Fly Electric!

2.4GHz Diversity

This page describes Spektrum range and diversity tests with my own 2.4 receivers. Spektrum receivers should be very similar. Data presented here includes average signal strength (RSSI) and the number of perfect signals received in every second.

Details of various flights can be viewed if you click on the graphs. Most flights included two receivers. Rx70 has two aerials orientated at 90 degrees to each other. Rx21 has just one antenna. Both received the same signals on two alternating frequencies within 22ms periods. The Rx70 antenna was swopped after every two frequencies (ie: every 22ms). Some flights may have had other 2.4 traffic.

I have a few pages on 2.4 so look for the links to those pages at the foot of this page.


ANTENNA DIVERSITY


Flight 3
(Click for Flights 1 to 5 and larger graphs)

Flight 1
(Click for larger graph)

The chart on the left is an example of a flight to 1300 feet (click to see 5 flights). The traces at the top of the graph (blue/pink) show successful receives (the 44-46 represent 100%). These demonstrate how well the receiver works at this altitude and how when one antenna is weak the other is often stronger thus showing the benefits of multiple antenna orientated correctly. Note how losses usually increase on the descent. This is because the model was deliberately brought down in a spiral.

The traces at the bottom of the graph on the left (purple/yellow) show signal strength (RSSI). The scale ranges from 0-31 so the flight starts at max 31 and then signal strength reduces as the plane gains altitude. The receivers typically operate at around 50% signal strength in the range tested (1000-1300 feet). Likely to continue working well at greater heights.

The chart(s) on the right compares the signal strength of the two antennae (blue line) and two frequencies (yellow). They are shown separately if you click on the graph. The deviation is shown for every second. Power doubles every 3dB so this helps you understand the significance of the deviations. When the graph is above the '0' line one antenna is receiving a stronger signal, and when below '0' the other is stronger. This demonstrates how the antennae (blue line) detect significantly different signal strengths as the model moves about. Notice how common it is for one aerial to be much stronger than the other (ie away from the 0 line), again demonstrating the benefits of antenna diversity. By comparison, differences due to frequency (yellow line) are small. More on this below.


FREQUENCY DIVERSITY


Rx70
(Click for Flights 1 to 5 and larger graphs)

Rx21
(Click for Flights 1 to 5 and larger graphs)

The above charts show relative performance of each Frequency on both receivers. Although there are cases where one frequency is 'received' better than the other, generally the channel in use has little effect on signal strength or performance.


AEROBATIC CHALLENGES


Rx70
(Click for 3 flights larger graphs)

The above chart demonstrates antenna diversity during aerobatics. In these tests the plane was rolled continuously in the flight. The flights were at low altitude. While the intention was not to assess range, the first flight was within 100-200m and had few losses. The other flights went much further away and revealed more losses. Where there are losses, antenna diversity again shows its benefits with one aerial usually compensating for the other.


SATELLITE/REMOTE RECEIVERS


Master vs Satellite performance
(Click for 2 flights larger graphs)

The charts you can see by clicking on the one above assesses the effects of having two receivers with generous separation between them (eg: like Spektrum's remote receivers). When the model was rolled continuously (flights 9 & 10), the model's orientation keeps changing so reception becomes fragmented and significant differences exist at different times. So the more receivers and aerials you have the better.

When the wing was kept level (flights 12 & 13), the receiver on the wing in clear air (Rx21) received much better than Rx70 masked by motor, lipo etc. So good separation between receivers/satellites aids reception.

2 or 3 signals are lost on both receivers every 4 seconds. The data gathered is saved to memory every 4 seconds. This causes the receiver to get out of sync with the transmitted frequencies. This is likely to account for at least 1 of the losses. They are much more frequent than losses on all 3 aerials so cannot be transmitter nulls. May need more investigation.

The test environment: Rx70's Ant0 aerial was orientated vertically and the Ant1 horizontally down the length of the fuz. Rx21's aerial was horizontal with the wing spar. In other words all three were at 90 degrees to each other (ideal setup). The plane was flown directly away from and back to the pilot in an attempt to maximise any on-board masking losses for Rx70 (from motor/lipo/servos etc). The single Rx21 aerial was mounted to try to minimise masking. It was also parallel to the Tx aerial most of the time but changing or being out of phase due to continuous rolling. An attempt was made on most flights to gain altitude when far from the pilot thus the altitude line reveals when distance increased.


More information on 2.4GHz can be found here:
* Handheld 2.4GHz scanner
* 2.4GHz lockout logger
* Overview of 2.4GHz
* My 2.4 GHz Receivers
* Spektrum technical FAQs

Top of page
Click on the links above for more info.
Click on the links below for other pages.

Home Art of the Possible Absence of Matter Links Updates Email
SITE MAP