Spectrum Scope for the KX3

In this era of reduced activity on the CW bands, I find a panadapter or spectrum scope to be very useful and I’ve missed having one on my KX3.  Some years ago I tried a PX3 but they are very expensive and I seem to remember that I found them a bit clunky in some ways.  I’ve been searching for an affordable alternative.

For some time I’ve watched the Spectrum DSP offered by quantumsdr.com but have been quite skeptical.  I could find no reviews on line, and the documentation was sketchy and confusing.  Finally, though, as their products consolidated into the M3+, I decided to take a chance.  At $299, it is much less expensive than a PX3 and promises much more.  I’m very glad I did, but I’m also glad I waited because the M3+ is a more polished product than earlier versions.

The M3+ offers a spectrum display as well as a full-featured DSP, and can also be used as a stand-alone SDR, all in a compact, light-weight case.  Since the KX3 already offers an internal DSP, I am only using it as a spectrum display.  I have tried the DSP; it does work and has some nice features, but I’m not a fan of the stylus-based touch interface it uses.  However, if I were using this on a rig without DSP I’m sure I would be happy to get used to the interface.  (The controls, if not the touch interface, are very similar to the RS-918 rig I used to have.)

It is important when ordering to specify that it will be used with the KX3.  That way it comes configured and with the required cables. The documentation supplied can be daunting - it is extensive and not very well organized - but with the quick-start guide I offer below, it is essentially plug-and-play.

By toggling one of the touch buttons at the bottom of the screen, the display can either be used passively, tracking the tuning KX3 tuning knob, or in BISYNCH mode the KX3 can be tuned by either it’s knob or by moving the stylus on the display screen. (A third option allows the KX3 to be tuned only from the screen.) There are several options for tuning via the display, but the default is by sliding the stylus horizontally until the desired frequency is reached.  I mostly tune conventionally via the KX3 with the display marker tracking the tuning.

For the spectrum display, the most used touch controls are several of the boxes along the bottom.  Each box has two commands, one above the other.  A short press accesses the top command while a longer press accesses the bottom one.  For example, a short press on the one to the far left accesses the MENU and the power off button.  (After you access the menu and return, you may need to long press the next button, BALANCE, for the display to return to its normal rendering.) I rarely need to use the rest of the buttons.

Under the S-meter at the top is a blue bar with boxes.  You can change the mode there, reverse CW, select the kind of trace you want to use on the display, or change bands.  The other two - AGC and AMP - seem to be for the M3+ DSP, but I haven’t explored this.

One menu selection I made was the Display Spectrum FFT Window.  It came with Hann selected but I chose Blackman, which the documentation says is the default and seems a bit nicer to my eye.  I also changed the color of the marker to better see the signal under the frequency marker.

There are YouTube videos explaining how to navigate the rather unusual menu interface.

A desk stand is available as an accessory.  I prefer to have my scope above rather than beside the rig, however, and built a wooden stand to hold it there.

The unit is quite compact and light weight so will easily lend itself to portable operation.

All-in-all, I’m very happy I took the plunge.

Quantum SDR Spectrum Display Quick Start for KX3

(By K4LXY)

Notes:

*The M3+ is a spectrum display (or “panadapter”), a DSP unit, and also can be used as a stand-alone SDR receiver.  Since the KX3 already has an excellent DSP, the following is primarily for using the M3+ as a spectrum display with the KX3 though the initial steps for using the DSP are the same.

*The KX3 preamp must be turned on for all bands when using the spectrum scope in order to raise the signal level high enough to avoid scope AGC amplification of local noise and spikes.

*The following assumes the M3+ was ordered for the KX3 and thus configured for that when shipped..

1.  Appropriate cables are supplied. The I/O connection on the M3+ goes to RX I/O on the KX3.  CAT on the M3+ goes to ACC1 on the KX3.  The third cable need not be used unless you are going to be using the DSP as part of the transmit line.  (See p. 70 in the downloadable manual for a diagram.)

1. DC power to the unit must be noise-free, at least for the DSP.  It may be powered by 7-17v from a clean power supply or battery, or alternately may be powered by a USB-c cable.  (The 12v line from my solar power bank was too noisy, but the USB-c connection on that pack works fine for me.)

1. The M3+ will start when power is applied and if connected as above, should begin to function as a spectrum display after it goes through its start-up routine.  To safely close it down and save settings, touch Menu (bottom left), then long press Power Off (bottom right).

1. A number of YouTube videos show how to use the touch screen.  When using the M3+ only as a spectrum scope, the touch screen will be mainly for making configuration changes or if you wish to tune with the screen as opposed to the KX3 tuning knob. To have the option of tuning with either the screen or the KX3 knob, select BISYNC by toggling the soft button along the bottom of the screen.