# RMCSat: An F10.7 Solar Flux Index CubeSat Mission
## 2 F10.7 Index
Using a bandwidth of 100 MHz, equivalent to the DRAO F10.7 measurements, the equivalent antenna temperature contribution from a radar system such as the Next Generation Weather Radar (NEXRAD) is 6.1 \(\times\) 10\({}^{14}\) K [18]. Such a signal would saturate the receiver. Fortunately, the low duty cycle and short duration of signal pulses mean that it is not expected to cause significant issues for the overall utility of measurements. The 2695 MHz band is a protected frequency and is not expected to have radar inference. Consequently, it can be used for comparison to identify RFI within the F10.7 data. Cosmic microwave background radiation is a homogeneous field that has near-perfect blackbody radiation at a temperature of 2.748 \(\pm\) 0.016 K. The antenna temperature contribution is 2.09 K, but being constant, it is easily taken into account. The galactic center also produces radiation and an antenna temperature contribution of 2.86 \(\times\) 10\({}^{-3}\) K. For a directional antenna like that of RMCSat, issues in solar flux measurement accuracy will occur where the galactic center is within the main beam and solar activity levels are low. Given the fixed position of the galactic center, this contribution can be anticipated and accounted for. System contributions are generated from thermal noise resulting from resistance in radiometer components and transmission line losses between the antenna and receiver [23; 24]. The magnitude of fluctuations in system noise limits the minimum detectable antenna temperature change. Since fluctuations are random and have shorter timescales than the primary signal, they can be reduced towards a zero mean by averaging the total signal over a selected integration time [23; 24]. The analysis of the radio environment of RMCSat indicates that the thermal radiation from Earth is the greatest concern, followed by RFI. Proposed mitigation options include a fixed orientation of the satellite towards Earth, a secondary antenna, and measurements are taken across two close but separated channels. The fixed orientation places the Earth in the lowest gain region (sidelobe and backlobe) of the primary antenna. Fluctuations that are detected can then be attributed to changes in the brightness temperature of the surface below. A secondary antenna directed at the Earth offers a means to capture the surface signal and use it for comparison with the primary antenna signal. Changes in Earth emissions will be apparent in the secondary antenna signal. Post-processing can be used to remove the Earth component from the primary signal. A wide beam secondary antenna is necessary to replicate the area visible to the main payload antenna and allow for an accurate comparative signal. Preliminary modeling indicates that sufficient accuracy can be achieved using this method [18]. In place of a single 2800 MHz channel, the use of two close but separate channels is selected to account for electronic RFI signals and the saturation of the receiver when these are present. Measurements are taken at 2785 MHz and 2815 MHz (designated F10.7- and F10.7+ respectively) with a narrower bandwidth of 20 MHz for each to minimize the chance of an RFI signal present in both channels. The dual channels provide data continuity if one channel is affected, and provide a method to distinguish between RFI signals and solar burst emissions. The inclusion of 2695 MHz monitoring in the mission provides additional control, as interference found in all three channels indicates a solar burst as the most likely cause. For a meaningful F10.7 solar flux record, the measurements obtained by the F10.7 - and F10.7+ channels can be combined in post-processing to obtain the equivalent average 2800 MHz value. Finally, the calibration of a radiometric sensor is critical to system accuracy. Importantly, the space-based solar monitoring regime will allow up to three RMCSat observations per day that are concurrent with the DRAO solar observations. This will allow a highly accurate reference for calibration and validation of RMCSat values.