Spektrum DX7 2.4 and wireless camera 2.4 500 mW?

44 posts in this topic

Posted

JetPilot,

Is your comment from experience?

Jim

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Posted

I work prof with radio gear for Tetra and GSM bands.

I can say it is a BAD idea to have both a TX and RX in the same frequency band on the SAME plane ! for example: Video downlink and RC controlling.

it is doomed to failure ! parform bad or even crash.

Why:

it is impossible to filter powerfull tx away from the rx,

with small and light filters, in the same band.

there must be many many MHz distange from TX to RX before filters can be made to perform good and still be light enought to be on RC planes.

if no filters are used, blocking will happen the RX will start to mix all sorts of unwanted signals into the rx.

The mounting distance possible in RC planes are often limited,

on normal planes its possible to have 10-20 inch distange from TX to RX

this is always a good idea, to keep as much distance as possible,

between TX and RX stuff, nomatter what kind of bands they use.

Today I have made a telemetri system for a friend in my club,

it opperates on 435MHz using licence band, so we can transmit as much as we like legally, but the GPS module opperating at 1.57GHz was blocked allreade at 100mW 20cm distance. we needed much more power, and still good margin.

solution, added 5 pol low pass in the tx signal and added 5 pol hi pass filter on the GPS.. now it works..

such a 5 pol filter made with coils and capacitors for the GPS weight 2 gr !

attenuation at 1.57Ghz 0.3dB !! (yes I am proud of that)

attenuation at 435MHz 60dB !!

the TX filter also has 60db attenuation for 1.57GHz for spurious killing.

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Posted (edited)

^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

....................That is exactly what I was going to say :D .............................

Edited by JetPilot

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Posted

Only way it would work is to use digital encoding. Such that each component has a "signature" and knows which signals to "listen to".

I think it could be done anyway. I'm no EE, so I don't know how to go about doing it. But it seems possible.

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Posted (edited)

Even then you'd have problems. You have an unwanted signal that is thousands of times stronger than the one you want, that forces the input stage of the RX to attenuate the incoming signal a lot not to saturate... which makes you attenuate the useful signal at the same time, when what you'd want is actually amplify it...

Edited by Kilrah

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Posted

What if you were to put everything on the same frequency. Then use the encoding process. Something that tells the receivers if it is a signal it wants to listen to, or one it wants to ignore.

Think of a local computer network. All computers are connected to the same switch/hub. Yet they are all able to decipher what data goes where. Sorry, I really don't know how one would go about doing it. But from a conceptual point of view, it seems possible. This would probably require completely different receivers though, so I don't know if it's something that one of us could do. Maybe a job more for Lawmate, Futaba, Hitec, etc.

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Posted

What if you were to put everything on the same frequency. Then use the encoding process. Something that tells the receivers if it is a signal it wants to listen to, or one it wants to ignore.

If you put everything on the same radio and have it working as a two way communications system, that is something very different than using the Speckturm system we are talking about here... That is called a RADIO MODEM system, then you have data going both ways, and it is computerized, and all done with the same radio. This is not practical for 99.99% of us to do. Maybe one day someone will sell a ready made plug and play system like that, but not now.

Back to the Specktrum system with a 2.4 GHZ transmitter also on board, it does not matter if the receiver tries to ignore the video or not, it is so overpowered by the Video TX on the same plane that it cannot see anything else.

Picture me putting a small LED display directly into the sun, and then telling you to ignore the sun and to read me the numbers on the LED. You would not be able to, the sun would be so overpowering that you would never even see the LED. Same thing with the Specktrum, the 2.4 GHZ video TX is signal is so strong, that its like looking into the sun, it will never be albe see anything else even if it is smart enough to ignore the Video Signal.

JettPilot

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Posted (edited)

OK, it's not good to mix 2.4Ghz video with 2.4Ghz R/C BUT is it possable to make it work ?

I would like to use 2.4Ghz R/C on a large gas heli due to the big safty advantages but also need a video down link. Ultamate range is not needed as it will be flown vis at less than 500ft.

The only band I can use for the video link is 2.4Ghz !

Now I know that 10mW video power will be ok for this range.

If I mount the video TX under the heli with the camera and use an inverted ground plane aerial or patch pointed down I think there will be no interference to the R/C link at the range I need.

If I mount my video RX patch so that my R/C TX is behind it I think there should be little interference to my video picture.

OK...who thinks it's worth a try ???

Terry

Edited by Terry

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Posted (edited)

Just posted this in another thread as well, but I think for those outside the US there is a real problem in availability of systems. Our airwaves are so saturated that for RC aerial photography, which means flying in congested area with higher risk of RF interference, the 2.4GHz RC control systems are a must and the 900MHz band is a GSM band, so that we have a problem with AV downlinks. And it is critically imporan re finding a solution.

I-ve just been trying to figure out what frequencies are legal in Europe. On the site of our national Telecom Agency I-ve found the National Frequency Register (http://www.agentschap-telecom.nl/nfr/index.html) and in there the following which seem to be "license free" frequencies which I guess would be the frequencies we're limited to for our purposes and dependent upon available systems.

National Frequency Register, version 13-03-2007

Lower frequency Upper frequency Application License-

regime Power Channel-

space Duty-

cycle Occupation

6.765 MHz 6.795 MHz Non specific SRD No 42 dBµA/m at 10m All kHz 100%

13.553 MHz 13.567 MHz Non specific SRD No 42 dBµA/m at 10m All kHz 100%

26.957 MHz 27.283 MHz Non specific SRD No 42 dBµA/m at 10m All kHz 100%

26.957 MHz 27.283 MHz Non specific SRD No 10 mW e.r.p. All kHz 100%

40.66 MHz 40.7 MHz Non specific SRD No 10 mW e.r.p. All kHz

433.05 MHz 434.79 MHz Non specific SRD No 1 mW e.r.p. Power density limited to -13 dBm/10 kHz for wideband channels. All kHz 100%

433.05 MHz 434.79 MHz Non specific SRD No 10 mW e.r.p. All kHz <10%

434.04 MHz 434.79 MHz Non specific SRD No 10 mW e.r.p. 25 kHz 100%

868 MHz 868.6 MHz Non specific SRD No 25 mW e.r.p. All kHz <1,0%

868.7 MHz 869.2 MHz Non specific SRD No 25 mW e.r.p. All kHz <0,1%

869.3 MHz 869.4 MHz Non specific SRD No 10 mW e.r.p. 25 kHz 100%

869.4 MHz 869.65 MHz Non specific SRD No 500 mW e.r.p. 25 kHz The whole frequency band may also be used as 1 channel for high speed data transmission. <10%

869.7 MHz 870 MHz Non specific SRD No 5 mW e.r.p. All kHz 100%

2400 MHz 2483.5 MHz Non specific SRD No 10 mW e.i.r.p. All kHz 100%

5.725 GHz 5.875 GHz Non specific SRD No 25 mW e.i.r.p. All MHz 100%

24 GHz 24.25 GHz Non specific SRD No 100 mW e.i.r.p. All MHz 100%

61 GHz 61.5 GHz Non specific SRD No 100 mW e.i.r.p. All kHz 100%

122 GHz 123 GHz Non specific SRD No 100 mW e.i.r.p. All kHz 100%

244 GHz 246 GHz Non specific SRD No 100 mW e.i.r.p. All kHz 100%

I believe 433 and 868 are used for some telemetry. Not sure whether there are any good usable AV links over those and how much risk an AV link on those bands would introduce or run for interference with other systems on those bands.

Edited by Arthur P.

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Posted (edited)

The problem for me here in the UK is not finding a frequency but finding one that is affordable.

I have been using 459Mhz for my R/C link but it's expensive to do and the new 2.4Ghz systems are as good if not better at a fraction of the price.

For video we can use 1384Mhz at 500mW but the cost is very high and the TX is big.

Terry

Edited by Terry

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Posted

Hmmm, the more I think about it the more I think I will stick to 459Mhz for the R/C link. The price is high but will still be far less than investing in 5.8Ghz video and far less risky.

Terry

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Posted

now let me answer the original question:

-This is not based on assumptions, guessing, or other B.S. this is my experience, how I've been flying:

Spektrum DX7 + AR7000 (2.4Ghz)

Video link , 500 and 200mW , 2.4Ghz - 8channel.

1.- video channel selection does not matter. - I use ch 8 on 500mW, 4 on 200mW

2.- video TX antenna have to be placed well away from AR7000 - I use 60 cm cable before the "antenna" (made of the end of the cable)

4.- Spektrum DX7 will cause noise in the recieved video, to avoid this: I use a tripod with video receiver 6m cable, then my video-googles. I am 5-6 meters away from video receiver's antenna.

5.- turn on the model first, (with AR7000, it's no reason to turn on TX first) - video transmitter must be active first.

6.- switch on DX7 - while being close (>1m) to the video transmitter's antenna. - now DX7 finds some optimal channels.

this is how I fly.

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Posted

What about Futaba 2.4GHz for R/C control? I know that Spektrum uses 2 fixed channels, but Futaba changes the frequency all the time.

"The frequency of Futaba 2.4GHz FASST shifts hundreds of times per second..."

I guess that is even worse for the quality of the video link?

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Posted

It's nice to hear you can use 2.4Ghz for both R/C and video but reports of total success are few and far between. The separation you need between TX's and RX's both in the air and on the ground show the system is running very close to failure. In this hobby we have enough problems with interference as it is without making it even harder.

Bottom line for anyone thinking of going this route is think hard before you try it.

Terry

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Posted

Yes, The Futaba type of spread spectrum modulation (FHSS) is generally more prone to errors because of only one active channel at any time, that will now-and then hit some "busy" frequency .. when that happens often, there will be trouble.

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Posted

Hi Andre and all the others,

Sorry for the others but first post... have been working on VR for about 3 years now and it has been pretty much a lself earning experience all the way...

I started with and easystar and with just a CMOS self contain camera at 10 Mw.. Being an Aussie we are on 36Mhz and I started pre 2.4 TX days.

My background is as a HAM operator..

This post could go on for just about ever and most, I would have to say has more than likely been said already in this forum.

So equipment I use... JR 9xVer11 36 meg.. not good for the headtacker R1.. port assigment issues..

Bought a Futaba 9CHP to solve that problem.

Also use a DX7 2.4 but not with the video TX of 500mw and 1000w.. always stay with X2 different freq in VR. much safer and the futaba get me around 3 miles. :D using pal cam.. OSD, GPS,

Interested in you comments about the compatibility issue I have a 2.6 m Ventus and could get the AR7000 and the 500mw video TX well away.. but I consider the problem that a RX failure could be very expensive .. range is reduced condsiderably!!!!!

As I get time to look through this forum and not repeat postings .. I will be able to become more active and assist...

I have not done a lot of VR latley or at least video posts.. have some on youtube user name "RichardVRFlyer" in my earlier days... using sail servos to get close to 360 degree pan.

using a patch 8dbi and a bi pole for RX.

Using swithmode voltage regulator for different votltages for dropping from 11.1v lipo and up from 5 v to 12v low loss ,low and heat

Glad to answer any questions when I can have, I moved into Slope and thermal flying.. which make this type of flying even more of a challenge.

enough said.

Cheers

Richard

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Posted

I use 2.4Ghz radio so have been considering 1.3Ghz or 900Mhz video transmitters. Any reason you want to stick with 2.4Ghz for video?

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Posted

Legality in places where the other bands aren't allowed...

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