A Case for the KX1
Bruce Grubbs, N7CEE
Special to the ARS Sojourner
This is both an informal review of the Elecraft KX1 and
a description of a homebrew, ultralight case for the rig. I've now carried
the rig on several day hikes, experimented with antennas, and operated
in the November 2003 Spartan Sprint. I'm not going to describe the features
completely- elecraft.com does that well, and you can also download the
manuals from their website.
The KX1 cabinet is 3.0 x 5.3 x1.2 inches and the overall dimensions are 3.0 x 5.8 x 1.4 inches. All the controls are on the top, rather than the front of the radio. As designers and users of trail friendly radios have known for years, top mounted controls have many practical advantages operating in the field without a table and chair. You can operate with the rig on your lap while leaning against a tree or sitting on a rock, and you can easily operate from your sleeping bag in a tent. There's even a built in bright white LED for logging.
My postal scale claims a weight of 15 ounces for the KX1, all three accessories, a pair of earbuds, and internal lithium batteries. That weight includes everything but the antenna. Add 3 ounces for a wire antenna and you have a surprisingly capable backpacking QRP station for just over a pound.
The basic KX1 transmits CW on 40 and 20 meters, and receives from 5.0 to 9.5 MHz and from 12.0 to 16.5 MHz. Since the rig has LSB and USB receive modes as well as CW, the extended coverage lets you receive the major broadcast bands as well as WWV. Adding the 30 meter module not only gives you 10.1 to 10.5 MHz CW transmit but also adds 8.0 to 12.5 MHz receive and enhances sensitivity in the 5.9 to 6.4 MHz segment. Since I've been considering a small SWL receiver for hiking trips, the extended receive coverage of the KX1 was an strong selling feature.
Receive current drain is specified as 35 mA with accessories. My unit uses a bit more current but is still a real battery miser. The transmitter puts out from 1.5 to 4 watts depending on battery voltage. A three digit LED display is used to show operating frequency in the same manner as the LCD on the K1, and also shows menu options and keyer speed, battery voltage, etc. It can be set to timeout 5 to 60 seconds after a button press or movement of the tuning knob, or can be left on indefinitely. The brightness can also be changed. I forgot to set the LED to stay on during the Spartan Sprint and didn't find the timeout to be a problem.
You can also use the menu to turn on CW feedback for frequency, menus, and all controls. This is probably the first commercial radio that is usable by sight impaired operators without modification. That feature will be useful in camp on cold weather trips when I want to be completely in my sleeping back. The KX1 could be operated by exposing just one hand to the cold air while the rest of me stays snuggled in my toast down bag.
Everything arrived on schedule the third week of October, just before a weekend that I happened to have free. Early in the parts inventory, it appeared I was missing a capacitor, but the parts list turned out to have a typo, calling for two parts where only one was required. I completed the inventory of all four kits and was delighted to find there was nothing missing.
I built the KX1 first, as per Elecraft's advice. As with my K2, K1, and accessories, the instructions are clear and precise, and the KX1 went together like a Swiss watch. One word of advice- when the manual says you need flush-cut diagonal cutters, you do. Leads must be cut off very close to the solder pads in order to squeeze the circuit board (3 boards with accessories) into the case.
I really like Elecraft's practice of building the radio in stages. Not only can the builder isolate problems as you go, but you also have the gratification of having working circuits early in the assembly. There are four stages with the KX1. First you build and test the control circuits, then the receiver, and next the transmitter. The final step consists of stuffing everything into the case.
The only problem during assembly, which turned out not to be a problem, was the AC voltage checks per the last step on page 28 of the manual. I got a slightly high reading using a Fluke DMM on U1 pin 1, but the control circuits appeared to work normally, so I ignored it. It turns out these low voltage AC readings can vary, depending on the meter.
After finishing the basic KX1, which took about 8 hours spread over Friday evening and Saturday morning, I set up an A/B receiving test with my K1 using a full size 40 meter vertical. Much to my delight, the KX1 receiver held its own with the K1 both on 40 and 20 meters. The K2, using a slightly better antenna, did quite a bit better than the KX1 and the K1, which is not surprising.
After playing with the basic KX1 for a while, I assembled the 30 meter module, the paddle kit, and the ATU. All worked flawlessly. In this photo, you can see the main board and the ATU board above it. The 30 meter module attaches to the top of the main board and is not visible.
In this shot of the KX1 setup on a hike, you can see how the KXPD1 paddle attaches to the front of the rig and uses the radio as a base, eliminating wires and letting you operate on your lap or next to you. At the upper right, I've attached an end fed wire antenna with a BNC to binding post adapter. The counterpoise wire is attached to the bottom of the rig under one of the two knurled screws that secure the case. Earbuds plug in at the lower right side. The upper left side has a standard Elecraft-sized coaxial power jack for external power. In this case I'm using a 12 volt homebrew NiMH pack, visible above the transceiver.
Power options for the KX1 are very flexible. When using the internal 6 AA cell batteries, Elecraft recommends Energizer 1.5 volt AA lithium cells. Six of these cells weigh just 3 ounces and produce a nominal 9.0 volts. Elecraft claims they'll allow 20 hours or more of casual operating. I have yet to use up my first set of lithiums, so I don't have field results to report. You can also use alkaline cells, at 5 ounces per set and less battery life. NiMH cells aren't recommended in the internal battery holder due to their low voltage (7.2 volts) , and cannot be charged in the radio. Now comes the flexibility. I have a 10 AA cell NiMH pack, seen in the field photo (KX1field.jpg) that I built for use with the K1 and a 1.4 watt solar panel. If you plug external power into the KX1 with internal batteries, it uses whichever source has higher voltage. So, when I'm operating where weight is not critical, I can use the NiMH pack without having to remove the internal batteries. At home, I can plug into my station power supply (solar charged 12 volts SLA batteries). Since two sets of lithium batteries are much lighter than the NiMH pack plus solar panel, I'll probably end up using lithiums on long backpack trips.
A low battery warning flashes on the LED display when the voltage falls below a level preset in the menu. For example, you can set the threshold to 10.5 volts for an external 12 volts SLA or NiMH battery, or 7.5 volts for internal 1.5 volt AA cells. It's very easy to change the batteries by removing two thumbscrews, which are visible in this photo.
Several years ago I settled on end fed wire antennas for all my backpacking trips. As I've written before, I find that dipoles and more complex antennas are too much hassle at the end of a long day of hiking. An end fed antenna has the huge advantage of requiring only one support. Since band conditions were very bad on my first field trials of the KX1, I focused on testing antennas, knowing that the tiny size of the KXAT1 limits its tuning range compared to the K1 ATU.
First, I tried a short wire antenna based on Elecraft's recommendations in the ATU manual. This antenna used a 28 foot radiator and two 16 foot radials made from #26 stranded Teflon coated wire. SWR was 2.1 or better on all three bands. This was acceptable, but I tried a 42 foot wire with one 16 foot radial. This tuned to 1.1 on all bands. At 3 ounces, this will probably be my standard backpacking antenna for the KX1.
I have an 82 foot wire with 33 foot radial that I've been using with the K1. With the KX1 ATU, the antenna tuned to 1.0 on all bands. I'll probably carry the longer wire on shorter hikes when there's plenty of tall trees, and especially if I plan to work a contest during the trip.
I also tested a vertical based on a 14 foot panfish pole. I originally built this antenna for a 10 day trip which would mostly be above timberline in Wyoming's Wind River Range. The antenna has a 14 foot vertical radiator with an additional 19 foot wire clipped to the top and strung out horizontally, creating an inverted L. There are eight 7 foot radials, and it's fed with about 15 feet of 300 ohm TV twinlead. With this self supporting antenna, SWR was 2.5 or better on all bands. I'll continue to use the panfish vertical on trips in areas with no trees at all- barren desert and above timberline.
Of my two home antennas, the KX1 ATU tuned the full size 40 meter vertical to 1.3 or better all bands. This antenna is fed through transmit twinlead and a 4:1 balun. The only antenna I tested that the KX1 ATU couldn't handle was my home station's 170 foot horizontal loop, which is fed through TX twinlead and a 1:1 balun. I used a ZM-2 tuner to match the loop to the KX1 with the internal ATU disabled. (Both the K1 and K2 ATU's handle the loop easily.)
On November 3rd I finally I got to use the KX1 transmitter for something other than antenna testing. Although band conditions were very poor during the Spartan Sprint, I managed to work 10 stations during the 2 hour contest, all but one on 40 meters. Signals were right down in the noise but I did work several east coast stations. I compared signals on the K2 occasionally, and I really don't think I would have done much better with the big rig. The variable crystal filter on the KX1 handled the QRM nicely, and the control layout on the little rig worked well even on my desk sitting in a chair. Elecraft uses the their familiar tap and hold methods to squeeze multiple functions out of a limited number of controls, and I found the design to work well during the sprint. I had no trouble changing keyer speeds when I needed to, and I really like how a tap of the main tuning knob is quickly changes tuning rates between 10 and 100 Hz. There's also a quick 1.0 kHz rate that is useful for moving quickly across a band. This rate becomes 5.0 kHz in LSB or USB mode, which makes tuning to a broadcast station or WWV pretty painless.
There are three frequency memories for each band, for a total of nine memories. These are not only useful for the usual in-band frequencies, but also to store well out of band broadcast stations or WWV. One of the 9 memories is high priority and can be recalled by pressing BAND and the tuning knob simultaneously, without having to scroll through the menus. I'm currently using memory 1 to store the QRP frequency on each band, memory 2 to save the nearest time station (WWV or CHU), and reserving memory 3 for temporary storage. The high priority memory is set to 7040 kHz. Receiver incremental tuning (RIT) is available by tapping the RIT switch to lock the transmit frequency. The tuning knob then varies the receive frequency plus or minus 5 kHz. Tap the RIT button again to turn off RIT while preserving the offset. Hold the RIT button and the RIT offset is cleared.
I set up the internal keyer memories to send CQ and the exchange before the sprint, but didn't end up using them because of the slow pace of the contest. Sending a message memory is done by setting the menu to PLY then pressing 1 or 2. The menu stays on the last selection as long as the radio is powered, so in practice you press MENU then 1 or 2 to send a memory. Memories can auto repeat, and the delay is settable via the menus.
I also like the paddle action. It has a light but firm touch. I'm right handed, and I found that it was easy to accidentally key the the paddle with my palm if I tried to operate the controls with my right hand. Instead, I used my left hand to tune and operate the controls. By resting my left hand lightly on the panel, I also anchored the rig a little better when using the paddle. (The paddle is reversible for those who are left handed. It's also possible to use the front panel switches to send CW in a pinch.)
OK, now the details on the KX1 case. I discovered that a Kleenex Cottonelle moist wipes box would just fit the KX1, with depth to spare. So, I used some closed cell sleeping pad foam to make inserts to hold the accessories and protect the front panel of the KX1. I was hoping to fit everything in the case, but couldn't quite figure out how to squeeze in the antenna wire. I'm working on that. Meanwhile, I did find room for the paddle, BNC adapter, and earbuds. These fit in cutouts in two layers of 1/4 inch foam. A third layer of 3/8 inch foam protects the front panel. The top two layers have cutouts for the 4 knobs on the radio. The transceiver goes face down on top of the third layer of foam. I also have room between the rubber feet on the bottom of the rig for a folded up reference sheet, although I don't expect to need it for long.
The complete station with 42 foot wire antenna is remarkably compact. And finally, here's a shot of the KX1 set up in the field with the external battery pack, and the plastic case visible at the top of the photo (KX1fieldcaseextbat.jpg).
So where does that leave the K1? Does the KX1 replace it? In my opinion, no. Not everyone wants or needs a backpacking transceiver. For portable operations such as day hiking, motels, and the like where weight and bulk isn't as critical, the K1 offers several advantages over the KX1. The controls are more convenient for tabletop operation. The K1 has greater flexibility in choice of bands, the crystal filter is more versatile, and the ATU has a greater matching range. There's also a noise blanker option. And of course, the K1 has a built in speaker and about twice the transmit power.
In summary, with the KX1 I think Elecraft has nailed the design for a backpacker's QRP transceiver. It has everything I've always wanted in a trail friendly radio, and nothing I don't want. I'm still amazed at how many functions the designers crammed into this little radio while keeping the front panel controls simple and intuitive.
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Bruce Grubbs, N7CEE, is an expert outdoorsman, QRPer, builder and contributing editor to The ARS Sojourner. He lives in Flagstaff, AZ.