I have been interested in flying fpv for some time and now that I have enough flight hours under my belt I want to give it a shot. I've done some research and determined that 900mhz is the way to go. The part I'm getting confused on is the power...100mw, 200mw, 800mw....etc.
Can I get some advice and/or a lesson on what I need and why? More power = more distance, but is there a legal limit in the US?
Replies
The best answer that I have for you is it depends... most 900MHz VTx systems that I've seen require an Amateur Radio Technician-class license for legal operation in the US, which is governed by Part 97 of the FCC rules. If you have a system operating within the guidelines for the 915 MHz ISM band, it's covered by Part 15. Haidar is absolutely correct: the antenna (and feed line, etc) that you use makes all the difference in the world. Transmit power is good, but an efficient (as close to 1:1 VSWR as possible) transmit antenna and a good directional (high-gain), tracking receive antenna will probably be more bang for your buck. However, be careful with directional antennas; the EIRP limitations can kick in with high-gain antennas, though they are more relaxed under Part 97 than under Part 15.
Are you familiar with link margin calculations? This site: http://www.afar.net/rf-link-budget-calculator/ has a good calculator, but you will need to know something about your receiver sensitivity. How far are you trying to go with your signal?
Good luck!
what makes you say 900 is the way to go? I was thinking of trying the 5.8GHz as they have higher power.
I have a 900mhz with a 100mW vtx. My needs are only for 200m range for AP heli and Quad. 1 thing i learnt is that an efficient antenna matters more than power of the VTX. As such, i have done away with the stock antenna and converted to a DIY V-antenna. Not only is it cheap to make, but the range i am getting equals that of 200mW vtx.
this is a good read: http://www.rcgroups.com/forums/showthread.php?t=1159968