Boscam 5.8 GHz with 2 inch coax cable - RC Groups
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Oct 08, 2013, 06:06 AM
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eluminerRC's Avatar

Boscam 5.8 GHz with 2 inch coax cable

Hello guys!

Here is my problem.

I was doing a project where I've tried to put Boscam 5.8 GHz video receiver into my HK 7" monitor in order to get compact, park flier, FPV ground station. I've manage to do this and I'm pretty happy how this turned out (check the pictures).

However, I have a problem now (which I've expected, but not that drastically). My video range dropped significantly and now I can't get over 100 m (300 feet). Now, when this was "stock" I could easily go over that.

Of course, a lot has changed so I was expecting a range drop. But this is too much to the point where it's useless even for park flying.

Here's what I've tried and didn't work:
- I thought that my transmitter 2.4 GHz antenna and my 5.8 GHz video antenna are now to close. I've moved the monitor/ground station 30 feet from the transmitter and same thing happens - so, this is not a problem.
- I've tried all 8 channels and I get pretty much same result on every single one - so, this is not a problem either.
- Since I'm now powering my entire ground station from transmitter pack I was thinking that maybe this has something to do with it. However, no. When I power my FPV equipment from separate pack (on the ground and on the craft) I get pretty much the same result.

These things were easy to try and that's why I've tried them first. Here is what I'm thinking now:
- I basically had only one place inside the monitor to put VRX and even this was really tight. However, this was in the middle of the monitor so every port, switch, LED and RP-SMA connector would be useless there. So, I've desoldered everything and put short cables/wires and mounted them on the housing. Now, LED, switches and RCA connectors are not the problem, but RP-SMA connector and 2 inch coax cable could be. However, as far as I've researched this shouldn't be a problem on such a short distance. What do you think guys, is this 2 inch extension a problem?

- Next: I've noticed 2 big and 3 smaller coils on the monitors main PCB. I know that coax cable should be protected from interference, but still, could these coils be the problem?

I'm willing to try something in order to solve this but I wanted to get couple ideas where to start because any interventions now are pretty complex.

As far as craft side goes, I don't think the problem is there because nothing has changed since last time.

Thank you!
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Oct 09, 2013, 03:58 PM
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eluminerRC's Avatar
Oct 10, 2013, 12:53 AM
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I think you have eliminated most things and now I would try shielding the rx by covering it with copper tape or similar & then ground it. I would guess the monitor will be spewing some rf as it would have a dc-dc converter & other oscillators.

Nice job by the way, looks neat
Oct 10, 2013, 06:22 AM
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eluminerRC's Avatar
Originally Posted by Mantovani
I think you have eliminated most things and now I would try shielding the rx by covering it with copper tape or similar & then ground it. I would guess the monitor will be spewing some rf as it would have a dc-dc converter & other oscillators.

Nice job by the way, looks neat
Thanks for the answer.

I'll try two things this weekend. First, I'll remove display and desolder the monitors PCB board so it's not powered on. Then I'll try to fly using some other display connected with video cable (TV or EasyCap on laptop). This way I'll eliminate the influence of the monitor on the rx. If this is the problem, then some shielding will be required.

If this won't work, then I'll make CP antenna and solder it directly to the rx eliminating the coax cable and connector losses.

Then we'll see. If neither of this will work, then I'm out of ideas for now.
Oct 11, 2013, 09:35 PM
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HansAuf's Avatar
You may have already thought of this, but I'll mention it just in case. The Boscam VRX is RP-SMA. Is the extension cable you have connected possibly SMA? It's very easy to miss this and it would exhibit the behavior you are seeing.
Oct 11, 2013, 10:09 PM
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Moto Moto's Avatar
That's a nice looking assembly. What are you using to mount the screen on the transmitter?
Oct 13, 2013, 07:14 AM
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eluminerRC's Avatar
Hello guys! Problem solved!

@HansAuf: Yes, cable is RP-SMA.
@Moto Moto: There is metal "L" peace already on the monitor that is for sliding monitor onto something. I've just unscrew it and screw it on other way so the "L" peace is heading out of instead in the monitor.

Now, here is the solution.
The problem was that aluminium case is actually a shield for the VRX. So, when I took it out the case, there is no shielding so it's prone to RF noise.

So, I've took copper tape and completely enclosed the VRX. But I mean COMPLETELY (you have to put some kind of tape on the inside to prevent shorts). I've tried to put only single peace over it but that didn't work. So, only thing that left uncovered are 4 small openings where wires and coax cable comes out. Of course, I've grounded the shield. And that is it, works as before.
The problem is in RF noise from the monitor, because when I've disconnected it everything worked fine. Even if it's on standby it creates a lot of RF noise.

Thanks for the help guys, especially Mantovani.
Oct 13, 2013, 08:09 AM
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HansAuf's Avatar
Nice. Glad you got it worked out.
Oct 13, 2013, 06:56 PM
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Good to hear you had success

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