Elecraft KX 2

The Elecraft KX2 is a QRP rig I use for Ham Radio. For its small size it has a ton to offer, as well as some interesting quirks that are different from most radios. Below are my findings. Note: All computer settings are for Mac OS.


Since most of my time is doing FT8, setting up the KX2 correctly on my Mac was important. Elecraft rigs handle Data modes differently than other radios on the market, so the normal method of changing audio gain to modify power output will not work well on the KX2 (there's a good reason for this as noted below).

For connection to my Mac I use the USB cable included with the KX2 from Elecraft, and a Sabrent USB sound card which is only $8 and very small.

WSJT-X Settings



Note: Split mode is used in WSJT-X so that your audio for FT8 will always be around 1500hz and WSJT-X will change the frequency instead to compensate. This allows you to work stations beyond your bandwidth. If you can decode it, you can work it. This is true for any radio, not just the KX2.

KX2 General Settings

Note: AF and Mic Gain will be set later.

Mac Audio Input/Output Settings

Open Audio MIDI Setup app (located in Applications/Utilities). Select the USB Audio Device and then select Input. Change the Master volume level to 0dB ("Value" should be around 0.12).

Then select Output, and set the Left and Right channels to 50% (-11dB).

In WSJT-X set the power level (lower right slider) to -25dB. Also set the "Start Hz" in the waterfall config to 400hz (see quirks below as to why).

Once set, you shouldn't need to change these settings. Any tweaks to audio in/out are done on the KX2 (outlined below).

KX2 Audio Input/Output Settings

Audio cable hookups are KX2 Phones to Sabrent Mic (pink) and KX2 Mic to Sabrent Line (green).

Tune the KX2 to a quiet portion of the band with no signals. Adjust the AF Gain on the KX2 until the audio meter in WSJT-X (green bar in lower left) is around 30dB. Note that this can fluctuate per band. Set this before you start transmitting.

Set WSJT-X TX offset to 1500hz and then hit the Tune button (middle right). Adjust the Mic Gain on the KX2 until the ALC Meter is showing 4 solid bars with the 5th bar flashing. This is the point (4-5 ALC) where no ALC is being applied. This is usually Mic Gain of around 30. Check this level before you start transmitting.

You can now set the Power Level on the KX2 directly and it will always be the actual power output. 5w is always 5w out. No guessing like other radios.

Note, do not use the KX2 like a typical radio (ie, set the power to max and use the audio level to control the power output). Elecraft radios always attempt to output at the Power Level set, even at low signal input. This is usually a benefit but can cause issues with data modes if the audio levels are adjusted incorrectly (causing "power hunting"). This is why it's important to set these levels once, then use the Power Level to adjust the radio's power output, not the audio level.


DATA A Mode Filter Bandwidth Oddities

When setting up WSJT-X I noticed something interesting with the filter bandwidth of the KX2 between DATA A and USB mode. While you might expect these to be the same (they're both USB), they're different in a couple ways.

First is the start of the bandwidth itself. If you take a 3kz bandwidth (centered on 1500hz), USB will start its bandwidth at around 200hz. But strangely, DATA A mode won't start its bandwidth until 400hz.

USB bandwidth @ 3khz

DATA A bandwidth @ 3khz

This means there's actually 200hz less bandwidth in DATA A mode than USB mode. I'm unsure why this would be. Lest you think you should just use USB mode to gain a bit extra bandwidth, watch what happens when we up the bandwidth to 4khz.

USB bandwidth @ 4khz

DATA A bandwidth @ 4khz

Effective bandwidth only increases by 500hz because we are centered on 1500hz (2k on either side and the lower end is cut off). But notice what happens in USB mode above 3k. The signal strength is significantly reduced, whereas on DATA A mode it is consistent all the way through. So while you may lose 200hz on the bottom end you get a much more even bandwidth in DATA A mode than in USB at 4khz.

Filter Bandwidth Display not Always Accurate on DATA A Mode

The filter graphic on the KX2 shows a graphic representation of filter bandwidth set, but when it comes to DATA modes, the graphic isn't always accurate. There have been several times I've switched to DATA A mode and it showed a ~3khz filter on the passband graphic but the bandwidth was actually set closer to ~500hz. This obviously makes WSJT-X fairly useless, but it's also easy to tell when it happens because the waterfall in WSJT-X will be very narrow. As soon as you turn the dial to increase the filter, the graphic display on the radio snaps to a narrow bandwidth graphic (as if it knew the graphic was incorrect and it corrects itself).

Thankfully once you set a DATA A mode filter for a band, it remembers it in the future. But you may run into this problem if you try WSJT-X on a new band you hadn't used before.

WSJT-X Waterfall "Noise"

This isn't unique to the KX2 but it's something I noticed when the bandwidth in DATA A mode started at 400hz. I got "noise" in my WSJT-X waterfall. At first I thought this was the KX2, but it turns out that the WSJT-X waterfall is sensitive to the bandwidth edges.

Consider the following waterfall config, with a start at 0hz, the end at 3300hz, using a 3khz bandwidth on the KX2.

0-3300hz @ 3khz Bandwidth

Notice the "noise" both outside of the bandwidth and at the bandwidth edges, as well as the somewhat uneven display between the edges. This is solved in WSJT-X by confining the waterfall to just inside the bandwidth of the KX2. In this case we do this by starting the waterfall at 400hz ("Start" input) and ending it at 2900hz ("Bin/Pixel 3", or resize the waterfall window).

400-2900hz @ 3khz Bandwidth

Notice how smooth and uniform the waterfall is now. This will allow signals to stand out much better when using WSJT-X. This works with any rig, not just the KX2.

Transmit Bugs in Older Versions of WSJT-X

Several transmit bugs exist in older versions of WSJT-X when used with the KX2, all of which were fixed in v2.5 and above. The first is using "Rig" for split mode. In earlier versions it would take a full second longer to start transmitting when using the "Rig" setting instead of "Fake It".

v2.4.x is even worse as it can take up to 4 seconds to start transmitting after you tell it to. This may not seem like a big deal until you consider most people will have the "Call 1st" box checked, meaning they'll call back to whoever got to them first. If you're several seconds late transmitting every time, making contacts will be more difficult.

If you have a KX2 and are on an older version of WSJT-X, be sure to update to at least v2.5 to get the speediest transmit cycle.

Tuning "Pops" and Noise Blanker

Tuning around bands quickly can sometimes produce "pops" in the audio. While I'm not sure why this is, simply turning on the Noise Blanker to its lowest level (1) takes care of this nicely. Thus I always leave it on (except in Data mode).

Low S-Meter Readings

The KX2 typically has "low" S-Meter readings compared to other rigs. This is apparently because the S-Meter is calibrated with the Preamp ON. Since many don't use the preamp on lower bands, this should be taken into consideration if you want a more accurate reading. Without the preamp on, just add 4 to your S-Meter readings. For example, if the rig is reading S1 without the preamp, then in reality you are hearing an S5 signal.

USB Cable Drivers

The USB cable from Elecraft uses an FTDI chip. I was having issues in Mac OS X when unplugging the USB cable, it wouldn't unmount from the OS. Plugging it in at a future date would show two USB cables attached. This lead to a bus conflict and I could not connect the radio to the Mac. I could only solve it by rebooting the Mac.

I found updated FTDI drivers that have helped (though not solved) the problem. You can find them here.

Page last modified on December 28, 2021, at 09:02 PM  Edit
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