PX3 Panadapter FAQ
Q: What is a panadapter used for?
A: A panadapter, also known as a spectrum scope, is a device with a 2-dimensional display showing frequency on its X-axis and signal amplitude on its Y-axis. This allows you to “see” signals on a given band, over a much wider range than you can normally only hear them. The most basic use of a panadapter is to simply locate signals; sometimes a band will seem “dead” on your receiver, while the panadapter will show one or more stations. In this case you can use the PX3’s marker (QSY) knob to “point” at a signal of interest, then push (tap) on the knob to move the KX3 to that frequency. This is a great way to find DX stations, and you can often tell what the station’s operating mode is once you become familiar with their various patterns. Another common use is to observe the nature of a split-pileup, using the PX3 to see who a DX station is working, then set your own transmitter to about the same frequency. (For additional information and illustrated examples, please refer to the PX3 owner’s manual, which can be downloaded from our PX3 web page.)
Q: What is a waterfall display?
A: The PX3 can show a “waterfall” display, which shows a running history of band activity. Signals “pour” down the waterfall, in time, with their color showing how strong they are. Each type of signal creates a unique signature (with a little practice you can even copy Morse code right on the waterfall display, in the form of colored dots and dashes). When the reference level (REF) is adjusted so that the band’s noise floor is right at the bottom of the spectral display, the waterfall will be mostly dark, with signals appearing as light areas. This tells you at a glance where signals have recently been, even if they’re not transmitting at the moment.
Q: Why is the PX3 always placed to the left of the KX3 in example photos?
A: This minimizes physical cable length between the two units, keeps them spaced close together, and keeps the PX3 away from the KX3’s antenna jack, which may be important if an end-fed wire antenna is being used. The PX3’s supplied cables have compact, right-angle plugs, and can be routed underneath the PX3 to maintain a clean station appearance.
Q: How does the PX3 (used with the KX3) compare to the P3 (used with the K3)?
A: The PX3 has nearly all of the same features as the P3*, including the same high-resolution color display, 2 to 200 kHz SPAN, fast sweep rates, and 8 programmable “hot keys” to do quick setup. The primary difference between the two is in the interface to the transceiver. The P3 digitally down-converts the K3’s 8.215-MHz I.F. signal, while the PX3 uses quadrature baseband demodulation (I/Q) to convert signals from the KX3’s RX I/Q output jack. The PX3’s method requires less interface and demodulation circuitry, resulting in a significantly lower-cost unit with lower power consumption (consistent with portable use). For details on how baseband I/Q demodulation impacts performance, see the next item.
* “Fixed tune" mode is not yet available in the PX3. If this feature is added at a future date, it may have somewhat different performance than in the P3, in terms of displayed bandwidth and allowed offset from the currently-tuned frequency.
Q: How does PX3 performance compare to PC-based panadapter applications?
A: The PX3 can display spans of up to 200 kHz, whereas most PC-based panadapters using I/Q demodulation are limited to about 40 kHz spans. The PX3 is also very tightly integrated with the KX3, making it very convenient to use.
Like PC-based panadapter applications, the PX3 makes use of baseband RX I/Q signals from the KX3. These signals are sampled by an analog-to-digital converter (ADC), then mathematically processed to create the spectral and waterfall displays. Because the process is analog, it is subject to possible noise pickup from various sources, including switching power supplies, 60-Hz AC, ground loops, and interface cables. In the case of a PC panadapter application, a sound card must be used, and performance will only be as good as the ADC used on the sound card. The PX3’s ADC is very high performance, resulting in a low noise floor, and the supplied cables are very short to minimize noise pickup. However, the PX3 is still subject to pickup from some noise sources, and the operator may see a few discrete spurs from station power supplies, etc., especially when wider spans are used (over 70 kHz or so). I/Q demodulation may also show a greater number of artifacts, such as opposite-sideband images, than I.F.-derived digital down-conversion (which is used in the P3). However, when the PX3 is properly aligned, such artifacts will be significantly suppressed (typically by 60 dB or better).
Q: Does the PX3 have noise blanking?
A: Yes. When pulse-type noise is present that might cause the display to “jump” up and down or become otherwise impacted, the user can turn on the NB function (in the menu) and adjust its level (another menu entry). The NB should only be used when really necessary since, as with all NB functions, the blanking algorithm may interact with strong on-air signals to create unwanted artifacts.
Q: Is any test equipment needed to build the PX3 kit?
A: No. The only builder alignment step is to null the opposite-sideband image at one frequency on each band, and this is accomplished using the PX3’s built-in RF signal source.
Q: If large signals cause visual artifacts in the spectral display, what steps can I take?
A: (1) Try using a narrower SPAN setting. (2) Try turning off the KX3's preamp, or setting the preamp gain lower (using the PREAMP menu entry, which is per-band). (3) The KX3's attenuator can also be used when needed. (4) If you see artifacts close to the center of the PX3's screen, try shifting them to the side by setting the KX3's RX SHFT menu entry to 8.0 rather than NOR. This is especially effective for small SPAN settings. (5) If you have a shortwave broadcast station in close proximity that is causing problems, you might consider inserting a notch filter to attenuate it. But usually the previous steps will suffice.
Q: If small signals are obscured by noise or other artifacts, what steps can I take?
A: (1) Try using a narrower SPAN. Baseband spectrum demodulation is subject to more artifacts and noise at wider spans. (2) Try turning on the KX3's preamp. (3) If you see noise at the very center of the spectrum plot on quiet bands, try setting the KX3's RX SHFT menu entry to 8.0 rather than NOR.