Best Frequency for Video Downlink/FPV

[emalpica]

Searched all over the forums for this and didn´t quite find the answer I´m looking for, so I apologize in case I´m double posting.

I´m looking to buy a new FPV system and video downlink for AP. So far I´ve seen the following frequencies for video 900 Mhz, 1.2Ghz, 1.3Ghz, 2.4 Ghz and 5.4Ghz. at both 500mW and 1000mW

From what I understand 1.2 is illegal in the U.S. but where I´ll be flying there are no such restrictions for any of the frequencies mentioned above, wich one would be the best suited for FPV/Video Downlink Flying in terms of range and most importantly, interference with a 2.4Ghz Tx/Rx Radio?

I plan on using 2 x 2.4Ghz radios for airship control and camera gimbal (DX8 and DX6i). I was thinking of going 900Mhz 500mW as it seems to be the most popular, but any advice towards the new system will be greatly appreciated!!

[HeliShredder]

It is recommended by many to use a higher frequency for the video link than for the RC link. While I don't have experience myself (just putting together the system) this makes sense for a number of reasons. First, the video transmission does not interfere with the RC link (due to harmonics). Second, the range of the video link is typically lower than that of the RC link, which is better since you can turn around when the video degrades.

When using 2.4GHz RC link your best option IMHO is 5.8GHz for video. Have a look at this review. You can get a good system fairly cheap. Note that they get about 1km range with 3dBi antennas on both sides. If you use a high gain patch antenna (say 15dBi) with a tracker on the receiver side you should easily be able to get 4km LOS range with this system.

[emalpica]

Looking for 5.8 Ghz alternatives ATM

anyone know if 1.2Ghz would interfere much with 2.4Ghz R/C? would anyone care to explain or link a reference regarding harmonics?

Thanks!!

[HeliShredder]

You're welcome. 1.2GHz is one of the worst frequencies you can use together with a 2.4GHz RC link since the 2nd harmonic of 1.2GHz is at 2.4GHz. What this means is that your video Tx will emit some RF power at 2.4GHz which results in a reduced range of your RC link. Have a look at this article on on wikipedia for an explanation what "harmonic" means. You can use a filter to make it work better but it is in my opinion better not to use 1.2GHz in the first place.

[halley]

Originally Posted by HeliShredder

You're welcome. 1.2GHz is one of the worst frequencies you can use together with a 2.4GHz RC link since the 2nd harmonic of 1.2GHz is at 2.4GHz. What this means is that your video Tx will emit some RF power at 2.4GHz which results in a reduced range of your RC link. Have a look at this article on on wikipedia for an explanation what "harmonic" means. You can use a filter to make it work better but it is in my opinion better not to use 1.2GHz in the first place.

The actual frequency usually recommended is 1.280 GHz or 1280 MHz. It is sometimes called 1.3 GHz when non-technical people round the number up. Its first harmonic (not second) is just doubling the frequency. That's 2.560 GHz.

This is well outside the range for flight control radios. From the first source found on the web: "Futaba divides the 2400MHZ band into 36 channels each channel centered 2.025MHz from each other starting at 2405MHz and ending at 2477MHz or 2479MHz depending on the transmitter." I didn't bother checking the FASST chip datasheet to confirm. Spektrum uses the same general range, if not the exact same chips, to accomplish the radio link. (They differ in how they use the channels, and in their protocol.)

Also, it's generally the lower frequency that causes problems for the higher band, and not so much the other way around. So we're concerned about the low video band messing up the high Spektrum/FASST flight-control band.

The Spektrum/FASST receivers are all-digital, heavily filtered, and detect interference, so I don't see this as a problem for them.

Even if the video receiver has a horrible saw filter (as most do), they should easily be able to discriminate noise on 1239 MHz (half of the highest 2.4 GHz channel) from video signal on 1280 MHz.

It could be worse for the video on 1240 MHz, but USA receivers are generally locked out of this channel or should be, as this is not an approved band. You still need an FCC Amateur Technician class license to use 1280 MHz in the USA, and the license does not authorize 1240 MHz for video due to a low side band.

[emalpica]

Thanks for your help! cleared my head now,

Looking at these combos/transmitters

For 1.3Ghz

http://hobbywireless.com/cart/index....roducts_id=514

For 5.8Ghz

http://hobbywireless.com/cart/index....30738faebe4181

http://www.iftrontech.com/5.8GHz-Tra...duct_info.html

The Mondo Stinger seems like a neat option, a bit out of range for my budget though, especially since the price tag is transmitter only.

Also saw some options from HobbyKing, but haven't heard very good things about their transmitters in specific and they never seem to have them in stock, so didn't even bother linking.

I think I'll go with HW's 1.3 Ghz combo, unless anyone has another recommendation!

[HeliShredder]

Have a look at the 5.8GHz system from BEVRC. It's cheap and quite good according to this review.

[Tahoe Ed]

In looking at the system that is offered by Hobby Wireless, the specifications look the same as the BEV system. Some of the descriptions are the same. If you are in the US it will save you some delivery time. The cost is about the same. I ordered from BEV before I saw the Hobby Wireless. I will say that the patch antenna is cheaper at BEV.

[Flying Tivo]

Go for the 1.2-1.3Ghz 800mw, that is what im using. Just get a harmonic filter on the TX and the tx will run a lot cooler with it. No problems with interference. I have gone up to 300 meters with no problem and very clear signal.

Felipe

[galexis]

Less than a $100 shipped to your door, but I would pay extra $20 for the expedited:

Camera: Great low light resolution:

http://www.securitycamera2000.com/pr...a-0.01Lux.html

Video transmitter:
1.2G (take off the heavy heat sink) http://www.securitycamera2000.com/pr...ion-700mW.html

[galexis]

Less than a $100 shipped to your door, but I would pay extra $20 for the expedited:

Camera: Great low light resolution:

http://www.securitycamera2000.com/pr...a-0.01Lux.html

Video transmitter:
1.2G (take off the heavy heat sink) http://www.securitycamera2000.com/pr...ion-700mW.html

[darkfa8]

so what is the verdict on video RX/TX frequency here in the USA for best range & non-interference with a 2.4GHz FASST control system?

[jrlederer]

I am itching to burn a hole in my savings account right now after getting my first experience watching this new world of FPV -- whoah!

I agree with the above post -- as of today, Dec 2010, what is the verdict from those who have hands on experience?

Is FPV as cooool as it first appears or is there a lot of hassle that makes this one of those impulses worth letting pass me by. If loving high tech gadgets is wrong, oh Lord, I do not want to be right.

This hobby is starting to become more expensive than the drug habit it aimed to replace!!! (just kidding... ha ha ha)

THanks and have a nice day to all!
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for those who don't mind holding my hand for a second here, and possibly offering me more specific help to my circumstance please feel free to read on. Any and all replies would be greatly appreciated....thanks in advance.

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My budget would allow a robust setup most likely, but thinking of the learning curve associated here and the inevitable glitches or interference or whatever from a long list of possible mishaps that could go wrong may steer me toward a 'beginner' system first, and then once the skills are sharpened, to then go to a higher quality setup.

I guess what I'm tryiing to wrap my head around here is...how far does the dollar go when it comes to functional return of investment? Will a $200 setup deliver me relatively the same experience as one costing 5-10x that much or can you tell where your dollar bought when it's 'showime'?

Is a crash a total loss since it is delicate optics and lenses, or am I being overly worried and is it durable enough that its worth putting in a decent sum of money toward the initial investment?

i also have a relatively wide spectrum of heli sizes to choose from and different than average electronic skill i.m.o., an example is that i am a General Class ham radio operator and so if that is a smart option to go to the reserve frequencies for clearer reception, i would be able to do so.

Also, I have this product that a girlfriend of mine a few years back bought me for Christmas called Helicommand RIGID. I would hope that it works, as i never got around to installing it as at that time when i received it i was using a radio with too few channels than necessary for it to operate fully functionally...and then by the time i stepped up to a better trasmitter, i had already gotten over the frustrations of crashing all the time and so never saw the need to go through the effort of getting it all configured....but it was/is supposed to be top of the line as far as stabilization goes...?

I could use that or the FBL system or just the normal flybar equipped setup of the days of yore if there is a reason to do so. I hope this is not too off topic and that i haven't babbled too far off what was my aim here. the heli sizes to choose from are all Align brand trex 250SE, 450PRO FBL, 450PRO, 500 ESP TT, 550 ESP TT. Which is best for a newbie to the video thing that is...i think im a decent pilot, after all this time, i'd hope so...i guess once i record something i'll let you guys tell me.

thanks again and have a beautiful day...even though its raining here in los angeles....which is another topic enirely that one day i'd like to get in to the nitty gritty of constructing...waterproof? resistant? heli that can be flown rain or shine....one of these days.







i

[pr0ject42]

Really there are a few factors involved, first is the hardware you're using junk? If so, it doesn't matter what spectrum you're squatting on.

So the very basic rule of thumb is that the lower the spectrum, the better performance it has with non-line of sight situations. Of course this is going to be also greatly variable due to multipath reflections, other interference and gain/loss of your system.

So in some areas running 900 MHz might be awesome, others with lots of public unlicensed stuff (baby monitors, cordless phones, etc) you could run into issues. I can't believe anyone would want to use 2.4 GHz, you are sharing that band with wi-fi, bluetooth, hell microwaves will spatter interference in the 2.4 range and of course there are cordless phones, baby monitors, etc also looming in this range. 5.8 GHz there are all kinds of frequency hopping microwave systems that use this band, along with wifi and whatever else plus it has poor non-LOS performance.

I do know in Europe, GSM is operated on the 900MHz, so I'd stay away from that stuff over there, as they usually use frequency hopping and I'll bet that commercial grade RF equipment made by Nortel/Nokia/Ericsson will stomp all over your transmissions and not even bat an eyelash.

I personally would stay low in the band, make sure you don't put a bunch of connectors in your RF setup (reduce loss) leverage gain with antennas (remember every 3dB gain, you have effectively doubled your output power) and leverage gain with diversity, spread those Rx station antennae as much as you can (there is a spatial gain associated with this) along with the obvious picking the stronger signal coming in.

If you can get your hands on a spectrum analyzer, it might also help pick a good performing band for your area, however these things are insanely expensive so a better idea is to just go talk to the folks who are already doing this in your area and see what they gotten the best results with.

What I don't understand is why hasn't a manufacturer done a a single band Tx and Rx for both your control and video link, thus you maintain a sane link balance with video and control of the craft. You could also keep it down to one antenna on the craft and on the ground (or two for diversity) but reducing the overall complexity of the system set up and fewer points of failure.I guess there is more money in marketing two different chunks of hardware?

[aaronredbaron]

Eagle Tree is actually working on a "Eagle Link" which will integrate video and control in one system on 1.28 gHz (thread about it on RCG). As far as 2.4 gHz goes, its true performance can be crappy in urban areas, but they do offer great performance in less crowded areas. Lots of FPV folks don't care to fly with other modelers, so they could care less about 2.4 gHz control being an issue. I already had a 2.4 setup from my AP days so I started FPV with it. I've gone to 1.28 gHz, but I still use my 2.4 gHz stuff. If I am at the beach or if there is nobody at the field, my 2.4 gHz stuff still works very well!

(picture came from RCG thread)