For some applications, it is required to work with spectral inversion.
If you are using for instance a C-band LNB, then it's LOF is commonly 5150MHz.
But instead of adding the intermediate frequency to that LOF, the intermediate frequency is obtained by subtraction!
Ku Low-Band: LOF = 9750 MHz
RF = 11383 MHz
IF = 11383 MHz - 9750 MHz = 1633 MHz
C Band: LOF = 5150 MHz with spectral inversion
RF = 3780 MHz
IF = 5150 MHz - 3780 MHz = 1370 MHz
Interestingly, because you are now subtracting the RF from the LOF, you end up with an inverted spectrum, where the left side has a higher frequency value than the right side!
Many SAT field meters just work like this (if they support spectral inversion at all), but it is kind of odd working on a mirrored spectrum.
In the last release of my software, this was already supported. All you had to do was to introduce a negative LOF value. This way, the software would recognize a spectral inversion and show the correct frequencies, however the spectrum was rendered mirrored from high frequecies to low frequencies.
I was not happy with that and thought that the spectrum should be rendered correctly.
So I sat down yesterday and spend a whole lot of time fixing this.
The result is a new version with FULL SUPPORT for spectral inversion. Just enter a negative LOF value and you will get an inverted spectrum, which none the less is rendered correctly: lower frequencies on the left side, higher frequencies on the right side!
In the process I found an existing bug for marker 2, which got fixed (and gave me a lot of headache while implementing the spectral inversion).
Here is the high band spectrum of Hispasat 30.0W, shown with the LOF set to 10600 MHz.
Go ahead and download the latest release here: