Custom FrSky R9M 868MHz antennas giveaway

As you might have realized, from time to time I’m making an antenna and I have the equipment for it. I’m also strongly considering to produce a small batch of antennas for FrSky R9 long-range radio system since there is a high demand for such antennas.

Custom FrSky R9M dipole antenna

I have made a first small series or FrSky R9M dipoles tuned for the 868MHz EU-LBT version of this radio link and I want to give away 3 of them to my Patrons. If you want one of the 3 antennas:

  1. go to and become my patron if you are not one yet
  2. go to Custom FrSky R9M antenna giveaway post and comment with “I want one”
  3. wait one week until 5th of September 2018

On that day I will randomly choose three commenters and send them brand new, custom made 868MHz FrSky R9M antenna.

FCC 915MHz version giveaway will follow, I’m waiting for parts to arrive in a few weeks.

DIY Moxon antenna for TBS Crossfire and FrSky R9M

Moxon antenna in layman terms, it’s probably a simplest linearly polarized directional antenna. It’s like a bent halfwave dipole with a bent reflector in a back. Think about it as a very simplified Yagi antenna. It does not have much gain but has very good backward rejection. And thank’s to a simplicity, Moxon is super easy to build at home. And I’m proud of radio carrying handle snap mount. I think I did a good job over here.

I’ve built mine with some 3D printed parts, 0.8mm copper welding wire, 22cm of RG174 coax and RP-SMA plug. And some glue of course! Result? It’s definitely directional 🙂 I’m not using it very often, but it’s small enough to be taken everywhere where I take my X10S.

Realacc UXII circular polarized 5.8GHz FPV antenna – Lumenier AXII chinesium clone

Cloners gonna clone and chinesium keeps being chinesium! It did not take long for Banggood / Realacc to clone Lumenier AXII FPV antennas and call them Realacc UXII circular polarized FPV antenna. Coincidence? I do not think so.

Realacc UXII circular polarized 5.8GHz FPV antenna

I've ordered few of those in December, they arrived last week and this is what came in package

Realacc UXII circular polarized 5.8GHz FPV antenna

Realacc UXII circular polarized 5.8GHz FPV antenna

Unfortunately, in this case, the build quality was typical chinesium. As soon as I opened one of them, antenna disintegrated… oh bugger…

Realacc UXII circular polarized 5.8GHz FPV antenna

I only hope the other (the one I did not open) works like expected. I did not test them in real life conditions since the weather is rather bad over here. This weekend maybe… In a meantime, here is a video of what is happening inside Realacc UXII 5.8GHz antenna.

Video tutorial: 5.8GHz Inverted Vee antenna for FPV

Today another video tutorial. It’s just simpler to show how to make something on video than with text and images. So, without further ado: How to make Inverted Vee antenna for 5.8GHz FPV at home. All that is required is:

  • coax cable (here RG316)
  • SMA/RP-SMA connector
  • copper welding wire
  • caliper
  • soldering station
  • basic tools

At the end we have small and light FPV antenna that just works. Sometimes it’s just worth to make something by yourself, right?

3D Printed 433MHz Moxon Antenna With Arm And Snap Mount

It’s still middle of winter here in northern hemisphere, but I’m slowly preparing for next flying season. One of my goals is to push my DIY HC-12 Telelemetry System to a next level. In both range and quality. For quality I’m planning small hardware LTM decoder with LCD. For range, I want to reach at least 1.5km with 9600bps FU3 mode and 2.5km with 1200bps FU4 mode.

Continue reading “3D Printed 433MHz Moxon Antenna With Arm And Snap Mount” »

Improving cheap radio range

Radio range of my first drone, UDI 829A was pretty pathetic. OK, it was (still is, I only have to finally replace motors) pretty indestructible, quite stable and reasonably priced. But effective radio range as quite short. More less 50 meters. Above that limit strange things started to happen. The reason was pretty simple. Just take a look at this picture.

Antenna too short

Can you see the transmitter antenna? Yeap, that it this short cable. Not only it does not go into “antenna cover” of the receiver, it is also horizontally polarized and when receiver is held in a normal way, pointing into a drone, it emits almost no signal in this direction. This and an additional single whip antenna on the receiver makes it virtually impossible to have a good radio range.

So, I’ve decided to fix that and install external antenna that would work with vertical linear polarization and actually emits some power in drone’s direction.
This tutorial shows how to do it for UDI 829A, but will work almost all cheap drones. Their transmitters are very similar inside and as long as there is antenna pad or connector, it can be done. Continue reading “Improving cheap radio range” »

Antennas: power loss on polarization mismatch

Most people in RC hobby knows that receiver and transmitter antennas should match polarization. But what would happen if there was a mismatch? For example when transmitter uses linear vertical and receiver circular left hand? There would be a loss of power, attenuation. How much? Look at table below. Remember: -3dBi means half of power is lost during polarization change and you need +6dBi power (4 times more) to increase range by factor of two.


Vertical Horizontal LHCP RHCP
Vertcal 0dBi -20dBi -3dBi -3dBi
Horizontal -20dBi 0dBi -3dBi -3dBi
LHCP -3dBi -3dBi 0dBi -20dBi
LHCP -3dBi -3dBi -20dBi 0dBi
  • -20dBi is practical value. In theory, all power should be lost during this conversion. But we are living in not perfect world and always some power will go though
  • Vertical – Linear Vertical Polarization
  • Horizontal – Linear Horizontal Polarization
  • LHCP – Left Hand Circular Polarized
  • RHCP – Right Hand Circular Polarized