How Do I Estimate the Transmission Distance of a 50 watt 2m Radio

Can anyone point me to a reference for calculating (estimating) the transmission distance of a 50-watt, 2-meter radio? The transmitting antenna will probably be 5-7 meters above ground. Probably the same height for the receiving antenna.

On 2m, I seem to recall 10W from a 1/4 wave vertical (vehicle roof mounted) being sufficient to get into a repeater that was 20 or 30 miles away. So 50W should do considerably better than that, though you will still likely have blind spots behind mountains.

While it might work, it is also illegal and ill-advised since it is clear that the proper training, licenses, and intended usage is not involved.
So unless you are going to the south pole, or an island/jungle location lacking government, I wouldn't recommend the two meter band for communicating research data.
I don't want to discourage you if you find radio interesting. The following is intended as educational..... and I hope helpful to your plans, not to simply rant about the rules.
The 2 meter band is devoted to "Amateur Radio" on a primary basis in the USA (where you are registered) and many other countries.

Usage for -- as you describe -- "discussing a research project and how we could transmit data from a site without reliable cell coverage," if the research project is commercial, federal or university research, is not an activity for which an amateur radio frequency is a legal use.
Possibly you could use GMRS for the voice component of this... and GMRS radios are readily available. If you need to move data there are various microwave frequencies. Wifi with a dish can go several miles to a location with cell or landline service. Satellite service for low speed data is not terribly expensive if you are doing this for any kind of sponsored research.

See FCC regs 97.113(a)(3) Prohibited Transmissions ...prohibited...3) Communications in which the station licensee or control operator has a pecuniary interest, including communications on behalf of an employer.... there are a few exceptions but you probably don't qualify.

Also 97.113(a)(5) prohibits "Communications, on a regular basis, which could reasonably be furnished alternatively through other radio services." e.g. commercial or satellite services that you can go pay for, or frequencies that can be allocated to universities or other research organizations.

If two researchers were licensed ham radio operators and wanted to communicate about safety issues (e.g. rescue of personnel, or a fire) or socialize using 2 meters because cell, satellite, or other services were down, that would be normal and expected. But you can't use it for your paid profession.

People break the law every day, speeding to and from work and running red lights. The FCC can't watch the airwaves all the time, so why not do it anyway?

Well, Two meters is already pretty full. You may not hear people talking when you listen, but a small, handheld 3 watt transmitter on 2m may cause a distant repeater 30 miles away to get stuck on transmit, repeating everything it hears and you won't know... Why? It repeats on a different frequency than it listens.

Many repeaters are located on high mountains and hilltops and are often part of a volunteer amateur radio emergency plan for the community as well as a kind of pre-internet chat room for the local radio club. The audience affected by an unintentional jammer can be quite large. In New Mexico several repeaters are networked state wide through point to point links. Other networks use VOIP and the internet to link the radio repeaters. Repeaters in high or coastal locations can simply be very well positioned. For example, the Catalina Island repeater in southern california covers much of san diego, los angeles, and santa barbara -- easily 200 miles by car and thousands of amateur radio enthusiasts -- with the use of the kind of radio you mention (a 50-65W mobile model) and an automobile antenna. In the coastal areas a handheld with a whip would be sufficient. This repeater had a jammer who was thrown in prison for FCC rules violations, for among other things, interfering with a distress call from a sailboat. FCC Fines for operation without a license, or in contravention of the rules, are typically not prison but do weigh in around US$10,000. CBers with amps have also gotten these sizable tickets after an FCC house call.

Besides the FCC rules the hams have organized allocation committees for two meter frequencies in every state and it is usually impossible to get a pair of input/output frequencies for a hilltop repeater unless some other repeater group agrees to move to another band or agrees to tolerate and reduce the interference (by directional antennas or power reductions) or becomes defunct -- thats how full it is -- even though it may seem empty if you listen some afternoon. There are also sections, like 145.8-146.0 Mhz, set aside for satellite uplinks -- so if you transmit there you will interfere with every low earth orbit 2m->70cm satellite that flies by overhead. These LEO satellites often hear handheld, portable stations... If it is in a fixed location, location of a 2m hidden transmitter is a fairly straightforward exercise. If the transmitter is obviously located behind a big fence that says "XYZ corp.", or "Oregon Southern Highlands Institute of Technology" then there is a procedure to follow to complain.
 

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