Eutelsat satellite frequency spectrum 16E vertical polarisation downlink

Measured with 1m dish. Ku band 12.5 - 12.75 GHz frequency spectrum.
LNB=11.3 GHz local oscillator frequency.

There are three vertical polarisation down transponders between 12.5 and 12.75 GHz.  Each spaced 83.3 MHz apart and each with 72 MHz bandwidth.

The slope downwards at the top end of the upper transponder, noticeable as a tilted top to the largest carrier to the top right and also in the descending noise floor of this upper transponder may be due to increasing losses in my cable or LNB.

The noise floor in the centre transponder is about 2 dB higher than in the outer two transponders.  This may be because the centre transponder is operating at at higher transponder gain step than the others, thus showing the uplink thermal noise.  Alternative explanations are high levels of inter-modulation in this transponder, a wide bandwidth (72 MHz) underlying spread spectrum carrier occupying the whole transponder, cross-polar interference from a 72 MHz wide carrier on the opposite polarisation transponder due to my poor polarisation alignment or due to interference from a 72 MHz wide carrier on the same frequency on an adjacent satellite e.g. Astra (19.2E) or Hotbird (13E) due to a poor side-lobe pattern performance of my antenna.

In the lower and upper transponders the noise floor in the middle of those transponders is low and level with the noise floor elsewhere in the transponders showing that these transponders are not suffering significant inter-modulation overload.