================================================================================ hf_upconverter_ascii.txt — TM-SDR-SCH-001 Rev A HF Upconverter: 0–30 MHz → 125–155 MHz for RTL-SDR Dongles Document: TM-SDR-SCH-001 Rev A ================================================================================ OVERVIEW -------- Input: 0–30 MHz HF signal (SMA, 50Ω) LO: 125.000 MHz TCXO oscillator module Output: 125–155 MHz IF to RTL-SDR (SMA, 50Ω) Bypass: SPDT relay passes HF direct (for 6m+, no upconversion needed) LNA: Optional SPF5189Z pre-mixer amplifier (+19 dB, NF 0.6 dB) KEY SPECIFICATIONS ------------------ Frequency range: 0.1 – 30 MHz input (100 kHz – 30 MHz) LO frequency: 125.000 MHz ±2.5 ppm TCXO IF output range: 125.1 – 155 MHz Conversion gain: −2 dB (passive SA612A) or +17 dB (with SPF5189Z LNA) Noise figure: 4 dB (SA612A only) / 1.2 dB (with LNA in cascade) IIP3: −14 dBm SA612A input / +12 dBm with LNA+pad Image frequency: >155 MHz (suppressed by IF BPF, >45 dB rejection) LO leakage to RF: < −40 dBm (SA612A internal balance) LO leakage to IF: < −60 dBm (suppressed by IF BPF) Supply voltage: 5V USB, 80 mA typical PCB size: 70 × 50 mm BLOCK DIAGRAM ------------- [SMA IN]──[RELAY K1]──────────────────────────────────────────[SMA OUT] HF 50Ω bypass ──>──>──>──>──>──>──>──>──>──>──>──>──>──>─ (direct) │ v (upconvert path) [LPF1] [SPF5189Z] [SA612A] [BPF1] 30 MHz ──>── LNA +19dB ──>─ Mixer ──>─── 125-155 ──>──[SMA OUT] 7-pole (optional) │ MHz BPF IF to RTL-SDR │ [125 MHz TCXO]──[buffer]──>──[LO drive] SCHEMATIC — INPUT SECTION -------------------------- SMA J1 (IN) center ──────────────────────────────────────────── node A SMA J1 shield ─── GND RELAY K1 (SPDT, Axicom V23105, 5V coil): COM ─────────────────────────── node A (from J1) NO (Normally Open) ─────────── node B (to LPF1 input) NC (Normally Closed) ───────── node C (to SMA J2 output, bypass) Relay coil: pin 1 ─── +5V pin 2 ─── GPIO_BYPASS via ULN2003A driver NOTE: K1 normally routes to upconverter path. Assert GPIO_BYPASS HIGH → K1 energizes → direct bypass to J2. SCHEMATIC — INPUT LOW-PASS FILTER (LPF1) ----------------------------------------- 7-pole Butterworth LPF, cutoff 30 MHz, 50Ω in/out node B ──+── L1 ──+── L2 ──+── L3 ──+── L4 ──+── node D (LPF out) │ │ │ │ │ C1 C2 C3 C4 C5 │ │ │ │ │ GND GND GND GND GND Values (50Ω, 30 MHz, 7-pole Butterworth): L1 = L4 = 120 nH (Coilcraft 0805HS-121 or wound) L2 = L3 = 280 nH (Coilcraft 0805HS-271 + 0805HS-100 in series) C1 = C5 = 47 pF (NP0/C0G, 50V) C2 = C4 = 100 pF (NP0/C0G, 50V) C3 = 120 pF (NP0/C0G, 50V) Attenuation at 125 MHz: >60 dB Insertion loss: <0.5 dB from 1–30 MHz SCHEMATIC — OPTIONAL LNA (SPF5189Z) ------------------------------------- Install for weak-signal work; bypass with 0Ω jumper JP1 for strong signals. node D ── JP1 (0Ω) ──────────────────────────── node E [LNA bypassed] node D ── C6 (100pF NP0) ─── SPF5189Z pin 1 (IN) [LNA active] SPF5189Z (SOT-89-3, Infineon): Pin 1 (IN): via C6 (100 pF) from node D Pin 2 (GND): directly to ground plane Pin 3 (OUT): via C7 (100 pF) to node E Pin 3 (Vcc): 3.3V via L5 (100 nH RF choke) and C8 (100 pF bypass) Gain: +19 dB at HF frequencies (spec: 19.5 dB at 900 MHz) NF: 0.6 dB IIP3: +27 dBm IP1dB: +17 dBm Vcc: 3.0–5.0V, 60 mA WHEN TO BYPASS: Strong stations (>S9+20): bypass LNA to prevent SA612A overload Contest operation: always bypass DX hunting / weak signals: engage LNA SCHEMATIC — SA612A DOUBLE-BALANCED MIXER ------------------------------------------ SA612AN (DIP-8, NXP) — Double-Balanced Gilbert-cell Mixer ┌───────────┐ node E ── C9 ─── │1 SA612A 8│─── +5V via R1(470Ω) + C10(100pF) (RF in) 10pF │2 7│─── LO in (125 MHz via C11 10pF) │3 6│─── LO bypass cap C12 (1nF to GND) GND ───│4 5│─── IF out (+) ──── node F └───────────┘ │ Pin 5 (IF+): Differential IF output IF− (internal): left floating or AC to GND via 100pF NOTE: SA612A datasheet pins: Pin 1: RF input (+) Pin 2: RF input (−) — bypass to GND via 470 pF (single-ended input) Pin 3: GND Pin 4: GND Pin 5: IF output (+) Pin 6: IF output (−) — bypass to GND via 100 pF Pin 7: LO bypass — 100 pF to GND Pin 8: Vcc (+5V via decoupling network) Single-ended RF input wiring: Pin 1 ─── C9 (10 pF) ─── node E Pin 2 ─── C13 (470 pF NP0) ─── GND Single-ended IF output wiring: Pin 5 ─── C14 (100 pF) ─── node F (to IF BPF) Pin 6 ─── C15 (100 pF) ─── GND LO input (125 MHz, 200 mVpp required): Pin 7 ─── C11 (10 pF) ─── 125 MHz TCXO output Pin 7 ─── C12 (1 nF) ─── GND (bypass) SA612A Specifications: Conversion gain: +14 dB NF: 4.5 dB (SSB NF referenced to RF port) IIP3: −14 dBm IP1dB: −24 dBm LO power req: −10 to 0 dBm (200 mVpp = −7 dBm into 50Ω) Vcc: 4.5–8V, 25 mA Usable IF bw: DC to 75 MHz SA612A OVERLOAD CAUTION: IP1dB = −24 dBm. With strong HF signals (broadcast, commercial), add 10–20 dB of attenuation before mixer. Strong signal = intermodulation. Use external attenuator or switch out LNA for strong signal conditions. SCHEMATIC — 125 MHz TCXO LOCAL OSCILLATOR ------------------------------------------- Module: NDK NZ2520SD 125.000 MHz TCXO (3.3V CMOS output) or equivalent (Abracon ATXO-505, Fox FXO-HC536R-125) TCXO Module (4-pin SMD or through-hole): Pin 1 (OE/NC): not connected or 3.3V Pin 2 (GND): GND Pin 3 (Vcc): 3.3V via C16 (100 nF) || C17 (1 µF) to GND Pin 4 (OUT): 125 MHz CMOS output ─── R2 (51 Ω) ─── C11 (10 pF) ─── SA612A pin 7 Output level: 3.3V CMOS (0/3.3V square wave) Frequency stability: ±2.5 ppm from −40 to +85°C Phase noise: −130 dBc/Hz at 10 kHz offset (typical TCXO) NOTE: CMOS output is square wave, rich in harmonics. Fundamental (125 MHz) drives mixer; harmonics (250, 375 MHz) create spurious responses at: 250±IF, 375±IF, etc. IF BPF eliminates these. LO buffer (optional, improves isolation): TCXO out ── R2 (51Ω) ── [74LVC1G04 inverter] ── 51Ω ── SA612A pin 7 This provides 50Ω impedance and isolates TCXO from mixer LO port. SCHEMATIC — IF BANDPASS FILTER (BPF1, 125–155 MHz) ----------------------------------------------------- 3-pole Chebyshev BPF, 0.1 dB ripple Center: 140 MHz, BW: 30 MHz (125–155 MHz passband) Input/output: 50Ω node F ── C18 ──┬── L6 ──┬── C20 ── node G (IF out) │ │ C19 C21 │ │ GND GND Values (3-pole, 50Ω, 140 MHz center, 30 MHz BW): L6 = 82 nH (Coilcraft 0805CS-82N or wound, Q > 40 at 140 MHz) C18 = C20 = 5.6 pF (NP0/C0G, 50V) — series coupling C19 = C21 = 33 pF (NP0/C0G, 50V) — shunt resonator caps Passband insertion loss: <3 dB Stopband at 30 MHz (LO harmonic path): >40 dB Stopband at 250 MHz (2nd LO harmonic): >30 dB Stopband at 125 MHz (LO feedthrough): >35 dB ALIGNMENT: Adjust L6 core (if wound) for minimum insertion loss at 140 MHz. Measure with VNA: S11 and S21. Target: S11 < −15 dB, S21 > −3 dB at 140 MHz. SCHEMATIC — IF OUTPUT AND IMPEDANCE MATCHING --------------------------------------------- node G ─── C22 (100 pF NP0) ─── SMA J2 center (IF OUT to RTL-SDR) SMA J2 shield ─── GND RTL-SDR input impedance: 75Ω nominal. Upconverter output: 50Ω. Mismatch loss: 0.2 dB (negligible for this application). Optional: Add 75Ω resistor shunt at J2 to improve match (adds 1.8 dB loss). SCHEMATIC — POWER SUPPLY -------------------------- USB Micro-B J3: VBUS (pin 1) ─── F1 (polyfuse 500 mA) ─── D1 (SS14 Schottky) ─── +5V rail GND (pin 4) ─── GND +5V rail ─── U1 (AMS1117-3.3, SOT-223): IN (pin 3): +5V GND (pin 1): GND OUT (pin 2): +3.3V ─── C23 (10 µF tantalum) || C24 (100 nF ceramic) ─── GND Distribution: +5V → relay K1 coil (via ULN2003A) +5V → SA612A Vcc pin 8 (via R1 470Ω, see above) +3.3V → TCXO module Vcc +3.3V → SPF5189Z Vcc (via 100 nH choke) +3.3V → 74LVC1G04 (optional LO buffer) Total current budget: SA612A: 25 mA TCXO: 20 mA SPF5189Z: 60 mA (when LNA engaged) Relay K1: 30 mA (when energized) Logic: 5 mA Total max: 140 mA GPIO CONTROL INTERFACE ----------------------- Controlled by ESP32 SDR Controller (separate board) or jumpers for standalone operation. GPIO_BYPASS (active HIGH → relay energizes → direct bypass): ESP32 GPIO ─── ULN2003A IN ─── ULN2003A OUT ─── K1 coil (−) +5V ─────────────────────────────────────────── K1 coil (+) GPIO_LNA (active HIGH → JPR1 switches LNA in): For relay-switched LNA: same as bypass control For jumper: install 0Ω at JP1 to engage LNA (manual only) Serial (optional 3.3V UART to ESP32): TX from ESP32 ─── UART RX on upconverter MCU (if local MCU used) Status/control via AT-style commands BILL OF MATERIALS — HF UPCONVERTER ------------------------------------ Qty Part Value/Type Package Notes ───────────────────────────────────────────────────────────────────── 1 U1 SA612AN DIP-8 mixer DIP-8 NXP, ~$2 1 U2 AMS1117-3.3 LDO regulator SOT-223 1 U3 74LVC1G04 Single inverter SOT-23-5 optional LO buf 1 U4 SPF5189Z LNA SOT-89-3 optional LNA 1 U5 ULN2003A 7× Darlington array DIP-16 relay driver 1 TCXO 125.000 MHz ±2.5 ppm SMD/DIP NDK/Abracon 1 K1 SPDT relay 5V coil, RF-rated SIL-4 Axicom V23105A 2 SMA SMA edge connector 50Ω edge mount PCB 1 USB Micro-B USB connector PCB 1 F1 PTC fuse 500 mA 1812 1 D1 SS14 Schottky 1A 40V SMA 1 R1 470 Ω 0805 1 R2 51 Ω 0805 2 R3,R4 51 Ω 0805 terminations 1 L5 100 nH RF choke 0805 for SPF5189Z 1 L6 82 nH inductor, Q>40 0805 IF BPF 2 L1,L4 120 nH toroid or 0805 0805 input LPF 2 L2,L3 280 nH toroid or 0805 0805 input LPF 5 C1-C5 47/100/120 pF NP0/C0G 0805 input LPF various bypass caps 100 nF ceramic 0805 decoupling various RF caps 5.6/10/33/100 pF NP0 0402/0805 PERFORMANCE BUDGET (cascade calculation) ----------------------------------------- Configuration: LNA + SA612A (LNA engaged, typical weak-signal operation) Stage Gain NF IIP3 ───────────────────────────────────── Input LPF −0.5 dB 0.5 dB +60 dBm (passive) SPF5189Z LNA +19 dB 0.6 dB +27 dBm SA612A mixer −2 dB 4.5 dB −14 dBm IF BPF −2 dB 2.0 dB +60 dBm (passive) ───────────────────────────────────── Cascade NF: 1.5 dB (Friis formula, dominated by LNA NF) Cascade IIP3: −10 dBm (dominated by SA612A IIP3) Cascade gain: +14.5 dB Configuration: SA612A only (LNA bypassed) Cascade NF: 5.0 dB Cascade IIP3: −13 dBm Cascade gain: −4.5 dB RECOMMENDATION: For MDS (minimum detectable signal) and DX work: engage LNA. For broadcast-band and strong-signal environment: bypass LNA, add 10–20 dB external attenuator at SMA IN. SPURIOUS RESPONSES TABLE -------------------------- LO = 125 MHz. Spurious outputs at M×LO ± N×RF for M,N integers. Spurious Formula Example (RF=7 MHz) IF (MHz) Notes ─────────────────────────────────────────────────────────────────── Desired 1×LO + 1×RF 125+7 = 132 132 wanted Image 1×LO + 1×RF 125+18 = 143 143 IF=143, RF=18 IF feedthru LO only 125 125 filtered 2nd LO harm 2×125±RF 250±7 243/257 filtered by BPF Half-IF spur 1×LO + 0.5×RF 125+3.5 = 128.5 128.5 SA612A internal 3rd order 2×LO − RF 250−7 = 243 243 filtered IMAGE NOTE: image frequency = 125 + (155 − RF) = 280 − RF_MHz. For RF=7 MHz (40m): image at 280−7 = 273 MHz → not in HF band → no problem. For RF=28 MHz (10m): image at 280−28 = 252 MHz → not in HF band → no problem. Input LPF provides >60 dB image rejection for all cases. ================================================================================