The UV-5R family of radios are cheap 4W micro handheld transceivers with reasonably good stock features especially given the price. They can be modified to bypass the on board MCU, which is a write once chip that cannot be modified.
The UV-5Rs are software controlled radios (not SDRs) they have hardware filters that prevent the same kinds of band expansion as the UV-3Rs.
 General Info
- CHIRP - a free, open-source tool for programming your amateur radio. (appears to support the UV-5R)
 Recommended Modifications
- Receive sensitivity is pretty severely lacking. UV5R had issues at WaterPoint 4 on nets C/H/G. No received signal at all. All other HTs at the same location had perfectly fine Rx.
 Recommended Accessories
- A wide based flush fit BNC (or similarly durable connector) adapter (sometimes called an antenna saver) given the short mating cycle "SMA connectors are rated for up to 500 mating cycles" citation via Wikipedia
- example: SMA Male to BNC Female Connector
- Also you can replace the adapter much more easily than the SMA connection in the radio.
- You can even apply some threadlock (the light duty stuff) to the threaded part and still keep the groundplane continuity because of the wide base on the adapter touching the rim of the SMA socket.
- Get a dedicated antenna for VHF and UHF (or whichever you will use the most). The dedicated antennas will do wonders for performance as the stock antenna is really pretty horrible and multiband antennas in general can only be so good on any given band they are tuned for before the others suffer, so they end up being okay at best on all of them. If you followed the above then get a BNC terminated antenna and don't worry about adapters for the antennas.
 Hardware Versions
There are a large number of internally identical radios with very nonstandardized names in the UV-3R and UV-5R family.