we will take a dive into how these antennas work and then get onto the details on how to do FrSky Receiver Antenna Replacement when the time comes.Let’s admit it, we have all crashed and probably stripped or broken our receiver antennas at one point in time. Even not tying up your receiver properly can cause it to get in between the props and get chopped off - ouch! Just because you lost your antennas does not warrant for a new receiver, right? Of course not! Antennas are consumable and can be easily replaced and so in this How to series article.

 Construction of a Receiver Antenna

 Are typical antennas on a receiver basically a piece of wire? Well, not exactly. These monopole antennas are actually made up of coaxial cable (or coax for short). This is exactly the type of cable found on your TV connection from your satellite dish or you local cable provider.

This cable is usually made up of 4 parts out of which 2 are insulation and the other 2 for the signal.

The outermost casing/covering is usually a black plastic sheathing to protect the insides from physical stress and damage (but we all know that these breaks quite easily!).

 The second layer is a ground layer composed of thin wire strands tightly intertwined. The purpose of this layer is to provide protection against noise and disturbance to the signal and also to prevent the signal from being transmitted till the actual antenna region - the part where no grounding wire is there.

 The third layer is another small insulation layer. This is applied directly on the active element/main wire to prevent shorting out with the ground layer.

 The final fourth layer is the actual wire where the signal travels from the device it is connected to. This is the actual “antenna” also called the active part when the previous 3 layers of shielding are removed.

 

Calculating and Stripping Correct Antenna Length

 The active part of the antenna is determined by the wavelength of the radio signal to be propagated. This is due to the correlation between wavelength and antenna length.

 The resonant frequency of an antenna is the frequency at which both the inductance and the capacitance get cancelled out and the reception (or transmission) is at the highest level. This happens to be at a quarter of the total wavelength of the signal being propagated.

 For a normal 2.4GHz receiver, this length is 31.23mm. Why?

The formula to calculate the antenna length is given by

Length = C(speed of light)/(Frequency*4)

In case you strip your antennas active element(the transparent part where the black plastic shielding is not present), the easiest way to revive and reuse the antenna is just to strip a portion of that shielding to expose 31.23mm of the active element.

To do this, follow the steps given below carefully.

  1. Make a clean cut right on the antenna right before the area where it got stripped.
  2. Measure 31.23mm from that end and strip the insulation until you are left with the active element.

 

Replacing the Antenna?

 In case you lost the entire antenna and need to replace it, you can order replacement FrSky antennas from HorusRC. In most cases like the XM/XM+ or the RXSR, replacing the antenna is as easy as unplugging it from the receiver and attaching the new antenna. While FrSky Receiver Antenna Replacement is being done, make sure you are grounded properly as static discharge from your body can damage the ESD sensitive RF chips on the receiver.

Do keep in mind to purchase the correct antenna for your receiver as some receivers have different connectors and active element length(why? Read on!).

Some Receivers Come with Shorter (or Longer Antennas)?

The 1/4 wavelength of 2.4GHz is 31.23mm, so why do some receivers have different antenna length? For example, we measured the antennas on a few different Frsky RX’s to be:

  • R-XSR – 23.5mm
  • X4R-SB – 33.25mm
  • XSR – 26mm
  • XM+ – 23mm

This is because FrSky is tuning their antennas in their receivers itself.
As I previously mentioned, the length of the active element is depended on the inductance & capacitance, and if we could change the values of both, theoretically, we could have any length active element we prefer! This might be why some receivers come with longer or shorter antennas than 31mm.

So in case you are trying to strip the antenna, it is always better to keep the original length of the antenna that your receiver came with since not all are optimized for ¼ wavelength.

It is also vital to keep your active element straight when you are mounting it.

 Conclusion

In this How to article, we have talked about antennas, its length and how to FrSky Receiver Antenna Replacement in the worst-case scenario. Hopefully, in most cases, you can just resort to stripping the antenna a bit to expose the active element and save money.