A while back I posted a tutorial on how to make your own Crossfire RX antenna, here is a LINK.  The primary reason for building your own was to get the antenna up higher than was reasonably possible with other antennas like the Immortal T, away from CF, batteries, etc.  Even the long version of the Immortal T is still too short.  By building the antenna yourself it gives you the opportunity to set the length to what you needed for your application.

There was one problem with this hack and that was when the antenna was put in the antenna tube, the ground side of the dipole was laying against the feedline of the antenna.  That meant that at some angles of flight the feedline would block the TX signal from the ground side of the dipole.  Blocking the ground side of a dipole isn’t ideal as that part of the antenna is important, even though most of the work is done by the active element (the other side opposite of the ground).  Although at the ranges that most long range quads fly, this blocking didn’t seem to be a problem for me (my personal best so far with the original homemade antenna is 8.1 miles), it was a concern for some.  So as is in this hobby the search for a fix was looked for and discovered.

As you can see in the first picture, the original method was for the ground wire to be soldered to the end of the shielding of the feedline.  In the new system there is no ground wire, just the exposed shielding is folded back on the feedline at the same length as the original ground wire and the active element, 78mm for 915Mhz (USA spec), and 82mm for 868Mhz (euro spec).





The process of folding the shielding back takes some finesse and experience, but once you get the hang of it, it goes pretty easily.  It’s important to not nick the shielding when removing the feedline sheath, because if you do when folding the shielding back that area will likely fail.  Some are using clear fingernail polish or model airplane dope to clear coat the shielding to the feedline once in place.  It does make for a nice complete look.  I used the clear fingernail polish.  It didn’t seem to affect the feedline sheath.

Some who have made this antenna “say” the VSWR (Voltage Standing Wave Ratio) is better than the old method.  No one has provided any proof of this though.  And given that VSWR is not a worry on a receiving antenna but SNR (signal to noise ratio) is the concern, I question that anyone has really done a comparison test on either hack.  Some have indicated the old method yields a VSWR reading in the area of 2.8:1 vs this new method being in the area of 1.5:1.  But, I have never seen anyone post actual test data, so those numbers could be pure .
 
Clearly this method fixes the problem mentioned above, however slight the problem may be, but it’s a tad more challenging to bring to fruition.  I will make all my future antennas with this new method, but I likely won’t change my old ones to it as they seem to work fine for me as I stated above.  If I find there is a significant improvement, I may go to the trouble to change out all my old antennas to the new method. 
 
I plan to try out this antenna mod this fall when ambient temps allow me to fly again.  If there is an obvious improvement, or detriment I can show in field testing, I will share it.  I also ordered some specially designed Immortal T-esque antennas built by Alex Greve on special group buy.  I will also review those if they end up being anything noteworthy.

I was going to make a video on how to do the mod, but another guy, Dauv McNeely already did it so here is a video for those interested.

Dauv uses super glue to hold the shielding in place after getting it in position.  I used clear fingernail polish.  Not sure if one works better than the other, but you definitely want to make sure the shielding stays in place.  The braid of the shield has a natural desire to shrink back.

Once the mod is done, hook it up to your RX and put it into an antenna tube and send that bad boy!

So, just when I say I haven't seen any proof of the performance of the antenna built this way, Jeremy Mariscal sends me info on the VSWR for these antennas.  Jeremy is a pretty squared away guy who is an engineer for Space X.  Even though VSWR is not the most important measurement for a receiving antenna, the two photos do show the kinds of readings they are getting off of this new method.  Jeremy said that the other method would yield VSWR readings in the area of high 2s+. 

VSWR is considered good in the 1.5:1 -2.0:1 with 1:1 being perfect.  There are no perfect antennas, and if you buy a pre-built antenna for other uses, i.e. ham radio, wifi, etc., they usually are in the 1.5:1 to 2.0:1 range in the specs.  The two pics below show they are getting 1.4:1 to 1.8:1 on this method of build.  

I asked Jeremy if he had any SNR data for the antenna and he didn't.  So we still don't know the most important reading for an RX antenna.  But for my fellow data junkies, here is a slice of info for you.

LOL...I almost understand that stuff, John!

So if I am reading it correctly, the customs do perform better than stock?

Well Kaity, in a word, I definitely think so...

All I can tell you is anecdotal.  I have the original mod on 3 of my quads and they ALL out perform the Immortal T.  And the improved version is said to be better, at least on paper and visually.  Having not tried the new version I can't personally say if or how much better than the original version the new one is, or if it too is better than the Immortal T.  

What I can tell you is the new version should be better, and those that have done the new mod say it is better.   

So that should make things clear as mud.   If you are inclined to make your own, I'm confident you will be glad you did.   And if you are interested in having one but don't want to make your own, when I make some for me, I can make one or more for you.  

Hopefully when the temps cool off, I can come back here with some decent analysis and answer some questions.  But then again, I may have forgotten how to fly by then....late September seems so far away right now.

(30-Jun-2019, 10:22 PM)Krohsis Wrote: Hopefully when the temps cool off, I can come back here with some decent analysis and answer some questions.  But then again, I may have forgotten how to fly by then....late September seems so far away right now.

Wow, we just had our 2nd day this year with temps over 90. Although it has been really wet and raining all the time which is keeping us from flying. About half of Ohio's counties have severe flood damage.
I guess we all have Mother Nature to contend with one way or another.

Scott

(01-Jul-2019, 01:03 AM)Scott_M Wrote: Wow, we just had our 2nd day this year with temps over 90. Although it has been really wet and raining all the time which is keeping us from flying. About half of Ohio's counties have severe flood damage.
I guess we all have Mother Nature to contend with one way or another.

Scott

Yeah, mother nature has a way of giving us a backhand every now and then.  Hopefully you have avoided the flooding.

We have been colder, wetter and windier this year by far.  But the high heat we always get for about 8-10 weeks is here, and I can't fly in that.  So no complaints really, just stating the facts, and I wouldn't want to live anywhere else.  After 30 years of being cold and wet in the Pac NW, it is a blessing to be in the Mojave.  I just need to invent water cooling for the electronics on the quads....then I could fly in 115* heat.

Lordy - finding out what those long RX antennae are on people's LR builds was like pulling teeth. Clearly my GoogleFu needs some work.

I don't know as much as I should about RF, but have been dipping into longer range (sounds pretty dumb now that i've written it out). I've long since used the "Immortal-L" knowing it's a compromise, but one that I'm willing to make for durability and ease of mounting. It also performs much better for me than a flat immortal-T. Crossing into the nulls when you yaw can be devastating for LQ. In quick tests at like 2.5km a slow yaw with a flat T can drop LQ into the 80's vs an immortal L which can make the yaw and round trip without LQ ever dropping below 98-99. I'm only using the baby crossfire TX unit and don't yet feel like pulling the trigger on a diversity unit.

People have been extremely critical of the immortal-L (the immortal L has performed well for me, still maintaining 100LQ out to 3km and only just dropping down to 50hz at around just >2km). Plenty of diagrams have been posted about how its rf pattern isn't ideal. But those same people seem to post pictures of their setups which are vertically mounted immortal-T's with the bottom half the antenna blocked by a battery/the frame. I really wonder if a half blocked immortal T is really that much better than an immortal-L. Looks like i have all old Immortal-T's before they placed the balun in there so you can probe which side is the "active" side; with the stock dipole people are emphatic about placing the "active" element straight up - but not so with the immortal-T's. I don't totally understand that. The responses to if orientation matter on the immortal T are underwhelming. The gist being that no-one really commits to if orientation matters at all and that the antenna should just be mounted totally unobstructed, which isn't super practical and not what people are doing in practice. The basic immortal T makes mounting it unobstructed almost impossible on quads because it's so short (longer ones now available). People who are fairly experienced LR pilots even talk about how they use the stock whip and just bundle up the "ground"/black side and stuff it into the quad. The V1 immortal T's are just like the stock dipoles in a hardened case, so something doesn't really add up. Clearly there's a lot of bad information. I understand that this stuff isn't ideal, but finding out where the best places are to make compromises is a very difficult conversation to have in the trollfested waters of the internet.

Since I don't have the longer immortal T and have been seeing these crazy long antenna on people's LR builds I started to dig and ask questions and FINALLY someone linked me to the above video. I had see Alex Greve's video, but that clearly wouldn't fit in a forever tube.

I have finally ordered the cable from the above to test this out! Thanks for posting about this and your previous tutorial and the results above!

Any updates on the performance of this compared to the V2 immortal T's and/or the next gen version?

In case you haven't seen Alex's video: