The main function of the video transmitter (VTX) is to do just that - transmit the video back to your goggles. Most commonly used VTXs transmit in the 5.8 gigahertz range on five bands and eight channels within each band.
The precision at which the VTX operates at your desired channel along with its power output options and physical size and weight are important parameters to consider (especially for Micro FPV Drones), along with cost of course. As with FPV cameras, VTXs now come in both analog and digital varieties. There are many analog versions to choose from and I have yet to use a "bad" analog VTX - my recommendations are listed below for Micro FPV Drones.
If you've decided to "go digital" (as explained on the Micro FPV Cameras page of this site), you don't have as many options. You can either go with the DJI digital system at this point or Fat Shark's Shark Byte.
If you go with the DJI system, for Micro FPV Drones, I'd recommend the Caddx Vista video transmission system (air unit) over that of the full-up DJI system. Its both lighter weight (19 grams) and less cost ($90). Of course, with either of these, you'll need the DJI FPV goggles which run about $530.
If you don't want to spend that amount of cash and get "locked in" to the DJI ecosystem for digital FPV, I'd recommend the Fat Shark Shark Byte TX5S.1 VTX shown in the image below. It's a single-board that works with the Shark Byte receiver module you can attach to your existing analog FPV goggles (receiver module is $250 instead of $530 for DJI) . The TX5S.1 VTX AIO board weighs only 7 grams and is comparable in cost to analog VTXs at about $50.
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