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Thread: Lawmate 2.4gHz 500mw Tech

  1. #1
    bonafidepirate Keith's Avatar
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    Lawmate 2.4gHz 500mw Tech

    ** This thread is dedicated to getting clean power to the LM 2.4gHz vTx --- and clearing up the picture **



    ** FROM DANIEL WEE **
    There are some interesting things (irregularities) about this module. To begin with, the channel assignments of the old LM500 is as follows:-


    • CH1 - 2410 MHz
      CH2 - 2450 MHz
      CH3 - 2430 MHz
      CH4 - 2470 MHz
      CH5 - 2370 MHz
      CH6 - 2490 MHz
      CH7 - 2390 MHz
      CH8 - 2510 MHz
    The new version of LM500, however, has a different sent of frequencies, as follows:-


    • CH1 - 2410 MHz
      CH2 - 2430 MHz
      CH3 - 2450 MHz
      CH4 - 2470 MHz
      CH5 - 2370 MHz
      CH6 - 2390 MHz
      CH7 - 2490 MHz
      CH8 - 2510 MHz

    Isn't that a 500mW 2.4GHz Lawmate on there? I've had a hell of a time getting clear video from mine. Other than that it's a great vTX. The stock regulator it comes with (that's built into the cable) puts a lot of noise into the video, as did all 3 BECs I tried. I also tried all 4 options with an LC filter which did help, but didn't clear up up completely with any of them. I ended up building a linear regulator which gives crystal clear video, but it's based on a 7805, and running on 3-cells the reg. gets HOT! Even with a heatsink... I'd imagine it's pretty inefficient too. If you find a good way to supply clean power to it, let me know!

    Keith
    Last edited by SENTRY; 9th September 2011 at 12:27 PM.
    AKA Bonafidepirate

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    Moderator Derek_S's Avatar
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    So at least we know a 7805 will(should) give use clean video... I have used them before too and they get super hot, but whatchya gonna do? Maybe we can try that next.
    Last edited by SENTRY; 9th September 2011 at 12:13 PM.

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    Moderator Derek_S's Avatar
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    Quote Originally Posted by Keith View Post

    Isn't that a 500mW 2.4GHz Lawmate on there? I've had a hell of a time getting clear video from mine. Other than that it's a great vTX. The stock regulator it comes with (that's built into the cable) puts a lot of noise into the video, as did all 3 BECs I tried. I also tried all 4 options with an LC filter which did help, but didn't clear up up completely with any of them. I ended up building a linear regulator which gives crystal clear video, but it's based on a 7805, and running on 3-cells the reg. gets HOT! Even with a heatsink... I'd imagine it's pretty inefficient too. If you find a good way to supply clean power to it, let me know!
    Ever considered running it on the balance plug but only at 2s..? Another option is to use 2 7805s in parallel, so they split the current load, but I am not sure if that is viable or a good solution either....
    Last edited by SENTRY; 9th September 2011 at 12:13 PM.

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    A possible solution to cool down the 7805 is to series 4- 1n4001 diodes in front of the regulator. 12v___-diode-diode-diode-diode (about 8v)______7805 regulator.
    Doing this has worked for me with a couple of applications including my GCS which gets no airflow. It seems the heat is dissipated through the diodes better than the regulator. . finishing with the 7805 ensures a consistent 5v throughout the entire battery life. Unless Sentry tries to run main batts it down to 5v again. LOL the regulator still gets warm but not as nearly as bad without that the heat scared me.

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    Moderator Derek_S's Avatar
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    Yeah, that would work or even a resistor to dissipate some heat, maybe a 1/2w size one, but not sure of the ohms off the top of my head. Something to drop V down some..

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    bonafidepirate Keith's Avatar
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    I hadn't looked into those diodes, but I have thought about using zener diodes, it's not uncommon to see those used to drop voltages into a vreg.
    AKA Bonafidepirate

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    You can get the diodes at the Shack for under $2 they weigh next to nothing.

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    Quote Originally Posted by Keith View Post
    Nice! I'd still be scared of the prop when launching it though... lol

    Isn't that a 500mW 2.4GHz Lawmate on there? I've had a hell of a time getting clear video from mine. Other than that it's a great vTX. The stock regulator it comes with (that's built into the cable) puts a lot of noise into the video, as did all 3 BECs I tried. I also tried all 4 options with an LC filter which did help, but didn't clear up up completely with any of them. I ended up building a linear regulator which gives crystal clear video, but it's based on a 7805, and running on 3-cells the reg. gets HOT! Even with a heatsink... I'd imagine it's pretty inefficient too. If you find a good way to supply clean power to it, let me know!
    What I do is to drop the 12V down (the cameras supply) to 5V using a switching regulator (noisy), then have a linear regulator after that to drop it down to the 3.3V needed for the video TX (200mw 5.8GHz). doing it this way is quite common for reducing/eliminating the noise from a switching regulator and it also means the linear regulator stays pretty cool as it's only having to drop a volt or 2 and keeps the efficiency fairly high.

    The switching regulator I use is just the insides of a cheap 12V to 5V switching USB car cigerette adapter off ebay.

    I have no noise problems what-so-ever doing it this way.

    So what you could do is to do the same but modify the switching regulator to give you say 7V (5.5V if you use a LDO linear regulator), then drop that 7V down to 5V using your 7805. That would give you a nice clean supply whilst maintain most of the efficiency of a switching regulator and have MUCH less heat generated.

    Here's a piccy of mine - I'm just testing it all at the mo so is just a lash-up.

    Attachment 2810

  9. #9
    on a vacation brosius85's Avatar
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    i use a seperate 3s lipo and standard lawmate regulator. never had any interference. 420 rmrc 12v cam and 500mw 2.4 Lm tx

    you can say what you want about extra batts being a weak point or whatever but to me it is so much cheaper and easier than trying to filter and troubleshoot interference in the system when running off the flight batts.

    i dont even use shielded wire at the moment LOL not a single ferrite ring or filter in my video circuit. no interference to speak of.

  10. #10
    bonafidepirate Keith's Avatar
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    Quote Originally Posted by brosius85 View Post
    i use a seperate 3s lipo and standard lawmate regulator. never had any interference. 420 rmrc 12v cam and 500mw 2.4 Lm tx

    you can say what you want about extra batts being a weak point or whatever but to me it is so much cheaper and easier than trying to filter and troubleshoot interference in the system when running off the flight batts.

    i dont even use shielded wire at the moment LOL not a single ferrite ring or filter in my video circuit. no interference to speak of.
    I use separate batteries as well. When I say noise, I don't mean interference getting into other components on board, but lines in the video. Not motor noise either, they're uniform diagonal lines. It's switching noise from the power supply.
    AKA Bonafidepirate

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