Cruising with ham radio -
HF e-mail basics, Part II

By Jim Johnston

In my last article I discussed e-mail operations using single-sideband (SSB) radios. This article will cover the device that controls the radio called the terminal node controller (TNC).

If you log onto the Amateur Electronics Supply Web site at www.aesham.com, you will find a vast array of TNCs. If you are only interested in HF e-mail, there is only one practical TNC to purchase and that is the SCS PTC IIe. Do not purchase this TNC if you are planning on using the services of Pin Oak or Globe Wireless. With either of these providers you must use the TNC that works with their services.

I also want to point out that the TNCs furnished by these suppliers are the only FCC type- accepted TNCs available for marine public service use. There will be more detail about this particular point later, but for the present I will cover the PTC IIe for use by cruising non-hams and amateurs who are only interested in obtaining e-mail. For those cruising amateurs who want to utilize additional modes such as CLOVER or GTOR, you may wish to purchase a KAM '98.

Some writers compare a TNC to the modem you use to connect to the Internet over a telephone line. In some ways this is true, but there are several significant differences. Your telephone modem only deals with one type of protocol transfer. The TNC has several modes of operation, plus several protocols that can be invoked. Non-amateurs may only be interested in PACTOR or CLOVER plus Fax (WEFAX) and SITOR (Telex). These three modes provide the cruiser with all the basic HF digital e-mail and data needed. Hams utilize these three modes, plus CW, TRRT (teletype), AMTOR, PSK31, GTOR, CLOVER, and PACKET.

Why do hams need all these additional modes? I think CW (code) is self-explanatory. There are hundreds of thousands of amateurs around the world who converse on CW. With the use of a TNC, CW transmissions can achieve 100 words per minute-faster than most people can type or use a code-sending key.

Although CW is a form of digital transmission, the first true digital transmission for hams was RTTY. The FCC allowed amateurs to use this mode in January 1953. By the summer of 1958, I had a mechanical teletype machine in the garage working other hams around the world.

Next came AMTOR (telex), SITOR in the mid-1960s, and finally in 1983, the FCC allowed hams to use PACKET (which had been used by European hams for five years.) Improvements in PACKET led to PACTOR, CLOVER, GTOR and PSK31. You can trace the evolution of the digital communications for the past 40 years.

So why don't hams settle on the latest technology and let the older modes fade away? For the same reason some cruisers don't have the money to invest in new equipment. There are hams in Nepal who can only afford a 20-year old TNC. The TNCs built today must be backward compatible with these older modes, if for nothing else than to allow a "handshake" to foreign amateurs. There are perhaps 100,000 older KAM TNCs scattered in all countries around the world. They will be with us for many years to come.

Then there is the question that always seems to come next when I give a lecture: "Why do we have to use ham equipment? Aren't there commercial TNCs that perform the same operation?"

The answer is yes but only in the case of Pin Oak and Globe Wireless TNCs, which have been modified to meet FCC type-accepted requirements for hardware and are offshoots from amateur equipment.

I am building a caution notice for non-amateurs that the SCS PTC IIe, KAM '98 and MFJ 1278B are very versatile pieces of gear in an amateur's hands, but they can lead you into big trouble when not programmed properly for use in commercial bands.

Take the KAM '98 for example. It has 231 internal command references, 24 of which are very important when used in the PACTOR mode. It is possible for you to turn on such commands as BEACON, CQ, or DIGIPEAT so that when you set the frequency for a commercial provider or your radio, the system sends a CQ or BEACONS on the commercial frequency. The commercial station and the FCC take a very dim view of this kind of operation. You can be fined up to $10,000 for improper transmissions on a public marine frequency, and be sure you read this next sentence carefully. A digital PACKET transmission carries your call sign. Your station is electronically fingerprinted with every transmitted PACKET you send. The Public Coast Station records the transmission and files a complaint with the FCC.

The type-accepted TNCs sold by Pin Oak and Globe Wireless have these commands locked out so you cannot, on purpose or accidentally, cause obnoxious transmissions on the marine frequencies. Beware that after you load a software program such as Airmail, do not go into Dumb Terminal Mode OR Command Mode and start making changes to the parameters (called PARMS in most manuals). It can lead to big trouble.

Now that you begin to understand several differences between a TNC and a standard telephone modem, let me just cover one more technical point. The most significant difference is the internal firmware called PAD, (Packet

Assembler Disassembler). This programmed chip gathers typed characters from the laptop and sends them in PACKET groups to the radio. It also translates incoming packets back into serial asynchronous data streams. It is programmable to change the packet size. It also makes the decision to key the Push-to-Talk of your transmitter, and then with a tiny programmable delay, sends the prepared packet to your radio's microphone input.

In the early days of amateur PACKET radio, the TNC was actually called a PAD. It is the PAD that obtains information from the various PARM files such as address, your call sign, control, size, and error checking and puts them in proper sequence with the data from the laptop to form a packet.

Let's look at which make or model of TNC will best serve your needs. As I indicated previously, there is no question that the SCS PTC IIe unit is the only practical unit for non-amateurs. This view is based on the availability of commercial shore stations which can obtain FCC license for PACTOR I and PACTOR II transmissions. Obviously, they can also obtain licenses for TELEX operation, but the speed of transmission for telex is far below the ability of PACTOR II transfer data rate.

On the other hand, if you have an older single-sideband radio and are not considering upgrading the radio, there is the alternative of purchasing lower cost TNCs that handle AMTOR (TELEX) and WeFax such as the MFJ 1278B at $280 or the KAM 98 with the same capability for $400, or you could consider the HAL DXP-28 at $396. You can also find used units on the Web or at your local Hamfest.

For a majority of the amateur cruisers, the SCS PTC IIe is probably the best approach for their e-mail needs. For amateur digital enthusiasts who are cruisers, PACTOR II is not the fastest technique for transferring e-mail at sea. Always remember that PACTOR II is a half duplex mode requiring overhead to transfer control back and forth, whereas other modes such as PACKET and CLOVER are full duplex and provide greater data thruput with less overhead.

George Hunt, an amateur who is currently cruising in the Bahamas, transfers his e-mail messages at 9600 baud by using PACKET via VHF to an AMSAT satellite. Other techniques and modes are available which provide faster transfers but require more in-depth knowledge of the digital parameters within the TNC.

Unfortunately for the non-amateur, the manuals supplied with the TNCs are filled with strange terms and very little background on how these parameters interact with each other. There is a very steep learning curve associated with handling these TNCs, and the only sure way to become knowledgeable is to practice with a local mentor.

The critical point of this hardware installation is the interconnection between the radio and the TNC. This cable must be shielded and as short as possible. I recommend placing a ground lug on the rear of the TNC in order to ground the entire TNC case to the same ground strap that grounds your radio. Be sure the cable shield is solidly grounded to the connector shell. And, finally, use a clip-on or open frame ferrite coil or choke to eliminate any RF that tries to enter the system in this very sensitive microphone circuit. On most SSB radios you will find a rear accessory jack. The pin connections are different for the different makes of radios, so be sure you solder these correctly. If your radio does not have an accessory plug in the rear, you will have to use the microphone jack on the front panel. MFJ builds a mike/TNC switch model 1272, which works with most radios and all TNCs. Contact the company at (601) 323-5869, or search their Web page at www.mfjenterprises.com to obtain the proper switch for your radio input.

The SCS PTC-IIe uses an eight-pin DIN connector to connect with the radio. There is a diagram in the instruction manual for connecting the proper leads to the corresponding pins on the radio connector.

For those cruisers who want to settle for the PACTOR I speeds available with the KAM 98, the Kantronics Company makes this cable connection very simple. They sell pre-wired cables to fit their KAM 98 to the ICOM, SGC, FURUNO and SEA SSB radios, at a cost of $25. Contact Kantronics through their Web page www.kantronics.com.

Regardless of which TNC you finally install, you will need a data cable between the TNC and the laptop. This data cable is supplied with the TNCs, but if you need a longer cable you can obtain one at any computer store. Be very sure you purchase a shielded data cable.

It is important to understand that when you are dealing with a transmitter that is emitting 100 watts of RF power in a digital signal, the ether is filled with RF energy everywhere within the confines of your boat. The fiberglass hull does not shield the area around your radio. It is quite common to find RF signal levels in the range of 5000 or more microvolts/meter inside a cabin that is 20 feet from the backstay! You must use good shielding and grounding techniques to eliminate RF feedback into the microphone input of your radio.

In my next article I will cover software and new e-mail stations that have just become available.

73s, de Jim, WB4GQK