2.4 or 5.8?

To discuss all things relating to flying models via remote video

2.4 or 5.8?

Postby ArjanH » Mon Jan 24, 2011 9:16 am

Hi Guys/Girls

I have been thinking for a while now about getting into FPV and have been doing a bit of reading. I found that a lot of serious FPV'ers use the old MHZ radios because they apparently get better range and that this also lets them use the 2.4GHZ range because it gets better range than the 5.8 stuff. Can anybody confirm this? How much difference is there?

Also, I have an old 2 channel, 2 meter balsa floater that can easily carry the extra weight and is just gathering dust in my garage. With a bit of modification I should be able to mount a motor/camera pod and breath some more life out of an old favourite. Should I bother or just go and get something EPP from HK or Himodels?
ArjanH
 
Posts: 22
Joined: Sun Aug 29, 2010 2:22 am

Re: 2.4 or 5.8?

Postby RCModelReviews » Tue Jan 25, 2011 3:25 am

There are many factors which affect the range of a video signal but generally speaking (because of something called "path loss") a 2.4GHz signal will travel further than a 5.8GHz signal. By the same token, a 1.3GHz or 900MHz signal will travel even further.

Your choice of FPV video frequency will depend on what's legal in your area. The 2.4GHz and 5.8GHz bands are usually legal in most countries but not all allow use of the 1.3GHz and 900MHz bands -- so you need to check.

The longest-range solution is a 900MHz transmitter with a hi-gain receiver antenna. In theory, this could deliver tens of miles of range.

I'm not a fan of 2.4GHz video links for several reasons...

Firstly, there is more chance of having your video signal interfere with RC planes. Even if your own model is on a long-wire FM/PCM frequency, there may be other models flying in the area and video transmitters are one of the hardest forms of interference for any 2.4GHz RC system to contend with. Non-hopping systems like DSM2 are the most at risk.

Secondly, you run the risk of getting interference on the received video signal from a wide range of sources -- from other RC transmitters to cordless phones, microwave ovens etc. Losing your video signal when your plane is beyond visual range will almost certainly mean the loss of the model -- unless you've got a "return to launch" system such as that on the FY21AP.

Right now I'm using a 200mW 5.8GHz system that I've tested out to over 1KM (1100 yards)and it looks as if I'll probably get to about 1.5Kms (nearly a mile) before the signal degrades too much. For longer distances I'll use a high-gain receiver antenna.

If I wanted to fly beyond a 2-3Kms (a couple of miles) then I'd almost certainly go to 900MHz -- if I could find a system that transmitted on a part of the band that was legal and if (here in NZ) I had a HAM radio license.
RCModelReviews.com, just the facts.
User avatar
RCModelReviews
 
Posts: 2120
Joined: Tue May 04, 2010 3:40 am

Re: 2.4 or 5.8?

Postby Kamu » Sun Jan 30, 2011 3:42 pm

I was always impressed with what Trappy was able to do with his 1W 2.4GHz video tx. He got some serious range with that.
Kamu
 
Posts: 34
Joined: Sat Jan 08, 2011 8:25 am

Re: 2.4 or 5.8?

Postby RCModelReviews » Sun Jan 30, 2011 11:11 pm

Don't forget that Trappy's videos are not taken from the FPV camera but from another (non radio-linked) unit so the quality of the video is always "perfect".

In the right conditions, 1W of 2.4GHz signal will travel a surprisingly long distance, especially if you're using a directional receiver antenna with enough gain.

Good receiver antennas are the secret to long-range setups. You can keep raising the power as much as you like but, thanks to the inverse-square law, doubling the power does not double your range. In fact, all else being equal, you need four times the power to get double the range.

However, you can effectively double the range by simply adding another 3dB of gain to your receiver antenna.

So, if you have a 200mW video transmitter and currently use 2dBi antennas at each end (those little black plastic ones) then, if you want to double the range, you can either use an 800mW transmitter, or invest in a 5dBi antenna for the receiver.

If you want to quadruple the range, you can either invest in a 3.2W transmitter for the transmitter, or use a receiver antenna with 8dB of gain (probably a patch antenna) -- which is pointed in the appropriate direction.

Given that increasing the power of the transmitter produces other problems -- such as high battery drain, possible desensitization of your RC receiver, etc, and costs a lot of money -- the best return on investment often comes from investing in better receiver antennas.

This is why I'm currently working on a series of DIY articles which focus on building practical high(ish) gain receiver antennas for FPV work.
RCModelReviews.com, just the facts.
User avatar
RCModelReviews
 
Posts: 2120
Joined: Tue May 04, 2010 3:40 am

Re: 2.4 or 5.8?

Postby Allan Warner » Mon Jan 31, 2011 9:46 am

Allan Warner
 
Posts: 46
Joined: Tue Aug 24, 2010 9:45 pm

Re: 2.4 or 5.8?

Postby Kamu » Mon Jan 31, 2011 3:23 pm

RCModelReviews wrote:Don't forget that Trappy's videos are not taken from the FPV camera but from another (non radio-linked) unit so the quality of the video is always "perfect".

In the right conditions, 1W of 2.4GHz signal will travel a surprisingly long distance, especially if you're using a directional receiver antenna with enough gain.

Good receiver antennas are the secret to long-range setups. You can keep raising the power as much as you like but, thanks to the inverse-square law, doubling the power does not double your range. In fact, all else being equal, you need four times the power to get double the range.

However, you can effectively double the range by simply adding another 3dB of gain to your receiver antenna.

So, if you have a 200mW video transmitter and currently use 2dBi antennas at each end (those little black plastic ones) then, if you want to double the range, you can either use an 800mW transmitter, or invest in a 5dBi antenna for the receiver.

If you want to quadruple the range, you can either invest in a 3.2W transmitter for the transmitter, or use a receiver antenna with 8dB of gain (probably a patch antenna) -- which is pointed in the appropriate direction.

Given that increasing the power of the transmitter produces other problems -- such as high battery drain, possible desensitization of your RC receiver, etc, and costs a lot of money -- the best return on investment often comes from investing in better receiver antennas.

This is why I'm currently working on a series of DIY articles which focus on building practical high(ish) gain receiver antennas for FPV work.


Yep, a GoPro if I am not mistaken. Nice camera. What I meant was not so much quality but usable video feed (enough picture to fly with).

I did not know about power vs range and dBi vs range. I wonder if there is any nice websites that explain all the basic concepts to the layman.
I stumbled across this: http://cgi.ebay.com.au/24dbi-High-Gain- ... 19bf6bcd49 .... :)

One thing that I have not been very sure on is if you have a 24dBi antenna like the above, is the range of data being transmitted through the antenna also increased?

I am anxiously awaiting those build articles/videos. Along with the other things you have teased us all with ;).
Kamu
 
Posts: 34
Joined: Sat Jan 08, 2011 8:25 am

Re: 2.4 or 5.8?

Postby RCModelReviews » Mon Jan 31, 2011 11:13 pm

Those hi-gain antennas are very directional so you would certainly want to use automated antenna tracking because if they're pointed even slightly away from the model (+/- 5 degrees) then the signal will be lost and you'll have no signal.

I plan to get ahold of a parabolic antenna with a 24dB gain as soon as the Chinese New Year is over. When fitted to the standard video receiver, this will increase the range of a 200mW 5.8GHz video transmitter to about 6Kms and that of a 200mW 2.4GHz video sender to about 10-12Kms. That is more than the effective range of most 2.4GHz RC equipment but, as I suggested, a tracking system will be required -- so you'd also have to use a hi-gain antenna for your RC transmitter.

It would also be important to use an RC system with telemetry so that it can accurately report back the exact position of the RC model so as to allow the tracking system to calculate the correct direction and azimuth for the antenna to be pointed.

Even so, there are risks to flying like this. If you disappear below the horizon or behind a hill or trees, you will be out of the "line of sight" so regardless of the more powerful antennas, you will lose video and/or RC -- with possibly dire consequences.
RCModelReviews.com, just the facts.
User avatar
RCModelReviews
 
Posts: 2120
Joined: Tue May 04, 2010 3:40 am

Re: 2.4 or 5.8?

Postby Allan Warner » Tue Feb 01, 2011 9:30 am

I may have this totally wrong but I thought VRx antena(ground station) aiming could be done one of several ways that does not require RC telemetry. Recieved video signal strength/quality(also used for switching between directional and omni aerials) or GPS co-ordinates from the OSD. OSD is sent via the audio channel of the video and on 5.8gHz video you normally have two(stereo) audio channels. Thus, one spare unless of course you like to listen to wind noise. Joking apart, I would think audio from the plane could be a usefull feed back on how things are going. I'm trying to get an understanding of FPV set ups for my own 'adventure'(????) in this aspect of RC. I'll go and stand in the naughty corner for a couple of hours if I'm wrong.
Allan Warner
 
Posts: 46
Joined: Tue Aug 24, 2010 9:45 pm

Re: 2.4 or 5.8?

Postby RCModelReviews » Wed Feb 02, 2011 12:52 am

Anything that relies on a signal from the video system to orient the tracking of the video receiver antenna is (IMHO) a little bit dodgy.

If the signal is lost (for whatever reason) then how does the tracking system know how to point the antenna -- because without the signal it's searching for, it has no coordinates to use to calculate bearing and azimuth.

It is far simpler and more elegant to use the telemetry downlink on an RC system that provides this info. Remembering that if that signal can't be heard then you also can't control the model so everything becomes somewhat academic.

The nice thing about using the RC telemetry for the downlink is that you could turn the tracking off, turn it right away from the direction of the model then turn it back on and it would be back to receiving the strongest signal in just a second or two. That won't happen if you're reliant on the video/audio signal to deliver the tracking info.
RCModelReviews.com, just the facts.
User avatar
RCModelReviews
 
Posts: 2120
Joined: Tue May 04, 2010 3:40 am

Re: 2.4 or 5.8?

Postby Coyote » Wed Feb 02, 2011 1:50 pm

Firstly, there is more chance of having your video signal interfere with RC planes. Even if your own model is on a long-wire FM/PCM frequency, there may be other models flying in the area and video transmitters are one of the hardest forms of interference for any 2.4GHz RC system to contend with. Non-hopping systems like DSM2 are the most at risk.

Secondly, you run the risk of getting interference on the received video signal from a wide range of sources -- from other RC transmitters to cordless phones, microwave ovens etc. Losing your video signal when your plane is beyond visual range will almost certainly mean the loss of the model -- unless you've got a "return to launch" system such as that on the FY21AP.


That depends entirly on what power your vtx is at. Anything above 100mw and none of those will have any effect what so ever. Microwave ovens ? No not at all. The only risk you might un if flying low over housing is illegal 2.4ghz cctv units or 1.2ghz cctv units, afterall 2.4ghz is the second harmonic of 1.2ghz.

Yes you have to multiply your transmitter by 4x to achieve double the range, but far easier to increase the gain of the antenna

Trappy uses a 500mw lawmate transmitter not a 1W

Those hi-gain antennas are very directional so you would certainly want to use automated antenna tracking because if they're pointed even slightly away from the model (+/- 5 degrees) then the signal will be lost and you'll have no signal.


Lol, no not at all. A high gain antenna like a patch or a yagi has a beam width of more that 40 degrees normally. So taking 40 degrees as an example you can point it 20 degrees at least each way from the plane. Ive flown my radian 0km out and 2.3km to the right of my forward facing " directional" antenna just to disprove this theory. My directional yagi that shouldnt be able to see the plane was receiving perfect picture.

Anything that relies on a signal from the video system to orient the tracking of the video receiver antenna is (IMHO) a little bit dodgy.

If the signal is lost (for whatever reason) then how does the tracking system know how to point the antenna -- because without the signal it's searching for, it has no coordinates to use to calculate bearing and azimuth.

It is far simpler and more elegant to use the telemetry downlink on an RC system that provides this info. Remembering that if that signal can't be heard then you also can't control the model so everything becomes somewhat academic.


I use antenna tracking on my fpv planes using an EZOSD with telemetry send down the audio channel. How can it be dodgy ? The antenna is pointing directly at the plane, the video is received the audio too. If the signal gets broken up the antenna remains pointed at the plane according to last position. With is beam width at distance its that large it would take the plane minutes to fly out of the reception of the antenna. All the flights ive done it never happened once. If with any system the video is lost having telemetry is pointless anyway. You cant fly a plane you cant see.
Coyote
 
Posts: 2
Joined: Wed Feb 02, 2011 1:31 pm

Next

Return to FPV

Who is online

Users browsing this forum: No registered users and 0 guests

cron