DJ7TH Hi Rolf,
I guess that the strong signal near 2708 MHz is just an artifact resp. alias, similar to the birdies on an analogue receiver.
It also disappears, for example, if you set the SA to a center frequency of 2408 MHz.
Reducing then the span step by step from 61 down to 33 Mhz, again, our spurious signal moves from right to left through the spectrum.
At 32 MHz span it has reached 2407.8 Mhz once more, at 31 MHz span it disappears miraculously...
But it gets more interesting.
At 2408 MHz I have permanently a smaller signal with about 10...15 dB above the noise floor,
independent of span and center frequency.
However, this signal also disappears completely if a span of 3 MHz or less is set.
73 de Roland