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Lupy

problem with black box osd and mobicom tx

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I also posted this question on RCgroups, but I know that there are more tech people here.

I recently bought a mobicom 900mhz tx 1.2watt. I also got a couple of the rx's to use with the oracle. Ground tests show much more ( over 2X ) range than the airwave 500mw tx. This was with dipoles on 900mhz vs ground plane and patch antennas on the 2.4ghz. I am currently trying to get them in the air.

My problem is trying to integrate a black box osd. I have tested the OSD on the airwave tx, and it works fine. The Mobicom TX works fine with the camera and mic alone. When the OSD is inserted into the mix, the picture is lost, audio isn't affected. The carrier signal seems to still be there. Ocasionally, I will get a second or two of video, then it is gone. I have tried adding another cap on the video signal, no change, I have tried putting a video amp/ splitter on it, no change, I have tried moving the osd a couple of feet away, thinking maybe the 900mhz tx is swamping something, no change, separate power lines, etc.

At this point, I am moving ahead without a osd, but would really like to figure out what is going on. I would like to use an osd, but want to know if another osd might work, before spending the $$ on it.

Thanks for any help

Ken

Edited by Lupy

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I found that the Black Box OSD had a design snafu with its video input. It was not terminated to 75 ohms (at least mine wasn't), which might explain your problem. I don't know of a instant fix for that, but you could try terminating Video-In with a 330 ohm resistor to see if it solves the problem. Lower resistor values will probably reduce camera brightness, so try to stick with high resistor values.

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by terminate, I asume you mean to put a 330ohm resistor from the video in signal (from the camera) to ground. This didn't seem to have any effect.

I did discover that if I turn the video to disable, the data screen goes through the 900mhx tx just fine.

I know that in normal operation, camera and Black box connected directly to a camcorder, video enabled, if then the camera is unplugged, the whole display dies. So for some reason, the adition of hte 900mhz tx is making the Black box think that the camera isn't plugged in.

No real Idea on where to go from here, pretty strange.

Ken

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by terminate, I assume you mean to put a 330ohm resistor from the video in signal (from the camera) to ground. This didn't seem to have any effect.

That is what I meant; Sorry to hear it did not help.

So for some reason, the addition of the 900mhz tx is making the Black box think that the camera isn't plugged in.

I suppose there is a chance the Tx's strong RF is disturbing the BlackBox circuitry. One possible way to check for this would be to install a suitable dummy RF load on the Tx's antenna port (so that strong RF wasn't transmitted into the nearby equipment or wiring).

Beyond that, it sounds like unusually bad karma that takes the joy out of the hobby.

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it's pretty odd, I broke the video out line, so I could touch inputs for the camcorder or the 900mhz tx in real time, it's there for the camcorder even when the tx is still powered up, so I don't think it's swamping anything with RF. Now I realise that I should have hooked up both the camcorder and tx to the signal at the same time, to see if the picture drops out on the camcorder because of some drain the tx is placing on it, or if the tx is just more sensitive to having a nice video signal, and something about the osd combining the orig video with it's overlay is messing things up.

Something to waste more time with tomorrow......

Ken

Edited by Lupy

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