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Elecraft KX1 Trail Radio


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The Radio

As with the disclaimer on the K2 page, I have no connection with Elecraft except as their customer. I really like the two Elecraft radios I have, and the purpose of these pages is just to share some of my experiences with them. My KX1 came after I had built the K2. I bought it at Pacificon 2004, the ARRL Pacific Division Convention, specifically to take with me when we cruise through the Caribbean and the Panama Canal in late April 2005. It is #897. I had decided that the K2 was just a tad too big and a bit power hungry (I didn't want to take a couple of pound gel cell with me), and I was really intrigued by the KX1. We will have a cabin with a "balcony" (which really resembles a "shelf") and I figured I could find a way to use the boat as the ground plane for some sort of collapsible antenna.

The KX1 is 5.5" x 3" x 1.5" without the attached paddle. The basic model covers 20m and 40m, and requires something in the general vicinity of 50 ohms at the antenna jack. I got the 30m option because it is a lower power CW band, and gave me a nice spread of available spectrum. I also purchased the Auto Antenna Tuner since I was certain I'd have a hard time getting anything close to 50 ohms from most antennas. I also purchased the paddle option so I wouldn't need to take the relatively heavy Bencher paddle.

This radio is a marvel of cool engineering. The controls are on the flat face, so the radio sits firmly on the table. The paddle is attached by a captive screw, and will operate either way. I'm left handed, but when I learned Morse code in 1953, I learned to send right handed. This works well since it leaves my left hand free for writing. As with the K2 (and K1), most of the push buttons have two modes: "TAP" and "HOLD," each giving a different function

The Paddle

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The paddle is really unique, and makes "pedestrian-portable" possible. It does not really move. Instead, there are two circuit boards protruding from a machined base. Near the end of each, you solder down a silver wire. There are two formed leaf springs on the outside surfaces of the circuit boards, and each board-spring combination is covered with a slip-on rubber boot. Tapping the boot near the end compresses the spring, it touches the silver wire, and you send! It's a full iambic keyer, although I have never mastered sending CW by squeezing both sides of the paddle. I had been told that the KX1paddle was a bit of an acquired taste, however getting used to it took all of 60 seconds of sending out of a book. It's also a memory keyer with two slots for messages.

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In the photo, you can see the leaf spring and the silver contact wire. The rubber boots compress the spring almost to the point of contact and when you send, there is no real sense of anything moving. There is some amount of "feel" adjustment available by sliding the boots in or out a bit on the boards.

A small stero plug screws into the machined base, and plugs directly into the KX1 key jack (you can also plug a standard paddle in if you want). As with all Elecraft stuff, there are menu items you can set to invert the dash and dot sides, and to use a straight key. This turned out to be a good deal for me because I crossed the wires when building up the paddle assembly, so I just run in the inverted mode.

The Guts

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The basic radio (20m/40m) is contained on the main circuit board visible in the photo. The 30m option (not visible in the photo) is a small rectangular board that mounts on the bottom side of the main board. The Antenna Tuner Unit (ATU) is the narrow rectangular board at the top of the case. As with the K2, there are several sealed, subminiature relays on the main board. These relays are also used to switch in the active elements in the tuner. It isn't obvious from the photo, but after you finish the ATU, it mounts upside down, and its relays exactly nest into spaces between the relays on the main board. It is a really nice bit of electromechanical engineering!

The ATU has a controller and memory. When you use a new antenna, you use the ATU menu option to bypass the tuner (CAL mode), and then put it back into TUN mode. Then, when you put the radio into tune, the ATU relays clatter for a second or so, the antenna is matched, and the display tells you the forward power and the approximate SWR.

In the upper right corner, you can see part of the bottom cover which has holders for 6 AA sized cells. I took the picture when I had rechargeables in it, but it runs great off of dry cells as well. You can see the 12V power jack just under the wires leading to the batteries.

Building the KX1

The KX1 is a lot easier to build than the K2, primarily because it is not nearly as complex as the K2. All the hints and tips regarding inventoring and sorting the parts, soldering, triple checking each part and it's proper location on the board that I mentioned on the K2 page apply to the KX1 as well. Parts are mounted on both sides of the main boards, however the manual is very clear when to turn the board over.

I built mine in about 20 hours, but probably could have done it faster (not a good idea, however! This is another place where slow and deliberate is best). Every part was present, and the alignment went exactly as it should. The receiver is outstanding, and very quiet. When I first hooked up an antenna, I thought I might have a problem because the noise was really low, even with the AF gain turned all the way up. Then I tuned across a signal, and it just popped into the headphones, way too loud. It's a lot like the K2 in that regard ... signals just appear as you tune across them. The first QSO was with a member of FISTS, and he convinced me to join.

Operation

There are three buttons under the display which control most of the functions. Tapping the MENU button brings the menu into the display, and the knob scrolls through it. When you find the entry you want to change, you hold the MENU button, and now the tuning knob scrolls through the possible settings for that parameter. The display has only three characters and a decimal point, and when you first turn on the radio, the display first tells you the band it's on (e.g. "14"), then it switches and tells you the KHz part of the current frequency (e.g. "054"), and finally settles down to whatever tuning rate you've selected. You can also obtain this display sequence by tapping the BAND button once if you forget where in the band you are operating. Two quick taps on BAND cycles the operating band through each band.

The tuning rate is selected by either tapping or holding down the tuning knob. If you hold it down, you will tune in 1 KHz steps and the display will read "XXX". Tapping it toggles between 100 Hz and 10 Hz steps. So, if you are tuning in 10 Hz steps and your frequency is 14047.23 KHz, the display will read "7.23". Tapping the BAND button once will give you "14", then "047", and finally "7.23". It takes longer to describe it than it does to learn how to use it.

The KX1 has a continuously variable bandwidth crystal filter which you can vary from about 2.5 KHz down to about 350 Hz or so. It has remarkably steep skirts, and a very high attenuation outside the passband, so an interfering signal just disappears as you narrow the filter. There is also a high intensity LED on the left front of the radio. Turn it on and it will light your mini-log when you're operating from your sleeping bag.

One interesting feature is the ability to use the buttons as a paddle. I've only tried this once, and it was a little difficult to master, but I am probably going to give it a try in a Spartan Sprint. Probably the most interesting feature is the CW feedback capability. Turn it on, choose a speed between 10 and 40 WPM, and the KX1 will confirm all menu and control actions, and will tell you your frequency each time it is changed.

Power Conservation

The KX1 is intended for portable operation, so there are some power conservation features. Through the menu, the LED display can be set to automatically switch off after a selectable period of no activity. The brightness is also adjustable.

Spartan Sprint

The Spartan Sprints are a cool little QRP contest sponsored by the Adventure Radio Society. They occur on the first Monday of every month at 1800 - 2000 PST (Tuesday, 0200Z-0400Z when we're on Standard Time and 0100Z-0300Z on DST) Power limit is 5 watts, and the exchange is RST, state or province, and power output (e.g. "5W"). They've established 2 classes for entry: TUBBY where you use a normal radio at 5W or less and report the total number of QSO's, and SKINNY where you report the number of QSO's, and the weight of your radio in pounds. "Station weight" is the weight of everything between you and the antenna connector, and radios have to be enclosed with no innards showing. Skinny class scores are reported in points per pound.

The KX1 is a good radio for this contest, with one exception -- it doesn't cover 80m. Consequently, for me, the Spartan Sprint lasts about 1.5 hours (20m and 40m). In the last half hour, everyone has moved to 80m, so I generally go back to 20m and maybe squeeze out one or two more Q's from latecomers. With the paddle, 6 AA dry cells, and headphones, mine weighed in in November 2004 at 1.125 lbs. I made 21 QSO's in 1.5 hours for 18.7 points per pound. For December, I'm going to try a 9V alkaline battery. If I can get it to last for the 2 hours, it will cut my rig weight down to about 0.77 lbs. I'll update this with the outcome. Another possibility is to remove the paddle and use the buttons to send, but I'll have to get a lot better at sending that way first.

Power Update - 05 Apr 2005

OK, the 9V alkaline battery isn't such a good deal after all. Even though the Energizer website indicates they have a total capacity of around 800 mAh, they are designed for low current drains over long periods (e.g. smoke detectors), and do not support the relatively high drain while transmitting with the KX1. There's a much better solution, however.

The RC model hobby uses Lithium-polymer batteries which will support a continuous drain of 5C (where C is the capacity), and intermittant drains of up to 10C. These batteries come in very thin flat packages, and have a terminal voltage of 3.7V. Best of all, they weigh almost zero! I found an assembled pack of three at our local RC shop with a capacity of 850 mAh, a nominal terminal voltage of 11.7V (really more like 12.1 when just charged), and weighing about 1.8 oz. It's about 2" x 1" x 1/2", and all I had to do was solder a power connector onto the wires. You do need to have a charger designed for Li batteries, but my Maha C777+II works just fine. The battery will support a continuous drain of over 4A, and the terminal voltage stays around 11.6 until it is just about discharged. It easily gets me through a Spartan Sprint with power to spare.

QRP Operation

I've been pleasantly suprised at how much fun QRP operation is, and the KX1 is a really cool little rig. It is straightforward to build and use, has outstanding engineering and design, and enough features to make it fun to operate. I find that I leave the dial resolution at one digit after the decimal point (100 Hz). At this resolution, the tuning is clearly in steps, however you can tell at a glance where in the band you are currently tuning.

Panama Canal Update

Well ... this may not work out. The ARRL web site provides information on foreign operation for US Amateurs, and I decided I would obtain a reciprocal permit for Panama, and confine all other operations to international waters. This required that I obtain permission from the ship's captain, and a permit from the country in which the ship is registered (if it isn't the US).

So, being the "real" conservative that I am, and one who follows rules, I applied for the "America's Permit" for Panama, and wrote a letter to the cruise line (Princess) describing my intentions, the specifications of the radio, and the permission and info that I needed. I got a phone call back fairly quickly and was told that they did not allow radio transmitting from their ships as it could "interfere with the ship's operation." I'm currently deciding how I might proceed with some form of appeal, which might include taking the radio and asking the Captain when we're aboard. I think the answer I got was a corporate policy thing. Stay tuned.

05 May 2005: We're back and the Canal is awsome, especially to an engineer! I took the KX1, asked at the purser's desk, they sent the 1st Officer to see the radio, and he said "go for it, but not in common areas on deck, and please don't remove any paint." Full story of the trip at K6DGW/MM.

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