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ThomasScherrer

KX131 - KX151 - IFcam - ixus camera compare

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I tried to make a much more side by side performance test compare,

see and judge by your self,

http://www.webx.dk/rc/video-wireless/cam-c.../camcompare.htm

you can click on all files to get bigger size,

and you can also directory list and access all files directly.

you need a wide 1280 PC screen, or more :-)

else it will look wierd.

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The RFI measurements are very good things to know, so thanks for sharing. The noise in the USA R/C band has my attention. This data helps demonstrate why different folks experience different R/C range issues. Everything matters; video gear installations are the rarely the same, no matter how similar they appear.

It's great to hear that the KX-131 was too quiet to measure in your environment. It seems like a good all-around camera. I'm sticking with that one. :)

One measurement I have been hoping you would make is the input sensitivity of the popular A/V receivers. It seems nearly all FPV'ers are fixated on the Tx's RF power and ignore the Rx performance, which is very important. I'd like to know if any are better than the -85dBm spec that is commonly tossed around.

BTW, another good measurement to have is video signal bandwidth. Poor bandwidth can essentially make upgrading to higher resolution cameras a waste of money. I've causually sampled these measurements in the past and was surprised by what I found. For sure, not all A/V systems are the same (heck, even the same models seem to vary in performance).

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yes with the 131 I was not able to see any difference if it was on or off :-) amazing !!

maybe I can in a shilded room, but for this test I did not waste any more time measuring it.

yes the receivers have a few db in difference,

but not a huge difference, you need 8-10 dB to be able to feel it like a clear improvement on the field,

with 2-4 db improvement, people need to make a much more strict A/B test and even then they maybe fail,

we need test equipment to prove those small db's that is the bottom line.

Quiz:

what is the biggest change in power ?

1dB or 20% ?

all the video receivers I have tested uses the same IF filters,

so expect the same BW with them all, enought to transfer normal TV resulution without visible degrade.

so you can not transfer hi res pictures yet, but actually with moving pictures it is not the resolution I see as the problem,

it is the poor colors, , wrong colors, uneven color gain, poor light handeling, unlineary light, wierd clipping,

bad shutter range, bad auto range.

so far I have not seen a video cam that is possible to cary on a plane with the quality I like :-)

my plane is big so a 10 x 10 cm cam at 300 gr I could handle actually.

I guess real prof TV cams have their size and weight for some thing, picture quality !!

they share the SAME full TV resolution, but a world in difference when you see the picture.

they are like 20 x 20 x 10 cm and 3-6 kg in weight, and 20k$

why cant I get that picture from a 3 x 2 x 3 cm unit with a 30-40 gram total weight ?

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So could we know which BW you have measure on receivers? And more on, which would be the max resolution video equipment could handle with that measured BW?

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In practice, I think the Rx sensitivity is more varied. I would love to know if one had a few more dB than another. For example, I think it would be more practical to upgrade to a Rx with 3-4dB better sensitivity at our required bandwidths, rather than to change a Tx from 500mW to 1W (yes, both solutions are really not worth the effort, this is just an example). So, it would be interesting to see what you found.

There is also evidence of differences in video bandwidth. I'm not sure if it due to poor Tx or Rx design decisions, or just bad manufacturing. The reason I say this is because a few years ago I measured the bandwidth on a handful of Lawmate systems. I don't recall the exact numbers, but there was a variance of about 1 Mhz in that sampling. That would make a difference in the achievable camera resolution. I also believe that the measurements will vary among the same products, so it may be necessary to measure the one that is being used versus just looking at published numbers. But, regardless, the data someone collected would be good to have for reference.

I also found a massive difference if audio bandwidth (BTW, the recent Airwave modules are amazingly good in this area). Heck, some A/V makers still don't know how to properly adjust the video levels (it is a mess out there). All these little details suggest to me that our wireless A/V products are not all created equal.

I totally agree with you that camera performance is all over the map. That is why most of us have stayed with the ones that have proven themselves to work well in our R/C application. Very few cameras are worth installing in a model aircraft, so we have to be careful with what we buy.

Anyways, thanks for the measurements you have posted on your site. Your published data is generally not available to us from the mfg, so getting it secondhand is always a pleasure.

I am sorry to have detoured off-topic. It would have been better to have started up a new one for this discussion. I'll just hang on tight, with my fingers crossed, that one day you or some other fine fellow publishes more test data.

Edited by Mr.RC-Cam
Off-topic apology.

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Yo Waves

look at the centre of this page:

http://www.webx.dk/rc/video-wireless/video.htm

and a bit over centre here:

http://www.webx.dk/rc/video-wireless/tiny24.htm

RC-Cam: who uses Audio ? to hear the motor is running ?

or the power of the wind ? I dont get it :-)

also I expect Audio to have a much lower range than video, anyone can prove me wrong ?

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RC-Cam: who uses Audio ? to hear the motor is running ?

or the power of the wind ? I dont get it :-)

also I expect Audio to have a much lower range than video, anyone can prove me wrong ?

I guess he is refering to the use of audio to send data.

Terry

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I guess he is referring to the use of audio to send data.

Exactly. There has been some occasional interest in doing that. I recall that even ThomasS dabbled in such a project. :)

I expect Audio to have a much lower range than video, anyone can prove me wrong ?

The RF levels are lower for the audio sub-carrier. But even with the reduced bandwidth it uses, I noticed it is the first thing to go on a weak signal.

The audio performance is interesting. However, my intended point was that the various performance specs (video, audio, etc.) are not the same on all the wireless A/V devices. That was really what I was trying to say. Sorry for the confusion.

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Yo Waves

look at the centre of this page:

http://www.webx.dk/rc/video-wireless/video.htm

and a bit over centre here:

http://www.webx.dk/rc/video-wireless/tiny24.htm

RC-Cam: who uses Audio ? to hear the motor is running ?

or the power of the wind ? I dont get it :-)

also I expect Audio to have a much lower range than video, anyone can prove me wrong ?

Thanks thomas but with those measurements , I insist, which would be the max resolution our AV equipment could handle?

Could someone explain how to measure or what´s the relationship between that?

BTW I use audio to hear what´s going on on board, servos not vibrating, motor running ok without interferences, wind, other r/c airplanes coming by, and a large of etcs. <_<

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which would be the max resolution our AV equipment could handle?

Looking at the data that was shown, I would say that the measured system would probably support the full resolution of a 380 TV line camera. Higher res cameras could be used but their full stated resolution may not be achieved.

To help put this into perspective: If you are familiar with a common 240 line NTSC VHS recorder image versus a 420 line VHS-S image, then keep in mind that the VHS quality is 3Mhz whereas the VHS-S needs about 5.5Mhz bandwidth. In the middle of that is NTSC broadcast TV's 4.2Mhz, which is a bit above 300 lines. But, there are many other things to worry about too, such as signal linearity, low frequency response, etc.

But as ThomasS mentioned before, there are more important things that can also affect the image quality that are related to the camera itself. Better light handling, chroma accuracy, and so on, are king in our application. The camera choice makes a difference in these areas. His published KX131/151/IF camera tests are very helpful in this regard.

BTW I use audio to hear what´s going on on board, servos not vibrating, motor running ok without interferences, wind ...

Me too. I find that with reasonable sound levels, the airborne audio is comforting and seems to make the video watching experience more richer. Others hate the noise (which is why they invented volume controls :) ).

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you can tx unfinite number of lines :-) lust leave out the picture frame sync :-)

but dots pr line is limited by the MHz BW of the radio link.

the mentioned system have a -3dB BW at 4.6MHz

lets do the math,

one line is 15.6KHz

how many dots is possible = 4600/15.6 = 294 dots pr line

inputting any higher (width) resolution will be a waste of money :-)

the BW will limit it and you can not see higher resolution.

A VGA monitor with 1024 dots wide have a -3dB BW of 200MHz

and a line frequency of 60kHz

200000/60 = 3333 dots at 3dB, that is why the 1024 wide dots are so super sharp and you can see ONE dot.

info : http://www.hometechanswers.com/video/standards.html

conclution:

a way to get best picture with lowest BW is to use more lines if possible,

the hi res cams have also more lines in general, and that is why the picture looks better like more resolution.

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ThomasS, thanks for the pixel information. Your information is much better than mine since it's got some math. :)

Useful details to effective video resolution are described here in great detail, with useful formulas to calculate it (the math is a bit complicated, so get out the slide rule). http://www.maxim-ic.com/appnotes.cfm/appnote_number/750/

Edited by Mr.RC-Cam
Added link to video resolution white paper

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Interesting data.

About the BW limit, I've personally never seen a TX/RX set that would not show the improvement when going from a 380 line camera to a 480 line one and then to a 620 line one, or that would noticeably degrade picture quality with regard to a direct connection to the monitor. So I've always assumed that the bandwidth was "sufficient to carry the signal that is fed" on all those and not bothered more. Some I've had that stated a figure were saying 8MHz. If true, then it would supposedly be enough to carry anything a composite video signal is able to...

But I'd be interested in what Mr.RC-CAM means by "surprised by what he found".

RX sensitivity is also something that interests me, and that I might be putting my hands into now that I have that "new" little toy in the lab :)

For now, the TXs I've tested seem to all fall into +0/-3dB of the advertised figures, with some big differences between similar units for Lawmate (all the 3dB span...)

post-30-1205700492_thumb.jpg

Edited by Kilrah

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Some I've had that stated a figure were saying 8MHz. If true, then it would supposedly be enough to carry anything a composite video signal is able to

8Mhz video bandwidth would definitely handle any composite camera that a mortal would have access to. But that would be an extraordinary Tx/Rx system. If yours does this, then it's a keeper. :)

For now, the TXs I've tested seem to all fall into +0/-3dB of the advertised figures, with some big differences between similar units for Lawmate (all the 3dB span...)

FWIW, I have also found the Airwave and Lawmate Tx RF power levels to be close to their claims.

Edited by Mr.RC-Cam
Typo!

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