Merv's Brain Dump

Chapter 1 — Introduction and Scope

This manual covers four antenna switch designs: a manual high-power rotary switch (3 kW PEP), a manual compact rotary (200W), an auto-band relay switch (band-following with transceiver CI-V), and a motorized remote switch (ESP32-controlled relays, all 15 bands). All designs use SO-239 or N-type connectors and 50Ω coaxial paths.

Frequency coverage: 1.8 MHz through 1.3 GHz depending on connector type and relay specifications.

Power ratings: 100W CW to 3 kW PEP depending on design.

Chapter 2 — Theory of Operation

2-1 RF Switching Requirements

An antenna switch routes a single transmitter/receiver to one of N antennas without significant signal loss or impedance mismatch. Key parameters:

• Insertion loss: Signal attenuation through the selected path. Target <0.1 dB at HF; <0.3 dB at VHF.
• Isolation: Suppression of signal on non-selected ports. Target ≥50 dB at HF to prevent signal bleed to unselected antennas.
• SWR: The switch must not introduce significant impedance mismatch. Target SWR <1.1:1 through the operating band.
• Power handling: Contacts and relay coils must survive the peak envelope power (PEP) plus any reflected power.

2-2 Relay Types

Mechanical relays (Omron G2RL, Panasonic TQ2) provide low insertion loss but are limited to ∼10 MHz switching rate and wear over millions of cycles. They are appropriate for all antenna switching applications. PIN diode switches (MA4P504, HSMP-3814) switch in nanoseconds and have no wear, but require bias current and have higher insertion loss at HF.

2-3 Auto-Band Switching

The auto-band switch monitors the transceiver's CI-V (Icom) or CAT (Yaesu/Kenwood) bus to determine the operating frequency. A lookup table maps frequency ranges to antenna ports. On a band change, the ESP32 toggles the correct relay within 50 ms — before the first transmitted audio reaches the antenna.

Chapter 3 — Equipment and Materials

Chapter 4 — Construction

4-1 High-Power Manual Switch

1. Mount SO-239 connectors on the enclosure with <25 mm of center conductor exposed inside. Use Teflon-insulated wire between connector centers and rotary switch contacts.
2. Star-route all grounds to a single chassis point. Use heavy braid or 1/4” copper strap for ground bonds to minimize ground-loop inductance.
3. Verify DC continuity: selected port to radio port must read <0.2Ω. All other ports must read open (>1 MΩ) to the radio port.

4-2 Relay Switch

1. Mount relays in a grid pattern with <15 mm of coax between each relay and its associated SO-239. Longer stubs degrade VHF performance.
2. Bypass each relay coil with a 1N4007 flyback diode (cathode to +12V) to suppress the inductive spike when the relay de-energizes.
3. Mount ESP32 on a separate PCB with 10 nF bypass caps on each GPIO pin driving a relay coil. Relay switching transients can reset an unprotected microcontroller.

Chapter 5 — Operating Procedures

1. Manual switch: rotate selector to desired antenna port before transmitting. Never rotate the switch while transmitting — arcing at the contacts can weld them.
2. Auto-band switch: confirm CI-V address matches the transceiver's configured address (default 0x56 for IC-7300, 0x70 for IC-705). Monitor the CYD display to verify the switch follows band changes.
3. Remote switch: send band command via RS-485 or Wi-Fi API. Verify LED indicator (or CYD display) confirms correct port selected before transmitting.
4. Never transmit into an open switch port (no antenna connected) — reflected power will be 100%, potentially damaging the transmitter PA.

Chapter 6 — Calibration

1. Measure insertion loss with NanoVNA: calibrate SOLT at radio connector, then measure S21 to each antenna port in turn. Loss must be <0.1 dB at 1.8–30 MHz; <0.3 dB at 144 MHz.
2. Measure isolation: with radio port and Port 1 connected to NanoVNA, terminate Port 2 through Port N in 50Ω loads. S21 to each terminated port must be <−50 dB at HF.
3. Verify auto-band sequencing: step through bands on the transceiver. Log which relay energizes at each band; confirm against the band map table in firmware.

Chapter 7 — Verification and Acceptance

1. Insertion loss <0.1 dB at 7 MHz and 14 MHz on all ports.
2. Isolation ≥50 dB at 14 MHz between any two ports.
3. SWR at selected port <1.05:1 at all test frequencies (1.8, 7, 14, 28, 50 MHz) with a calibrated 50Ω load on the antenna port.
4. Auto-band: correct port selected within 100 ms of band change on all 15 configured bands.
5. Log: date, ports tested, insertion loss at key bands, isolation, SWR, operator.

Appendix A — Band–Port Mapping Template

Appendix B — Relay Coil Power Budget

Omron G2RL-1: 12V coil, 400 mA inrush, 50 mA hold. For 8 relays (all energized simultaneously in worst case): 8 × 50 mA = 400 mA steady-state, 8 × 400 mA = 3.2 A inrush. Power supply must handle the inrush; use a 5 A supply with a 1000 µF bulk electrolytic on the 12V rail.