Mission RGO ONE · Technical Guide
RGO ONE HF Transceiver
RFI Mitigation, Receiver Noise Reduction & Signal-to-Noise Ratio Improvement Guide
Mike Peace VK6ADA · r-390a.net Administrator
| Field | Detail |
|---|---|
| Author | Mike Peace, VK6ADA |
| Website | vk6ada.com.au |
| Resource | r-390a.net |
| Transceiver | Mission RGO ONE — All Series / Production Lots |
| Document Type | Technical Modification Guide |
| Applies To | Series 1–6 (core analog & digital signal chain) |
| Date | March 2026 |
This guide provides a systematic analysis of the RGO ONE’s published signal-chain architecture and identifies specific modifications using ferrite cores, inductors, bypass capacitors, and circuit-level changes to reduce RFI susceptibility, lower the receiver noise floor, and improve signal-to-noise ratio across all HF bands. It is intended for technically experienced amateur radio operators comfortable with SMD and RF construction techniques.
1. Architecture Overview and Signal Chain Analysis
The RGO ONE is a classic down-conversion superheterodyne design with a 9 MHz intermediate frequency, conceptually similar to the original TEN-TEC ARGOSY series. Its signal chain, as documented in the LZ2JR technical supplement, flows through the following major stages:
Antenna → Input Attenuator → BPF Array (GaAs PHEMT switched) → ERA-6SM RX Preamp → RX Mixer (ADE-1 / H-Mode) → 9 MHz Diplexer → ERA-6SM IF Amp → Crystal Roofing Filter (2.7 kHz 8-pole) → IF/AF Board (MC1350 / SA612 / MC33079) → AF Power Amplifier → Speaker / Headphones
The LO chain uses a Silicon Laboratories SI570 VCXO/XO as the main VFO and an Si5351A synthesizer for BFO, CW sidetone, and beep generation. Transmit uses a SA612 DSB modulator with a MOSFET linear PA rated at 50 W. Dual microcontrollers communicate via USB-UART through an FTDI chip. Bandpass filter and TX/RX switching uses Skyworks AS169 GaAs PHEMT SPDT switches — fully solid-state and clickless.
⚠ NOTE — The primary noise-injecting elements are the SI570/SI5351 synthesizer ICs, dual microcontroller clocking, and the FTDI USB interface. All three share the main PCB ground plane and power rails with the sensitive analog front-end.
2. Internal RFI Sources — Identification and Severity
2.1 SI570 VCXO — Main VFO Oscillator
The SI570 generates the main VFO from approximately 10.5–39 MHz using a fractional-N PLL architecture. This creates reference-frequency spurious at integer multiples of the internal divider update rate, fractional-N spurs, and CMOS output edge noise injected into the supply via ~3 ns rise/fall rail-to-rail driver switching. Without adequate filtering these edges radiate into the RX front-end through PCB traces and shared power rails.
✔ TIP — SI570 Supply Filter: Install a 6-turn common-mode choke on an FT37-43 (Mix 43) toroid in series with the 3.3 V supply to the SI570, followed by 100 nF X7R directly at the SI570 VCC pin, plus a 10 μH SMD ferrite bead (Murata BLM21PG) ahead of it. This three-element pi-filter is the single highest-impact noise reduction step.
2.2 Si5351A — BFO, Sidetone, and Beep Generator
The Si5351A is well-documented as a broadband spurious source. Its internal 600–900 MHz VCO harmonics and 25/27 MHz crystal reference harmonics can appear directly within IF passbands. The 9 MHz BFO output is the most critical path — noise here directly degrades the product detector noise floor.
✔ TIP — Si5351A Supply Filter: Filter the Si5351A VCC with a 1 μH SMD ferrite bead (TDK MPZ1608, 300 mA) followed by 100 nF + 10 nF ceramic bypass caps in parallel, placed as close to the supply pins as possible. Add a Mix 43 snap-on clamp on any wire running from the Si5351A to the main board.
2.3 Dual Microcontroller Clocking
Per the official firmware release notes, the main board MCU runs at 31.8 MHz (reduced from 32 MHz to resolve a documented “crackling noise” issue). Clock harmonics at the 3rd and 5th order fall at ~9.5 MHz and ~15.9 MHz, placing them within the 9 MHz IF region and the 15 m amateur band. UART baud-rate harmonics between the CPUs add additional burst noise on the power rails.
✔ TIP — MCU Supply Filtering: Install SMD ferrite beads (Murata BLM18SG331TN1D, 330 Ω at 100 MHz) in series on the VCC supply pins of both microcontrollers. Verify that 100 nF X7R or C0G bypass caps are present and fresh at each MCU supply pin.
2.4 FTDI USB-UART Interface
The FTDI chipset generates noise at 12 MHz (USB full-speed bit clock) with harmonics throughout the HF spectrum. When a PC is connected, the USB cable becomes an antenna coupling PC switching-supply noise directly into the RGO ONE chassis. Common-mode noise travels on the cable shield and couples into the antenna system.
✔ TIP — USB Isolation: Install a Fair-Rite Mix 31 clamp-on ferrite on the USB cable close to the rear panel. For bench operation, use an ADuM3160-based USB isolator between the PC and the transceiver to break the common-mode ground path entirely.
2.5 13.8 V DC Power Supply
Switch-mode power supplies inject common-mode and differential-mode noise onto the DC bus in the 50 kHz–30 MHz range. This distributes throughout the RGO ONE main board via the 13.8 V input.
✔ TIP — DC Line Filter: Install an outboard DC-line RFI filter: two Mix 31 snap-on ferrites on the DC cable, plus a pi-filter (100 μF electrolytic + 100 nF X7R). For maximum suppression, wind a CMC using 6 bifilar turns on an FT114-31 toroid — provides >30 dB suppression across 0.5–30 MHz.
3. Receiver Noise Floor — Stage-by-Stage Analysis
3.1 Input Attenuator
The RF MIXER board incorporates a switchable pi-pad/T-pad input attenuator (R10, R13, R14). When engaged it reduces the noise contribution of subsequent stages by the attenuator insertion loss. For most HF operation where external atmospheric and man-made noise dominates, the attenuator correctly reduces the effective system NF when strong signals would otherwise compress the mixer.
3.2 ERA-6SM Preamplifier
The ERA-6SM MMIC provides ~20 dB gain with a noise figure of 4.5–5.5 dB at HF. As the first gain stage its NF dominates the overall system via the Friis equation. Insufficient bypass on the bias resistor node allows Johnson noise into the signal path; ground return inductance can create instability through the bias network.
✔ TIP — ERA-6SM Bypass: Add a 100 pF C0G SMD cap directly across the ERA-6SM bias resistor, and a 10 nF X7R in parallel with existing bypass. Consider a second parallel ground via to halve ERA-6SM ground inductance.
3.3 RX Mixer — ADE-1 vs. H-Mode
The standard ADE-1 diode ring mixer offers IP3 of approximately +17 dBm with ~6.5 dB conversion loss. The optional H-mode mixer (G3SBI/PA3AKE design) uses MOSFET commutating switches to achieve IP3 in the +40 dBm class — a 23 dB improvement — with slightly lower conversion loss (4–6 dB), improving NF by ~1–2 dB. Earlier units with the ADE-1 benefit enormously from the optional H-mode board.
⚠ NOTE — Verify current production status before ordering: H-mode may now ship as standard on current production lots. Confirm with Mission RGO before purchasing the upgrade board. Ensure SI570 LO drive level meets G3SBI H-mode specs (~+10 dBm). Excessive drive degrades NF; insufficient drive increases conversion loss.
3.4 9 MHz Diplexer
The diplexer presents the correct 50-ohm termination to the mixer at all frequencies — passing the IF forward and terminating image/spurious frequencies in a resistive load. A poorly terminated mixer generates excess IMD and broadband noise from mismatched re-mixing.
✔ TIP — Diplexer Termination: Verify the diplexer high-pass termination resistor is a non-inductive 0402/0603 thick-film SMD type (49.9 Ω, 1%). A through-hole resistor has sufficient inductance at >10 MHz to prevent proper image rejection, adding several dB to the re-mixing noise floor.
3.5 Crystal Roofing Filter
The 8-pole 2.7 kHz ladder crystal filter at 9 MHz is the primary selectivity element, achieving 4–5 dB insertion loss when well-designed. No modification is typically required unless measured insertion loss exceeds 5 dB.
3.6 MC1350 IF Amplifier
The MC1350 provides ~35 dB gain at 9 MHz with 45 dB AGC range. Its NF of ~6 dB is satisfactory at this stage. The main concern is supply pin noise modulating the IF chain noise floor via the AGC circuitry.
✔ TIP — MC1350 Supply: Add a 10 μH SMD power inductor (Bourns SRR0604-100Y) in series with the MC1350 supply lead, followed by a 10 nF X7R bypass directly at the supply pin.
3.7 SA612 Product Detector
The SA612 mixes the 9 MHz IF with the Si5351A BFO to produce audio. Its supply rejection is limited — noise on the VCC pin appears directly in the audio output. Si5351A BFO noise injected into the SA612 LO port, and digital switching supply noise, are the primary audio degradation mechanisms at this stage.
✔ TIP — SA612 Supply Decoupling: Filter the SA612 VCC with a 47-ohm metal-film resistor (0402 SMD) followed by 100 nF X7R to ground — reduces HF supply noise by ~20 dB above 1 MHz. Verify the Si5351A BFO output connects via a series DC-blocking cap with no DC ground path shared between BFO return and SA612 analog ground.
3.8 Audio Chain — MC33079 and AF Amplifier
The MC33079 quad low-noise op-amp (Vn ≈ 4.5 nV/√Hz) is well-suited for AF preamplification. High-frequency supply noise on the MC33079 rails produces audio-frequency intermodulation that manifests as hiss under static or carrier conditions.
✔ TIP — MC33079 Bypass: Install 100 nF C0G ceramic bypass caps directly at each MC33079 supply pin (V+ and V−) in addition to any existing bulk capacitance.
4. Ferrite Core Selection and Application Guide
The choice of ferrite material is critical — the wrong mix at the wrong frequency provides little benefit and may introduce distortion or insertion loss.
| Part / Series | Mix | Freq Range | Application in RGO ONE | Notes |
|---|---|---|---|---|
| Fair-Rite Mix 31 | #31 | 1–300 MHz | CM chokes, USB/DC leads, antenna CMC | Best all-round HF choke material |
| Fair-Rite Mix 43 | #43 | 25–300 MHz | SI570/SI5351 supply chokes, IC power rail filtering | Optimal 10–80 m performance |
| Fair-Rite Mix 61 | #61 | 200 MHz–1 GHz | VHF spurious, SI5351 clock output line | Low HF loss; upper HF use |
| Fair-Rite Mix 77 | #77 | 0.1–50 MHz | LF/MF chokes, audio hum suppression | Excellent below 10 MHz |
| Amidon T-50-6 | Iron #6 | 10–40 MHz | BPF inductors for 10–17 m bands | High Q, thermally stable |
| Amidon T-68-6 | Iron #6 | 10–30 MHz | BPF inductors 12–10 m, larger form | Better power handling |
| Amidon T-50-2 | Iron #2 | 2–30 MHz | BPF inductors 40–80 m bands | High Q, low loss <30 MHz |
| Amidon T-68-2 | Iron #2 | 2–20 MHz | 80 m–40 m main BPF coils | Preferred for lower HF |
| Murata BLM21P series | SMD bead | 30–3000 MHz | SI570, SI5351A, MCU supply pins (0805) | 330Ω/100 MHz; 600 mA |
| TDK MPZ1608 series | SMD bead | 30–1000 MHz | IC supply pin filtering (0402/0603) | Compact, low DC resistance |
4.1 BPF Inductor Core Selection
For 80 m and 40 m BPF inductors, Amidon T68-2 (iron powder #2) provides Q values of 200–250 at 3.5–7 MHz. The 20 m through 10 m filters benefit from T50-6 or T68-6, which maintains high Q above 15 MHz where #2 material loses efficiency. Replace any BPF inductors wound on unknown or degraded cores with known-specification Amidon/Micrometals equivalents, then realign with the trimmer for peak response at band centre.
⚠ NOTE — Rewinding BPF inductors is only warranted if measured insertion loss exceeds 3 dB or alignment is thermally unstable. Do not rework filters within specification — the risk of a winding error outweighs marginal improvement.
4.2 Common-Mode Choke — Antenna Port
Common-mode noise on the antenna feedline is one of the most significant noise contributors in modern shack environments. A CMC wound on Mix 31 or Mix 43 material provides 20–30 dB common-mode rejection without affecting the differential-mode signal.
- 1:1 CMC at the antenna port: 10–12 turns of RG316 through an FT140-31 or FT240-31 toroid. Provides >30 dB common-mode rejection from 1–30 MHz; FT240-31 handles 50 W TX.
- Alternatively, 5–6 turns of the main feedline through a large Mix 31 snap-on clamp at the shack entry point.
- For CASCADE-390 SDR IF tap cables (if installed): add a Mix 43 clamp-on ferrite to prevent SDR clock noise ingressing the IF chain.
4.3 DC Power Rail Three-Stage Filter
- Stage 1: CMC — 6 bifilar turns on FT114-31 toroid. Blocks common-mode noise from the supply.
- Stage 2: 100 μF electrolytic + 100 nF X7R forming an LC pi-section with the CMC.
- Stage 3: Additional 100 nF X7R at the RGO ONE 13.8 V input connector for PA transient handling.
5. Specific Circuit Modifications by Module
5.1 RF MIXER Board — LPF Pulldown Resistor Modification
Described in the official RGO ONE firmware release notes, this modification switches the TX Low Pass Filters only during TX operation, removing them from the RX signal path entirely. In earlier firmware the LPF inductors remained in-circuit during receive, creating resonant structures that produced spurious responses and degraded LW/MW broadcast interference immunity.
⚠ HIGHEST PRIORITY — If your RGO ONE is running firmware older than the LARGE SIGNAL HANDLING MOD version, update firmware and add the pulldown resistor per the official release notes. This is the highest-priority hardware modification for dynamic range improvement.
5.2 SI570 VFO — Local Supply Filter
Recommended filter circuit at the SI570 VCC pin:
- 10 μH SMD power inductor (Bourns SRR0604-100Y, SRF ≈ 80 MHz) in series with the supply
- 100 nF X7R 0402 ceramic directly at VCC pin to GND
- 1 nF C0G cap in parallel for VHF bypass
- Murata BLM21PG331SN1L ferrite bead (330 Ω at 100 MHz) ahead of the inductor
✔ TIP: If the LO trace is longer than 30 mm, add a 33-ohm series resistor near the SI570 output to reduce edge rate and minimise LO trace radiation.
5.3 Si5351A BFO — Supply Filter and Output Bandpass
A 2-pole Chebyshev LC bandpass filter centred at 9.000 MHz, fitted between the Si5351A BFO output and the SA612 LO port, rejects harmonics and spurs that would otherwise appear in the audio via the SA612 demodulation process.
- Wind a 2-pole Chebyshev LC filter using T25-6 toroids and NPO capacitors, centred at 9.000 MHz with 200 kHz bandwidth
- Typical values: L = 1.8 μH (21 turns on T25-6), C = 156 pF series cap to ground — verify against measured Si5351A source impedance before building
- Provides ~40 dB rejection at 18 MHz (2nd harmonic) and >50 dB at 27 MHz
5.4 IF/AF Board — Complete Noise Reduction Package
- MC1350 IF amp: 10 μH inductor + 10 nF X7R at supply pin
- SA612 product detector: 47 Ω metal-film + 100 nF X7R RC decoupling at VCC pin
- MC33079 AF preamp: 100 nF C0G at each supply pin (V+ and V−)
- AF final amplifier: 10 μF tantalum + 100 nF X7R at supply input
- MUTE circuit: 10 nF cap across mute transistor collector–emitter to eliminate audible PTT switching clicks
5.5 BPF Board — GaAs Switch Control Line Filtering
- Add 10 nF bypass capacitors at each AS169 switch supply pin if not already present
- Add a 100 Ω series resistor between the MCP23008 output and each AS169 control pin to reduce switching edge rate
6. External and Ancillary Improvements
6.1 External Antenna Common-Mode Choke
- Wind 10 turns of RG316 or RG58 through an FT240-31 toroid for a 1:1 CMC — 25–35 dB common-mode rejection across 1.8–30 MHz
- Mount as close to the RGO ONE rear-panel antenna socket as possible
- FT240-31 handles the full 50 W TX power without saturation
6.2 PC-to-Radio Galvanic Isolation
- Use an ADuM3160-based USB isolator between the PC and the RGO ONE FTDI rear port to break the PC chassis ground loop
- Install Mix 31 clamp-on ferrites at both ends of the USB cable
6.3 Optional Noise Blanker Module
The RGO ONE supports an optional IF-type Noise Blanker plug-in module with 50 dB blanking range. For operation in environments with impulse noise from switching power supplies, EV charging equipment, or solar inverters, this module is strongly recommended. Set the NB threshold conservatively to avoid desensitising the receiver under crowded band conditions.
7. Measurement and Verification
7.1 Noise Floor Baseline
With antenna disconnected and a 50-ohm termination on the antenna input, the S-meter should sit below S1 on all bands. Use a panadapter (CASCADE-390 SDR IF tap, if installed) to visualise the noise floor — spurious signals appear as discrete peaks above the thermal noise floor.
7.2 Spurious Signal Mapping
Scan 0.1–30 MHz with the antenna terminated. Compare before-and-after spectral plots following the SI570/SI5351 supply filtering modifications. Spurs should fall by 15–25 dB after ferrite and bypass capacitor implementation.
7.3 Two-Tone Dynamic Range Test
Place two equal-amplitude tones at −20 dBm each, 10 kHz apart, within a single HF band. Third-order IMD products should be at least 70 dB below the fundamentals with the ADE-1 mixer, and >80 dB with the H-mode upgrade.
8. Modification Priority Summary
| Modification | Targets | Priority | Cost | Reversible |
|---|---|---|---|---|
| SI570/SI5351 Ferrite & Bypass Filter | RFI / Synth Spurs | HIGH | Low | Yes |
| Dual MCU Clock Supply Filtering | Digital Noise | HIGH | Low | Yes |
| USB & DC Cable Ferrite Chokes | Common-mode RFI | HIGH | Low | Yes |
| LPF Pulldown Resistor Mod (FW) | RX DR / BCI | HIGH | None | Yes (FW) |
| RX Antenna Common-Mode Choke | Conducted Noise | HIGH | Low | External |
| H-Mode RX Mixer Upgrade | Dynamic Range / IP3 | HIGH | Medium | Yes (board) |
| BPF Toroid Core Upgrade | Front-End Selectivity | MED | Medium | Yes |
| IF Diplexer Termination Resistor | IMD / Noise Floor | MED | Low | Yes |
| ERA-6SM Bypass Capacitor Upgrade | Preamp Stability / NF | MED | Low | Yes |
| MC1350 IF Amp Supply Bypassing | IF Chain Noise | MED | Low | Yes |
| SA612 Product Detector RC Filter | Audio Noise / Hum | MED | Low | Yes |
| 13.8 V DC Supply EMI Filter | Power-Line RFI | MED | Low | Yes |
| Internal Ground Strap | Ground Loop RFI | MED | Low | Yes |
| NB Module Installation | Impulse Noise | MED | Medium | Module |
| AF Chain Op-Amp Bypass Upgrade | Audio Floor / Hum | LOW | Low | Yes |
9. Recommended Parts List
All parts are available from Mouser, Digi-Key, Element14, or RS Components Australia.
| Part Number | Description | Application |
|---|---|---|
| Fair-Rite 2643167851 | Mix 43 snap-on clamp ferrite | USB and DC cable choking |
| Fair-Rite 2631165802 | Mix 31 snap-on clamp, large | Coaxial feedlines, DC power |
| Amidon FT240-31 | Mix 31 toroid, 2.40″ OD | Antenna port CMC (50 W rated) |
| Amidon FT37-43 | Mix 43 toroid, 0.375″ OD | IC supply common-mode chokes |
| Murata BLM21PG331SN1L | 330Ω ferrite bead, 0805, 600 mA | SI570, SI5351A supply filtering |
| TDK MPZ1608S101A | 100Ω ferrite bead, 0402 | Microcontroller supply pins |
| Samsung CL05B104KO5NNNC | 100 nF X7R 0402, 10 V | General purpose bypass caps |
| Murata GRM0335C1E100JA01D | 10 pF C0G 0402 | RF circuit bypassing |
| Bourns SRR0604-100Y | 10 μH SMD power inductor, SRF 80 MHz | IC supply filters |
| Amidon T50-6 | Iron powder #6 toroid | 15/10/12 m BPF coil rewinding |
| Amidon T68-2 | Iron powder #2 toroid | 80 m/40 m BPF coil rewinding |
| ADuM3160 module | USB full-speed galvanic isolator | PC-to-radio USB noise isolation |
| Vishay Dale CMF55 49.9R 0.1% | Non-inductive SMD resistor | Diplexer HF termination |
| Bourns SRR1260-100Y | 10 μH power inductor, high current | MC1350 supply isolation |
10. Conclusion
The RGO ONE is a well-engineered HF transceiver with a fundamentally sound signal chain architecture. Its use of the H-mode mixer option, high-IP3 MMIC preamplifiers, custom crystal filters, and GaAs PHEMT switching places it in the upper tier of homebrew and small-production HF transceivers. The primary opportunities for improvement centre on the digital subsystems — the SI570/SI5351 synthesizers and dual microcontrollers introduce supply-coupled noise that is manageable with targeted ferrite and bypass capacitor modifications.
The most impactful modifications in order of effort versus return are: (1) installing the official LPF pulldown resistor hardware modification with the latest firmware; (2) filtering the SI570 and SI5351A supply rails; (3) adding a common-mode choke at the antenna port; (4) isolating the USB interface from the PC ground; and (5) upgrading to the H-mode mixer board if operating from the standard ADE-1. Together these modifications can be expected to reduce the internal noise floor by 10–15 dB, eliminate most visible spurs on the panadapter spectrum, and significantly improve IMD performance under contest or DX conditions.
RGO ONE HF Transceiver — RFI Mitigation & Noise Reduction Guide
All component values are indicative — verify against your specific PCB revision and measured parameters before implementing.
Mike Peace VK6ADA · r-390a.net Administrator · vk6ada.com.au · March 2026