RF Signal generators

The SG380 series is intended for analogue RF generation, while the SG390 series adds internal vector waveform generation as a standard function. Both families provide AM, FM, phase, pulse and sweep modulation, together with 1 µHz frequency resolution and matching 2.025 GHz, 4.05 GHz and 6.075 GHz model choices. SG380 instruments can accept external I/Q signals through an optional 200 MHz input, whereas SG390 models include dual 14-bit, 125 MS/s baseband generators and a 300 MHz external I/Q path. The SG380 is therefore appropriate when analogue modulation covers the test requirement. The SG390 is the relevant choice when internally generated PSK, QAM, FSK, MSK, ASK, VSB or custom I/Q signals are required.

The 2.025 GHz models are the SG382 and SG392, the 4.05 GHz models are the SG384 and SG394, and the 6.075 GHz models are the SG386 and SG396. Each instrument also provides a separate BNC output from DC to 62.5 MHz, so the maximum model frequency applies specifically to the N-type RF output. Selection should include the highest fundamental carrier, modulation sidebands and any margin needed for future test plans. If an SG380 application needs coverage above 6.075 GHz, the optional doubler extends the SG384 from 4.05 to 8.10 GHz and the SG386 from 6.075 to 8.10 GHz. That option has different amplitude and spectral specifications from the main N-type output, so it should be assessed as a separate RF path.

The BNC output is intended for signals from DC to 62.5 MHz and provides 0.001 to 1.00 Vrms into 50 Ω, together with an adjustable ±1.5 VDC offset. This makes it suitable for lower-frequency sine-wave work, baseband stimulus and tests that require a controlled DC component. The N-type connector covers 950 kHz to the selected model limit and provides RF power down to −110 dBm, with up to +16.5 dBm available within the specified frequency bands. Both outputs are designed around 50 Ω systems, but the BNC output is DC coupled while the N-type output is AC coupled. Engineers should choose cables, terminations and protection arrangements according to the active connector rather than treating the two outputs as interchangeable.

The standard OCXO is suitable where <±0.002 ppm stability from 0 to 45 °C and <±0.05 ppm annual ageing meet the uncertainty budget. Typical phase noise at a 1 GHz carrier is −80 dBc/Hz at 10 Hz offset and −116 dBc/Hz at 20 kHz offset for the 2 GHz and 4 GHz models. The optional rubidium timebase changes the specified temperature stability to <±0.0001 ppm and ageing to <±0.001 ppm per year. A rear-panel input also allows the generator to lock to an external 10 MHz reference between 0.5 and 4 Vpp. The correct choice therefore depends on whether the system is dominated by short-term phase noise, long-term frequency drift or traceability to an external laboratory reference.

All models support amplitude, frequency, phase and pulse modulation using either internal waveforms or an external modulation input. The internal generator provides sine, ramp, saw, square, pulse and noise functions, with rates up to 500 kHz at lower carrier frequencies and 50 kHz at higher carriers. AM depth is adjustable from 0 to 100%, while FM deviation begins at 0.1 Hz and varies with the selected carrier band. Phase-continuous sweeps can use sine, triangle or ramp functions at rates up to 120 Hz. This allows one instrument to cover conventional receiver tests, frequency-response sweeps, gated-carrier measurements and externally controlled modulation without requiring a separate low-frequency generator in many set-ups.

The SG390 series uses two 14-bit baseband channels operating at 125 MS/s to generate I and Q signals internally. Symbol rates extend from 1 Hz to 6 MHz, with up to 16 Mbits of symbol memory and one to nine bits mapped to each constellation point. Supported modulation families include PSK, QAM up to QAM256, FSK, CPM, MSK, ASK and 8- or 16-level VSB. Pulse-shaping choices include Nyquist, root Nyquist, Gaussian, rectangular, linear, sinc and user-defined FIR filters, while additive white Gaussian noise can be applied from −70 to −10 dBc. In practice, this permits protocol-oriented receiver and demodulator testing without assembling a separate arbitrary generator, I/Q modulator and noise source.

Every model provides 10/100 Base-T Ethernet, IEEE-488.2 GPIB and RS-232 interfaces, allowing it to work with both current networked systems and established test racks. RS-232 supports rates from 4800 to 115,200 baud with RTS/CTS flow control, while Ethernet uses TCP/IP with DHCP enabled by default. All instrument functions can be controlled and read remotely, and up to nine configurations can be retained in non-volatile memory. The half-rack enclosure measures 8.5 × 3.5 × 13 in and weighs 10 lb. Single and dual mounting kits allow one instrument or two side-by-side instruments to be fitted into a standard 19-inch rack.

The SG38x family contains 256 kB of microcontroller flash, an 8 Mbit serial EEPROM and 4 MB of parallel flash. Its factory reset overwrites the EEPROM containing instrument and interface settings, while firmware and FPGA configuration storage remain unchanged. The SG39x family contains an 8 Mbit serial EEPROM and 4 MB of flash used for user waveforms; the reset overwrites the EEPROM and sector-erases the waveform flash. Instrument settings are reset by powering up with BACK SPACE depressed, while remote-interface settings are reset by holding the decimal-point key during power-up. Organisations with controlled-data requirements should include these actions in their decommissioning procedure and account for the memory regions that retain firmware or configuration data.