Elecraft KX1 Transceiver: Frequently Asked Questions
Updated 3-22-06

Assembly
Q: How many toroids are in the kit?
A: 4 in the KX1 itself (including 1 transformer), and 4 in the KXAT1 ATU (also 1 transformer). All are easy to wind, but will no doubt be offered by the Toroid Guy as well.

Q: Are the 30-m and 30/80-m options installed internally?
A: Yes. The KXB30/KXB3080 are small modules that fit between the main board and the inside of the top cover.

Q: I don't need 30 or 80-m ham-band coverage. Do I still need the KXB30 or KXB3080 option?
A: The 30-m and 30/80-m modules have an important use besides just covering the additional ham bands and adjacent SWL bands: they improve the KX1's receive sensitivity on one of the most important SWL bands: 49 meters (5.9 to 6.4 MHz). The KX1 firmware automatically switches in the KXB30's or KXB3080's tuning capacitors--if a module is present--whenever the operator tunes below 6.7 MHz. This re-resonates the 40-m band-pass filter at about 6.2 MHz.

Q: What's the cabinet made of?
A: Aluminum, .05" thick. It's rugged, lightweight, easy to work (and modify), and results in a nice-looking enclosure. Magnetic fields should have little or no effect due to the DDS VFO, so a steel enclosure is not necessary from that perspective.

Q: What's that diagonally-mounted resistor that shows up in the PCB photo?
A: The board shown is the first prototype. Production units have no such "feature."

User Interface
Q: Can the logbook lamp be relocated for more convenient use by left-handed operators?
A: The lamp casts usable light well beyond the KX1's front edge, meaning you can position the log quite far from the keyer paddle. So lefties may not feel the need to relocate it. That said, you probably could move the LED to the other side, although there may not be enough room on the right side to use the supplied T1-3/4 sized white LED. It may be necessary to use a T1 size LED. (I wish we could have provided two, but we had to stop designing at some point.) By the way, the log lamp has its own on/off switch, and draws only about 7 mA from an internal battery.

Q: Is the VFO controlled by a pot or a shaft encoder?
A: An encoder. The very expensive, ball-bearing type used in the K2 would not fit into the KX1 cabinet (not even close), but the encoder we selected has a metal sleeve, performs well, has 80 counts per turn, and includes a pushbutton switch. The switch is used to select the VFO tuning rate (10, 100, or 1000 Hz per step).

Q: How many frequency memories are provided?
A: There are two memories per band. We may increase this to three or four if code space permits. The reason we included memories is that the KX1's DDS VFO can tune a wide range, and the operator may want to set up one memory for a selected SWL band segment and the other in the ham band.

Receiver
Q: What's the receiver architecture?
A: The KX1 receiver is similar to that of the K1, Sierra, NorCal 40A, SST, and other low-current-drain QRP transceivers. Both the low current drain and low parts count are achieved by using active mixers (NE602 or equivalent). The input band-pass filter is double tuned. A dual-JFET muting circuit is used to allow balanced audio feed to the audio amp, which, again to preserve low current drain, is an LM386. Hiss-reduction circuitry is included, so that the audio sounds very pleasant. The KX1 includes effective AGC.

Q: What SWL bands are covered?
A: The KX1 has tuning ranges of 1 to 5.5 MHz (80 m--requires KXB3080 option), 5 to 8.5 MHz (40 m), 8 to 12.5 MHz (30 m--requires KXB30 or KXB3080 option), and 12 to 16.5 MHz (20 m). The useful tuning range is somewhat less than this because of the KX1's narrow double-tuned ham-band filters. Despite this, signals in the nearby SWL bands (such as 49 m and 31 m) are quite strong, and you can even (in some areas) receive WWV on up to four bands--2.5, 5, 10, and 15 MHz.

Note: Sensitivity in the 49-m band (5.9 to 6.4 MHz) can be dramatically improved by installing the KXB30 or KXB3080 option. KX1 firmware automatically switches in the tuning capacitors on the KXB30/KXB3080 (if installed) when the operator has 40 m selected and tunes below 6.7 MHz. This re-resonates the 40-m band-pass filter at about 6.2 MHz.

Q: Which sideband can be copied on each band?
A: Both! There are three selectable receive modes: normal (CW), USB, and LSB. Normal mode (CW) is optimized for ham-band use; it selects LSB on 80 and 40 m, and USB on 30 and 20 meters. It also sets the VFO's fast tuning rate to 1 kHz per step. USB and LSB modes are provided primarily for SWLs: they allow you to receive either sideband when listening to SSB or AM stations, and they also set the fast tuning rate to 5 kHz per step. In all three receive modes, you can make cross-mode contacts conveniently (see Transmitter, below). Note: on 80 m, USB mode is not available.

Note: Using LSB mode on 20 meters results in slightly lower sensitivity, due to roll-off of local oscillator injection into the mixer caused by the DDS low-pass filter. For this reason we recommend using CW or USB receive modes on this band, unless you really need LSB. (Transmit performance is not affected by the choice of receive mode.)

Q: Can I use the KX1 with a speaker?
A: Yes. The KX1 can drive a small speaker. But for lightweight backpacking, ear buds are preferred. They cut out wind noise, and are very comfortable for use an hour or two at a time. They also weigh just half an ounce or so. Best of all, two people can listen to the radio if desired: one gets the left ear bud, the other the right. (We demonstrated the KX1 at Hamcon in this way: two listeners at a time. Some new friends were made this way :)

Transmitter
Q: Why not use class E for the final amplifier?
A: Our present class C final has excellent efficiency (typically 70%). Given typical T/R duty cycles, and given that the low-level circuits and class-A driver stages contribute a fixed amount of overhead current, improving PA efficiency to 90% would not substantially increase battery life at this TX power level. Also, we optimized for low component count (one low-pass filter and one relay shared across 3 bands), and a class E implementation would have required more components. We do plan to experiment with class E circuitry. If and when we can demonstrate high reliability in field conditions, as well as no serious penalty in terms of multi-band rig component count, we may use class E in the future. Until then we'll stick with the nearly bulletproof, SWR-protected class C designs that we've used before.

Q: What's the transmit power output (max) with various battery types?
A: Maximum output varies with supply voltage: about 4 watts at 12 V, 1.5-2 W at 9 V (six alkaline or lithium 1.5 V cells), and 0.75-1.25 W at 7.2 V (six NiMH cells). Also see the discussion of battery types that follows.

Q: What is "cross-mode" operation? When would I need this capability?
A: The KX1 is a CW transceiver, but is quite capable of receiving SSB signals. There are times (either just for fun or during an emergency) when you might want to contact a station that is operating in SSB mode. To do this on some CW transceivers can be very difficult, either because the filtering is too narrow on receive or because the transmitter doesn't have an appropriate offset. The KX1 solves both problems: its filters can be widened to about 2 kHz, and in all three receive modes (CW, USB, LSB), the transmitter and receiver are offset by about 600 Hz. So, when you tune in an SSB signal and then call them, they'll hear you at about a 600 Hz pitch.

Internal Battery
Q: Why AA cells?
A: We used AA's because they're versatile, and because they're available world-wide. This is critical for a backpacking/emergency radio. (Try replacing a custom rechargeable Li-ion battery pack on short notice, on a weekend, miles from the nearest big city!)

Q: What battery types do you recommend?
A: Alkalines will provide quite a bit of operating time. However, for extended backpacking or travel use, we've found that the ideal battery is a 1.5 V lithium nonrechargeable (Energizer type L91, available at camera stores as well as REI and other specialty travel/camping stores). These are more expensive than alkalines, but are rated at 2.8 amp hours and have a very flat discharge curve. This means that they'll continue to give you 1.5 W or so of output for some 20 to 30 hours of casual operation! Alkalines are also 1.5 V and will provide 1.5-2 W of power output initially, but their sloping discharge curve means that power will drop to 1 W or so less than halfway through their charge life. If you can settle for about 1 W output, you can use NiMH cells, which like lithium cells feature a flat discharge curve. These are 1.2 V rather than 1.5, but they're rechargeable some 500-1,000 times so are very cost effective if you go on lots of trips and/or share them with your other portable electronics.

Q: Why six cells instead of eight?
A: Six cells provide up to 9 V, which is enough to produce up to 2 watts output from our class-C final output stage. Using six cells also worked well with our target front panel size of about 3 x 5", leaving just enough room for the ATU. The six cells are split into two three-cell holders to provide a gap for the crystal filter and BFO crystals (4) as well as the center-mounted key jack.

Q: Can batteries be recharged inside the case?
A: In theory, yes, with some modifications to the DC input circuitry. However, we DO NOT recommend this. NiMH cells--the most likely rechargeables to be used in this application--get very warm during charging. Doing this safely requires a separate enclosure for the batteries, as well as individual monitoring of the six cells for voltage and/or temperature. This is best done using an external quick charger. The six cells can be very quickly and easily removed by virtue of two thumbscrews. The holders are attached to the bottom cover.

ATU
Q: What types of antennas can be matched by the KXAT1?
A: Due to size constraints, the KXAT1 has a more restricted matching range than the ATUs we offer for the K1 or K2. The K2's ATU has 17 elements, the K1's 10, and the KX1's 7. So, during field trials, we optimized the L and C values in the KXAT1 to provide a good match on 40-20 meters when using typical random-wire, tree-supported antennas (20' or longer for use on 40/30/20 m, 16' or longer for 30/20 m, and 12' or longer for 20 m only). Wire lengths that are close to a half wavelength on any band may be very high impedance and should be avoided. Using antennas meet these criteria, matches are typically under 1.5:1, but 2:1 or even 3:1 will not bother the final amp transistor, and losses due to such an SWR will still be low. On 80 m, the KXAT1 will sometimes help "tweak" an antenna that's close to resonance, but its L and C values are too small to tune up a short random wire on this band.

Q: Do I need a balun?
A: The KXAT1 can be used directly with unbalanced antennas such as those described above. You'll only need a balun if you're feeding balanced line. A balun can't hurt as long as it is very low loss. In some cases a balun can be useful for reducing the impedance of an antenna and/or for improving isolation between a hi-Z antenna and the KX1.

Q: What's your favorite field antenna?
A: A rotatable log-periodic at 100', fed with home-made ladder line. (Just kidding!) What we recommend in the KXAT1 manual for 40-20 m is about 24' of #26 insulated copper-clad steel antenna wire (available from The Wireman), used as a vertical or "sorta-vertical" radiator. You'll also need at least one ground radial, 16' or longer (more on that below). The wire can be tossed into a tree, or, if a tree is not available, supported by a portable mast or other support. The 24' length can be loaded on all three bands (20, 30 and 40 meters), and the wire itself weighs under 1 ounce. Performance of this antenna varies with wire length, height, ground characteristics, and the nature of surrounding objects, but in general will be much better than a short, loaded vertical, and may outperform a low-mounted dipole or inverted vee. Even on 40 meters, the 24' length will perform very well once matched by the tuner. A 33' wire length should be avoided since it's close to a half-wave on 20 meters. For 80 m, a resonant antenna is recommended. It should be possible to use an 80 m antenna on multiple bands. A loading coil is another possibility to get a shorter antenna running on 80 m.

Q: In his talk at Hamcon, Wayne claimed that coax or other feedline is not always necessary. What's up with that?
A: During field trials, we did not use any type of feedline. The vertical radiator was connected directly to the center conductor of the KX1's antenna jack (via a BNC->binding post adapter), and tossed into a tree. One or two counterpoise wires of 16-24 feet were then laid on the ground. This is safe and practical at QRP power levels, and eliminates the need to carry coax, baluns, etc. It also avoids coax losses, which can be significant. At 14 MHz, some brands of RG1740ƒ3favored by hikers for its light weight0ƒ3have a loss of over 3 dB per 100'. Old coax that's been kinked and wrapped dozens of times may be worse.

Keyer Paddle
Q: Can I used my regular paddle rather than the KXPD1 option paddle?
A: Yes. The KXPD1 paddle plugs into a standard 1/8" stereo jack on the front of the KX1. You can plug in any type of hand key, keyer, or keyer paddle in lieu of the KXPD1.

Q: How does the keyer paddle work?
A: We designed the KXPD1 specifically for the KX1. The precision spring-steel levers are fabricated to our specifications via photo-etching. When you press on them, they touch contacts on two similarly-sized PC boards. The levers are ideally tensioned, as well as protected, by silicone rubber grips, again custom-fabricated for this application. Finally, an extruded aluminum bar of the proper shape is machined to form a rugged bracket which retains the 1/8" plug, PC boards, and levers. The paddle is angled at 45 degrees for ease of use. It's physically reversible for left- or right-handed use, and is secured with a thumbscrew. The result is a paddle with a light touch that can be used with gloves on, requires no adjustment, is impervious to temperature changes, and weighs just one ounce.

Q: Can I use the KXPD1 paddle as a hand key?
A: Yes. Just set the INP menu entry to HND, as on the K1.

Q: Can front-panel switches be used to send CW in a pinch?
A: Yes. There's a "button CW" mode which permits the BAND switch to be used as a hand key, or the BAND and RIT switches to be used as a keyer paddle. You have to exit button CW mode to use these switches for their normal functions, so typically you'd use this feature only in an emergency.

KX1 / K1 Comparison
Q: How does the KX1 compare to the K1?
A: Both are QRP CW transceivers with internal ATU and battery. Either could be built by first-time builders who have mastered soldering. However, they are intended for two different purposes:

The KX1 has been optimized specifically for backpacking, other ultralight travel applications, and as an emergency or backup transceiver. It features:

The K1, in contrast, is a dual-purpose (home/travel) station with traditional front-facing controls like a desktop rig. It has a much larger cabinet, allowing for some luxuries that don't fit into the KX1: To summarize: The K1 is a very capable 4-band CW rig ideal for contesting, DXing, and general QRP use, with very convenient controls and well over 5 watts of power output. The KX1 is a lean, highly-integrated, ultra-portable rig with "trail-friendly" format that you won't hesitate to take anywhere0ƒ3from moutain peaks to your favorite easy chair.

Q: Is a noise blanker planned for the KX1?
A: Not at present. It would have to be an all surface-mount design, and it would occupy the space intended for the 30-meter option module.

Miscellaneous

Q: Can the KX1 be modified to work on SSB or PSK31, etc.?
A: Maybe, but with great difficulty. There's no extra PCB space for the balanced modulator, signal routing, final amp bias, and control circuits needed to create a viable SSB-capable transmitter. Beyond that, SSB at 1 to 2 watts can be very frustrating. In our experience, about 5 to 10 watts PEP is required to provide reliable SSB contacts under typical conditions. To get to this power level and still offer decent operating time for extended trips, you'd need a much larger battery, or a custom lithium-ion pack, and a larger cabinet to accommodate all those additional stages. (An alternative to increasing cabinet size would be to go entirely surface-mount, but now you're talking about an assembled unit, not a kit.)

Q: Is a custom, crush-proof carrying case planned?
A: We're looking into it. Meanwhile, for day hikes we've found that an Eagle "Protect-It" Field Pack, available from REI (etc.) does a good job. This is a fanny pack, and should not be stuffed into a backpack as the KX1's on/off switch might be turned on accidentally. Another option for serious packers is a pelican case. We'll announce any news about custom carrying cases as soon as we have the details.

Q: Some have described the KX1 as providing "accessibility" for blind hams. Can you describe this feature and what it can be used for?
A: The KX1 includes full audio CW feedback on switch press, including in the menus and for frequency readout. This feature allows the KX1 to be used in situations where you can't conveniently look at the LED display, such as when operating mobile (bike or car). It also provides a backup to the display for use in very bright sunlight. Finally, it will make the KX1 immediately accessible by blind hams, a community that very much benefits from ham radio. We're happy to be able to help them out.


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