Carsten Groen's (OZ9AAR) personal place
Interests and experiences
Dual RF Head - USB
As the Dual RF Head sensor works very well for its intended purpose (giving out analog voltages scaled logarithmic), a logical step was to make another version that would have USB connectivity.
Hence the "Dual RF Head - USB" was born.
The device can be used as a FWD/REF power sensor, connect it to the FWD and REF ports of an directional coupler and the Dual RF Head USB will calculate the real forward and reflected power as well as the VSWR value. You can also use the device as a simple "two channel milliwatt meter" with >50 dB dynamic range with ±1 dB.
The sensor has the same frontend as the original analog Dual RF Head. In addition, it has a precision voltage reference (1.800V), a Cortex M0+ microcontroller (NXP LPC845) and a FTDI "serial to USB" chip (FT231XQ).
The sensor presents itself as a virtual serial COM port and all communication (and update of firmware) occurs over this USB-C connection.
More information coming shortly....
Background
As explained above, this design is heavily influenced by my Dual RF Head project.
Both designs are based on the same dual logarithmic sensor chip, the ADL5519 from Analog Devices. The chip is not exactly cheap, but it has some very nice features, primarily:
- Wide bandwidth: 1 MHz to 8 GHz (useable to 10 GHz)
- Dual-channel and channel difference output ports
- Integrated accurate scaled temperature sensor
- 62 dB dynamic range (±3 dB)
- >50 dB with ±1 dB up to 8 GHz
Datasheet for ADL5519
I added an 10 dB attenuator on both inputs, this ensures a better return loss on the two inputs (RL around 20 dB on both inputs).
The analog signals from the ADL device are measured by a 12 bit ADC inside a Cortex M0+ processor, the NXP LPC845. The design uses a 1.800V precision voltage reference. The processor connects (via a serial port) to a FTDI FT231XQ "serial to USB" chip.
Power for the device is taken from the USB-C connection, current consumption is around 70 mA (on the 5V).
The design
The PCB board is made on four layer FR4, 0.8 mm thick (controlled impedance).
The ADL5519 logarithmic sensor chip outputs five analog signals. These are OUTA, OUTB, OUTN, OUTP and TEMP.
OUTA/OUTB: These are the logarithmic outputs from the two channels, A and B. The output is close to -22 mV/dB.
OUTP/OUTN are outputs directly from the ADL5519, these are the sum and difference outputs.
TEMP is "temperature" output. The ADL5519 measures the temperature and outputs an analog voltage based on the temperature.
These five analog values are read by the processor inside the device. The processors firmware will take these analog values and filter them, calculate fwd/ref/swr based on calibration factors.
Both these calculated values and the five raw measured values will be output via the USB-C connector (as a virtual serial port).
The data can be read by a PC program (using simple COM port driver), or you can use the PC tool for the device (TBD).
