FPV : 900MHz Vs 5,8GHz

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ujjwaana:
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I am planning to progressively foray into FPV + Autopilot (= UAV??) , buying the better (VFM) item at a time.

2.4GHz system is out of question as I have a 2.4G Radio to control the plane. So the options left are 900Mhz and 5.8GHz.
Which one is claimed to give solid quality video form longer range ? With 900Mhz, I would go with a 1500mW Tx and if I choose 5.8G, I would go for a 500mW Tx.

The review on other sites comparing 900MHz and 5.8G are rather contradictory. As an electronics DIY myself, I would go for higher frequency. The chances of plane going between an obstruction is also unlikely, though it should work Beyond Visual Range (BVR) as long as the plane and ground station  are still in line of sight.

The 900Mhz (1500mW) Tx/Rx combo from HK has huge QA issue. Tx soldered like by kids.
http://www.hobbyking.com/hobbyking/store/uh_viewItem.asp?idProduct=13443

I have found much higher quality 5.8Tx at other sites :
http://www.lowpricerc.com/product_info.php?cPath=36&products_id=1476

Does any one knows similar good quality Tx/Rx for 900Mhz ? I would not pay premium for ImmersionRC and FatShark stuff

Suggestion from people with experience would be highly appreciated.

SunLikeStar:
The 900Mhz 1500mW system is too heavy for me. I am thinking about getting 900Mhz 500mW and making a patch antenna for it. Here is a link to a very cheap and effective DIY antenna http://www.rc-cam.com/gp_patch.htm
People have got upto 2 mile with this setup. However i am still undecided on this.

RotorZone:
Here's some advice I was given. Talking to some one who has been doing this was helpful. There are a lot of small things which make a big difference in your success rate that you gain from experience. Just like scratch building or setting up a heli, there are best practices you won't even think about while doing it for first time. Not many are captured in this post, but it is a start.

====================
Best plane for FPV:
I use a Multiplex EasyStar but have come to realize that, even though it has far more space then most R/C planes, there's 2 other planes in particular that offer more room and somewhat better flight characteristics.  When it comes down to it, lots of compartment space and good glide characteristic, over shadow most all other features in an FPV plane.  Choosing one that limits you to only a camera and video transmitter means no GPS navigation or autopilot support, and a high likelyhood of loosing it upon the first video or R/C link fail.  The EasyStar is still a good FPV plane but it's lack of a mid-section compartment (under the wing) usually means choosing between either installing a 3S lipo or a 2S lipo+autopilot.
 
In the budget class around $130 there's the Skysurfer.  It's a clone of the EasyStar but with the advantage of including brushless motors (with the upgrade option), ailerons, and most importantly lots of space in the mid section.  Here's the RCGroups FPV thread for the SS.  You have to re-enforce the wings with glass fiber tape and put a CF rod in the wing spar but that's about it for FPV readiness in this plane.  Because it's significantly smaller and the total cost of ownership is lower than the Skywalker, I'd tend toward the Skysurfer as a replacement for my EZ if I had to start over.  It's a very popular plane and is out of stock temporarily, but you find that waiting months for the right FPV component is par for the course more often than not.
 
The Cadillac of FPV planes is currently the Skywalker.  It's got tons of space (almost too much) and lots of wing area for gliding.  The downsides are that you'll need a bigger motor, lipo and prop to drive it; and getting parts or replacing it in a crash will of course mean a bigger expense than the Skysurfer.
 
Whatever plane you choose, it's important to realize that the plane, motor, servos and R/C receiver combined will end up representing only about 1/5th of your FPV investment, so using a plane you happen to have around, isn't always a good idea if it means diminishing the chances that the other 4/5's of your equipment won't make it home safely every flight.  For example, using a plane that flies great but that has very little compartment space, means cramming lots of RF components next to each other.  The likelyhood is that you'll find out that they don't work together when (and only when) you get a 1/2 mile out and R/C control or video is lost.
 
R/C control:
Most R/C folks these days use either a 2.4GHz Spektrum or spread spectrum type radio.  Unfortunately these are generally the worst choice possible for FPV for the following reasons.
 
-No warning that range is about to be exceeded
-No analog RSSI pin to connect to an OSD, so you can know when range is about to be exceeded
-Lockouts last several to tens of seconds, meaning no chance at regaining control when signal is lost
-Not PPM based, so virtually non-existent headtracker support
-2.4GHz is very line of sight and easily blocked by trees, building or any obstacle
-Because 2.4GHz a higher frequency than 900Mhz or 1.2GHz video, it's almost guaranteed that any errant RF interference will knock out your R/C control before your video even becomes fuzzy
-Standard Spektrum range is typically between 0.6 and 0.8 miles best case. FAAST is about twice that but still has all of the same limitations above
 
With that said, you can use 2.4GHz but an autopilot is highly recommended, so that your plane will come back when you fly out of range.  Not just any autopilot though, but a 100% rock solid one that can fly your plane better than you can in the windiest conditions.  The Bay Area is not known for calm winds at ground level and even less so above 400ft.  I know of only one AP that's expected to be reliable enough and it's the RVOSD Gen 5 (which won't be out until May or June with an estimated price tag of $335 to $350).  It's also a great all-around navigation package, but requires a good deal of space in your plane and weighes about 80 grams.
 
Budget minded FPV folks like me will use a 72MHz radio.  I got a Hitec Laser 6 because it was cheap at $75, should have decent range of a mile or maybe two, provides RSSI output, and is compatible with my zero-drift Flytron headtracker.  The Futaba 7C is said to be a better choice though, and also compatible with various head trackers.  I think the 7C or 7CH/7CA  also supports UHF radio modules, but do your homework on the radio and receiver before taking my word for it.  There are so many choices and so many $1000 dead ends when it comes down to range, programmability, FPV usability and compatibility with headtrackers.  Even a top end Futaba with a Dragon Link UHF can sometimes be more susceptible to RFI than a 2.4GHz Spektrum.  Long story short is that a high price doesn't buy you immunity to all types of RFI, so the video components you chose and where you fly, should determine the R/C link you choose and vice-versa.
 
Video transmitter/receiver:
A year ago this was an exceptionally difficult decision.  Luckily time has distilled the good choices down to a couple. Here's goes.
 
1.2GHz is the best choice for video range and is off of WiFi and cellular frequencies but it will reduce your 2.4GHz R/C receiver's range.  The worst part is you won't know by how much until your plane is between 1/4 and 1/2 mile out.  Using a low pass filter is said to help but there's no empirical confirmation of that just yet.  If you the want to be on the safe side, then 900Mhz is the only other option that plays nice with 2.4GHz radios.
 
In the 1.2GHz arena, the Fox 800A 800mW is the best all around choice.
For 900Mhz, the 800mW RangeVideo VTx and VRx are the best choice.
 
Between 500mW to 800mW is the sweet spot between range vs interference created.  Folks who think more is better will go for the 1.5 or 2.5 watt video Tx's and usually end up killing the reception on their R/C receiver and GPS sensor.
 
The video transmitting and receiving antenna you use, and it's placement, will literally make the difference between getting 200 yards and several miles of range out of either video solution above.  A few days ago Randy Sowder flew his FPV Skywalker plane 4.5 miles across the SF Bay using an older 700mW Fox 700 video transmitter.  Under the best circumstances, that same transmitter will only give you between 1/2 and 3/4 mile range using the stock omni antenna.  The Fox 800A was used by Crist Rigotti in Iowa to fly out 15.5 miles and back, but it too will only give you about a mile range using the stock antenna and only when unblocked by any component on your plane or the ground.
 
No email could begin to even summarize the information needed to cover antenna optimization for FPV, so please look to RCGroups FPV forum for what works well.  The best topics are those covering V-dipole antennas (all of them are not created equal; DPCAV's is good and Range Video's is not so good), cloverleaf/pinwheel circular polarized antenna design, and patch antennas (tracking, diversity and tuning).
 
Patrick Lupo

ujjwaana:
Wow Rajesh, its a nice piece of Info. Wish Anwar creates a separate FPV/AutoPilot Section and move the thread there, or at least makes this one as a sticky.

But still, I am in a lurch to choose between 900Mhz and 5.8GHz ! As fas a Harmonics and subsequent EMI is concerned, I believe using a lower frequency for Control (Servo/Throttle) RX and higher Frequency for less critical Video would be better.
somehow I am getting lured towards 5.8G system....
 

anwar:
But isn't a direct multiple/harmonic more of a problem, as compared to having just a higher frequency :headscratch:

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