RS-UVPA Power Amplifier
The RS-UVPA is a 5W power amplifier designed to integrate with the RS-UV3A transceiver, boosting output power for improved range.
Overview
Section titled “Overview”The RS-UVPA provides:
- 5W output on 2m and 1.25m bands
- 4W output on 70cm band
- Low-noise preamplifier for improved RX sensitivity
- SWR protection to prevent amplifier damage
- Band-keying outputs for external amplifiers
Specifications
Section titled “Specifications”| Parameter | Specification |
|---|---|
| TX Frequency Range | 144–148 MHz, 220–225 MHz, 432–450 MHz |
| RX Frequency Range | 130–500 MHz |
| Drive Level | 200 mW – 1W |
| Output Power | 5W min (2m/1.25m), 4W min (70cm) |
| Spurious | > 53 dBc, typically 60 dBc |
| Antenna Impedance | 50Ω |
| SWR Trip | 3:1 |
| RX Gain | 2–3 dB or 12–15 dB (jumper selectable) |
| RX Noise Figure | 1.5 dB max |
| DC Power | 8V – 15V DC |
| TX Current | 2A max |
| RX Current | < 50 mA |
| Size | 120 × 75 × 25 mm |
Operation
Section titled “Operation”Once installed, the RS-UVPA operates transparently—it automatically switches between TX and RX and selects the correct band filtering.
SWR Protection
Section titled “SWR Protection”The RS-UVPA includes SWR protection:
- SWR LED illuminates when high SWR is detected
- Amplifier is disabled for remainder of transmission
- Normal operation resumes on next transmission
Antenna Required
Always connect an antenna or 50Ω load before transmitting. Operating without a load can damage the amplifier despite SWR protection.
Installation
Section titled “Installation”Compatible Hardware
Section titled “Compatible Hardware”| Board | Compatibility |
|---|---|
| RS-UV3A Rev A | ✓ Full support |
| RS-UV3 Rev D | ✓ Full support |
| RS-UV3 Rev C | ✓ Full support |
| RS-UV3 Rev B | Contact HobbyPCB |
Required Modifications
Section titled “Required Modifications”Before installing the RS-UVPA on the RS-UV3A:
Step 1: Prepare the RS-UV3A
Section titled “Step 1: Prepare the RS-UV3A”- Remove solder from SJ1 — This solder jumper routes RF to the SMA jack. Use solder wick to clear it.
- Remove the VIN power connector — It interferes with the amplifier’s power connector. The RS-UVPA will supply power to the RS-UV3A.
Step 2: Add Headers to RS-UV3A
Section titled “Step 2: Add Headers to RS-UV3A”Solder three headers to the RS-UV3A:
| Header | Pins | Purpose |
|---|---|---|
| AMP | 6 | Amplifier interface |
| PW | 2 | Power switch |
| PA | 2 | RF connection |
Soldering tips:
- Solder one pin first
- Verify header is seated flat and perpendicular
- Solder remaining pins
Step 3: Mate the Boards
Section titled “Step 3: Mate the Boards”- Align headers on RS-UV3A with sockets on RS-UVPA
- Press boards together firmly
- Install jumper across PW header (or connect switch)
The RS-UVPA has a redundant PW header for switch connection.
Step 4: Enclosure Mounting
Section titled “Step 4: Enclosure Mounting”The board stack can be mounted using:
- PCB mounting holes
- Extruded enclosures for 120×75 mm boards (e.g., Hammond 1455K1201)
- HobbyPCB enclosure (available on website)
Important: Transfer the plastic cap from the RS-UVPA’s SMA connector to the unused RS-UV3A SMA connector to prevent confusion.
Connections
Section titled “Connections”| Parameter | Specification |
|---|---|
| Connector | On RS-UVPA (shared with RS-UV3A) |
| Voltage | 8V – 15V DC |
| Current | 2A max (TX) |
The RS-UVPA provides power to the RS-UV3A through the interconnecting headers.
Antenna
Section titled “Antenna”Connect antenna to the RS-UVPA SMA jack (not the RS-UV3A jack when mated).
Control Outputs
Section titled “Control Outputs”The RS-UVPA provides band-select outputs for keying external amplifiers:
| Signal | Description |
|---|---|
| 2m Key | Active during 2m TX |
| 1.25m Key | Active during 1.25m TX |
| 70cm Key | Active during 70cm TX |
RX Preamplifier
Section titled “RX Preamplifier”The RS-UVPA includes a switchable LNA (Low-Noise Amplifier):
| Mode | Gain | Use Case |
|---|---|---|
| Low Gain | 2–3 dB | Overcomes amplifier insertion loss |
| High Gain | 12–15 dB | Improved weak-signal reception |
Select mode via jumper on the RS-UVPA board.
When to Use High Gain
Section titled “When to Use High Gain”- Weak signal work (DX, satellites)
- When the RS-UV3A’s sensitivity is limiting
- Base station installations with long feedlines
When to Use Low Gain
Section titled “When to Use Low Gain”- Strong signal environments
- To avoid receiver overload
- Mobile installations in urban areas
Drive Level Adjustment
Section titled “Drive Level Adjustment”The RS-UVPA is optimized for the RS-UV3A’s ~200 mW output. If using with other transmitters:
| Drive Power | Notes |
|---|---|
| < 200 mW | Reduced output power |
| 200 mW – 500 mW | Optimal range |
| 500 mW – 1W | May require attenuator adjustment |
| > 1W | Not recommended |
For drive levels above 500 mW, internal attenuator adjustment may be required—contact HobbyPCB for guidance.
Troubleshooting
Section titled “Troubleshooting”Low Output Power
Section titled “Low Output Power”- Check drive level from RS-UV3A (
PW1= high power) - Verify antenna connection
- Check for SWR LED illumination
- Measure DC input voltage (should be 8V–15V)
SWR LED Always On
Section titled “SWR LED Always On”- Check antenna connection
- Verify antenna is for correct band
- Measure antenna SWR with analyzer
- Check for damaged feedline
- Verify RS-UV3A is transmitting (TX LED)
- Check header connections between boards
- Verify power is applied to RS-UVPA
Receiver Desensitized
Section titled “Receiver Desensitized”- Check antenna connection
- Try low-gain preamp mode
- Verify no strong nearby transmitters
Using with Other Radios
Section titled “Using with Other Radios”The RS-UVPA can be used with other VHF/UHF transmitters that provide up to 1W output, including:
- Hamshield (Arduino shield radio)
- Other RS-UV3 variants
- Low-power transmitter modules
For non-RS-UV3 applications:
- Connect TX output to RS-UVPA input
- Connect RS-UVPA output to antenna
- Provide PTT signal for TX/RX switching
- Provide 8V–15V DC power
Contact HobbyPCB for detailed integration guidance.
Regulatory Notes
Section titled “Regulatory Notes”When using the RS-UVPA:
- Output power increases to 5W (37 dBm)
- Ensure compliance with band plans and power limits
- Spurious emissions meet FCC Part 97 requirements
- Operator is responsible for proper station identification