Portable WSJT


Portable WSJT: How a New Mexico VHF operator makes meteor scatter contacts from his parked car

Based on manuscript submitted to CQ-VHF in January, 2003

The VHF contest scene in the southwestern United States is dramatically different than in the east. The population density out here is low and contest activity is minimal at best. I learned this first hand as a participant in three VHF contests in 2002, operating all three as a rover in New Mexico. I have driven many hours from my home in Albuquerque to remote corners of the state in a futile search for VHF DX. What usually happens is I'll work a couple of stations back in Albuquerque (DM65) in the center of the state and little else. Sometimes I'm not so lucky. More than once, I've been in a grid for several hours calling CQ and worked nobody! That's right, nada, zilch, zip. You can't even count the grid as a multiplier if you don't make at least one QSO. This is discouraging, to say the least.

In principle, the Rocky Mountains offer some of the best locations in the continental United States for VHF DX. I have accumulated a list of spectacular vistas in rare grids at elevations well in excess of 7000 feet. Alas, like the proverbial tree falling in the woods, if there are no stations out there to copy my signals, am I even making noise?

I kept working on my setup: more power and better antennas. Bobby Smith (N5XZM), Albuquerque's big gun on VHF+, provided much of the ingenuity and even some of the equipment to improve my rover. But what is really needed in the southwest is increased activity and more grid multipliers to help our scores. Sure there is 6-meter sporadic-E, but that's primarily in the summertime and even then it's very hit-or-miss. I was looking for a way to expand my DX horizon without breaking the bank. For me, WSJT meteor scatter was just what the doctor ordered.

This is not the definitive article on portable WSJT nor is it the first time it's been done. On December 27, 2001, Andy Flowers (K0SM) made what is believed to be the first portable WSJT QSO in North America from grid DN90. Prior to the availability of WSJT, KD5BUR and later the W8WN-WD8KVD team took their high speed cw setups on the road for meteor scatter contacts. What I'll relate here is how I managed to make portable WSJT work on the cheap with relatively simple upgrades and additions to my existing 2-meter rover setup.

What does it take?

With less than 50 QSO's in a typical contest weekend, I've never had the need for a portable computer to do the logging. I have plenty of time -- way too much time -- to record contact information by hand on a piece of paper. To operate WSJT in the rover, however, I was going to need a laptop.

The minimum computer requirements for WSJT 3.0 are a 75 MHz Pentium class processor, 24 Mb RAM, and a Windows 95 or newer operating system (a LINUX version of WSJT is in development). While used laptops can be found for next to nothing, these tend to be of the 386 and 486 vintage, which are simply too slow to handle the program decode algorithms. After some investigating, I narrowed my search to IBM ThinkPads for a combination of reasons including their widespread availability on the second-hand market, access to drivers and documentation on IBM's website, and the ThinkPad's reputation for ruggedness and immunity to RFI.

I elected to play it safe and go for a laptop with more than the bare minimum specs for WSJT. I studied the online auction market for about a week before jumping in. There are lots of strategies in the online auction game, but one thing I like to do before bidding is contact the seller by email. There's always some question you can ask that's not covered in the item description. If they don't communicate with you in a timely fashion at that point, well, what's the likelihood they will if something goes wrong after the auction, such as damaged goods or a missing shipment?

I wound up with a ThinkPad 760 XL featuring a 166 MHz Pentium processor, 64 Mb RAM, 2.1 Gb hard drive, 20X CD ROM drive, swappable floppy drive, PCMCIA 56k modem, and AC adaptor cable. It was shipped to my door with Windows 95 for exactly $200. It cost more than 10 times that amount brand new in 1997, but that's the usual story with less-than-new PC's. Here's a couple more suggestions on the computer: First, make sure you have a modem. You'll want to have flexibility to download programs and drivers without the hassle of moving data through the CD or floppy drives. My laptop came with a removable modem that plugs into one of two PCMCIA slots on the side of the case. A modem can be obtained for very little cost on eBay. Second, unless you're a laptop whiz, you'll need some support documentation to tell you where all the connectors and components are located and how to access them. My ThinkPad has a user's manual resident on the hard drive and it was immensely helpful for getting things up and running.

It's rare to find a used laptop with a working battery, but with an operating time of three hours at best between charges, you'll want to dispense with the onboard battery anyway. The major drawback of laptop batteries is that they are prohibitively expensive to replace. I decided to power the laptop from the same deep-cycle battery that runs the radios. Having a common battery for the computer and radio can be a potential path for noise and interference, but I have not had any problems. To make this work, I had to get a 12 volt adaptor cable for the PC. Not all adaptor cables are the same, so make sure you have the correct one for your model laptop. I acquired a used one on eBay designed for mobile automotive use with a cigarette lighter plug. Instead of snipping off the plug and wiring direct to the battery terminals, I rigged up a female cigarette socket at the battery to allow for quick disconnect. This also gives me the option of using the car's cigarette lighter to power the laptop, although I can't imagine ever doing that. One of my unbreakable rules is that the car battery is strictly off limits to any and all rover-related equipment. In New Mexico, some of the best operating spots are more than 50 miles from the nearest traffic light. These are not places where you want to get stuck!

If your used laptop has a lot of miles on it, you may have to deal with the small lithium CMOS battery that runs the internal clock and maintains the BIOS parameters. You can determine its state of health by watching how well it keeps time over the course of a week. If it's really slogging, it would probably be wise to replace it.

The radio-PC interface is pretty standard stuff and there are lots of different ways to do it. I bought a Rascal kit from BUX Comm. The Rascals are inexpensive, have all the parts you could possibly need for your particular application, assemble quickly, make prudent use of an opto-isolator between the computer serial port and the PTT, as well as a pair of isolation audio transformers for the sound card. My 2-meter transceiver is a Kenwood TM-255a that allows me to do the radio interfacing through a data port on the back panel. I also wired an auxiliary line from the Rascal to provide hard keying of the 2-meter brick amplifier.

An important consideration in WSJT communications is time synchronization between stations. The program has to know when to transmit and when to listen. This is particularly important in the ultra-weak signal JT44 mode of WSJT, where synchronization to better than 1 second is desired. Fixed location operators often accomplish this by automatically setting their PC clocks at periodic intervals using various NBS time references on the Internet. This, of course, is not an option when operating from the remote corner of an uninhabited grid, many miles from the nearest Internet connection.

The clock problem is solved with a handheld GPS unit that no serious VHF rover will be without. I use the inexpensive Garmin Etrex. You can keep an eye on the GPS time and PC clock while operating WSJT, but this is a big nuisance. A better idea is to automate the time-synch process and then just forget about it. The GPS has a serial port interface that permits communication with a PC. One must acquire a specialty cable to make the GPS-PC connection, but there are several aftermarket cable manufacturers advertising regularly on eBay. I bought a brand new interface cable there for about 1/3 the cost of a Garmin unit. For a little bit more, you can get a deluxe cable that also provides power to the GPS from the car lighter socket. I decided against this complication, primarily to eliminate the growing cable clutter. The GPS will run continuously for almost 24 hours on two AA alkalines.

You'll need software to keep the laptop dialed into the atomic clock on the GPS network. I use shareware called NMEATime that can be downloaded for a free 30-day evaluation from visualgps.net. The program costs $20 to register, entitles you to a lifetime of free upgrades, and may be installed on as many machines as you own. It runs quietly in the background and can be configured to synch your computer via various Internet clocks or a GPS. For portable WSJT, I have NMEATime reset my PC clock every 2 minutes.

The GPS also displays what grid I'm in and I've loaded its memory with the six-digit grid coordinates of dozens of WSJT meteor scatter operators. It quickly tells me how far away they are and where to point the antenna; this is very helpful when I'm working through a busy sked.

You'll notice a critical component of this setup is the serial or COM (communication) port of the PC. In the arrangement I've described here, a dedicated COM port is required for both the PC-radio interface and the GPS interface. That means two PC serial ports are needed. Like all Pentium laptops made in the mid- to late 1990's, my ThinkPad has just one. This can be solved in some setups by keying transmit with the VOX instead of the PTT, but my transceiver doesn't provide this option. Instead, I added a second serial port to the laptop with a PCMCIA card serial adapter made by Eiger Media. I obtained this as new old-stock on eBay for $50. Make sure any hardware addition comes with a driver for your operating system or it will be essentially worthless to you.

Click here for Part 2.


WB2FKO demonstrates portable WSJT on 144 MHz at an Albuquerque, NM tailgate; January 2003.