V3X vs V4b

[DB9JG]

Mr Orange (V3x) vs MrBlack (V4B)

For a short time, there appeared a MiniRadio version in the well nown shops — probably an unauthorized prototype that had slipped out of a Chinese factory — soon nicknamed Mr Orange. It featured a front-facing speaker and a side-mounted rotary encoder. According to rumor, a few of these units found their way to Western radio enthusiasts who were hoping for an improved MiniRadio.

One of the Mr Orange V3X units found its way to my workbench — where it finally met Mr Black (V4, AMNVOLT). 😉

The circuit design turned out to be quite promising, as it includes an MMIC RF amplifier at the SMA input and a diplexer for AM and FM signals after the amplifier. This effectively eliminated the Theremin effect that used to result from a 3.4 GHz leakage.

My tests, however, showed that while the filtering was proper, the +25 dB gain of the RF amplifier caused overload effects in the SI4732, leading to cross‑modulation, interference, unstable gain control, and audible pumping effects.

To solve this, I reduced the gain to around +4 dB by adding a 680 Ω resistor in the AM path after the RF amplifier — a simple but effective modification.

For testing, I also used a NanoVNA, with CH1 connected to the AMi at the SI4732 and CH0 linked to the SMA connector through a 10 dB attenuator. In a second test setup, the capacitive antenna was simulated by connecting a 12 pF capacitor between the signal source and the input.

I then compared the Mr Orange V3X with a modified Mr Black V4(b) using an antenna splitter that fed both a signal generator and an active broadband MiniWhip antenna. The V3X now delivers similar performance, with slightly lower gain but still a good SNR below 500 kHz and above 25 MHz.

The V3X design, thanks to its MMIC and external TXO clock, brings clear advantages: no Theremin effect and significantly fewer birdies or backlight PWM interference.

The observed benefits of the improved RF path, the stabilized clock generator, and the apparently cleaner supply voltages should definitely be considered in any future MiniRadio design.

The side‑mounted encoder wheel is a nice idea — but not when combined with the USB‑C socket right behind it, and certainly not while tuning the radio on a stand.

(FYI: I did not examine the undocumented I²S circuitry added in the V3X.)

My video demonstrates the cross‑modulation behavior of the V3X before the gain reduction. The signal source was a non‑directional beacon received in AM mode.

After the modification, the V3X now performs comparably to the V4 on this frequency.

73, 55 de Peter, DB9JG

Details at https://peterneufeld.wordpress.com/2026/02/08/mrorangev3x-vs-mrblackv4b/