KX3-2M/KX3-4M Module FAQ


KX3-2M Module

Q:  Can the KX3-2M/4M module be installed along with other internal KX3 options, such as the ATU?


A:  Yes. The module is about the size of a credit card and only about 1/8” (4 mm) thick. It fits on top of the KXAT3 ATU module, and does not displace any of the other internal options.



Q:  What is the KX3-2M/4M module’s power output?


A:   RF power output is 2.5 W minimum (2.5 - 3 W typical) from an external 13.8 V supply , and 1 to 1.5 watts from internal batteries.



Q:  What is the receive sensitivity (MDS)?


A:  Typical MDS in either the 2-meter or 4-meter ham band is about -144 to -145 dBm.



Q:  What frequency range will the module cover?


A:  On 2 meters: About 120 to 165 MHz, allowing copy of weather-band stations at 162 MHz, airport tower AM in the 120 MHz range, etc. On 4 meters: About 65-72 MHz. Sensitivity gradually falls off outside the associated ham bands.



Q:  Can I use the KX3-2M/4M module with FM repeaters?


A:  Yes. The KX3 provides excellent repeater support, including programmable offsets, PL tones, REVerse, and up to 100 general-purpose labeled memories. Memories can be grouped for scanning and manual channel-hopping.  For European transverters, the KX3 provides a 1750-Hz tone burst selection. This can be set up to generate an 0.5-second tone burst at the beginning of each transmission. The user can also hold the PITCH switch indefinitely in order to generate longer tone pulses, if necessary. Also see the SLEEP settings description in the next item (below).



Q:  Does the module provide a DC signal at the antenna jack for external switching functions?


A:  Yes. We’re adding a menu entry to control this. When the signal is turned on, 5 volts (through a 4-kohm series resistor) is applied to the SMA jack. This can be used to control external devices such as a higher-band transverter, amplifier, or antenna switch.



Q:  What is the current drain on 2 or 4 meters?


A:  Total transceiver current drain is typically 300-350 mA on receive and 1.7 A on transmit at 3 watts, running from a 14 V supply. This is a bit higher than on the HF/6-m bands because we incorporated a high-dynamic-range, low-noise amplifier (LNA) in the front end.


There are also SLEEP settings that apply in FM mode (when the receiver is squelched) that can reduce average current drain by up to 50%, depending on the SLEEP time selected by the user.



Q:  Is there any band pass filtering to limit strong out of band signals from pagers and other fixed services outside the band?


A:  Filtering is included at all stages of the receive path, including a 10-element band-pass filter ahead of the mixer. But because the module is so small, there's no room for a high-Q, tuned band-pass filter at the input; instead, we use low-loss low- and high-pass filters to preserve sensitivity. To reduce the need for narrow input filtering, we used a high-intercept LNA (low-noise amp). This increases current drain of the radio on 2 and 4 meters somewhat compared to other bands, but we felt it was an acceptable tradeoff.


Since the KX3-2M/4M module has its own antenna jack, you could use an external high-performance 144-148 or 70-71 MHz band-pass filter if required.



Q:  What is the frequency stability?


A: Standard (uncompensated) frequency stability is sufficient for FM or AM operation. For CW/SSB/data use, it will be necessary to perform the KX3's extended VFO temperature compensation procedure, providing typical stability of about ± 10 Hz on 2 or 4 meters. This range is compatible with 170-Hz-shift RTTY but may not be compatible with some narrowband modes such as JT65 and WSPR.



Q:  Can I use the KX3-2M/4M module as an I.F. for higher-band transverters?


A: Yes, in general, though it is important to distinguish between frequency-mixing transverters and frequency-multiplying transverters. If your high-band transverter uses a mixer (as most do), with the 2-/4-meter module's output used additively rather than with multiplication, then the total frequency stability will be a simple sum of the 2- or 4-meter module's and the transverter's. If however the high-band transverter uses frequency multiplication of the 2- or 4-meter I.F., the total stability can be a multiple of what is described above, and it may or may not suffice for your application. (Frequency-multiplication transverters are pretty rare these days, and are typically limited to CW use only.)



Q: Does the KX3 support DTMF (dual-tone multifrequency signaling)?


A: Yes; the KX3's numeric keypad can be used to enter DTMF tones. After holding down PTT, tap "FREQ ENT" to enable DTMF entry, tap the desired digits (or hold for longer tones), then release PTT. All special DTMF characters are available on other KX3 switches:  ATU TUNE (*), MSG (#), MODE (A), A/B (B), DATA (C), A>B (D).



Q:  I sometimes hear a weak interfering signal from the KX3-2M on a nearby 2-meter receiver. Is this normal?


A: Some short-range emissions from the KX3-2M module maybe be unavoidable, depending on your station configuration. It may be possible to reduce specific emissions by relocating one antenna or adding filtering to power or control cables. (The KX3 uses lightweight sheet metal construction consistent with its primary function as ultraportable HF QRP rig, and it is not practical to provide 100% shielding at VHF.)