Measure EMF Radiation from High Altitude Balloon
Chip manufacturers address this kind of sensor with a good selection of devices. These provide a voltage output proportional to RF power over a broad range of frequencies - they are not radio receivers because they don't discriminate one signal source from another. Some respond to multiple sources, adding them in a root-mean-square (RMS) fashion, while others don't. Am unsure which is appropriate for your particular application (your specs are not well defined).
Some (many) of these chips are sensitive enough so that an antenna can be attached directly. Your antenna may be a significant challenge, and will influence greatly the frequency band over which signals will add to the output. Your antenna should be carefully designed to be non-directional, since it will likely be spinning and possibly swaying.
Be aware that cell transmitters carefully direct signals in desired directions. Not many users are above a cell site, so less signal is directed "up" than "out and around". But as you go higher, your antenna "sees" more sites.
Engineering is best done to provide a solution to a need. Your need is not mentioned - more like "this might be an interesting thing to measure". Start with a more concrete and useful goal.