Observing in "Fast" Mode

Fast Mode Observing Setup

Purpose

The normal operating mode of EOVSA is to tune across the entire 1-18 GHz band (50 tunings) each second, which means taking data in a given frequency band for 20 ms (actually 19 ms after 1 ms of settling time) per second. Some solar phenomena, especially coherent emission, varies on a much shorter timescale, making it of interest to have an observing mode that repeats a given frequency with higher time resolution. Luckily, the frequency-agile nature of EOVSA allows this.

Implementation

We have implemented a mode that we call "Fast Mode" where the system dwells on one or more bands for a larger fraction of a second and records data at a higher rate during that dwell time. This is subject to the system requirement of a 1-s repetition rate, but is otherwise quite unrestricted. For example, it is possible to sit on one band for 0.8 s and then tune to 10 other bands at a 0.02 s rate to finish out the 1-s cycle, with this cycle repeating every second. Many other combinations are possible.

Hittite LO Command File

The first requirement of the system is the local oscillator (LO) tuning itself, which is performed by a Hittite 40 GHz signal generator. An example control file is shown below:

LIST:DWELL

0.01975,0.01975,0.01975,0.01975,0.01975,0.01975,0.01975,0.01975,0.01975,0.01975,

0.01975,0.01975,0.01975,0.01975,0.01975,0.01975,0.01975,0.01975,0.01975,0.8,

0.01975,0.01975,0.01975,0.01975,0.01975,0.01975,0.01975,0.01975,0.01975,0.01975,

0.01975,0.01975,0.01975,0.01975,0.01975,0.01975,0.01975,0.01975,0.01975,0.01975,

0.01975,0.01975,0.01975,0.01975,0.01975,0.01975,0.01975,0.01975,0.01975,0.01975,

0.01975,0.01975

LIST:SEQUENCE 1, 2, 5, 6, 9, 13, 19, 20, 26, 37, 51

The first command LIST:DWELL gives a list of 52 durations, one for each of our possible tuning bands