Matt,
I am currently appraising a commercially zoned parcel on which is located a cell tower. The space occupied by the cell tower is leased by a major cell phone company. Like you, I know the I and need the R to I can determine the V.
The comments you have received thus far are interesting, however I have an additional issue with the one I'm working on. There is a business located on this parcel (parcel is about 15,000 SF) and the business owner feels the way his business is growing, the land will have more value to him to use in his business than what the tower lease brings in.
I point this out to you, as it shows yet another factor that must be considered in establishing a discount rate.
The range of 12% to 18% discussed by Lee Lobban is certainly likely, however if the owner (or buyer) of the land can generate more income by putting the land to a different use, then even 18% may be too low.
Your property has a TV tower, which occupies quite a bit of land due to the "guy" wires usually needed to support such a tower. Also, these towers are usually away from densely developed areas. So, under these circumstances, your situation may not be similar to mine whatsoever.
Jerry