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.
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.