How to Mount Crossfire Antenna – All About Alignment

by Oscar
Published: Last Updated on

Long range radio systems such as TBS Crossfire and Frsky R9M typically use dipole antennas on the receiver and transmitter. The optimal antenna positioning can be different from traditional 2.4GHz systems which normally have diversity monopole antennas on the receivers.

The alignment of your TX and RX antennas plays a big part in signal strength and range. And it’s important to think about the possible orientation of the antennas during flight in order to maximize range and reliability.

Crossfire Dipole Antenna Explained

There are two ends in a dipole antenna used in Crossfire – one end is the antenna element and the other is ground. Both ends are equally important!

Crossfire dipole antennas commonly come in two forms, one is the Immortal-T antenna – a T-shape antenna in well protected rubber material. It’s heavier but much more durable and easier to mount.

The other antenna form exists in loose wires. It’s cheaper, lighter and flexible. But it’s vulnerable to “prop strike”.

Important!!! Crossfire uses different frequencies depending on the region: 915MHz for the US and 868MHz for Europe. In order to maximize your range, you should get the correct antenna that is tuned to that frequency you intend to use.

Stay away from carbon fibre!

Before we start, bear in mind to keep antenna as away from carbon fibre as you can. Especially avoid putting the antenna element too close to carbon fibre (the parts without shielding), which can “de-tune” the antenna and have a negative impact to your reception.

Different Antenna Positioning and Range

The alignment of transmitter and receiver antennas plays a huge role in your range.

crossfire antenna alignment orientation effect range signal strength

Case #1 shows the optimal antenna alignment for maximum range – both of antennas should be parallel to each other.

When your quad rotates 90 degree, it goes into case #2, where one end of the RX antenna is at 90 degrees to the TX antenna, and your range will be reduced. To avoid this, you could mount your RX antenna vertically (as well as your TX antenna). This is not easy to do on a mini quad due to space, more doable on a wing or plane. But since we don’t often fly long range on mini quad, many just mount the RX antenna horizontally (as well as TX antenna) for convenience.

The worst case scenario is case #3, where the tips of the antennas are pointing at each other. This can be easily avoided by making sure you are always facing your aircraft (if you are mounting the antennas horizontally), or just have both of your antenna placed vertically.

Further Reading: Make sure to monitor RSSI/LQ while flying long range!

How to Mount Crossfire Receiver Antenna?

For “loose” dipole antennas, I use two pieces of zip tie wrapped around the arm, and secured by heatshrink tubes.

With T-Immortal style antennas, you can strap it to the arms with two zip ties, probably the easiest and most common way to install your antenna.

Image credit: beeb

Or be a little bit more elegant and use a 3D printed mount

Here is a bad example, as both ends of the antennas are touching the carbon fibre.

It’s best to keep the ends of the antenna as far away from carbon fibre as possible, since that’s where the active element is.

Please let me know if you have any questions or comment.

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20 comments

Mark 26th November 2020 - 4:08 am

Thank you Oscar for all your hard work and efforts.

A quick question, I understand carbon fiber is a NO-NO for antenna placement, how about foam, battery and electronic (FC / ESC excluding VTx).

Thanks.

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MIchael Bibby 18th September 2020 - 2:04 pm

Its probably already been in the comments section already, but in the example you gave for how not to mount a crossfire dipole, probably the worst factor is the metalwork of the motors themselves, more than the proximity to the carbon fibre. The radiation pattern and SWR of a dipole is effected by nearby metal more than anything, especially when its in the same orientation as the elements themselves (but a dipole wont really be effected by, say, the metal poll that it is mounted on, because its orientated 90 degrees to its axis).
One question I have (being quite new to longrange FPV), is: does anyone make a good 1/2 wave, ground-independent, end-fed vertical antenna for use with crossfire that could easily be mounted on a drone? I guess it would have to be ground-indepedent because of the lack of metal on a drone, but maybe not. I’m pretty sure, if it was to be efficient, it would need a matching circuit to balance the impedence at the feed point, but then again it is only a receiving antenna, so maybe not. Anyway, there are plenty of 800/900 mhz antenna’s out there (for various applications), but I don’t see anyone adapting them for use on drones (yet).

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Steffen 4th May 2020 - 4:21 pm

Hey there. Since Frsky R9 and CRSF are on 868MHz in Europe, I presume the antennas are interchangeable, right?

Cheers Steffen

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Oscar 3rd June 2020 - 12:19 am

Correct

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Randy 16th February 2020 - 10:31 pm

do you (or anyone here) have the .stl file (or know where to get it) for that 3D printed mount? looking to upgrade my quads…

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Jorge 15th January 2020 - 10:28 am

I have a 868Mhz immortal T antenna, if i go to the US and change my frequency to 915Mhz but keep the same antenna will my performance go down significantly?

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Oscar 24th January 2020 - 4:47 pm

As far as I know their antennas are made to work for both frequency, so you shouldn’t notice too big of a difference.

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Jan Demant 12th October 2019 - 1:24 pm

:) Ty for UL and all your great work
Where did case #3 go, in antenna positions? :)

LOolz

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Charles 6th September 2019 - 7:28 pm

BEST VISUAL EXPLANATION ON THE INTERNET !

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Dennis 18th June 2019 - 4:00 pm

Does it matter if the antennas are rotated relative to one another while still being parallel (i.e. parallel, but not in the same plane)? Thx!

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Oscar 27th June 2019 - 5:42 pm

Yes, you get some signal reduction when turning one antenna away from the other even when they are parallel.

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Kenn Elliott 7th June 2019 - 5:39 am

What about the R9 with two flat antenna on the ends of two wires? What’s their best orientation Oscar?

Kenn

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Andreas 4th June 2019 - 9:38 am

Hey,
how do I recongize if I have a 915 MHz or a 868 MHz T Antenna? They look similar and I don’t know how to discern.
Thank you!

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Oscar 6th June 2019 - 5:58 pm

From Frsky, they should be have a color heatshrink indicating the frequency. Not sure how TBS differentiate it as I no longer use their system.
But anyway when you buy any receiver or antenna, there should be an option where you can select which frequency you want.

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Jens J 24th May 2019 - 11:01 am

Have you had a prop-strike on that contraption? The reason I’m wondering is that it’s easy to underestimate just how destructive they can be: just the other day I had a worn out prop nut which came lose (my bad for not checking it) at takeoff – the throttle was at maybe 20% – this made the prop detach from the motor shaft, cleanly cut through both antenna tubing and antenna and take off a chunk of the XT60-connector before launching into space, never to be seen again. I’ve had prop strikes damage pretty much anything but the actual carbon fiber on other occasions. So it seems to me, the only real protection from strikes is a tube of carbon fiber or steel, neither being a very good idea… Me, I just make sure to mount things where there is as slim chance as possible of a prop ever getting to them.

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Oscar 26th May 2019 - 2:45 pm

Well, maybe try to avoid having a loose prop? That’s never happened to me.

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DIEDERIK THIERS 9th May 2019 - 3:45 am

Any suggestions on how to mount the wire “floppy” antenna’s?

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Jarrett 19th October 2018 - 3:24 am

In the L rx configuration, i assume the active element is in the vertical position, and ground out back, correct?

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Jon 16th October 2018 - 11:51 pm

I mount the crossfire immortal T antennas in the vertical (y axis) plane out of the back of the quad, I have found this gives consistently the best link quality. (I have 3 x 250 and below crsf quads using the crsf nano rx) The downside of this is that it takes more effort during the build. To stiffen up the pigtail section and reduce the likelihood of prop strikes I cut a 6mm OD PU tube along the axis then hot glue and heat shrink in place. I also 3D print a support out of something light weight like HIPs or PLA that I can hot glue three antenna into; this reduces any rotation force being put onto the ufl connector and helps keep the antenna in position – the total additional weight of the pu, 3D printed part and dabs of glue is 1 to 2grams depending on the quad, insignificant on a 4 or 5” quad

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zak 16th October 2018 - 2:00 am

you can turn the stock antenna into a ‘ghetto’ T using 2 pieces of antenna tube and some heat shrink

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