This can be quite a complex decision to make as there are five very popular video frequncies to chose from each have their pro’s on con’s when it comes to range, image quality, cost and legality in your country.
The most common frequencies are:
- 5.8 GHz
- 2.4 GHz
- 1.3 GHz
- 1.2 GHz
- 900 MHz
(Note: GHz = Gigahertz, MHz = Megahertz. 1GHz = 1,000MHz).
Generally speaking the lower the frequency you use the less power you need but there are ofcourse many other factors to consider the main two being interference from other sources (for example the 900MHz band is widely used by UK GSM networks) and again ofcourse legalities.
Higher frequncies will be absorbed by organic materials like trees and even moisture in the air (these are microwaves so hence why they are used for cooking) and they will also tend to reflect off the ground and solid structures which creates a phenomenon called ‘multi-pathing’ which manifests its self as ghost like images on your video feed.
Multi-pathing and further more polarization issues (where both antennas are not quite aligned) can be remedied by using circular polarized antennas such as the Clover-Leaf or Skew-Planar-Wheel design, both offer excellent results and are a must have upgrade for micro-wave based systems (2.4 & 5.8GHz).
When buying or building antennas remember there is a science to getting it right and high-end (thus more expensive) antennas will be designed and tested using expensive equipment to give the best performance at the specific frequencies that they operate on.
Legalities (United Kingdom & Europe)
In the UK OfCom control the allocation and licensing of radio frequncies and the “Legal” choices for UK FPV’ers are very limited to say the least. At the time of writing this post current legislation gives the following choices:
- 5.8GHz @ 25mW (0.025 watts).
- 2.4GHz @ 10mW (0.010 watts).
Both of these CAN give you reasonable results with well matched antennas but out of the box with standard whip (vertical) antennas the range is normally well with-in line of site.
Note: For your video transmitter and receiver to be 100% legal they must carry a CE or R&TTE certification.
So what’s on the market?
There are many video transmitter & receiver manufacturers the most popular being:
Its worth noting that you should check the actual channel assignment of the video gear in question because even though two or more manufacturers may be supplying “5.8Ghz” video gear each channel will have its own fixed frequency and you must be sure that these match on the transmitter & receiver.
Recently there has been an increase of more and more sensitive and higher quality video receivers plus forward leaps in antenna design which results in much better range at much lower power output!
The FatShark / ImmersionRC NexWave RF (http://www.nexwaverf.com/) video receiver modules as released at the beginning of 2013 are an excellent example of recent developments that have advanced FPV video technology along with stunning trials showing quad-copter fitted with a 25mW video transmitter managing to still give a good video feed at over 1.6km away