I built KX1 #1740 last month (March 2007) but waited until I had accumulated some experience to discuss it. With 100 QSOs in the log, I think I'm ready to let the cat loose. My comments will be most useful to people thinking about buying one.
I live in a condo so I can only put up antennas at night, but I live near a nature preserve with lots of trees. I wanted the portability of the KX1, as opposed to features found in the K1, which was too big for my purposes
I got 'em all, 80-30, paddle, ATU
Went together pretty easily. I merged the 80-30 mods into the original construction with no difficulties. I was shorted one RFC (pays to have a junkbox) and one RFC was supplied in mini rather than micro size but I made it fit. The instructions were very good. For the 80-30 mod part, having the instructions point to the correct area of the board, as is done in the main assembly manual, would have been helpful. But the radio worked first time and that's what counts. I spent a long time building it because my eyesight is getting poor and I didn't want the heartache of making a mistake. There is some close-quarter work involved in installing the 80-30 upgrade. Be prepared to take longer than you expected.
Before I got my kit I read every KX1 post to the Elecraft reflector for the previous year, and downloaded and studied the manuals. I strongly recommend anyone planning to build an Elecraft kit do the same. I knew in advance where I might run into trouble (such as a wire that can go astray on the little board that comes with the 80-30 upgrade), and gained the confidence to build the 80-30 mod right in, testing on 40 and 20 M first, then adding the 80-30 main board and testing on 80 and 30 M. I built the ATU first, so that when the radio was finished I didn't have to wait to put it on the air. I work slowly but that doesn't mean I'm patient. :)
Performance - General
I use a 1.4 AH gel cell in the field, and get >4 W out on all bands. The receiver has a low enough noise floor that I can hear band noise on all bands, though I sometimes wish for a little more audio gain to pull out the weaker signals. I use and recommend Sony MDR-828 earbuds, which are much more sensitive than some cheaper ones I tried. And they're inexpensive, typically less than $7.00 on eBay.
Performance - Specifics
Most of my contacts have been made on 20 and 40 M. Lately, for field use I've only been on 20 M, using a ground plane hanging from a branch, so the base is about 8 feet (2.5 m) off the ground, three sloping radials, fed through a coiled-up RG-58 balun. The SWR is 1.1 in the middle of the band, don't need the tuner. This antenna outperforms the inverted vee I tried first.
I've worked 30 countries on 20 M with this setup in a month, including such juicy stuff as ST2R, EL2DX (who answered my CQ on 14060!), 3XD2Z and 6V7F. I worked 6V7F in a pileup that required using the RIT to work split, which is hard work, and it took me about 15 minutes to get through. The west coast of Africa is a chip shot from my South Florida location, but I'm not complaining. Oh, and K2HYD/HR9, whom I found calling CQ on 14060. He was running a KX1, too!
I've also used the rig at home on 40 M, with an inverted vee. On 40 at night, strong signals blow past the filter and things get a little more difficult, but that's not the environment for which the radio was designed. I have worked TA3D, 3DA0PM and SU9FL on 40 with the rig, and 3DA is farther from here than Japan. I will work a JA with it on 40 eventually, it's a matter of staying up late enough. I've also used the KX1 from home in a couple of sprints.
Today I tried a random length of wire on 30 M from the park, to get an idea of what might work on an upcoming trip to England, Holland and France. I thought the higher angle radiation might get me more US QSOs but domestic activity on 30 seems light. I did work MI0SRR and G0RTN just before sunset, so even funky antennas will bring in DX sometimes. Too bad I have to be out of the park by sunset, and it's a half-hour walk back to my car.
The random length of wire was a little long for 30 M. Even though I added bypass capacitors to the ATU as recommended by Wayne, it went haywire a couple of times. I will make sure to keep the antenna shorter in future, or use a better counterpoise. But this was intended to be a worst-case kind of setup, something like I might encounter in a city park on the trip.
I've used all the features on the rig, and there are a bunch. Once you get a little practice you can quickly change keyer speed, jump in and out of RIT, or do any other necessary operation. I haven't done much SWLing, but I have listened to WWV a few times to get a feel for propagation. I have yet to make a QSO on 80 M, been too busy on the other bands.
I plan to swap in a set of rechargeable Lithium-Ion batteries for the trip, but the 1.4 AH gel cell has worked very well for an afternoon's operating. The battery, radio, headphones, paddle, clock and power cord fit in a cheap pencil case from Walgreen's. My balun is wrapped on the cover for a stack of CD-RWs, and other antenna bits and pieces go inside the cover, which sits on top of the pencil case in my knapsack. Add a folding stool and a bottle of water and I'm ready to work some DX.
I wasn't sure how I'd like the KPD1 paddles, but they are actually very good. I use a Bencher paddle at home and have no trouble going back and forth. I rest the rig on my knee, and having an integral paddle really makes it convenient to use. That was a great idea!
The internal tuner can be handy when you have to use a makeshift antenna. Due to its small size, though, its matching range is much smaller than most external tuners, automatic or manual. While it will load a 20-30 foot (6-9 m) piece of wire on 40, 30 (if you have that option) and 20 meters, you may be dissipating a fair amount of power in the tuner, and marginal antennas never perform very well. See this page for information on a fishing-pole supported random-length antenna I tried.
I'd like better filter skirts for when I can use a better antenna, but understand you can only squeeze so much into the little box. A bit more audio would be nice but my hearing isn't as good as it used to be -- too many Jethro Tull concerts in my youth. I'm going to wish for the high bands pretty soon, but understand there's no way to get there with the existing DDS. I guess I'll have to go back to the bench and build something -- what a concept. Oh, one last thing. I never got a chance to call N8S, the Swains Island DXpedition, because whenever I heard them on 20 they were working a 7-kHz split, and the KX1 RIT only covers plus or minus 5 kHz. But that's the only pileup in which I faced that problem. A dual-range RIT would be neat to have, though.
Do the 80-30 mod simultaneously only if you can stay active on the kit, so you can keep track of what you're doing. Doing it separately, later, is not a big deal, and might save you some grief.
Use Sony MDR or other sensitive earbuds. I use Sony MDR-E828LP earbuds, specified at 108-db/mW sensitivity. Some "better" earbuds offer unneeded wider frequency response, but lower sensitivity; typically 100-dB/mW. The KX1 audio amplifier does not produce nearly as much audio as your home-station transceiver, and you will definitely benefit by using more-sensitive headphones. If you prefer headphones that fit on top of your ears, you might try the Sony MDR-NC6. It's a noise-cancelling headphone (uses a single AAA cell) with 106-dB/mW sensitivity. The advertised 10-dB of external noise reduction might offset the 2-dB-lower sensitivity.
The suggested Pomona BNC-to-Banana-Jack adaptor is okay, but having the antenna tied directly to the radio is not always convenient. Resonant antennas are better, if possible. I have a BNC-to-alligator-clip cable that I prefer to the Pomona adaptor for random wires, because it provides some slack and moves the connection point away from my hand. It's more to carry, but worth considering if you have space in your pack.
I bought an MFJ-107B LCD 24-hour clock. I slipped the clock part out of the aluminum stand and put mating pieces of hook-and-loop fastener on the bottom of the clock and the top of the KX1, on the right side. So now I don't have to do mental gymnastics to calculate UTC (my mind is going, Dave, I can feel it), and I can still hold the radio in one hand. I'm right handed. If you're left handed, mount the clock on the other side.
Using Internal Batteries
I did install 3.7-V Li-Ion batteries, by rewiring the battery boxes so they were in parallel. The cells work great; the problem is, the KX1's POWER and LED switches can be turned on inadvertently while carrying the radio in a pack. I killed the batteries in Europe last year, after only one day on the air. If you use internal cells or batteries, my advice is to remove them when transporting the radio.
The KX1 is neither cheap nor inexpensive. The quality is very good, but you pay for what you get. I had to think about it for 3 years before I finally pushed the button. Having the park to operate from made the difference. This is not the optimum radio for a home station, but it wasn't supposed to be. For a portable CW radio, however, I don't think you can do any better. The receiver will let you hear other QRPers down in the noise, and I get many compliments on the quality of the transmitted signal. For the types of antennas you're likely to use afield the receiver is more than adequate. I've been able to work a lot more DX on 20 during the last month than I ever expected. Thanks to having the KX1 I am able to spend many more hours on the air every week, without demolishing my sleep schedule or stumbling around in the dark hauling up antennas. And I'm looking forward to operating from Europe. I wouldn't consider taking a much larger radio on the trip, but it will fit in my attache case, so I can demonstrate it to the nice lady at the airport.
Someone on QRP-L just asked about classic QRP radios. I don't know if the KX1 has been around long enough to be considered a classic, but it will be. It's an amazing piece of technology, designed in the USA, no less. If your budget is a little tight, consider the basic radio and the paddles. You'll be glad you got them. You'll have to make resonant antennas, but you only need a single support for a ground plane or inverted vee. The 40 and 20 M bands will keep you busy for a long time, and you can add 30, or 80 and 30, plus the ATU down the line. My only question is, if there are more than 1740 KX1s out there, why have I worked only one other KX1? Get 'em on the air, folks! I still need 17 states.