The Microwave Source consists of three components:
Reference Frequency Source
The necessary reference frequency is ~25MHz. Currently this is provided by the Phase-O-Matic. The Phase-O-Matic output is around 270mV Pk-Pk. The reference frequency is programmed via a Rabbit module, and is controlled via ethernet connection from the Lattice sequencer code.
Voltage Controlled Oscillator (VCO)
The VCO is an Analog Devices ADF4360-5 board. This is phase-locked to the reference frequency at 25MHz and generates an output frequency of 1250MHz at -3dBm. The desired reference frequency, output frequency, and output power can be programmed via serial connection.
- If the VCO is powered off via the switch on the case, it will need to be reprogrammed when it is powered on again. The instructions for reprogramming the VCO are given here.
- Although the ADF4360-5 has a quoted output range of 1200-1400MHz, the accessible range seems to vary depending on the programmed output frequency (see Sprague thesis, p.18). Setting the output frequency to 1250MHz gives an accessible range of 1160-1300MHz.
- It was noticed in February 2011 that after about a month of use the accessible frequency range had changed, and output frequencies higher than 1180MHz were no longer possible when the VCO was programmed for 1250MHz. While the serial cable was still connected to the VCO reprogramming did not fix the issue, and programming to a different frequency yielded a new (yet still unexpected) frequency range. The solution was to disconnect the serial cable, power cycle the VCO, reconnect the serial cable, and then reprogram the VCO. After doing this everything returned to normal.
The microwave signal from the VCO is amplified with a Minicircuits ZHL-10W-2G+ amplifier. The amplifier will provide 10W output for a -3dBm input signal, but any reduction in input power will lower the output power. The correct sequence for using this amplifier is: 1) Turn on power supply 2) Apply input signal. The power for the amplifier can then be left on during a series of experiments, with the input signal switched off and on as required.
A Minicircuits ZASWA-2-50DR+ switch is used for the input signal to the amplifier. This switch has a ~2dB insertion loss, and so a '2dB amp' (actually a 9dB amp + 7dB attenuator) is used to ensure that the input signal is not reduced below -3dBm.