Micro Quadcopters like the Hubsan X4 has limited lifting capability, so the FPV gear must be as light weight as possible and also capable of running off 1S LiPo. There are currently a few Transmitters / FPV combo (camera + VTX) that I found suitable for this task. If you find any other options and alternatives please let me know.
TX5823 200mW 5.8Ghz video transmitter
I used this transmitter in various build, it performs pretty well. Only problem is can get over-heat easily due to the power it has in such a small dimension. But it’s definitely one of the lightest, cheapest VTX for your DIY FPV system. I recently made a 5.8Ghz FPV system with this VTX.
It uses Band E, and is not compatible with ImmersionRC but Boscam.
Micro FPV SPMVA1100 Spectrum
Includes: VTX + Camera + Antenna
This is probably the most expensive FPV combo on the market currently. It’s compatible with Fatshark and ImmersionRC. Good thing is it works straight out of the box, and there is no DIY work.
Pico FPV Combo
Includes: Camera + VTX + Antenna
I have not tried this one yet. It uses 900 MHz & 1.3 GHz frequency which will give you the best wall penetration performance. But most people will find these frequency inconvenient because most people probably have a 5.8Ghz video receiver already, there might be extra cost in investing in a 1.3Ghz video receiver just for this FPV combo.
AltitudeRC 5.8GHz 25mW
I bought this VTX and will be testing it on my micro quad. It weights a little more than it says in the specification. But the quality seems very nice, and there is minimum amount of soldering. It’s compatible with Fatshark and ImmersionRC.
I built a micro FPV setup with this video transmitter and a 2g mini FPV camera.