BPYL / Video link / Development
Video that stays alive. In forests, behind hills, at very long distances.
A low-cost digital video link on a Semtech LR2021 radio. In a forest test it kept the link well past the point where an analog VTX lost it.
- 100 Hzfrequency hopping
- 150–950 MHzconfigurable band
- −113 dBmminimum receive power for video
The problem
When the picture dies, the mission is over.
Even if the aircraft still flies. Analog FPV video breaks up in forests, behind hills and at range, often before the control link is lost.
We wanted a picture that degrades gradually and recovers on its own, instead of disappearing.
How it works
Six choices that keep the picture alive.
- Sub-GHz radio
- Semtech LR2021 in LoRa mode for long range (tens of kbit/s), or FLRC mode for higher bitrate (about 500 kbit/s) at shorter range. Sub-GHz goes through vegetation far better than 5.8 GHz.
- Frequency hopping
- 100 hops per second across the band, so narrowband interference only hits a fraction of the packets.
- Forward error correction
- Extra repair packets let the receiver rebuild lost ones without asking for a resend.
- Stripe refresh instead of keyframes
- Each frame refreshes one stripe of the image. Damage clears within a fraction of a second, and there are no large keyframes to cause latency spikes.
- Broadcast only
- The aircraft only transmits. There is no return link to break, and any number of receivers can watch the same feed.
- Two receivers
- Two ground receivers on separate directional antennas. Packets from both are merged before decoding.
Field tests
Results from the field.
Side by side with analog FPV
FAQ
Questions we get asked.
Is it a mesh network?
No. It's a direct link: the aircraft transmits, the ground receivers listen.
What bitrate and resolution?
Tens of kbit/s in LoRa mode and about 500 kbit/s in FLRC mode. Low-resolution H.265. Resolution and frame rate depend on the mode and are still in development.
What's the range?
We haven't measured it in open terrain yet. The forest tests above show what it did there.
Does control run over the same link?
Not yet. Control currently uses a separate 2.4 GHz ELRS link. Control over the same link is planned.
Which frequencies and power?
Band and output power are configurable, so the link can be set up for the frequencies and limits that apply to the user. Our tests ran at 868 MHz.
Is the source code public?
Not at the moment.
Can I buy one?
We're not selling it yet, but we'll make a small batch if there's enough interest. Write to us and tell us your use case.
Development
How we built it.
Contact
Testing long-range video?
We're looking for partners and field-test opportunities, for UAVs and ground robots alike.