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Vidalcris

Compatibility issue (Emphasis) ?

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Hi,

I got flickering/desync when i try to use EWRF e7082TM VTX with any moduls on my Fatshark attitude V1 (RX5808 pro plus, Eachine Pro58 or stock VRX)

When i use this VTX with my Eachine VR D2 goggles there is no problems, just normal noise but no flickering at all even in the worst conditions.

Also when i use my Fatshark attitude with Eachine VTX02 or 03 (all my other VTX also in fact..) this is working correctly.. not as good as the VR D2 but not far.

 

@Mr.RC-Cam

I have read pretty all your reply about this  but i just would like to be sure that i'm not wrong.

For me now its a compatibility issue in the emphasis process (like you explain on your posts)

 

Here is the video i did to try to show the problem : (Left is EWRF)

 

EWRF.png

I'm talking with the manufacturer and the engineer are working on this and they will send me a new units to see is the problem is gone.

I'm not really able to say them why this is happening. Is the capacitor value bad ? or this is also the resistor ? or maybe this is more complex than this ? :P

 

Thanks for your help :)

 

Edit : I played a lot with a 75Ohms resistor without any change in the flickering problem.

There is no resistor at all in the Fatshark video in. (when i add one the contrast is better, but the flickering is still there.)

The resistance of the VTX video in is exactly 75Ohms.

The resistance of the VTX02 or 03 is around 175Ohms. (The resistor is cool to add on those, the contrast is better then)

Edited by Vidalcris

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I'm not really able to say them why this is happening. Is the capacitor value bad ? or this is also the resistor ? or maybe this is more complex than this ?

From the video and your comments it seems that two main things contribute to your problem:

(1) Your vTx behaves badly in your indoor flying environment as compared to your other vTx's. This suggests that it is a marginal design that acts poorly unless the RF signal is perfect. This symptom is commonly caused by an incorrect video level or a video emphasis filter design mistake (or both things together).

(2) You're flying indoors. Plus you might be using a linear polarized antenna on your micro quad. So the multipathing interference will often be a nuisance under these conditions. A marginal vTx design will show more problems when it interacts with multipathing and signal fading situations. The manufacturer may not have tested their design under these conditions.


There's no way for you to know why it is happening; You need full schematics and expensive test equipment. It's up the the design engineer to identify the exact problem and fix it. Could be as simple as a resistor change to increase the video amplitude or something more complex involving several component values in the video pre-emphasis filter. Or maybe something else.

To provide a reliable (correctly implemented) fix, the manufacturer will need a few samples of the vRx's that do not work correctly with their vTx. They should check the video waveform for proper sync shape and confirm proper amplitudes of the H-Syncs, V-Syncs, colorburst, and full white luminance. Also, they should confirm that the RF carrier's center frequency is accurate to ensure their channel control software was written correctly.

Keep in mind that if the manufacturer already makes a matching vRx for this vTx then it will no longer work correctly if it is used with the fixed vTx. In that case they will need to redesign their vRx too so that its video characteristics are matched to the fixed vTx.

 

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Most of the time i'm flying outdoor and the problem is more visible.

I did this video without any antenna on the VRX, i think that was not a good idea..

Anyway thanks a lot for your expertise :)

 

From my customer point of view they should just do like Eachine do.

I dont understand why some VTX (in fact most of them) are working fine with all my VRX :-/

Where are the VTX who are not working with my Eachine VR D2 ? :P

 

Manufacturer should choose a standart ... i know this is not easy but if they dont choose a standart then they should give us the information about the emphasis method used right ?

EWRF are not even able to give me a reply to this :-/

Customers should ask for a refund each time there is a compatibility problem. i'm pretty sure that manufacturer will then change their methods..

 

Edited by Vidalcris

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Manufacturer should choose a standart ... i know this is not easy but if they dont choose a standart then they should give us the information about the emphasis method used right ?

As I have mentioned in my various discussions in the past, there's several RF & Video related specifications that must be maintained in order to ensure a reliable FPV system. Video emphasis is just one of many important characteristics. For example, your exact problem might not be video pre-emphasis related. It could be incorrect video level, RF carrier error, or something else.

And even if all the important specifications are understood by the original designer, the end product sometimes works poorly. Performance issues can be due to economy priced components (tolerance issues) and inadequate quality control.

But I agree, a well thought out FPV video system standard that is observed by everyone would be great. Unfortunately, this holy grail idea is not likely to happen in China because of their manufacturing culture. And as many experienced engineers say with a smirk: The thing about standards is that there are so many of them to choose from. :)

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Oh ok, i hope they will be able to make it work for me then :P

They know which VRX i'm using..

I want the best signal but there is not a lot of VTX with smartaudio for nano quads :)

 

Thanks again Mr RC-Cam you are definitely the best to talk about this subject !

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Yeah sure i already looked at this but i think i will not be able to know what to do to have a better signal even with this material :-/

I dont have material to change cms components, just a TS100 with the smallest tip :P

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You can't detect a video level compatibility issue (a common problem) by simply viewing your camera's image on a monitor. You need a o-scope or this tool to do it. Even if you cannot repair the problem yourself, you will have identified a purchase that is not 100% compatible (which is valuable knowledge). 

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