As many of you know, I have been on a quest for the best 915mhz antenna for long range.  It has been a journey with a lot of fun and learning that has taken place on the trip.  I have provided tutorials and videos of the two previous generations of antennas developed along the way.  Both the Gen 1 and Gen 2 antennas have posts about them and how to build them on this forum.  I did a tutorial on the Gen 1 and provided a video of the Gen 2 done by another guy.
 
My involvement in this process of developing the best antenna was primarily with ideas for a better mousetrap.  The tech side was done by a real rocket scientist, an engineer at SpaceX.

Originally, I was going to do a tutorial with a video on how to make the Gen 3 (sleeve) antenna.  But in testing, the Gen 2 and Gen 3 were very close in performance with the Gen 2 easier to make and for less money.  So I decided it was a kind of a waste of time to do a Gen 3 tutorial.  BUT Harry, of ifly4rotors fame wanted me to provide some details and component info on the Gen 3 for him, and maybe others.  So, I decided if I’m going to go to the lengths to provide the basic info, providing a limited tutorial would be not that much more difficult.  So that is why this tutorial is here for those who care to read about it.

Some brief history:
 
The Gen 1 antenna was made from RG178 coax and the tutorial is here, https://intofpv.com/t-how-to-make-your-o...rx-antenna This version had issues where the main feedline blocked the passive element (a single wire) of the antenna which made for high VSWR readings, (2.2-2.4) and lower than desired SNR readings.  With that said, I flew out over 4 miles with a Gen 1 and still fly with that antenna on one of my older quads.  Even as bad as it was, it still performed better than an Immortal T.  The Gen 1 antenna was named the “Stevens Stinger” named by me after the guy who came up with the idea.

The Gen 2 antenna was made from 1.13mm coax cable.  The process for creating the passive element was to fold the ground shield over the outside of the coax outer sheath.  So this fixed the problems of the Gen 1 antenna.  And the VSWR went down to 1.5-1.7, and SNR went up as well.  So a better antenna.  My 8.1 mile run was with the Gen 2 and I still had 99 LQ at 8.1miles out, so a very good antenna.  This antenna was coined the “condom style” for how you roll the ground shield back over the coax.  This is the antenna I make for all my quads from this day forward, even though the Gen 3 is better.  Here is a link to a video on how to make the Gen 2 condom style antenna.
 
 
The Gen 3 antenna, named the “sleeve antenna” Due to the copper sleeve that makes up the passive portion of the antenna.  This design is much like the Isopole antenna from the Ham Radio world, see below.    This antenna is a very good antenna.  VSWR readings in the 1.1-1.3 range and SNR readings to die for.  But it is significantly more difficult to build and build correctly.  And the cost is around 10 times what it costs to build a Gen 2….only costing about $6.00 each, (discounting the cost for special tools) but still way more than the Gen 2.  The method of attachment to the quad is superior in my opinion, and there is no need for an antenna tube, as the antenna is self-supporting, as the coax is pretty stiff.



The development of the Gen 3 antenna was done by two guys who work for SpaceX and was tested with high dollar equipment at their disposal to include an anechoic chamber.  So, the design is sound.  All you have to do as the builder is not make mistakes and it will perform for  you.

Dimensions of the antenna itself:

The active element is 75.5mm for 915 Mhz.  This is shorter than the typical 78mm.  This is due to the overall length of the antenna and how the larger coax and over all make-up of the antenna resonates.

The passive element is 58mm.  Again this is different.  Usually the dipole configuration is equal lengths of the passive and active elements.  The make up of the sleeve is the reason for the difference.

The overall length OAL is to be 10.5 inches.  A small variance of up to a ½ an inch here won’t be a problem.

The development of this antenna was for 915mhz only.  For those of you who are on 868mhz, I have no idea what the dimensions would be for that frequency….and I don’t believe the gurus that fine tuned the design know either.
 
Parts for the build:

LMR 200 Coax
https://www.pasternack.com/50-ohm-low-lo...200-p.aspx

Copper tubing ¼ inch I.D.
https://www.ebay.com/itm/Watts-Pre-Cut-C...uSekar_wew
 
SMA male crimp connectors
https://www.w5swl.com/SMA-Male-Crimp-Con...fECmZLNYE8
 
u.fl to SMA pigtail
https://www.data-alliance.net/u-fl-to-sm...n-10-inch/
 
 
Tools for the build:
 
A crimp tool to crimp the SMA fitting
https://www.w5swl.com/Professional-Conne...p_973.html

And of course wire strippers, soldering iron, a wet cloth, solder
 
Antenna analyzer, this is a must!  Below is a link to the analyzer from Banggood. I can’t recommend BG, I think they suck big time.  I found mine on Amazon, but the prices for them are running about 100.00 more than I paid.  So search well.  There is a newer model, but I can’t attest to its performance.  The SpaceX guys bought the ones below if that tells you anything.



 
https://www.amazon.com/Impedance-Analyze...015&sr=8-4
 
 
The build process:
 
Let me start off by saying, attention to detail matters.  Little errors will yield poor results, and big errors will be a failed build.
 
To make the sleeve, there are a number of ways to cut it to length.  I first used a tubing cutter, but that makes the inside of the sleeve more narrow at the cut point.  If you have the appropriate reamer you can expand it out with that, even flair it.  Just don’t use anything that removes copper from the sleeve in the process.  If much copper is removed, it changes the resonate point, and you will have a poor performing antenna.  You can also cut the sleeve with a Dremel and cutoff disc.  Just be accurate with your cut.  Using the Dremel may require some dressing of the edge, so if you think you will need to dress the edge, leave enough length to do that and dress it to the correct length.   I played with different methods before my first build, you may want to as well.
 
I first build the antenna and sleeve section.  The reason is if you mess this up, as it is the most challenging, you won’t have wasted the SMA end by installing it only to have to throw the whole thing away because you screwed up the sleeve install.  I get a section of coax about 15 inches long.  I remove the coax down to the center copper core to a length of about 80mm.  You will trim the core to its 75.5mm length once you have the sleeve installed.
 
Once the core is exposed, you trim no more than a ¼ inch of outer sheath from the outer shielding, see picture.  This is where you are going to solder the sleeve to the outer shield.  Disregard the picture shows 75.5mm length of core,  you will still have 80mm at this point.



First, pre-tin the outer sheath in preparation to soldering the sleeve.  You will slide the sleeve over the outer coax and align the upper end with end of the outer shield.  This will be your solder point.  You are going to solder the sleeve to the outer shield wire mesh.  You have to be very careful not to melt the plastic underneath the outer shielding.  To prevent melting you will what to have your solder iron very hot.  Solder very small areas at a time, cooling with a damp cloth after each before moving on to the next solder point.  You need to make sure you get a good solder, no cold solder joints, but don’t hold the iron so long that you melt plastic.  Once you have done this, it should like the picture below.  Also do a continuity check to make sure you have shorted to the center core and the sleeve has continuity with the outer shield. (you check this by putting a probe on the sleeve and touching the other probe to the outer sheath at the butt end of the coax where the SMA will be installed)



If all went well, you have completed the most difficult part of the build.  You can cut the center core to 75.5mm now, or you can wait until you have completed the build, just remember to do so.
 
I don’t have any pictures how to install the SMA fitting onto the butt end of the coax.  If the narrative isn’t sufficient, I can do an addendum in this thread with pics.  I just didn’t want to waste a fitting for the tutorial if a narrative would suffice.
 
For installing the SMA fitting, first cut the coax to the OAL of 10.5 inches +/- a ½ inch.  Then strip the outer sheath off long enough to put the SMA Male end fitting on.  Strip enough of the outer shielding and center insulation off the center core to expose it for soldering the SMA center male post to the core.  This length is determined by the overall length of the fitting.  Once the SMA male post is soldered on, I guide the newly soldered post into the SMA fitting.  The back end (knurled section in the picture) of the SMA fitting is forced into the coax between the outer sheath and the web shielding.  While that is going in pay attention that the newly soldered pin is going into the SMA fitting straight, into the hole, and not binding.  Once seated, then you can crimp the outer band onto the coax and SMA fitting.
 
You will need to decide on the pigtail length from the merchant above.  The shorter the better.   The pigtail will connect to your receiver by the u.fl end.  Then the SMA female end of the pigtail will mount to the quad somewhere of your choice.  I made a mount that was at a 30* angle for inflight.  But you can drill in the frame and then bend the coax to your desired angle.  A picture of the pigtail is below.



I recommend you insulate the antenna from the frame, otherwise the negative side/passive side is connected to the CF frame and then the frame becomes part of a resonating antenna.  Not a good plan in my opinion.  I insulate my VTX from the frame when I mount it.  I know most do not.  But the same issue should exsist with that system, if you’re not insulated the frame is part of the antenna system.  Clearly because most don’t insulate their VTX antenna when they mount it, so it may not be a big deal.  But I can say that I tend to have really good VTX range over what others typically have.  So maybe there is a benefit.  Regardless my recommendation you insulate from your frame, your choice if you do or not.
 
The final thing you will want to do is put shrink tubing over the whole build.  I did learn that shrink tubing actually helped with bringing down the VSWR on my builds.  Usually by .1-.2 points.  Also shrink tubing makes the antenna less of an eye hazard when working around the quad, i.e. hooking up the battery, etc.  If you get poked in the eye with that uncovered copper core active element, it may cause serious damage to your eye.  So be careful.  Here is what the antenna looks like when shrink tubed up.


 
It took me 4 tries to get an antenna that worked well.  It was not the design that caused this difficulty, it was my lack of attention to detail.  I’m pretty good at soldering, but it still challenged me getting the sleeve soldered in place.
 
If you have questions about this tutorial or if you are having difficulty during your build, don’t hesitate to ask for help.

Good luck

EDIT:  There is helpful info on THIS thread if you are going to attempt this build.

{2020-09-29}

Hi Krohsis,  
Thank You very much for putting this thread together; Excellent, Great explanation and pictures.   

(29-Sep-2020, 01:05 PM)iFly4rotors Wrote: {2020-09-29}

Hi Krohsis,  
Thank You very much for putting this thread together; Excellent, Great explanation and pictures.   

I did it for you, brother!

Hope you have fun building it.

(29-Sep-2020, 01:28 PM)Krohsis Wrote: I did it for you, brother!

Hope you have fun building it.

Thanks 

Will this analyzer work

Hi Krohsis,

I have ordered the analyzer listed in the previous post from Amazon; also ordered the LMR-200 cable and SMA Male connectors from Pasternack. I already had the crimpers. I might even have the pigtail...will have to look.
Now, we wait.

Thanks again for sharing your knowledge in the well put together thread.       

NOOOOOO!  DON'T BUY THAT IT WON'T WORK!!

   just kidding, looks good to me. 

How's the build going, Harry?

(06-Jan-2021, 02:54 AM)Krohsis Wrote: How's the build going, Harry?

I had put that on hold for the holidays and to complete a couple of quad builds. I wanted to get at least one of the 7 inch builds done; then I built FrankenFly-2-4 to fly in the house, but that didn't work out {for flying in the house}. 

Since I have lost my favorite "Fly Field", I will table the 7 inch builds for now, 
so I can get back to the this Gen 3 antenna build. 

This is just the inspiration that I needed. 

Thanks. 

I look forward to the progression to the ultimate finished product!

Oh, did I mention it really isn't worth the hassle when the Gen 2 is fine...

(06-Jan-2021, 11:29 PM)Krohsis Wrote: I look forward to the progression to the ultimate finished product!

Oh, did I mention it really isn't worth the hassle when the Gen 2 is fine...

Yes, but I gotta do it anyway, just to see how it comes out; just had to take a break for the holidays 

However, I figure it will likely on go on a 7 incher due to the size and weight, but that is ok. 
With any good luck, I will have a 7 inch to mount it on     Yeah, Roadrunner, just call be Bandit 

Alex at VAS has a video on how to make a sleeve dipole much like the Gen 3 but somewhat easier.  His VSWR readings aren't as good as the Gen 3 but still in an ok range for quad distances and superior to a Immortal T.

Food for thought for all you antenna makers out there

(29-Jan-2021, 02:49 AM)Krohsis Wrote: Alex at VAS has a video on how to make a sleeve dipole much like the Gen 3 but somewhat easier.  His VSWR readings aren't as good as the Gen 3 but still in an ok range for quad distances and superior to a Immortal T.

Food for thought for all you antenna makers out there

Hi Krohsis,

Thanks, I will take another stab at building the antenna.

Hi @Krhosis, I have a quick question.
If I were to attempt a Gen 2 made from RG-316, would it be safe to leave the dielectric sleeve over the center conductor (twisted wire, not solid).
Essentially just rolling the shield back over the outer insulation. Obviously the length of each will be trimmed to the correct length.
The entire antenna would then be covered in shrink tubing for protection and additional rigidity.

[EDIT]OK, I just watched the IBCrazy video. I think I have my answer.[/EDIT]

(08-Feb-2021, 04:46 PM)AkaMrBill Wrote: Hi @Krhosis, I have a quick question.
If I were to attempt a Gen 2 made from RG-316, would it be safe to leave the dielectric sleeve over the center conductor (twisted wire, not solid).
Essentially just rolling the shield back over the outer insulation. Obviously the length of each will be trimmed to the correct length.
The entire antenna would then be covered in shrink tubing for protection and additional rigidity.

[EDIT]OK, I just watched the IBCrazy video. I think I have my answer.[/EDIT]

Hey there Mr. Bill,

It's been awhile since I used RG316, so I don't remember if there is also a foil glued over the insulative dielectric sheath or not, but if there is, then no.  But if there isn't and only the mesh shield, then yes you can leave the dielectric sheath on....in fact you want to leave it on.  RG316 would be a better choice as well as it is far less lossy.  It likely will be more of a challenge to fold the shield back over, but doable.

Good luck and share your results.

I finally got my VNA. Man I love this thing!
I gave the IBCrazy Gen 3 a try as my first serious antenna build. With the help of the VNA, I think it turned out pretty darn good!
VSWR = 1.35 at 915.00MHz
62.63ohms