DJI SDR Transmission

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YouTube Overview

Mads Overview Of DJI SDR Transmission

I have seen quite a a lot of questions around DJIs new SDR Transmission release from their transmission system range and a such I thought I would put this together as a reference on the new system and what it is compared to the others.

DJI SDR Transmission


While the name SDR implies something “new” the realty is that largely not actually the case when it comes to the core tech and that’s a good thing.


DJI SDR Transmission uses the same main RF System as DJI Transmission and all their other O3 based product. While these products may have the same video processing capabilities and IO technically they are all O3 or O3 Pro and only differ really in how much onboard processing and the IO they have.
The really great thing an about Ocusync or O3 is it’s always been an SDR and DJI can use a full two way link in main modes such as control Mode so it’s able to retransmit lost data data packets, this makes the link very robust especially compared to other WiFi based offerings.
DJI’s Ocusync systems are OFDM based using an RF system similar to LTE all based on their own custom hardware.


There are other systems on the market that are moment some use WiFi that offers a far less reliable link. There are products from the likes of Teradek that use Amimon RF systems that they now own that is biased on Joint Source Cannel Coding, a rather complex subject I won’t go into here and while some of these do offer higher resolution and according to their specs lower latency what they won’t do is compete with DJI on link stability and range.
No Perfect option.


In RF there is always a pay off between latency and link resilience, the more error correction you bake into the RF pipeline the more solid the wireless link will be and able to cope with interference and/or complex environments however this adds latency. It’s always a balance. You can build a link with incredibly low latency however put a sheet of paper between the transmitter and receiver and it will drop out.
There is no one perfect solution and DJI have built their systems around offering a balance of both long range, stable links and acceptable latency.
BUT on latency it’s VERY much worth noting that when comparing latency to other systems it’s not apples for apples.


For instance Teradek state less than 1ms latency however they are basically stating the wireless only latency and not including any form of video processing or IO latency on their system. Input processing, scaling and the inherent internal video pipeline will all add up and as such you will find HDMI In to HDMI out will be far higher than the 1ms published.


DJI on their spec for SDR publish 80ms as the latency however DJI have always been very fair and generally accurate with the numbers given, DJI’s spec will be end to end from hdmi in to hdmi out.
If you were to compare Teradek in the same way you will find its latency is much higher than that 1ms number but could be still less than DJI but at a cost of link resilience.
DJI Transmission vs SDR Transmission

DJI Transmission vs DJI SDR Transmission


With regards to DJI Transmission vs DJI SDR Transmission they are actually very similar products. Both are based on the same O3 Pro system. They differ though in IO and video processing.
For instance DJI Transmission has Dual band O3 Pro capable of transmitting upto a 40Mhz carrier bandwith with a maximin data rate of 40Mbps using H264 codec.
DJI SDR Transmission on the other hand is less capable, is a cut back version limited to a 20Mhz Carrier bandwith and 20mbps based on H264.


This means its has less bandwidth and data’s rate available to transit the video image over. This will result is some loss of image quality or link resilience over the original model.
RF Power wise there are differences as well, the DJI Transmission systems is capable transmitting at up-to 33dbm max in fcc regions whereas SDR Transmission is limited to 30dbm. Both of these are eirp but it’s the difference between 1W and 1.6w eirp power.
So again the SDR Transmission will not perform quite as well as the original Transmission system.
WiFi and USB Streaming.


Something new for DJI SDR Transmission is the new WiFi functionality, this allows you to directly stream to smartphones and tablets via the DJI App. This streaming is designed to be a localised stream allowing you to use your devices rather than hdmi or SDI displays. It’s not actually part of the main RF transmission system as such and the main TX to RX transmission is all via the O3 system.
This is a new feature to SDR Transmission and not available on DJI Transmission.
Video Input and Image Quality.


Both systems support same resolutions and frame rates on HDMI and SDI inputs/Outputs though the reduced bandwidth on SDR Transmission will mean the live feed does not look quite as good or hold up as well.


Looking at the devices them selves this is also IO differences between them.
The DJI Transmission TX has a single HDMI in as well as SDI in and out offering passthrough whereas SDR Transmission has just HDMI and SDI in with no passthrough.

The DJI Transmission Receiver has a single HDMI and Dual SDI output mirrored whereas SDR Transmission just has single HDMI and SDI outputs.

Power & Battery


Power wise there are changes, DJI transmission modules can be used on P-tap power and multiple battery options including DJI battery and NP-F via adapters. DJI SDR Transmission on the other had losses P-Tap but gains USB C power and will take NP-F as standard.


Software & Modes.


Both systems support Control/standard mode and broadcast modes and can be used with multiple DJI Transmission or SDR transmitters and receivers with in their ecosystem however there is a big BUT here below.


The BIG gotcha here, they are not cross compatible, you cannot use a DJI Transmission TX with a DJI SDR Receiver or any other form of combination. You cannot even use the DJI Transmission display with DJI SDR Transmitter. There are two entirely standalone systems with no cross compatibility
Compatibility With Other Systems.

There is big difference in other DJI products compatibility with these products too.
DJI Transmission is specifically designed to work with the Ronin 4D, MasterWheels, DJI Focus pro and others. DJI SDR Transmission is not compatible with the pro line of accessories other than basic video input but is compatible with the Ronin RS series and Camera control for specific camera models with these gimbals.

Others


There is a bunch of other changes on time code and talking ect Iv not covered you should look into before purchasing.

Final Summary

Basically DJI SDR Transmission is a cut back version of DJI Transmission that is a standalone product that only works in its own eco system. It’s based on the same core tech as DJI’s Pro Transmission products and it’s giving you 80% of the features for 25% of the cost. Quite incredible that.

It does gain some features like the WiFi functionality that is great to see compared to the Pro system however it’s not designed to be a replacement for DJI Transmission.
In the end DJI SDR Transmission would really fit into the Semi Pro class but again still offers massive capabilities at a much reduced price point

Hopefully this will help some folks.