RFI is often a very frustrating problem but the following information may be of help. You may have RFI and be unaware of it and following these precautions might increase your range.
If possible keep your wire/cable runs away from transmitters, coax and antennas. Never group coax cable together with wiring runs. Use shielding for your wiring runs and if possible grounded metal enclosures for sensitive electronics. Be sure your coax cables have soldered connectors, not crimped. Keep your antennas as far apart as possible. Use dedicated batteries for AV equipment rather than a BEC. Carefully choose which bands you want to employ on your UAV keeping in mind harmonic relationships. http://www.amateur-radio-wiki.net/index.php?title=Harmonics Use Low Pass filters for your transmitters to reduce if not totally eliminate interference.
Here is a useful discourse on interference: link to a White Paper from dpcav.com
Adding a grounding system to your electronics is a good thing to do. You can use the copper shielding from large coax cable (knitted wire) to place over your cable runs and then ground that. Good thing about the copper shield from coax cable is you can scrunch it together by the ends to make it larger in diameter to stuff your wires through and then stretch it out to make it smaller in diameter, like a Chinese finger lock toy. http://leadertechinc.com/PDFs/wire.pdf
Also you can, if you have enough spare length on your wire or cable runs you can wrap them through or around a ferrite core to cut interference. Although some people say that ferrite cores aren’t really very useful above HF frequencies. Here is a link to an interested discourse about RFI suppression and Ferrite material.
All are usable from very low frequencies 500 KHz and up to 150 MHz and beyond. Wurth product id RND-6 is good to 1+ GHz.
These links might get you some useful cores. http://www.readymaderc.com/store/index.php?main_page=index&cPath=11_66_71
We use a lot of vhf/uhf frequency radios in this hobby and those wavelengths are relatively short and unfortunately so are our wiring runs. Often and inadvertently those cable/wire runs are at a length that makes them resonant to the actual frequency we’re using or at a harmonic to that frequency. This makes the wire/cable an unintended antenna element. Shielding, filtering, antenna separation and grounding are your tools to eliminate RFI.