ATTENTION: There are 2 better choices if you are going to make your own antenna for the quad in the Crossfire system.
The Gen 2 (condom style) version is one choice. In this video
The Gen 3 (sleeve antenna) version is the best choice. There is a tutorial HERE....
All three versions, the one in this tutorial and the two Generations above, are better than an Immortal T.
If you're a Crossfire user you know there are two of the issues plaguing us when it comes to the RX antenna. How to mount the RX antenna and which antenna to use. TBS states that the antenna should be mounted vertically for the best performance. This is not because there is better power or such, because a horizontally polarized antenna actually works a little better for range. That's why long range Ham radio antennas are almost always horizontally polarized. The reason in FPV world why the antenna should be vertical is because when the antenna is horizontal the tips of the Immortal T antenna can point towards the transmitter causing a null in the signal and a failsafe. This doesn't happen with a vertical antenna, so that’s why they recommend the antenna be mounted vertical. The choices for antennas are limited, with the two most common being the antenna included with the RX, and the Immortal T. Both are dipole antennas, but the Immortal T is formed into a T shape. Well, there is another choice and that is to make an antenna yourself. The advantages are you will have an antenna that will be vertical, it will be longer than the one that comes with the RX, so it will extend well above any possibility of the carbon of the quad blocking the signal. This antenna design is the brain child of Mike Stevens.
Below is a tutorial on how to make this antenna. I have made 4 now and I will never have any antenna than this one on my quads. It performs excellent and is easy to mount. I thought perhaps some here on the forum could benefit from this tutorial. The pictures were done by a friend, Jeremy Mariscal. He gave me permission to use his photos in this tutorial. When he took the pictures, he didn’t provide a narrative, believing the pictures were sufficient. In most cases I agree, but I will provide a narrative to give a little more information for those who might benefit from that.
Some of the things you will need are:
Wire cutters
Wire strippers
Soldering iron
Solder
Shrink tubing
The coax cable the antenna is made from. That needs to be RG178 and have a female IPX/UFL connector on one end. I get mine from this link. They are good quality and the price is good.
https://www.ebay.com/itm/IPX-Female-to-I...1164101781
You will also need an antenna tube. There are many choices for this, including the many vendors of antenna tubes. I went with a suggestion by Kaitylynn here on the forum and used ¼" drip irrigation line. I got a spool of 100 feet of it and it cost me less than 5.00. I will never run out.
And you will need some zipties to attach the tube to the quad.
So let’s get started:
The parts of the antenna are the active element and the passive element or the ground plane. In this picture you can see the black antenna which is the TBS antenna. The light brown coax is the wire that will be the new antenna. On the black antenna, the passive element will be used on the new antenna. If you don’t have a TBS antenna, you can make a passive element from a piece of the center conductor out of the brown antenna coax. The passive element on the TBS antenna is the thinner black wire in the picture with the little bulb on the end. In the next couple pictures we will remove this piece from the TBS antenna.
First you will want to remove the shrink tubing from where the passive element is attached on the TBS antenna.
Next, you will unsolder the passive element from the TBS antenna. You can set the rest of the TBS antenna aside, it won’t be used.
The new active element will need to be the same length as the passive element, which for the Crossfire at 915Mhz is 78mm. For those of you operating at 868Mhz the length is 82mm.
At this point, you can cut your new coax to the length you want your antenna to be. This will be the overall length. This is personal preference. I tend to go longer than some, others make it shorter. You just want to make sure it’s long enough that the carbon fiber of the frame doesn’t block it in any manner during flight. The longer the coax the more loss. But in reality given the realistic usable length possibilities, it won't make a difference, i.e. 6" vs 12"
Next you will strip the outer plastic sheath of the coax to 78mm. You can strip it a little longer and then cut the active element later, your choice.
Go ahead and confirm the length.
Now remove the shielding of the coax. For those who have never worked with coax, the shielding is a wire mesh that surrounds the center conductor of the coax. Be careful when you remove the shielding as there is a thin plastic coating on the center conductor beneath it. If that plastic coating is cut, exposing the wire inside to other parts of the coax, you may short the antenna and it will be useless.
This is what it should look like when the shielding is removed.
Next you will want to expose the shielding beneath the plastic outer coating. Remove about 1/8” or 3mm of this plastic. You will tin with solder this exposed shielding next.
Go ahead and tin the shielding. Do so carefully and quickly or you may melt the plastic protecting the center conductor.
Now you will solder the passive element you removed from the TBS antenna earlier. (If you don’t have this piece, you can make one from the center conductor from part of the new coax you cut to size. You will want to cut it to 78mm. Then strip a small part of one end, perhaps 2mm. Tin the end and attach to the same spot as we are with the TBS passive element)
Also, now is a good time to check to see if you shorted the antenna. Use a multimeter to do a continuity check from the shielding to the center conductor on the IPX fitting. If it's open you're good to go.
Now put shrink tubing on the connection of the passive and active elements and you’re done.
You can put the antenna in the antenna tube with the passive element pointing down. There is the question that TBS says the passive element is to be 90* out from the active element. In a perfect world that is how it should be done. But in a practical application it’s not needed, and difference in overall performance between having the passive element 90* out from the active element, versus having the passive element 180* out, pointing down from the active element in the antenna tube, is insignificant. Pilots are going out 6+ miles with this antenna and sustaining 99 on their Link Quality. So this discrepancy is not an issue.
The Gen 2 (condom style) version is one choice. In this video
The Gen 3 (sleeve antenna) version is the best choice. There is a tutorial HERE....
All three versions, the one in this tutorial and the two Generations above, are better than an Immortal T.
If you're a Crossfire user you know there are two of the issues plaguing us when it comes to the RX antenna. How to mount the RX antenna and which antenna to use. TBS states that the antenna should be mounted vertically for the best performance. This is not because there is better power or such, because a horizontally polarized antenna actually works a little better for range. That's why long range Ham radio antennas are almost always horizontally polarized. The reason in FPV world why the antenna should be vertical is because when the antenna is horizontal the tips of the Immortal T antenna can point towards the transmitter causing a null in the signal and a failsafe. This doesn't happen with a vertical antenna, so that’s why they recommend the antenna be mounted vertical. The choices for antennas are limited, with the two most common being the antenna included with the RX, and the Immortal T. Both are dipole antennas, but the Immortal T is formed into a T shape. Well, there is another choice and that is to make an antenna yourself. The advantages are you will have an antenna that will be vertical, it will be longer than the one that comes with the RX, so it will extend well above any possibility of the carbon of the quad blocking the signal. This antenna design is the brain child of Mike Stevens.
Below is a tutorial on how to make this antenna. I have made 4 now and I will never have any antenna than this one on my quads. It performs excellent and is easy to mount. I thought perhaps some here on the forum could benefit from this tutorial. The pictures were done by a friend, Jeremy Mariscal. He gave me permission to use his photos in this tutorial. When he took the pictures, he didn’t provide a narrative, believing the pictures were sufficient. In most cases I agree, but I will provide a narrative to give a little more information for those who might benefit from that.
Some of the things you will need are:
Wire cutters
Wire strippers
Soldering iron
Solder
Shrink tubing
The coax cable the antenna is made from. That needs to be RG178 and have a female IPX/UFL connector on one end. I get mine from this link. They are good quality and the price is good.
https://www.ebay.com/itm/IPX-Female-to-I...1164101781
You will also need an antenna tube. There are many choices for this, including the many vendors of antenna tubes. I went with a suggestion by Kaitylynn here on the forum and used ¼" drip irrigation line. I got a spool of 100 feet of it and it cost me less than 5.00. I will never run out.
And you will need some zipties to attach the tube to the quad.
So let’s get started:
The parts of the antenna are the active element and the passive element or the ground plane. In this picture you can see the black antenna which is the TBS antenna. The light brown coax is the wire that will be the new antenna. On the black antenna, the passive element will be used on the new antenna. If you don’t have a TBS antenna, you can make a passive element from a piece of the center conductor out of the brown antenna coax. The passive element on the TBS antenna is the thinner black wire in the picture with the little bulb on the end. In the next couple pictures we will remove this piece from the TBS antenna.
First you will want to remove the shrink tubing from where the passive element is attached on the TBS antenna.
Next, you will unsolder the passive element from the TBS antenna. You can set the rest of the TBS antenna aside, it won’t be used.
The new active element will need to be the same length as the passive element, which for the Crossfire at 915Mhz is 78mm. For those of you operating at 868Mhz the length is 82mm.
At this point, you can cut your new coax to the length you want your antenna to be. This will be the overall length. This is personal preference. I tend to go longer than some, others make it shorter. You just want to make sure it’s long enough that the carbon fiber of the frame doesn’t block it in any manner during flight. The longer the coax the more loss. But in reality given the realistic usable length possibilities, it won't make a difference, i.e. 6" vs 12"
Next you will strip the outer plastic sheath of the coax to 78mm. You can strip it a little longer and then cut the active element later, your choice.
Go ahead and confirm the length.
Now remove the shielding of the coax. For those who have never worked with coax, the shielding is a wire mesh that surrounds the center conductor of the coax. Be careful when you remove the shielding as there is a thin plastic coating on the center conductor beneath it. If that plastic coating is cut, exposing the wire inside to other parts of the coax, you may short the antenna and it will be useless.
This is what it should look like when the shielding is removed.
Next you will want to expose the shielding beneath the plastic outer coating. Remove about 1/8” or 3mm of this plastic. You will tin with solder this exposed shielding next.
Go ahead and tin the shielding. Do so carefully and quickly or you may melt the plastic protecting the center conductor.
Now you will solder the passive element you removed from the TBS antenna earlier. (If you don’t have this piece, you can make one from the center conductor from part of the new coax you cut to size. You will want to cut it to 78mm. Then strip a small part of one end, perhaps 2mm. Tin the end and attach to the same spot as we are with the TBS passive element)
Also, now is a good time to check to see if you shorted the antenna. Use a multimeter to do a continuity check from the shielding to the center conductor on the IPX fitting. If it's open you're good to go.
Now put shrink tubing on the connection of the passive and active elements and you’re done.
You can put the antenna in the antenna tube with the passive element pointing down. There is the question that TBS says the passive element is to be 90* out from the active element. In a perfect world that is how it should be done. But in a practical application it’s not needed, and difference in overall performance between having the passive element 90* out from the active element, versus having the passive element 180* out, pointing down from the active element in the antenna tube, is insignificant. Pilots are going out 6+ miles with this antenna and sustaining 99 on their Link Quality. So this discrepancy is not an issue.