Since it doesn't matter where the receiver is located, why not just move it...
somewhere closer to the front. There should be plenty of room in a 7 inch
frame. 

(16-Apr-2022, 08:34 AM)MomoBrut Wrote: The T-dipole ELRS u-fl antenna (or any other for 2.4 GHz) is normally manufactured with a cable length of only 40-50 mm (short version) or 80-90 mm (long version). Other T-dipole antennas are simply not manufactured. Therefore, the receiver must be in front, otherwise the antenna cannot be in front of the drone body with horizontal polarization as it should be. As I wrote, the fuselage of a 7-inch drone is 270 mm long! So if the antenna cable is to reach from behind, it must be 200 mm long. Another place is out of the question. By the way, everything is already written here, you just need to read it carefully. Another solution is to use an extension u.fl-> SMA with a length of 200 mm and DIY a pole antenna with an SMA connector. I don't want to go this route yet, I want to have an antenna that just slides into the platypuss.

"By the way, everything is already written here, you just need to read it carefully"

Mea culpa. I haven't read 100% of the letters and the words written in this post, and I've haven't noticed the maximum cable length of existing 2.4Ghz antennas (I wasn't looking for that information).

I could have read the whole forum and know all the answers, but maybe not your point of view and the reasons of your choice. As an example, somewhere in this forum (I don't have time now to search where and who), someone wrote that could be a solution mounting both antennas (one horizontally and the other vertically) at the same end of the frame (usually at the front), this way you won't need an excessive cable length and you can avoid too much cable loss. Yes I read that you want to have an antenna that just slides into the platypuss.

At 2.4GHz the cable and adapter loss is quite a lot, you can search the exact information and post it here if you want (I don't have time for that now). Maybe TBS would answer me the same at my antenna request and I should accept a shorter cable.

To sum up... for me this discussion in more a brainstorming, where someone shows test results with a table, someone throws ideas, we can discuss how is important for the horizontal antenna to stay at the front and how moving at center would impact reception.... or... we could discuss (or better... test) if it is better to have shorter cables with slightly worst antenna placement or longer cable with perfect antenna placement? ...it's just a discussion...

PS. sorry if my english isn't perfect (probably I made a lot of mistakes). I just studied it for 6 months 20 years ago and I rarely use it. 

Unfortunately, no progress on the antenna. At the moment, I'm cutting, printing, soldering and gradually putting things together so that there is something to try out the antenna and this frame is being talked about all the time ...

(24-Apr-2022, 11:52 PM)MomoBrut Wrote: Unfortunately, no progress on the antenna. At the moment, I'm cutting, printing, soldering and gradually putting things together so that there is something to try out the antenna and this frame is being talked about all the time ...

Does the quad get some fangs to supplement the wide open jaw look?

GoPro will be in the jaws. The shots look weird if the action camera isn't in the roll axis. The shots also come closer to the ground during low flights, which gives a more dynamic impression. Frame is an open source FR7 project that I just modified a bit.

Today I finished the antenna, the first version yet.
I measured the antenna on an analyzer, at 2.43 GHz (the center of the band) the attenuation is -24.3 dB, which is a very good value.

From the original length of 400 mm of the original FrSky antenna, I got to 365 mm, because the insulation broke during the removal of the sleeve, so I had to shorten the antenna of the original pigtail a bit. I started with additional insulation on the active part of the antenna (the thinnest protective shrink tube at the end) at its active length of 31 mm. I gradually cut and the best result was measured when shortening to a length of about 27.5 to 28 mm. The total weight of the antenna as in the photo is less than 6 g. The antenna is perfectly flexible and at the same time, after bending, it returns to its original position exactly as in the original material tests, as I sent earlier.

It remains to do tests on the drone, but it must be completed first.

This is the only reason I havent switched my 7" to ELRS, even with the Matek diversity receiver existing antennas are too short to run front and back.  On my Chimera 7 the TrueRC 2.4 bardpole is plenty exposed for everthing but returning to home (kind of important! ha) so have been searching for a T style antenna with a 220mm-ish long cable to sit out front under the nose of the quad.  After skimming this thread I might have to go your route and build one.  Or see if Hugo at TrueRC will build one, they do custom antennas but I'm not sure they mean 1 off $15 items.

edit: For what its worth I asked TrueRC about getting 2.4 antennas with longer cables to allow for diversity setups on 7" quads with the receiver mounted on the back. So ~ 220 mm cabled dipole for the front which would allow for the existing 2.4 bard pole to be mounted a bit higher by extending the TPU bard pole mount another 50 mm higher to get even more exposure out the back.

So far, only my solution is really possible if one does not want to use extensions. It seems to me that ELRS hardware manufacturers are just trying to spew something out quickly so that there is something to sell. And people who have a 7 inch LR just aren't much, whoops and other crumbs are among the people a lot more.

It will take some time, but then I will show the result, how I did it all. Yesterday I maiden the drone with standard BF PIDs and it vibrated quite a bit, so now I have to deal with the vibrations and then I will deal with the range of the antennas.

The antenna production process:
1. The default for the antenna production is the original FrSky u.fl antenna with a length of 400 mm. This antenna is a sleeve dipole, the sleeve is in a shrink tube.
2. The tube is first removed and the active part of the antenna longer than 31 mm is visible.
3. Gradually press the area at the beginning of the sleeve with pliers at the point where the pigtail is crimped to the sleeve through its shielding. The crimp has the shape of a hexagon, gradually turn the pliers along the hexagon when squeezing. After some 10 careful squeezing, the pigtail will pull out of the sleeve. After pulling out, you will see 2-3 mm of exposed shielding, leave this part as it is, otherwise you will not be able to put the sleeve back on later.
4. Make the antenna body from a 3.5 x 1.8 mm PU tube, which you shrink into a 4 mm diameter shrink tube, leaving about 2 mm exposed at the beginning.
5. Slightly enlarge the original hole in the sleeve by drilling with a 1 mm diameter drill bit. The pigtail should go smoothly into the hole, including the exposed shielding.
6. Slide the sleeve onto the exposed end, it should be tight enough to hold itself in place. Only really insert 2 to 3 mm, there must be an air gap inside the sleeve.
7. Carefully pass the pigtail through the antenna body and sleeve from the other side so that the exposed shielding does not collapse. The exposed shielding must protrude from the sleeve so that the sleeve can then be crimped onto this shielding.
8. It is crimped with crimping pliers pattern D15 (hexagon), if you do not have it, it must be done carefully with pliers.
9. Shorten the active part of the antenna to 27-28 mm (preferably 27.5 mm). The antenna will then be tuned to the center of the 2.45 GHz band, after subsequent tube shrinking, which shortens the active part of the antenna.
10. Shrink the active part of the antenna into a tube 2 mm in diameter from its end to the part of the sleeve where it was crimped.
11. Now shrink the whole body to the part where it was crimped into a 5 mm diameter tube. On the other side of the antenna body, leave the piece not shrunk so that a stop can subsequently form for inserting the antenna into the hole in the TPU holder.
12. Make that stop from a piece of tube with a diameter of 5 mm.
13. Done.

I heard back from Hugo at TrueRC, they will make custom length ELRS dipoles for $2-3 over the normal stocked length. I’m going to order a couple 220mm length so I can stick with my plan to mount the diversity receiver at the back. Still interested to see how your antenna works out since it might be the best option for the rear vertical. Cheers!

(04-May-2022, 08:11 AM)MomoBrut Wrote: Yesterday I maiden the drone with standard BF PIDs and it vibrated quite a bit, so now I have to deal with the vibrations

Not to get too far off topic but if you are able to update to BF 4.3 UAVTech (Mark Spatz) has a preset for 7-8” quads that is an excellent starting point. Gets things very close to ideal without any tinkering. He has a video on how to access his presets directly from BF.

Yesterday I did RSSI measurements at a distance of 1 m. There are two antennas on the drone, in front there is a BetaFPV 2.4 GHz T-style dipole antenna with a balun in horizontal polarization, in the back is my antenna in vertical polarization. The drone was at a height of about 0.5 m on a pole above the ground, on the transmitter I gradually changed the polarization of the antenna, there is a T-style dipole antenna from Happy Model, the transmission power was 25 mW. At 1 meter, I always measured -8 to -9 dBm on average with the corresponding polarizations. I have not yet measured such high values ​​with any antenna. For example ceramic t-tower style antenna on EP2 never goes higher than -30 dBm, T-style antenna form HM on EP1 never goes higher than -12 dBm. With the perpendicularity of the polarization, the second antenna always dropped to values ​​around -20 to -21 dBm on average. The result of the test is that my antenna works very well, basically there are no obvious differences between my antenna and the antenna from BetaFPV. The second result is that I have not yet seen such high values ​​during tests with previous antennas. So it looks very, very good.

(04-May-2022, 03:23 PM)SeeWell Wrote: Not to get too far off topic but if you are able to update to BF 4.3 UAVTech (Mark Spatz) has a preset for 7-8” quads that is an excellent starting point.  Gets things very close to ideal without any tinkering.  He has a video on how to access his presets directly from BF.

I'm still on version 4.2. I know about the new version 4.3 and I'm also watching UAV Tech, there was simply no time for that yet, there is still some work on the drone, and I don't have enough time. I am currently reviewing 3D print files and projects, there are over 50 of them and I am already confused about what it is for. In any case, thanks for the reminder.

So it's done, first I send photos with details of the antennas installation, both my antenna at the back and BetaFPV antenna at the front. Both antennas are in the TPU holder, the BetaFPV antenna is in the front holder, which is also a bumper and does not significantly shield the active parts of the antenna. You can also see the detail of the overall installation and the Rx installation in the front of the frame. Photos are worth thousands of words ...

And finally the finished drone ...