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Newbie Tx Rx Placement Question

#1
Hello Everyone, first post
I'm building my first FPV plane a Bixler 2 and i have a question about placement of the video Tx and RC reciever. After lots and lots of research i know that it is said not to place the video Rx close to the RC reciever but does that mean the boxes or the antennas? I work on real airplanes for a living and rule of thumb is the boxes can be stacked on top of each other but the antennas must be seperated is this true also for the RC versions of things? I was planning to put the video Tx in the nose of the plane with the antenna sticking straight out the top of the nose and then placing the RC reciever in the large void under the wing saddle but running the RC antenna out to the tail.
Thanks for any advice

My setup
Imersion 600mw 5.8ghz video
Dragonlink UHF
Dragon OSD+ V2
 

Craftydan

Hostage Taker of Quads
Moderator
Mentor
#2
Rule of Thumb for RF systems, let data lines go long, keep transmission lines short.

you can bend/break this rule, but if you can afford to co-locate your RF module w/ it's antena, it's best.

two other points:

- unless your receiver only uses satellites, it will have it's antenna hanging off the box.

- most full scale A/C electronics are VERY well shielded (in a big heavy metal box). that's not to survive crashes (w/ the exception of the data recorder). it's to tolerate noisy neighbors. your FPV transmitter is probably shielded. I'd almost bet nothing else in your model is.

you can put the transmitter and receiver modules together, but I wouldn't trust it.

BTW, Welcome to the forum! feel free to drop by the "flight school" and "say Hi"!
 
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#3
Thank you very much for the advise and the welcome to the forum.
I kind of figured this would be the answer. yes you are right full scale equipment is more shielded. I guess I will try to figure out a way to move the Tx and Rx further apart. I really hate when people locate them on the outside of the fuselage my inner aerodynamisist screams no your ruining the air flow!!
I'm no avionocs/electronics expert but isn't coax cable like the ones used on the dragonlink antenna sheilded?
 

Craftydan

Hostage Taker of Quads
Moderator
Mentor
#4
This forum is a more the merrier kinda group. Glad you stopped by, and hope you like the air here enough to want to stick around.

I know enough about avionics and RF to say I'm no expert either, but that's mostly because I know and work with some who are (weird folk!). I'm glad I can pass along what I've learned.

I know what you mean about spoiling the lines -- something seems wrong about a streamlined nose suddenly growing a blocky wart-of-a-camera.


speaking of spoiling lines, have you seen the FPV pallet that HK has made for the Bixler series?

http://www.hobbyking.com/hobbyking/store/__22731__DIY_Bixler_FPV_Camera_Mount_.html

It cleanly replaces the canopy, and gives area to mount your camera, TX, antenna, and add a battery tap through the bottom. not suggesting buying it (unless you have an order ready to go in) -- it's way too easy to build your own.




Yeah, Coax is, by definition, shielded. Oh, now you've got me thinking. Sorry if I toss too many poorly formed ideas too quickly . . . (I apologize for the following brain dump. I get this way sometimes)



Taking a second look, noticed you're going for a 433M system -- 1/4 wavelength is a touch over 15cm -- Oooh uses a rubber ducky! You can build/install a waveguide for both systems! There *are* some things that can be done with this.


One alternative:

You *could* mount the dragon Rx in the cavity, run an waveguide (coax) through the fuse and down one wing, mounting the ducky on one wingtip. Then run coax from the pallet down the other wing and mount the video antenna on the other wingtip. Keep your couplings to a minimum and no sharp bends. My knee jerk is still keep your waveguides short and separate, but if you use good, matched coax, break it only where necessary and *NEVER* kink or sharp bend it, you'll be pleased with your work. (coax embedded in the wing would also give further stiffening/strength)

Another alternative:

Now I wouldn't mount the video antenna in front of the camera (who wants to look at their antenna?) but you could mount the video antenna on the nose pallet, behind the camera. Then push the dragonlink as far back as you can, pull the waveguide out the top (behind the wings), run along the spine and mount the ducky on the tail.



One note (you probably already know this) is the air is much more transparent to 433M than 5.8G. You will likely fly beyond your video before you fly beyond your control. Not a bad thing, just something to be aware of.

Finally, if you haven't built/bought better antennas for 5.8, start thinking about it. You can get impressive signal/range gains by replacing the whip antennas.

(again sorry for the brain dump. feel free to ask -- I don't always convert thoughts-to-words clearly)
 
#5
Option 2 was what i was thinking of doing. Straight shot down the tail no bends onlly 1 connection.
I did get some spironet antennas for my 5.8ghz so i'm hoping to get a mile or so out of them. I fly in a huge dried up lake bed with nothing around for miles which is one reason i went with 5.8ghz. If i Start flying further i'll upgrade to a better frequency. But i got the fatshark combo with the 600mw Tx for a good deal so that was the other reason.
I too work with some avionics guys and yes they are a strange group of people. With A&P's working around avionics techs it's like barbarians and rocket scientists!!
Feel free to brain dump all you like I'm following so far.