aTao wrote:You cannot really get a "High power" dongle, the feedback from the transmit to receive signals would mess things up, both for higher output and higher sensitivity. However there are things you can do with antenna design these either make the antenna bigger or directional, neither particularly good to put on a RC car. There are of course 2 sides to WiFi, namely the router. If the router was in the middle of the cars domain then you immediately cover its range better, if this is not possible then an antenna that covers only the area the car will inhabit will also improve things. A superior solution would be to have antennae placed around the area the car will be and wire them back to a single WiFi router (with plug in antennae) or several WiFi repeaters spread about.
Actually you can get high power wifi dongles and they do work. While it's true that indoors higher power doesn't mean better reception due to reflections, outdoors you do get better range. Couple it with a circular polarized antenna - which better rejects reflections - and with a high sensitivity receiver and you can achieve hundreds or thousands of meters of range.
There are numerous forums dealing with long range wifi between 2 static points so they focus on high gain (>30dBm) highly directional antennae which are not good for a RC car or quad.
For a moving target my advice is:
- ad-hod network between the ground station and the vehicle.
- omni cloverleaf antenna on the vehicle. It has a gain of 1.2dBi so almost a spherical radiation pattern which is desirable
- onmi cloverleaf or (only with antenna tracking) a directional 4-12dBi helical antenna
- a high sensitivity wifi adapter - like the alfa I mentioned in my first post. It has -96dBi @ 1-2Mb/s and -91dBm @ 11Mb/s
- if your legislation allows it, turn on high power mode on the alfa for an extra 10dBm.
Some things to note:
- 6dB translate in double range. So a 7dBi antenna will give you double the range of a 1dBi antenna. Same is true for the transmit power - but note that 6dB means 4 times the power and only twice the range.
- you need line of sight at this frequency. 2.4Ghz penetrates very little and even foliage will kill your link. Due to the long wifi re-connection process, you want to avoid disconnects at all costs
- mount your antenna as high as possible on the car.
- use circular polarization.
- bandwidth drops as signal gets weaker. This is normal and you have to take it into account
Having said these, you might be better of with something like this:
It's way lower frequency so better penetration, longer range. Very sensitive (-121dBm) and pretty powerful (20dBm) and has more than enough bandwidth for your needs (128-256Kb/s)