Posted by Jordi Muñoz on December 2, 2009 at 2:00pm
I love my Spektrum Dx7 and my 2.4Ghz JR XPS9303 and i refused to trade its solid rock performance by a 72mhz radio just to increase range of my FPV/UAV. So in collaboration with my friend JB we find out the cheapest and secure way to amplify the signal, it even works in some Futabas and virtually with any 2.4Ghz radio, but some modifications are required. Lets see some options:-Spektrum Dx7 this is the cheapest solution for a very reliable 2.4Ghz radio, i used it for about a year and i never had any signal glitch (unless i fly beyond 2000 feet). The problem with this one is that you have to modify it, you need a SMD to U.FL adapter, drill a hole in the side of your radio and just connect and screw the adapter, no soldering required. If you have more than 5 hours of experience with Legos your qualified to do this job. Then you just need to connect the booster. The one in the picture (middle) is already modified.-If you have the awesome JR radio but is 72Mhz you can buy the Spektrum 2.4Ghz module and just insert it in the back of your TX, personally this is my favorite setup. It's a good deal because includes a $99 dlls receiver for free! Note that JR TX alone cost around $600 dlls, but you can get it for less, i got mine for 300 bucks with Spektrum Module included on R/C Groups =P. Remember you are looking for the JR XPS9303.If you have one of the fallowing Futaba radios:7U Series Radios8U Series Radios8J Series Radios9C Series Radios9Z Series RadiosFN Series RadiosYou can just go and buy the Spektrum 2.4Ghz module, easy and with no hassles. It's also a good deal because includes a $99 dlls receiver for free!
One of the advantages of the Spektrum receivers is the build in diversity system, you can even buy one with 4 satellites like this one, or buy a super tiny, tiny setup like this one, or the traditional one.The diversity is crucial to have a reliable link when you are flying far away, also Spektrum has a receiver for Carbon Fiber airplanes (Carbon Fiber blocks RF signals).The idea is to have the best reliable hardware with an SMA connector and the SMA extension cable, after that you are ready for the final step: Get an amplifier. But we are talking about a few hundred dollars here, if you get the weakest one of 100mW it will cost you around $150 dlls. This is not pocket friendly in my point of view. So again our Asians friends come to the rescue, after making some research around the net I've found on eBay and a home Wireless Amplifier, so i decided to give it a chance and i bought it for 60 bucks including shipping! Wow that's a good deal! The one i got is this one.Note that the amplifier needs 6Volts to work, you can get a cheap 6V power regulator from here and just make the adapter. A 3 Cell LIPO is enough to supply it for a long time.
After receiving the AMP i did some tests, here are my results:Before using the amplifier, i was able to fly around 3000 feet away (~1 km) using a 900Mhz@500mW Video transmitter. I never lost the video signal, only the radio link...Using a 1.3Ghz@1Watt Video transmitter i was unable to fly more than 2000 feet away (~600meters). So the 1.3Ghz Video transmitter reduces my 2.4Ghz Spektrum range...Then i got my cheap Asian amplifier and using a 2.4Ghz Patch Antenna i was able to fly around 2.6 miles (4.18Km) away without a single glitch, but i was unable to continue because now my video was causing me problems, hehe!Not bad at all! Honestly i don't need more than 2 miles of coverage, is really a long way for an EasyStar. In conclusion the maximum range for my setup still unknown, but the range achieved is more that 2.6 miles and the +2 extra miles of coverage gained for less than $100 dlls is really a good deal for me!
Now just remember this:-The range will be different in other setups.-Never turn on your radio without antenna.-Never turn on the Amplifier without antenna.-Note that in some country's this amplifier may be illegal.Thanks for watching!
Without spending a lot of money on trackers and what not. Put the patch on something you can locate about 4 inches off the ground with abut a 1 watt transmitter on it for your R/C transmitter and the reciever patch for the Video would be mounted on the same thing, about 4 inches about the ground pointed slightly up from horizontal. Even at 60 degrees, at the distance of a couple of Kilometers that's a pretty wide window to fly in but you could always use your foot to adjust the direction if needed. I would suggest making or ordering (less than $20 US) one of IBCrazy's inverted V antenna's for your video transmitter. With a 1 Watt Transmitter on the Camera (and of course on a different freq. than your R/C Controls. This should serve you pretty well.
Thanks for your comments, Ed Stewart, are very important. You´re absolute right, but I´m not sure if I put a patch antenna, because it has a very little angle for fly, like a 60 degree in total (very restricted signal coverage) and I like to do FPV far away, like 2.5 kilometres. In that case, will I need somehow to redirect patch antenna for obtain a safe signal? Thanks for your contribution.
A great video explaining the subject is http://www.vimeo.com/8826952
It's kinda long but covers a lot of information.
A nice thread on the subject is IBCrazy's forum on RCGroups http://www.rcgroups.com/forums/showthread.php?t=1159968&highlig...
A nice explanation of DB Gain is there also, Quoted from his post:
Gain – Indicates the directivity of the antenna. The higher the gain, the more directional the antenna.
Dbi (gain) – This is perhaps the most commonly misunderstood concept. This indicates the transmitters wave compression compared to the idealized isotropic node antenna (which cannot exist). An isotropic antenna would have a spherical pattern. Higher gains have more directivity (compression), where lower gains are less directional. HIGHER GAIN DOES NOT MEAN HIGHER OUTPUT POWER!!! It simply means the antenna is more directional. Lower gains will have better general coverage where higher gains are more suitable for long range. However in the airplane’s case, it is constantly changing orientation and thus high gains can in fact be detrimental especially on the TX.
For example – Take the basic 2.15 dbi dipole. The radiation pattern looks like a doughnut with the antenna running through the center. Now let’s increase the gain to 3dbi (such as a full wavelength dipole). The doughnut gets flatter, but now has a larger diameter. Now let’s go way beyond reality and go for 100 dbi. It now looks like a flat washer (I’m ignoring the lobes concept here) with a very large diameter. That’s great for range, but what happens when you need to turn? What about when you climb? Your pattern now completely missed your receiver! Thus gain isn’t everything.
On the ground, this is very different. Your ground station is static and unmoving. Thus you can point it in the general direction of your airplane and pick up signals with little difference regarding the airplane’s orientation. However extremely high gains are very direction and in most cases should be avoided except for when making a distance run or when you have a tracking system that can keep your antenna locked on target.
Antenna's doing amplify and high DB ratings means it has to 'funnel' radiated power into a narrower window, the patches are directional, the lower DB rated ones have a wider 'window' for less directionality. The type you linked to radiate in all directions horizontally but have a virtual hole over head and the radiated pattern looks like a donuts. With a 20db antenna it would be a very flat donut. Unless your trying to fly outside of line of sight your better off with the stubby antenna on your stock unit. More of a nice Apple shaped coverage. Of course this is all assuming your holding the antenna vertically. Some amplification, possibly 1 watt or less would give you some extended range and fully directional antennas (patch, yagi or grid type) would be needed beyond that. A 2 watt microwave transmitter right there in your hands might even be dangerous.
how do you keep the 2.4 from messing up your fpv?
i use a 2.4 fatshark.. and the fm radio i was told i should use for better video ..
but i like 2.4 radio better .. id like to have a ground station do everything .. but i have no idea how
Comments
i got 5 miles .perfect signal until i ran out of power on the way back hahaha https://www.youtube.com/watch?v=u7jhv-yXQgY
http://www.vimeo.com/8826952
It's kinda long but covers a lot of information.
A nice thread on the subject is IBCrazy's forum on RCGroups
http://www.rcgroups.com/forums/showthread.php?t=1159968&highlig...
A nice explanation of DB Gain is there also, Quoted from his post:
Gain – Indicates the directivity of the antenna. The higher the gain, the more directional the antenna.
Dbi (gain) – This is perhaps the most commonly misunderstood concept. This indicates the transmitters wave compression compared to the idealized isotropic node antenna (which cannot exist). An isotropic antenna would have a spherical pattern. Higher gains have more directivity (compression), where lower gains are less directional. HIGHER GAIN DOES NOT MEAN HIGHER OUTPUT POWER!!! It simply means the antenna is more directional. Lower gains will have better general coverage where higher gains are more suitable for long range. However in the airplane’s case, it is constantly changing orientation and thus high gains can in fact be detrimental especially on the TX.
For example – Take the basic 2.15 dbi dipole. The radiation pattern looks like a doughnut with the antenna running through the center. Now let’s increase the gain to 3dbi (such as a full wavelength dipole). The doughnut gets flatter, but now has a larger diameter. Now let’s go way beyond reality and go for 100 dbi. It now looks like a flat washer (I’m ignoring the lobes concept here) with a very large diameter. That’s great for range, but what happens when you need to turn? What about when you climb? Your pattern now completely missed your receiver! Thus gain isn’t everything.
On the ground, this is very different. Your ground station is static and unmoving. Thus you can point it in the general direction of your airplane and pick up signals with little difference regarding the airplane’s orientation. However extremely high gains are very direction and in most cases should be avoided except for when making a distance run or when you have a tracking system that can keep your antenna locked on target.
i use a 2.4 fatshark.. and the fm radio i was told i should use for better video ..
but i like 2.4 radio better .. id like to have a ground station do everything .. but i have no idea how
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