2 layers43.5 × 40.7 mm
TR Switch
kholia/Simple-TR-Switch
VU3CER's non-RF-sensing, MCU controlled Simple T/R Switch with RX Grounding!
18 parts11
2 layers43.5 × 40.7 mm
TR Switch
kholia/Simple-TR-Switch11VU3CER's non-RF-sensing, MCU controlled Simple T/R Switch with RX Grounding!
- Size
- 43.5 × 40.7 mm
- Copper layers
- 2
- Thickness
- 1.6 mm
- Parts
- 17
- Nets
- 11
- Pads
- 48
- Tracks, vias
- 34, 55
- Pours
- 5
- Routed
- Yes
- KiCad
- KiCad 7 (file 20221018)
- Created
- 7 Feb 2022
- Updated
- 25 Jun 2024
Overview
TR Switch is an open-source printed circuit board by kholia, from the kholia/Simple-TR-Switch repository on GitHub. It is a 2-layer board of 43.5 × 40.7 mm with 17 parts on 11 nets, routed with 34 tracks and 55 vias.
Its parts include 3 diodes, 2 resistors, 1 IC, 1 transistor and 1 switch. It belongs with the radio and wireless boards of this library.
README
README.mdSimple-TR-Switch
This is a non-RF-sensing, MCU PTT-controlled Simple T/R Switch with RX
Grounding feature which can be built for less than 2 dollars!
It was designed, and tested for https://github.com/kholia/Easy-Transceiver project.
Various approaches
TX power is 10W from IC-705 operating in FM mode.
-
With a 2-channel relay as a T/R switch, when both RX Ground and Center are disconnected and left floating, a voltage of around ~2.2v is induced across RX connections which is unsafe for typical SDRs.
~2.2 Vpp is 10.93 dBm!
https://www.random-science-tools.com/electronics/dBm-Watts-volts.htm
-
With a 1-channel relay as a T/R switch which is switching the
Centerconnection only, and with all Grounds (TX, RX, Antenna) shorted, a voltage of around ~1.66v is induced across RX connections which is theoretically safe for common SDRs. -
With a 2-channel relay as a T/R switch, with all Grounds (TX, RX, Antenna) shorted, with
Centerswitching using Channel 1, and RX Center Grounding using Channel 2 during TX, a voltage of around ~500mV is induced across RX connections which should be fine for most common SDRs.
Comparisons
No external 12v power is needed unlike Easy TR Switch from https://www.qrpkits.com/ezseries.html.
The ~4000 INR SDR Transceiver and Receiver Switch Antenna Sharer TR Switch Box 160 MHz from Banggood doesn't work in Automatic Mode if there is
Broadcast/SW Interference in your area. The Banggood TR switch switches on
the RTX (red) and disconnects the SDR (RX) as soon as the antenna is connected
under BCI conditions, when operating in Automatic Mode.
BOM
-
5V 2A DPDT OEN MICRO RELAY 46-05-2C
Added Protection
Here is another additional mechanism to protect sensitive SDRs.
This is OK for HF (shortwave).
Alternate (but riskier) Option
Solid switching using BS170 could be another option.
The info folder has more information on this.
Credits
Thanks to VU2ASH (Ashok Joshi), K.P.S. Kang, and LW1ECP (Daniel Alonso) for all the help.
https://circuits-diy.com/optocoupler-relay-driver-with-pc817-2n3904/
Parts
17| Qty | Value | Footprint | References |
|---|---|---|---|
| 4 | MountingHole | MountingHole:MountingHole_2.2mm_M2_Pad | H1, H2, H3, H4 |
| 3 | 1N4148 | Diode_THT:D_DO-35_SOD27_P2.54mm_Vertical_KathodeUp | D1, D2, D3 |
| 3 | SMA | Connector_Coaxial:SMA_Amphenol_901-144_Vertical | ANTENNA1, RX1, TX1 |
| 1 | 120 | Resistor_SMD:R_1206_3216Metric_Pad1.30x1.75mm_HandSolder | R2 |
| 1 | 2N3904 | Connector_PinSocket_2.54mm:PinSocket_1x03_P2.54mm_Vertical | Q1 |
| 1 | 470 | Resistor_SMD:R_1206_3216Metric_Pad1.30x1.75mm_HandSolder | R1 |
| 1 | EL817 (OC) | Package_DIP:DIP-4_W7.62mm | U1 |
| 1 | GPIO (3.3v) | Connector_PinHeader_2.54mm:PinHeader_1x02_P2.54mm_Vertical | PTT1 |
| 1 | Omron G5V-2 / OEN 46-05-2C | Relay_THT:Relay_DPDT_Omron_G5V-2 | K1 |
| 1 | RelayPower1 | Connector_PinHeader_2.54mm:PinHeader_1x02_P2.54mm_Vertical | RELAY_POWER1 |
Questions
How big is the TR Switch PCB?
It measures 43.5 × 40.7 mm and has 2 copper layers, 1.6 mm thick.
What parts does the TR Switch use?
17 parts. The full list of its parts is on this page, with links to each part's symbol and footprint where PCBKit's library has them.
Where can I download the TR Switch KiCad files?
From the kholia/Simple-TR-Switch repository on GitHub, at the commit this page was made from: the board is v3/TR-Switch.kicad_pcb and its schematic RF-Limiter/RF-Limiter.kicad_sch. PCBKit opens the board in the browser, with nothing to install.
Can I use the TR Switch design in my own project?
Its repository states no licence, so its author keeps all rights: ask kholia before reusing the design.
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