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KeithLuneau

High input impedence, Lawmate transmitter...

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I just picked up a Lawmate 500mW 2.4GHz transmitter and receiver. When bench testing, I found that my Mini-DV camera doesn't detect any video from the receiver. I use this to record my flights, so it's kind of a setback... I have a small LCD monitor, which sees the video just fine. The Mini-DV camera has always worked flawlessly with my other FPV gear.

So reading more into it and searching a bit, I found an old thread that talked about high input impedance with the newer Lawmate transmitters at that time, that was in '07 I believe. I measured mine, and it's over 400 ohms, I forget the exact number. Did anyone ever get to the bottom of it, why they did it, how to fix it, etc? I would happily add an external resistor to ground to pull it down to 75 ohms, but I have no means of recalibrating the levels if I do that.

So, my question is, is it normal to have such high impedance on the input, and will that case my video levels coming out of my transmitter to be off, hence my recorder not detecting it? Would a simple video splitter/amp be enough to condition the video levels, or would that just be a band-aid fix to a bigger problem?

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is it normal to have such high impedance on the input,

No, it is a foolish design. Last I heard, Lawmate did not seem to understand what they have done is a bad thing.

will that case my video levels coming out of my transmitter to be off

Some cameras will not work at all with the Lawmate Tx's higher video input impedance. However, since this issue only affects your Mini-DV, and a TV monitor works, then your camera seems to be compatible. Of course the video levels might be messed up.

So, there is a chance this is just a simple video level issue, which unfortunately is a common problem that affects many systems (not just your brand). Before doing anything, it is best to get an o-scope on the video Rx's video signal and see what you find. There are instructions on how to do this posted elsewhere on the forum.

BTW, are you sure it is the Tx? Are you sharing the Rx video signal with two devices without a buffer, which is a no-no? Maybe the mini-DV's composite input mode is setup wrong? Or bad cables? Or an endless number of other evil things that make us miserable.

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I'm sure it's got something related to the Lawmate gear. I use the same cables, setup in the Mini-DV camera, etc. and it works with two other systems. I'm not sharing the output, just the Mini-DV hooked directly to the Lawmate receiver. I've tried the Mini-DV with various other sources and all of them are fine with it. Maybe my monitor is just more tolerant of the levels being off, or whatever other mess I've got here... ;) The picture looks great on the monitor. I can fly this way, but I do like to record flights from time to time, and fly using the LCD screen on the Mini-DV camera while it records.

The funny thing though, is that the main reason I bought the Lawmate gear was so many people keep making the comment about low quality cheap Chinese products, and until now, that's all I've used, with varying degrees of success. I picked up the Lawmate gear since so many people use it and say good things about it, I figure I'd see what I was missing. At the point, I'm honestly more impressed with the cheap-o "Bada New" transmitter and R2Hobbies receiver that I've been using for over a year. ;) Size and weight however, I couldn't believe how tiny the Lawmate transmitter is. The build quality is also better by FAR. I even tried using the R2 receiver with the Lawmate transmitter, but they don't seem to use the same channels, close but not quite... ;)

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I suspect that you will be happy with your Lawmate purchase after you calibrate the video levels. In case it is a compatibility issue, be sure to perform this task with the video camera you intend to use.

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Ok, ok, you're right... I flew the transmitter on my Slowstick today, same one you helped me with the RF noise issues. Quick range test showed good signals on the ground, so I flew at dark again. I'm kinda impressed with the Lawmate gear. Video was rock solid the whole time I flew it, except when I was high and behind the patch. I expected that. There was noticeable improvement with this gear over the other ones I use.

I flew using the monitor, and didn't record it. The picture was great the whole time, good colors, no tearing, etc. So far the only two devices I've hooked up to the receiver are the Mini-DV camera and the monitor. I've got a USB Easy Cap I'll try soon. If that works, I'll fly with that. I've used it in the past, and it records great, and the big full screen display is nice too. Just have to set my laptop up again and get it ready.

About the video splitter/amp, if I were to pick up one with adjustable gain for each output (like the Pyle), would I be able to dial each output until the video looked good and use it? Even though the levels may not be to exact spec, if it works that's the point right? It would just be cheaper than getting the o-scope and tuning it within spec, and still needing a splitter anyway... ;)

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Even though the levels may not be to exact spec, if it works that's the point right?

I hate to be a pain, but if you want to avoid future compatibility problems, ensure good color and dynamic range for best quality, then the dial-and-pray method is not the solution. Instead, getting the video level set correctly at the transmitter will help you achieve the best results. Fixing badly adjusted wireless video systems with a amplified buffer on the Rx is a last resort band-aide that will not be as good.

Here's the low down. The wireless video levels are rarely calibrated correctly by the factory. The video monitors and recorders can mask most of the problems, but you will be cheated out of getting the best possible video. So, do whatever it takes to hunt down a friend that has a scope and get your system calibrated. Or ask Santa to bring you the cool $50 digital scope discussed here: http://www.rc-cam.co...e-video-levels/

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Be a pain? Nah, like I said in the other thread, the help I've gotten here is invaluable!

I think I'll make the best of it for now, and get a scope when I've got the cash. Then I can pick up where I left off, and see if I can get things squared away, and maybe even tweak the other transmitters I've got too. :)

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Just a little more info... In preparing for a flight this evening, I just tested the Lawmate gear with my Easy Cap. It sees the video and captures just fine. I'm not sure what the deal is with my Mini-DV camera, but it still refuses to see any signal at all coming from the Lawmate transmitter. Guess I'll be using my laptop while I wait on a scope to investigate further... :)

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I ended making a flight at sunset again today, landed after dark in fact! That was scary... lol I made two trips out to known points just over a mile from the launch point. Video was rock solid the entire time.

I used my laptop and Easy Cap, which worked great for the whole flight. I guess I'll just chalk this up as an incompatibility between the Lawmate receiver and my Mini-DV camera. (It's a Sony DCR-HC40 for anyone else wondering what camera it is, might save someone else running into the same issue.)

For now I'll also assume that the video levels are probably off and could use some tweaking, and likely pick up the o-scope and find out!

Edited by KeithLuneau

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Did you manage to get this sorted out?

I'm having the same problems with my 1.2Ghz 1w system. The Lawmate Rx outputs PAL video that displays perfectly on my cheap monitors and on the home plasma but the Marshall field monitor I use for FPV doesn't recognise the signal. I've tried connecting other PAL sources to the Marshal field monitor and it recognises and displays the alternative sources perfectly. It's obviously an issue with the composite video signal that the field monitor doesn't like.

I'd love to get this sorted out.

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