TEST: AOMWAY NEXUS V1, HD FPV kit

[Drone News]

INTRODUCTION

2017 will be probably the year of FPV HD systems, i.e. a full video transmission with at least 720p resolution and low latency. The AOMWAY Nexus V1 is the first product from AOMWAY. We have a bundle including a transmitter, a receiver and two antennas. Only HD sources are accepted via HDMI connexions. This bundle integrates optimized QAM+OFDM modules transmiting the HD signal with the lower latency as possible. Officially any 1080p@30fps or 720p@30fps sources are accepted and the announced latency is 80ms, not really compatible with FPV racing. Let’s discover this HD system. I will update this review with more Advanced testings.

BOX CONTENT

+ 1 x Nexus transmitter
+ 1 x Nexus receiver
+ 1 x USB charging cable
+ 2 x DC power cable
+ 2 x 5.8G linear antennas

No instruction manual…. :(, probably I received a pre-release version directly from AOMWAY factory.

OVERVIEW

The system is no more based on analog modulation, typically AM to transmit the raw video for most 5.8G system. Here, the video is first compressed via efficient technics and only reconstruction coefficients must be transmitted. At reception, when coefficients are well decoded, the video is resynthetized. The coefficients are transmitted thanks to QAM+OFDM technics. QAM stands for Quadratic Amplitute Modulation, an efficient way to transmit twice more data or to divide by two the occupied bandwidth. OFDM represents a second layer where each previous codes are simultaneously transmitted on several carriers orthogonal each other. Like this if a noise, an adjacent transmission, etc. occurs at least for some of these carriers, the signal will be probably sill present/less impacted and will be reconstructed by simple inverse discrete Fourier transform.

Two blue metallic casing with similar size for both the transmitter and the receiver.

HDMI connectors can be found on the bottom side. For the Transmitter, it’s an HDMIin, an HDMIout for the receiver.

I regret the absence of light HDMI to microHDMI cable to connect the transmitter with a GoPro camera.

Transmitter

The transmitter includes a FAN to cool all the system. The list of 10ch is printed front. First evidence, the first channel is announced to be centered on 500Mhz while the last one on 572Mhz, so in the UHF band.

The HDMI input connector on the left. In the central part a 4 DIP switches Vfreq selector and finally a DC port to power the transmitter officially from a either a 3S or 4S. In practice, it’s working also for a 2S battery.

The 10 Vfreq have a bandtwitdh of 8Mhz and in fact have the same bandwitdh as for the DVB-T system. The unique difference is the central frequency shifted by only two MHz from the original DVB-T channels [24-33]. Clearly the Nexus can interfere with DVB-T system. It means potentially, you can also collect the signal on your HD TV on one of these cited channels. It’s obvious that in most of countries is completly illegal to transmit in the UHF band.

Antenna must be plugged via SMA connector. Impedance must match 50ohms. Two leds. One red for power status and a blue status one. Blinking during synchrinuzation and stay solid during transmission.

Surpringly, 5.8G antenna are given in the bundle as depicted here (courtesy Arxangel/RCgroups)

If these antennas are correctly matching the 50ohms impedance, the efficiency of an antenna 10 times smaller (535Mhz vs 5.8Ghz) is far to be optimal. According to https://en.wikipedia.org/wiki/Dipole_antenna, especially for short-dipoles, we have:

where we can see a quadratic factor (L/λ). So since here we have L«λ, the emitted power is clearly limited by the short size of the antenna.

Emitted power is measured around 500mW.

This value is probably not super accurate since the RF sensor was expecting more a 433Mhz source than a 500Mhz (lower supported Vfreq).

When the metallic casing is opened, on the upper side we can find a Power Amplfier unit feed with a coaxial cable.

On the lower side, another shielded large module, probably the main QAM/OFDM modulator.

We can guess also some traces for a USB and a UART ports probably here for the debug.

-WEIGHT

Standalone, the transmitter is super heavy… No miracle with a metal casing. This latter is here to cool and shield more efficiently electronics

The main PDB board indivually should scale around 40g.

The 5.8G antenna attached add an extra 20g…. to the system

and with the DC cable !!!! we have already 143g… It’s a a lot.

and we have to add the HDMI cable to the GoPro camera and the camera itself…. so a full HD FPV system around 250g !!!!! Out of the box the solution can’t be really carried with Phantom class quadcopter. Some weight must be saved absoluptly.

Receiver

For the receiver, same casing but no fan is present.

Now the DIP Vfreq selector is installed on upper side

-WEIGHT

20g less for the receiver

A simple heatsink is glued on the MCU to cool the system.

UNBOXING, ANALYSIS AND FIRST TESTINGS

Before to measure the latency of the system in practice, we have to measure the latency introduced by the HDcamera (here a blackview Hero2) + FPV monitor

Here in average we have 200ms of latency. It means also, for FPV racing a HD camera with a faster HDMI output is a must to have.

In practice, the Vfreq selection must be done with both TX&RX off. You can’t change the Vfreq on the fly. You need to power off all the system. When turned on, the system boot in less than 7-8s…. the blue light is blinking. Then the video appears… during a 4-5s. At this moment, the image is freezing and “no signal” appears. Don’t panic. Wait less than 10s and the video link is back. Now no more break.

In term of video quality, don’t expect to reach the native quality of your HD cam. No free lunch, in order to reduce the bandwitch, the initial HD flux is first compressed with a huge compression factor. You can notice the effect of this compression especially for oblique shapes, high contrast color changes. More the color quantization scale is also reduced, especially for uniform background parts. But in anycase, the rendition quality is far superior to any analog NTSC/PAL FPV system :).

Ok the moment of Truth …..

In average 400ms … so it means the AOMWAY system introduces 200ms of latency so far from the announced/advvertized 80ms value….

Well as you can see with the last test, the FPV link is broken after crossing one large wall …. No more whitesnow like in analog solutions but directly a black screen…I don’t think it’a problem of the emitted power but clearly more a direct limitation of the given antennas. I need to update the same testing with antenna more adapted to the 500Mhz band. I observed also a frame rate drop versus the distance/SNR degradation. Nothing catastrophic, something around 20fps.

CONCLUSIONS

Well the AOMWAY Nexus V1 is effectively a first edition of an HD FPV system and main certainly a V2, V3 will be introduced later. So yes the HD rendition despite the high compression level is far superior to any analog old school NTSC/PAL solutions. That’s great. I like also the general quality build and it’s working immediatly out of the box. But many things can be improved for the V1: i) provide better antennas more adapted to the 500Mhz/UHF band for better range; ii) reduce the weight of transmitter casing (3D printed ?). Probably around 50g can be saved at least; iii) provide a HMDI to microHDMI lightweight cable for FPV applications. More the latency must be improved…. 200ms is not compatible with FPV racing applications. Finally and probably the more important remark…. the system works in the UHF bands where exist in most of contries severe limitations to emit inside this band… In practice, this module is an out of law system.

PROS

+ HD FPV kit

CONS

– Working in the same band than DVB-T/UHF (500Mhz)
– 5.8g antennas not fully adapted
– Heavy transmitter
– 200ms of latency
– Frame rate drop versus distance
– Poor wall’s penatration with default antennas
– No lightweight HDMI-microHDMI cable provided.

This HD FPV kit have been courtesy provided by AOMWAY in order to make a fair and not biased review. I would like to thank them for this attitude.
You can find it actually for 240USD at http://www.banggood.com/Aomway-NEXUS-V1-FULL-HD-1080P-10CH-AV-FPV-Transmtiter-Receiver-TX-RX-Combo-p-1099344.html

Cet article TEST: AOMWAY NEXUS V1, HD FPV kit est apparu en premier sur Drone-Maniac !!!!!!!.

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