatible PACTOR II and III emissions, in combination with the AirMail software. PACTOR is an ARQ system - the receiving station will return each received character group to the transmitting station, asking for confirmation. The group will be repeated until a positive confirmation is received.
The PTC-IIpro was used for email, file transfer and real-time data links (chatting). These are some of the characteristics of the PTC-IIpro:
The PTC-IIpro is employed at commercial stations worldwide - and in the international store and forward network of WinLink amateur radio operators.
- Standard emission is PACTOR-II, upgradable to high-speed PACTOR-III. Compatible also with PACTOR I.
- With PACTOR III, the PTC-IIpro does maintain links under conditions with signal to noise ratios of minus 18 dB, transferring error-free data even when the signals cannot be perceived by the human ear. Phone and CW are sure losers in comparison.
- Built-in ability for GPS automatic position reporting (optional Y-cable required).
- USB or RS-232 and TTL interfaces for controlling transceiver emission/band/frequency. With AirMail software, unmanned mailbox reception/transmission is possible by scanning of all bands/frequencies in use by the station to be contacted. Compatible with transceivers from ICOM, Kenwood, Yaesu, SGC, SEA, Furuno, R&S and others.
TEXT AND PHOTO TRANSFER
With PACTOR, sending e-mail or text reports between ship and shore is an amazingly fast operation. PACTOR III is up to 5 times faster than PACTOR II. The optional PACTOR III license is a worthwhile upgrade.
We use the PACTOR III at sea with the AirMail application, for e-mail via WinLink database to shorebased computers, and for text and/or photo file direct transfer to and from other PACTOR user mailboxes - shorebased or at sea. Results are impressive, even under dismal propagation conditions. The AirMail software scan function allows continual automatic watch on several bands and/or frequencies.
E-mail from landbased computers to the shipboard station works extremely well. The e-mail will be addressed to <ship callsign>@winlink.org, is saved in the WinLink central database - and whenever the ship station contacts one of the 60-odd MBO stations, the e-mail is automatically piped to the shipboard mailbox.
"MBO" is acronym for "mailbox". Radio stations on the MBO list have mailboxes programmed to store and forward messages between PACTOR users and the landbased Internet e-mail system, via the WinLink central database. When a PACTOR user will call and connect to any MBO station, the called MBO station will automatically check with the database. If the database contains a message for the calling user, the message is immediately transferred to the called MBO station and from there to the mailbox of the calling station.
AN ACTUAL CASE OF TEXT TRANSFER
The below log transcript shows how an actual connection between SA8M (S/Y myJoy) and SAØM (the shore station) looks, using the AirMail terminal software.
The SAØM coast station near Stockholm was unmanned and scanning PACTOR channels on 3, 7 and 14 MHz. The SA8M ship station at sea in Skagerak made a PACTOR III call to SAØM on 3586.5, and connected to SAØM at 14:23:24 CET. Starting speed was the standard 200 but following connection, the speed increased considerably. Which, however, is not visible in the log.
Following the connect, one message of 3,693 characters in the SA8M AirMail outbox (1145_SA8M) was delivered from SA8M to SAØM. Two messages in SAØM outbox (1043_SA0M and 1044_SA0M), a total of 24,075 characters, were delivered from SAØM to SA8M.
The messages are automatically compressed to reduce transfer time. The file "sa8m_qrv.html" contained the html-code for one Internet page and was compressed 70% from 23,795 characters to 7,067 bytes. The PACTOR III efficient compression algorithm works wonders in reducing transfer time.
Transmitting power was 100W at both ends, using transceivers IC-706MkIIG. The shipboard antenna was an isolated backstay with an SG-237 automatic tuner. The coast station used a coax-fed W3DZZ trap dipole as inverted V, midpoint some 9m above rocky ground.
Disconnection followed automatically at 14:26:22 CET. In other words, the entire operation lasted less than 3 minutes including the connection setup and the transfer of a grand total of 27,768 characters. See the below log transcript.
The semi-automatic connection setup offers, compared to manual setup, an incredible reduction of the time spent on calling and searching.
SPEED COMPARISON PACTOR-III vs CW
In this sample, PACTOR III delivered absolutely error-free 27,768 characters in less than 3 minutes (9,256 char/min). A skilled manual Morse operator could manage 250 char/min and would need at least 120 min just to send the package.
Thereafter, an unknown number of minutes or hours shall have to be spent on finding and correcting errors made by the transmit- and receive CW operators, plus other errors introduced by adverse propagation conditions - and QRM as well as QRN. The time taken to type or write the manuscript is not counted, it should be equal for all modes.
2005/08/16 14:23:24 Incoming connect from SA8M on 3586.5(p3) kHz (Pactor3)
<Pactor3: , Speed= 200, Freq= +1>
Welcome to SA0M's AirMail box
SA8M de SA0M QTC 2 msg 24075 char>
; SA0M de SA8M QTC: 1 3693 2092
FC EM 1145_SA8M 3693 2092 0
Receiving 1145_SA8M "Lägesrapport för utskick och webb"...Decoded OK
; SA8M de SA0M QTC: 2 24071 7303
FC EM 1043_SA0M 276 236 0
FC EM 1044_SA0M 23795 7067 0
Sending "Positionen", 236 bytes (14% compressed)
Sending "sa8m_qrv.html", 7067 bytes (70% compressed)
; SA0M de SA8M
; SA8M de SA0M SK
2005/08/16 14:26:22 Disconnected from SA8M
Sending photos is just a matter of attaching the picture file. The below photo, showing the Öresund bridge as background, was taken with a compact digital camera and transferred to a shore computer via Pactor III.
The photo has not been manipulated after the transfer, save for a reduction of pixels to 72ppi to shorten loading time here on the Web.
In the transfer of photo files, PACTOR III really shines. High speed ARQ guarantees a picture quality without a single defective pixel - and without the formation of the strange artefacts which are common in non-ARQ systems.
For more information, go to the SCS homepage. Recommended software is AirMail, working equally well in the WinLink network as directly between ship and shore or ship and ship mailboxes. By frequency scanning, all active bands can be watched for calls. For more information and download, goto the AirMail homepage.
With the "coast station" SAØM located at JO89wk (Sollentuna near Stockholm) and S/Y myJoy moving from Stockholm to the Denmark Strait near Greenland, we found that 7MHz was the band that made PACTOR connection possible all the way. For traffic, we preferred the hours between 21:00 and 23:00 CET (this voyage was taking place in August).
Obstacles were, not unexpected, other stations ignoring the rule not to transmit on an occupied frequency. The IARU bandplan allows for just one PACTOR III channel in the 7MHz band. However, the band plan shall have to stand back when frequencies are needed for emergency traffic.
Memory ARQ modes like PACTOR are designed to overcome QRM and QRN as well as to compensate for insufficient signal strength. The task is accomplished by repetition. "Coast station" "SAØM" sends a character string to ship station "SA8M". Station "SA8M" returns the string and asks for confirmation. If confirmation is received, the string is accepted. Else, the string will be repeated by station "SAØM".
If a third station "X" succeeds in obtaining contact with a station "Y" on our frequency, we may get a situation were nearly all strings are repeated, and repeated again. Once in a while, a transmitted string may slip by and be confirmed - injecting new hope and keeping the connection alive. However, the average transfer through-put may drop to a few kilobytes per minute. DO NOT TRANSMIT ON AN OCCUPIED FREQUENCY!
Amateurs have been heard trying to convince ARQ stations into leaving a frequency - by employing high speed CW interference. This is an exceptionally stupid method, because the ARQ station will just keep on repeating parts of the message until every character or, in the case of picture transfer, pixel has been correctly received at the other end. Interference will only prolong the transmitting period.
The PACTOR III signal of reasonable strength occupies a 6dB bandwidth of 2200HZ, select 2.4kHz or greater receiver bandwidth. In other words, bandwidth requirements are the same as for SSB telephony. To optimize PACTOR transfer conditions, shut off speech compression, noise blanker, notch filters and DSP noise reduction. Select fast AGC. The frequencies are center frequencies, offset -1500Hz.
PACTOR IN EMERGENCIES
High speed transfer and automatic error correction (ARQ) are two of the qualities that make PACTOR III eminently suitable for emergency communications. Another advantage is the ability to transfer error free data even when the signal cannot be perceived by the human ear, at signal-to-noise ratios down to minus 18 dB.
Moreover, the PTC-IIpro scanning feature allows automatic reception and saving of messages on any band and any scheduled frequency, without operator intervention. Store and forward mailbox service is, in combination with frequency scanning, another valued function which helps taking some load off the shoulders of emergency operators.
Last but not least, the e-mail function provided by the system does support communication with any and all e-mail users on Internet - on a single radio link.