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-   -   2.4Ghz RC range and latency measurements. (https://www.rcuniverse.com/forum/rc-car-radio-equipment-201/4803333-2-4ghz-rc-range-latency-measurements.html)

SAMCPAKISTAN 08-14-2012 09:46 AM

RE: 2.4Ghz RC range and latency measurements.
 


ORIGINAL: rsilvers

This came out because of talk and promotion about output power and latency.

Here is what I found:

For range I put both units 20 feet in the air on a platform, and then walked away until I found a range for each where they would reliably work. I did not try to find a range where I could get the servo to move barely, but rather, where they worked reliably (likely in contrast to how a manufacturer rates them). Both antennas were vertical.

The Spektrum DSM was 636 feet.
The Nomadio was 531 feet.

I believe both claim about 3000 feet.

How can I explain the Nomadio having less range when Nomadio says it has between 7.5 and 10 times the output power?
(Nomadio claims either 75 or 100mw output while the Spektrum is 10mw).

There is a DSSS concept called processing gain: The processing gain is a measure of immunity to noise. The more the band spread of the signals, the higher the gain. Spektrum set up their data rate to allow for an 18dB processing gain over the FHSS that Nomadio uses. That means a 10mw implementation may have more range than a Nomadio 75mw FHSS system (it could be equal to an 80mw FHSS system). I had posted this weeks ago, and my hypothesis appears to be correct. Nomadio is probably hoping that people will assume that their greater power output equals more range when it fact it mostly likely only results in more power consumption.

No doubt if others test the range they will get different but similar numbers. In any case, do not assume anything about range without doing the test side by side.


I also measured the data rate and latency of a Spektrum DX3 and Pro receiver system using a Tektronix TDS-220 100 Mhz bandwidth digital oscilloscope.

The data rate being sent to the servo from the Spektrum 'receiver' is 20ms per frame, or 50 updates per second.
The data rate being sent to the servo from the Nomadio 'receiver' is 10ms per frame, or 100 updates per second.
(For comparison, JR PCM radios are approx 46 updates per second for Z mode, and 47 for S mode per channel. Standard FM PPM systems are about the same.)
The advanage here goes to the Nomadio 100 frames per second is excellent and how it should be done (I feel that anything in the 80 to 120 frames per second range is ideal).


Finally I did latency testing.

http://www.photomosaic.com/albums/Ho..._800.sized.jpg

Minimum latency of the Spektrum DX3 when using the channel-3 switch is 7-8ms.

Here you can see that the latency is over 6ms:

http://www.photomosaic.com/albums/Ho..._800.sized.jpg

Here you can see that the latency is less than or equal to 8ms:

http://www.photomosaic.com/albums/Ho..._800.sized.jpg

Note that this is minimum latency. If the frame is missed, you have to wait until another 20ms passes to pick up the next one. So it is 26ms max, and about 16.5 average.


The Nomadio salesman said that the Spektrum system had about 15ms of latency inherent in the transmission, and another 30ms of latency provided by the transmitter encoding the controls. That would be 45ms. I was not able to duplicate those numbers.

Spektrum's claim of '3ms' is quoted as 'the figure added to your radio's processing time' so I have not confirmed or denied that specific claim because I included the radio processing time in my calculations. If the radio processing time was 4 or 5 ms, then their figures seem accurate.


For the Nomadio I found that latency was always between 13.0 and 16.0ms so that is about 14.5ms average or 2ms (1/500 of a second) less than the Spektrum's average.

http://www.photomosaic.com/albums/Ho...4403.sized.jpg

http://www.photomosaic.com/albums/Ho...4408.sized.jpg

http://www.photomosaic.com/albums/Ho...4409.sized.jpg

Here the Nomadio has a small but measureable advantage for 'average' latency. Also worth noting is that the Spektrum has about 1/2 of the minimum latency of the Nomadio (though also has a greater maximum latency). I don't see an obvious winner on this stat.
Dear, thanks for guidance, but having an issue, if Tx & Rx is on before flight, we take the Tx away from model, after 60 to 80 feet, the servos start working without any movement from radio sticks? is it normal ?


Foxy 08-15-2012 02:10 AM

RE: 2.4Ghz RC range and latency measurements.
 
No it is not, your equipment is faulty. I bet its a spektrum system...am I right?

SAMCPAKISTAN 08-15-2012 10:55 AM

RE: 2.4Ghz RC range and latency measurements.
 
Dear, thanks for reply, we are using FUTABA 7C, today we open the radio & find out that antena wire is un linked, may be due to some Jerk?

Foxy 08-16-2012 01:21 AM

RE: 2.4Ghz RC range and latency measurements.
 
lol, maybe :)

But that's very unusual for Futaba stuff. I have a Futaba 3pk surface transmitter that is now going strong for over 8 years!


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