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About Mark963

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    RC-Cam Visitor
  1. Well, there isn't a lot of room to add much in there, and I'd hate to screw up the RF tuning by adding stuff that wasn't there when it was tweaked at the factory. Darn. Hmm... maybe a SOT23 jfet... no, probably not. Thanks.
  2. I picked up a couple "CM-707" 2.4GHz audio/video receivers pretty cheap. I've had a 10mW transmitter out past a half mile with some video still coming through... but it wasn't pretty. Still I think that means there is some pretty good sensitivity here. There's a 15 ohm resistor in series with the input to an LM7805 regulator. Apparently it provides a little filtering and burns off some heat if running it off of 12V as intended. I shorted that out and run it off a 600mAH 2S (7.2 to 8.4V) lipo. Without it shorted, it still works, but there's only 4.3V coming out of the regulator and I'm not sure that's enough to make everything work fully right. So... I poked around the module and I don't see any unused pins with anything that looks like an RSSI signal. I opened the module and there's an SL1461 "Wideband PPL FM Demodulator" that appears to have an AGC output signal on pin 7. A datasheet on it indicates specs like 400-800MHz operating frequency, -40dbm sensitivity, 0db input overload and there's a graph that shows AGC voltages of about 1.5V for -45db and lower input to about 0.25V for signals over -30db. Can this be used as an RSSI signal for simple (comparator, fet video switch) diversity system? Can I hook a series resistor on to it and pass that out to a high impedance circuit as an RSSI signal?
  3. That's good to know the input is AC coupled. I won't bother trying to poke at that then. To be honest, I slapped a 7805 on the transmitter and wired the camera straight to it and didn't bother checking the voltage. It might be even be starting to fall out of regulation with a COLD 2S battery on it - I think it was around 7V but still 75% full. I'll check into it some more. Thanks for the help!
  4. Where in the AWM631TX datasheet does it call out a coupling cap? I looked for it specifically before I started and found nothing, and that's why I intentionally didn't put one in. I did install the two bypass capacitors, one on the 5V supply input and one on the bypass pin per the datasheet, but nothing in series with the video signal like is called out for the receiver. Did I miss something or am I just being stupid?
  5. I've got an airwave AWM634 receiver and 631 transmitter. It appeared to work fairly well at room temperature (although there was always interference at home). Then I tried a range test outside (40 degree F day) and found that with the camera (CX161) and the transmitter sitting outside on a tree branch, the video began to loose sync. I started checking the range it when it started rolling and I thought I had lost signal, although there was no static. I was only a couple hundred feet away, so I went back to the transmitter and it was still rolling. Then for kicks I tried a different viewer - a portable DVD player with video in and it worked where the goggles wouldn't. My video recorder also doesn't like the signal and only grabs a few glimpses. I didn't use a capacitor to couple the camera's video out and the AWM631 transmitter. Maybe that will help. I might have dig out a scope and do some poking. It's a pain in the butt to troubleshoot something that gets worse with temperature.
  6. I think that brings up an interesting subject. What kind of performance changes can one expect for slight dimensional errors? I tried cutting the metal plates in a machine shop to the dimensions listed and then used a digital caliper to check and trim each surface. I'm afraid I was a little rushed on the holes for the SMA connector and it is off to one side - maybe about 1/3 of the way across the hole instead of half way. Similarly, I've got some balsa wood that measures about .195" and another piece that measures .205". Should I take time and try to sand the .205" down to exactly .200"? I'm thinking the glue might push it up anyway. I'm just wondering if 1/16" on one of the plates (for example) or this much on that part will vary the tuning that much.
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