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FredericG

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About FredericG

  • Rank
    RC-Cam'er
  • Birthday 11/12/1969

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    http://www.rc-flight.be
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    Belgium
  1. FredericG

    Audio track as modem data NMEA

    As Mr.RC-Cam mentions it depends on the BW of your setup. Perhaps you could check the BW before you buy something. My modems come from Eladio and I think they are on sale here: http://alai.h3m.com/~s0350672/catalogo/ Frederic
  2. FredericG

    Audio track as modem data NMEA

    Sorry, I missed your question. I reassembled the receivers again so that I can fly. I think I will wait until winter before looking into the issue again, the problem is not important enough for the time being. In Belgium you need to fly when the weather is good Frederic
  3. FredericG

    Audio track as modem data NMEA

    Well no, I did not kwow this I did a quick search on farnell for example but did not find anything. Even with your link, I have trouble finding my way to the right component I suppose that replacing the component is the most obvious route. However, Thomas mentions that these components do not like to be handled manually. Buying another receiver might not be a good solution as a friend mentioned that "it is a well-known issue that some lawmates have a low audio-bandwidth" Do you guys think that the trailing "N" and "d" could indicate a different bandwidth? Did they change this to have less noise? Thanks, Frederic
  4. FredericG

    Audio track as modem data NMEA

    Yes, these are the receivers that where used for the Oracle issue. I did not have a look at the video signal again but I have some info on the audio. I transmitted a block wave that looked like a triangle on the bad RX. When I turn the variable cap in on or the other direction the amplitude of the audio-signal reduces but the shape does not change. So, I suppose it correctly "tuned". I opened the other side of the RF-box. No adjustable stuff there. I changed channels, but with the same result. I had a look at the ceramic filters. One of them is identical on both boards, it says "X6.5B delta 7 Q" (the one for video?) The other one is different. The good receiver has "L6.5C ??? N", while the new one has "L6.5C ??? d" where "???" is perhaps also "delta 7" I took a picture for the bad receiver. The filter seems cracked... I tried to find on Internet what these codes could mean, but I did not find any answers. Thanks, Frederic
  5. FredericG

    Audio track as modem data NMEA

    On the other side of the mother board there is a small pot. What would that be for? It is also on the mother board that the switches are to select one of the 8 channels. How does that work? Would it be a good idea to test with another channel? I know a lot of questions Thanks, Frederic
  6. FredericG

    Audio track as modem data NMEA

    Well the receivers are not identical. The good one is a "portable" version with a build-in battery, I bought this one 1,5 years ago. The bad one is a "standard" receiver and I bought this one half a year ago. The transmitter was bought at the same time as the the bad receiver, so they should be compatible. What is interesting is that, while the video looks good, the image from the old good receiver looks "better". It looks brighter while the video levels are the same. My USB video capture device shows the image of the new receiver is "darker", my goggles do not show a difference. Could it be that also the BW of the video is reduced and that this affects the colors? When I open them I see they are both based on the same RF module. I can easily open the sardine can on one side. For the other side I would have to desolder it from the mother board. Unfortunately, this does not show the components, we can only see that the boards are from a different revision.
  7. FredericG

    Audio track as modem data NMEA

    Thomas, what do you mean with "audio carrier must be adjusted correctly on the transmitter so it is centrered"? Does this relate to the audio signal that is provided to the TX or is this related to the TX-RX link (the carrier on which the audio is modulated perhaps)? To be sure there is no misunderstanding. I use one TX and the signal is received by the two receivers simultaneously.... On the -scope graphs you see the audio signals of both receivers. Does the fact that the audio signal is reversed tell us something? Thanks, Frederic
  8. FredericG

    Audio track as modem data NMEA

    It looks you are absolutely right. I measured the bandwith with a sinawave and the cutoff-freq (-3dB) of the new receiver is only 2KHz, while the older one goes upto 20KHz. I was assuming that he limited BW was due to a design-change, but I suppose 2KHz is not acceptable for audio and should be seen as a defect. Right? Is there something I could check/fix or do I just send it back? Thanks a lot, Frederic
  9. FredericG

    Audio track as modem data NMEA

    Here I have dramatically lowered the signal amplitude: (1V/div) And here I have increased the signal: (2V/div) Frederic
  10. FredericG

    Audio track as modem data NMEA

    I integrated a DZL modem in my Oracle diversity receiver: The problem is now that the DZL modem does not seem to work in combination with my new 2nd lawmate receiver. I experimented with adjusting the level of the audio signal to the TX, but I never get a signal that is good enough for the modem to decode... It looks to me as if the signal heavily filtered. These are the signals that the receivers are generating, both signals 1V/div, the bottom signal is from the old receiver.
  11. Afterwards I did the same test with the system installed in my plane. Here the plane is outside and I am inside. This is with the OSD that generates some "blacker than black" The overshoots are gone but the black is a bit below black. I can however not see false sync-pulses. To be honest, I start wondering if this is really our problem. However, what else could it be? AFAIK, the sync pulses is the only thing the device uses as input. When I now enable both receivers, there is some switching, but not a lot. The sync pulses are hardly affected by the filter, so I suppose I can increase the cap safely. I might filter away the "blacker than black", but again, I wonder if this realy my problem. Thanks, Frederic
  12. This is interesting. I started measuring inside the Oracle. I looked at the video-signal after the filter and the sync pulses from the LM1881 (pin 1). The filter is doing a good job filtering the overshoots generated by the A/V system. As far as I an see (I should have a better scope) I cannot detect false sync pulses. This is with the "better" osd board printing much more "I" characters than before. What is very confusing is that the signal looks good to me, but when I enable both receivers, Oracle starts switching rapidly. This is indoors, I know, but the pulses look good to me... Very confusing. I do appreciate your help :->
  13. I still have another TX, exactly the same lawmate .5W. For reason it has become VERY sensible to vibrations, but OK for this test. I tested with both transmitters and both receivers. Unfortunately the signal at the RX looks the same. I include a more detailed picture. The bottom black line is the level of the sync tip, the dashed line should be around 100mv. In the datasheet of the LM1881 I have read that the threshold for the sync pulses is a fixed (typical) 70 mV. Some spikes must reach this value. I think this "better" OSD will also cause trouble and it would be a lot of work to swap the boards as I has lots of connections soldered to the board. I experimented with different OSD settings (output level, reintroduce sync, colors), but no improvement. As I use a TX/RX bought a year ago and one that was bought a month ago, I think we must conclude this is the way lawmate devices function, no? I suppose no camera will generate steep edges as the OSD chip does. I might soon switch to an OSD based on this new MAXIM OSD chip, but will things be dramatically different? I was hoping I would be able to suppress the overshoots with a simple RC-filter, while the sync-pulses still come trough. Do you think this might work? I did not try lowering sensitivity yet. Problem is, the weather turned bad again in Belgium :-( Thanks, Frederic
  14. Regarding the color-burst. I have also seen this, sometimes it is visible, sometimes it is not. I think this is because the scope is in digital mode and does not take enough samples. Is this reasonable? I think this is also the source of the "ragged" aspect of some of the signals that are taken at higher timebases, you do not see the real peaks. Another remark is that the last 3 images are taken with another spare board. It looks to me that this board puts black exactly at the black level while the board installed in my plane puts black slightly below the black level. In both cases, at the RX side there is over- and undershoot. Frederic
  15. Now, when I look at the signal at the RX side, there is over and undershoot. 0.2V/div: The problem is that I do not know how I could solve this. I thought that I could influence the "color" of the borders, but I did not succeed yet, I think this only works in "full mode" Could I filter the video signal before it is fed to the LM1881? Thanks, Frederic
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