EMECalc v9.09 was opened, a model for 1296MHz created, and the “get IPS data” button pressed.

The report shows solar flux at 1296MHz to be 106SFU.

On returning the model form, the solar flux at 10.7cm has been updated to 127SFU in agreement with the previous form. There is no sign that the solar flux at 1296MHz has been copied back.

We have a model at 1296MHz:

- after fetching current solar flux, it is shown as 127 @10.7cm;
- antenna gain is 30dB (upper right);
- Tsys=60K (red text at middle left);
- Y factor for Sun/ColdSky is shown as 12.31dB.

From these we can calculate G/T=gain-10*log(Tsys)=12.22dB/K.

We can also calculate the solar flux at 1296MHz that would give rise to a 12.22dB Y measurement for a system with G/T=12.22dB/K (ITU-R S.733-2). The solar flux is 63SFU, about half of what is shown on the form (admittedly labelled as @10.7cm), and nothing like its reported 106SFU at 1296MHz.

There appears to be some secret magic used here, (McArthur 2008):

This has been a significant break through as previous calculations were only accurate over a small sfu range. The ability to perform this calculation with complete accuracy has been the â€œHoly Grailâ€ I had been trying (unsuccessfully) to achieve for many years.

The correct Y factor for 106SFU @ 1296MHz for a system with G/T=12.22dB/K is 14.49dB, not 12.13dB as shown in EMRCalc v9.09.

I have not raised this with the EMRCalc’s author, why would I bother when he says (McArthur 2008):

The figures calculated by the software are â€œfirst principlesâ€ and if you do not get close to those predicted then it is your system and not the software that is the problem!

## References

- ———. 2007. Measuring system G/T ratio using Sun noise. VK1OD.net (offline).
- ———. 2009. Quiet sun radio flux interpolations. https://owenduffy.net/calc/qsrf/index.htm.
- ———. 2014. Measuring G/T. https://owenduffy.net/blog/?p=1490.
- McArthur, D. 2008. Sun noise and measurements. http://www.vk3um.com/Documents/SunNoise_Measurements.pdf (accessed 26/04/2014).
- ITU-R. 2000. Recommendation ITU-R S.733-2 (2000)Determination of the G/T ratio for earth stations operating in the fixed-satellite service .