@azonenberg @rubylith
This thing has 47 - 860Mhz analog BW with around 30 to 35dB dynamic range
https://www.aliexpress.com/item/1005007993191807.html
So might do what is desired with some mods.
And the bare TX diodes with a fiber pigtail are around 35eur in single quantities on ali as well:
https://www.aliexpress.com/item/1005004962580681.html
But I wonder if some FM modulated, free running 4 - 6 GHz VCO would be enough.
All my surplus 4GHz band VCO's have less than 200MHz of good tuning range.
You might have to downmix two high band osc's.