Quartzlock model A7A frequency/phase difference comparator

This paper describes various future avenues for improvement and extension of the Quartzlock A7 frequency/phase difference comparator. Initially a brief description of the instrument will be given, which will include outlining the current modes of operation. Along with this, a detailed description of the current methodology for achieving the stated time domain resolution will be given. At present the A7A frequency/phase difference comparator is for measuring a wide range of frequency standards, isolation amplifiers, frequency multipliers and dividers, and passive devices such as cables. The instrument includes a moving coil meter for rapid, unambiguous display of fractional frequency difference or relative phase difference between two sources. Outputs are also provided for an external counter to provide higher resolution analysis of the time domain stability of a source or amplifier. The instrument combines the production oriented capability of rapidly adjusting a source to within a certain tolerance using the panel meter, along with the metrology capability of a full time domain analysis of a source or passive component using data acquisition from the frequency counter. Quartzlock are presently investigating two potential avenues for improving the performance, and widening the potential usage for this instrument. These are improving the pc-based frequency counter and broadening the acceptable input frequency range. At present the frequency counter runs under DOS, which leads to numerous measurement and usability problems. Quartzlock are researching a windows native frequency counter, utilising a multi channel phase meter with better than 100 ps resolution and capable of storing 30000 time interval measurements. It would designed to enable a measurement run lasting maybe weeks and would be much more secure from data loss or interruption. The extension of the A7A to input frequencies other than the present 5 or 10 MHz involves numerous technical challenges, which are