Demonstrating 2.4 ghz video downlinks at shows

[Bryce Allcorn - BritFlight.co.uk]

   We have just been testing a wireless (radio) camera in the Hustle and were very impressed with the results.  

So much so that we are looking to stock them and would like to have them working at the shows this year... But the down-link as we know is in the 2.4Ghz band and I'm concerned this could be a problem at shows.

 

Any one had any experience of this?

 

Cheers,

 

Bryce.

 

 

 

 

 

 

[Tim Mackey]

I have some short term experience, and my guess would be YES there could be problem.

Its a shame / lack of foresight that the manufacturers of thes onboard camera systems have opted for the now very popular 2.4G band. Despite the GUID protocols etc, putting a reasonably high powered video transmitter in a model, alongside a 2.4G RC rx unit usually just swamps the signal being received from the tx. Not good.

I take it your test model was flown on 35Mhz ?

Any 2.4G models in close proximity to the tx may be affected ?

[Martin Harris - Moderator]

Posted by Timbo - Administrator on 23/03/2010 12:52:35:

there could be problem.

Its a shame / lack of foresight that the manufacturers of thes onboard camera systems have opted for the now very popular 2.4G band.

 

The possible major drawback in model radio suppliers opting for an open non-dedicated frequency!  It's not inconceivable that 2.4 GHz might give us major problems in the future if the wrong application comes along. 35 MHz, with it's narrow bandwidth restrictions, is at least virtually exclusive to flying and in the event of problems we have full recourse to the Home Office for enforcement.

[Bryce Allcorn - BritFlight.co.uk]

Yup, I still fly 35Mhz for the most part - slowly converting over to 2.4Ghz.  Am going to try the camera system with a 2.4Ghz set up to see if I get any interference.

 

Guess I won't be demonstrating this at shows then!

[Tim Mackey]

Oh I am pretty certain you will get interference. When I tried a system recently, ( FC03) not only did it stop my Spektrum rx from working, but it also knocked out my home computer LAN which also operates on 2.4G

[Bryce Allcorn - BritFlight.co.uk]

The wireless transmission from my laptop knocks out the DAB radio in the kitchen when within 2 or 3 metres...

 

I've just created a small video using the the camera/plane and 35Mhz.  (taxing round the warehouse, it's raining!)  Rather impressed so far.

[Frank Skilbeck]

I think the problem is if you have a 2.4 rx in that plane, because the video 2.4 transmitter is very close to the Rx it swamps it, hence the reason to use 35 mhz. But it shouldn't affect other planes on 2.4 as it will just appear as another 2.4 transmission to them and they should happily ignore it.

 

But if the show insists on 2.4 radio systems and doesn't allow 35 mhz anymore then

you are stuck. 

[Matt Halton]

Are some show organisers dropping 35 then? That's worrying.

[Bryce Allcorn - BritFlight.co.uk]

For us it's more that I wanted to demonstrate the system on the stand.  So it would be on most of the time.  While I doubt it would cause any problems being so close to ground level I obviously don't want to a) cause a crash and b) go against the show rules.

[John Privett]

Posted by Matt Halton on 23/03/2010 22:40:30:
Are some show organisers dropping 35 then? That's worrying.

 It was mentioned somewhere that the recent Top Gun event in Florida was 2.4 only.

[Tim Mackey]

Then in that case Bryce, why not just have a video playing on your stand of the footage you have captured eleswhere.

[Erfolg]

I have little knowledge and even less experience of the systems discussed, yet there seems to be a issue that has not been recognised.

 

That is, if a modeller is operating a model on 35, with a 2.4 down-link, they would not be affected. If the power of the down-link system is great enough to swamp a 2.4 tx/rx system, would it not be a real possibility of swamping any 2.4 model system in the vicinity immediately before launch?

 

Erfolg

[Tim Mackey]

Or possibly one that may accidentally or othyerwise fly very close to it.

[Bryce Allcorn - BritFlight.co.uk]

That is exactly why I asked the question Erfolg.  I wanted to 'real-time' demonstrate the equipment by having a camera mounted in a plane and the image displayed on a screen.

 

As Tim has suggested, I'll have to leave it at pre-recorded footage playing for fear of causing interference (although with transmission power of 10mW, it should be ok).

[Tim Mackey]

I think the 10mw output power is the same as the EU spec'd RC equipment Bryce.

To be clear, I am not saying that you will not be allowed to do what you propose, but the show organizers would obviously have to sanction any such project, and I just seriously doubt that they would allow it for fear of even the slightest increased risk.

[Bryce Allcorn - BritFlight.co.uk]

But I think you are right Tim.   And if someone did crash there would always be the "wasn't my fault, it was the video down link BritFlight are showing" type comments!  Easier not to go that route!!!

 

I'll bring a plane with the set-up installed to show and a video on a monitor showing some in flight footage (assuming all goes to plan with the set-up).

 

 

 

[Erfolg]

It is apparent that Bryce and Timbo are aware of the issues and propose operating any equipment appropriately.

 

What about others? Will there be a number of incidents before the issues are widely known and appreciated by others, like myself?

 

Is this a similar issue to that of some disapproving of mobile phones on or near the flight line. How real and potentially widespread is the potential of other 2.4 systems causing our systems a problem? Or is it just hypothetical?

[Tim Mackey]

No Erfolg its real as I explained in my earlier post - fitting a video tx in my spektrum equipped model caused instant rc rx signal blackout.

[Brian Parker]

How is this happening?
I've no experience of using a Video link, but if I may out of curiosity..

The video signal is 10mW=10db.

 The spread spectrum signal is 10mW =10db.

The RC spread signal uses a very wide frequency band, the width determined by the processing gain. The processing gain can be the region of 60db or expressed as a ratio of power  gain 1,000,000.

Wanted signals can be in the noise (10mW video signal unwanted) and the wanted signal should still be received, the unwanted signals are not seen.

The wanted signal/code is recognised/seen by the receiver and the data retrieved and processed by despreading.

How close was the receiver to the video transmitter and was it electrically isolated from the rest of the equipment?

[Phil Brooks]

I asked these very questions (re swamping) on another thread, and was shot down.  From what I can remember of that thread it would appear that one problem you may suffer Bryce is that, even if you use 35 Mhz for control, your downlink may be susceptible to interference from other 2.4 transmitters in the vicinity. This is the reason why FPV flyers prefer to go it alone.  May not be good for sales if your demo quality is degraded.

[Tim Mackey]

Not sure if your question is directed at me Brian - but if so, I can tell you very little

The video transmitter ( FC03 ) was approx 6 inches from the AR6100 Rx. The FC03 is completely self powered, and there was no physical connection betweemn it and the RC equipment ( although add on units can be deployed for remote pan and tilt which plug i nto a Rx channel. I did not use this. Furthermore, the wireless LAN connection to my laptop also stopped as soon as transmission started... the router /hub was approx 15 ft away and seperated by two brickwalls. switching off the video tx restored this immediately.

[Erfolg]

Brian

 

Very interesting, but what does it mean?

 

Is my world in peril

 

Erfolg

[Brian Parker]

Timbo,
 I thought your installation would be robust.

 I wonder what modulation protocol is used for downlink?

It seems almost impossibly dirty, does it have type approval?

 I wonder if the downlink problem arises at the point before spreading and immediately after dispreading. If so, then thorough screening might be an option.

 Although the best option would be to bin it before Eric Bray finds out.

 (See his thread on the campaign for EMC).

Erfolg,

What does it mean?

 As a very loose comparison.

You are standing at a locked door outside a room.

 If you have the key can enter.

The room is hostile, standing upright presents an easy target but you have a very small 'footprint'(narrowband), by lying down (spreading) you become a small target but have a large 'footprint '(wideband).

 You can cross the room unseen by laying down and crawling.

 At the other side is a door, if you have the key you can exit the room and stand up safely (despreading).

 And yes, your world is in peril.

[Clive Matthews]

Just to clarify a point here.

 

In my (very extensive professional) experience of video microwave downlinks, it is almost always the video downlink which is interfered with from external signals. This is in part due to the intensity of the data stream and encoding issues. The antennae used in such systems should have a narrow focus to be effective.

 

Timbos' experience  is probably rare and would suggest to me that the antenna focusing might have been poor, in any case it was a TX very close to a RX. This may have 'swamped' the RX.

 

I hesitate to say it won't, but in my opinion, it is extremely unlikely that a video link with correctly focused antennae would effect a model flying any distance away. 

 

Brian, did you leave a 0 out somewhere? 

[Brian Parker]

Clive,
 I don’t think so,

N=10log(10)*P(i)/P(ii)dB

 But then I could never count.

 When you mention 'antenna focus' are you referring to directivity or resonance?