This page concerns the hardware issues for a transceiver. The software design is explained by existing documentation about receiver and transmitter flow graphs.
Half or full duplex
It is necessary to decide whether you want half-duplex or full-duplex
Full-duplex is more complicated, especially if using a single antenna on the same band for transmit and receive.
Transmitter activation (PTT switches, etc)
When building a transmitter or transceiver, there are various ways to start and stop transmission.
- always on - as long as the application is running, transmission occurs continuously.
- widget - using the mouse or keyboard to control a widget on the user interface
- USB microphone with PTT switch - this may be linked to a widget on the UI - example some USB microphones have a "mute" button, which is not the same as a PTT button: press once to mute and press again to unmute. Others have a true PTT button - hold it down to unmute/transmit, release it to mute/stop transmission
- USB foot-switch - this may be linked to a widget on the UI - example
- VOX (voice detection)
Many commercial transceivers have some sort of serial/USB/network control interface. The hamlib project collects the low-level protocol details and provides a high level abstraction layer. In addition to PTT logic, hamlib handles frequency and mode control, and received signal strength reports. HID-PTT
The modified USB sound card interfaces are popular with the AllStar network (Using Asterisk to add VOIP linking to repeaters). Recent hamlib should know about HID-PTT too. DIY , or buy a URI from DMK Engineering
Connecting power amplifier and antenna
Based on these comments
- use an RX/TX path switch (only for half-duplex)
- USRP example: control it using the USRP device's GPIO pins
- use a circulator (more expensive solution, suitable for full-duplex though)
- Kuhne make some interesting power amplifiers that can take the low power signal from an SDR (typically 100mW or less) up to the desired level.