Thank you for this very valuable inputs Krohsis. I did not get a chance to test my antenna because I'm still in the process of building the quad. Unfortunately, I do not have a lot of spare and the 2 antennas that I ordered from 2 different stores in France had both the same length (76mm), as shown on my previous pictures. I have eventually made my own antenna following your tutorial using the passive element (76mm) from the stock crossfire dipole antenna and have cut the active element to the same length (76mm). I'll try as soon as I can and will let you know the results. I agree with you that the length of both of my stock antenna is a real mystery as it does not match any of the frequencies we are supposed to use (either 915 or 868mHz) but after 2 purchases in 2 distinct stores, I came to the conclusion that this is all I could get from TBS
If I'm not happy with the results, I'll try to build a better antenna, making the passive element myself from a small gauge unshielded wire. I just have a question (I'm sorry, it might look as a noob question....lol), I've found a 18AWG cable but it had a silicon protection around and has 3 or 4 metal wires inside. Should I remove the silicon protection, separate the wires and take only one to build the passive element myself, or should I try to find a 18AWG cable that only has 1 wire inside? Where can I find such a cable? Thx a lot

(05-Dec-2018, 07:39 AM)sebastiendamaye Wrote:   I've found a 18AWG cable but it had a silicon protection around and has 3 or 4 metal wires inside. Should I remove the silicon protection, separate the wires and take only one to build the passive element myself, or should I try to find a 18AWG cable that only has 1 wire inside? Where can I find such a cable? Thx a lot

The silicone sheath won't be a problem.  Actually you want it to keep the stranded wires together.  Stranded wire will work fine(so will solid wire), so go with what you have.

Can anyone post pics showing how they mounted theirs? Also do you need the donor antenna for the passive element? Thanks!

(18-Dec-2018, 01:15 AM)gs550t1981 Wrote:   Also do you need the donor antenna for the passive element?  Thanks!

No, you don't need a donor antenna.  You can make the passive element from regular wire.  If you have some 18-22 gauge wire, you can use that.  Just leave the sheath on and solder in place to the correct length.

(18-Dec-2018, 03:16 AM)Krohsis Wrote: No, you don't need a donor antenna.  You can make the passive element from regular wire.  If you have some 18-22 gauge wire, you can use that.  Just leave the sheath on and solder in place to the correct length.

18-22 gauge copper wire?

(24-Dec-2018, 02:22 AM)gs550t1981 Wrote: 18-22 gauge copper wire?

Yes, stranded wire or solid, it doesn't matter.  But if it's stranded, leave the sheath on to keep it all together.  Cut it to the proper length, trim a little bit of the sheath where you solder it to the antenna and you're good to go.

(18-Dec-2018, 01:15 AM)gs550t1981 Wrote: Can anyone post pics showing how they mounted theirs? 

You can get a printed mount, the cleanest, most professional way.  Or you can improvise.  Below is the mount I have on my 10inch.  I drilled a hole through the middle plate and put a allen head bolt through the hole.  I then put the antenna tube over the bolt head and a dab of glue to the bottom plate.  Then it is ziptied to the frame.  It works great, but not the prettiest.  This quad is a bottom mounted battery, so I didn't need to worry about the antenna placement through the top plate.   

I'll PM you what I have done on my other quads. 

If you fly acro, the antenna tube in this setup will break in a crash.  But for long range it isn't a problem, cuz us long rangers don't crash....

I had a propstrike on my Frsky T-antenna and it revealed the inside of the antenna elements. It is made from thin steel wire, much like a bike wire used for gear changing or brakes. This got me thinking if I should build my own antenna from a bike wire to make it as durable as possible, is this a good idea or should it be made from a better conductor like copper?

The old antenna is to short and doesn´t have good reception even when flying on 100mw @ 868Mhz

(19-Aug-2019, 11:21 AM)Andreas-sa Wrote: I had a propstrike on my Frsky T-antenna and it revealed the inside of the antenna elements. It is made from thin steel wire, much like a bike wire used for gear changing or brakes. This got me thinking if I should build my own antenna from a bike wire to make it as durable as possible, is this a good idea or should it be made from a better conductor like copper?

The old antenna is to short and doesn´t have good reception even when flying on 100mw @ 868Mhz

Can you build your own antenna from scratch, yes.  Should you, no!  

A better idea would be to buy a new antenna and shield it from prop strikes, either by re-routing it or some sort of tube to protect it.

Ham radio operators make antennas from scratch all the time.  In fact most dipole antennas (dipoles are what our quad RX antennas are) for ham ops are made from cable from hardware stores not dissimilar to the bike cable you mention.  But they also have ways of tuning at the bench with baluns (balanced/unbalanced) antenna tuners etc.

So, in my opinion your fix iisn't to build a better antenna.  Just protect the new one.

Thanks, the whole idea with building my own antenna was to improve it. I already have a new antenna but FrSky antennas have the "wrong" length and the performance is not the best. both FrSky T antenna and TBS Immortal T antenna is made of spring-steel and this got me curious on the subject

Do you mean that if building the antenna from coax cable (copper) you can cut it to the correct length according to your guide but if you use a different material it have to be tuned?

(20-Aug-2019, 12:12 PM)Andreas-sa Wrote: Thanks, the whole idea with building my own antenna was to improve it. I already have a new antenna but FrSky antennas have the "wrong" length and the performance is not the best. both FrSky T antenna and TBS Immortal T antenna is made of spring-steel and this got me curious on the subject

Do you mean that if building the antenna from coax cable (copper) you can cut it to the correct length according to your guide but if you use a different material it have to be tuned?

Different materials, how it's made, all work to how the antenna performs.  And each frequency can be different as well.  Not to mention the RX antenna is a coax based system and developing that yourself out of a bicycle cable would be far more difficult than just buying the correct product.  If you want to make your own antenna, you could do so by buying the correct coax.

You mentioned that the Immortal T and the FrSky T are both made of spring steel.  I believe you may be mistaken.  Below are the specs for both RG316 and RG178, the two most common coax cables for our hobby.  Both have a center conductor that is silver coated copper clad steel, but not spring steel.  The outer conductor (shielding) which is typically the ground and also shields the inner wire from outside forces, and keeps the RF transmitted in the center conductor contained inside.  The center conductor is silver coated copper braided wire in both.  Some coax can have more than one layer of shielding, but you don't usually see that in this hobby.  

RG316

RG178

(20-Aug-2019, 12:48 PM)Krohsis Wrote: Different materials, how it's made, all work to how the antenna performs.  And each frequency can be different as well.  Not to mention the RX antenna is a coax based system and developing that yourself out of a bicycle cable would be far more difficult than just buying the correct product.  If you want to make your own antenna, you could do so by buying the correct coax.

You mentioned that the Immortal T and the FrSky T are both made of spring steel.  I believe you may be mistaken.  Below are the specs for both RG316 and RG178, the two most common coax cables for our hobby.  Both have a center conductor that is silver coated copper clad steel, but not spring steel.  The outer conductor which is typically the ground and also shields the inner wire from outside forces, is silver coated copper braided wire in both.  Some coax can have more than one layer of shielding, but you don't usually see that in this hobby.  

RG316

RG178

I can see that bicycle cable might not be the best material to use due to RF performance, but my broken antenna resembled a steel wire so that is why I thought that bike wire would be a good material to use because it would be robust and strong. According to TBS it is spring steel: https://www.team-blacksheep.com/products...tal_t_v2_s

you are probobly right that coax cable is the best core material to use and I will try this, thanks!

Good Job Krohsis

This is an old thread but since it’s here as a “how-to” I though it might be useful to add some more information. Having been a “Extra” ham for many years and built/tested many of antenna of different types and for different frequencies I think I understand why TBS believes it ok to target the antenna between the two frequencies ( Euro and Americas ) and although not optimal, I agree it’s not a bad choice.

I think their reasoning may be that the mounting and installation of these antenna on drones, in most cases, is so far from optimal that the fact that they aren’t tuned to the exact frequency used will make very little difference. For an antenna to be resonant at exactly the frequency it was designed for requires that the antenna be mounted as far as possible from anything that is even marginally conductive because such objects change the characteristics of the antenna including impedance, radiation pattern and frequency. This effect is becomes less the further the object is from the so called “active” elements of the antenna however general guidelines are to mount antenna such that there is at least 1/4 wavelength spacing from other objects.

At 915MHz 1/4 wavelength is approximately 82mm in free space making it impractical on even large drones to maintain such spacing. As well the effects of the CF, wires, motor, battery, and the antenna waving around in the wind are difficult and possibly impossible to predict therefore the best one can do in this situation is position it as optimally as possible and if it doesn’t work well reposition it and try again. Odds are there is no perfect position and the fact that the antenna is not perfectly tuned for your operating frequency is likely a negligible effect compared to other influences on the antenna.

Welcome Wingspinner, and glad there is another Extra class ham here, NQ7T.

I will say that TBS' Immortal T is a very poor antenna.  Not sure why...maybe because they are trying to cover too much bandwidth, or perhaps something else.  Outside 2 miles the quality of signal degrades.  By the time you are out 5 miles the quality really falls off and in my opinion it is unreliable.  I have tried several varities of the IT, even those built special by VAS, and all perform pretty much the same.  I want to like the IT, but it just sucks.

As far as the length of the antenna, that is the rational for having the feedline as long as we do is to get the resonate part of the antenna above the CF and other RF reflective parts.  I run much longer than the 82mm you suggest (which is correct) is the minimum best length.  I and a few others tend to run about 9-12 inches, most others run 4 to 7 inches as they are more vain as to appearance.  I always side with functionality over appearance. 

Also, that tutorial is old as you mentioned.  It was the first generation of this RX antenna mod.  There have been significant improvements made since the Gen 1.  The Gen 2 was much improved, and the current generation, the Gen 3 is even better yet.  The Gen 3 antenna uses a sleeve of copper tubing for the passive element, and the whole antenna is built on LMR200 with a solid core.  

I have finally come up with a build routine that produces repeatable results, and I'm getting a VSWR measurements of 1.2 to 1.5 and SNR 18-21.  Once I have some field testing to share, I will do a tutorial on the Gen 3 as well.

73s!