I am working on a “zero video dropouts” system, even doing stunts at the range limits, or over my head. I am bored of being constantly reminded by the video dropouts that I am not “inside” the plane.
The first step is to understand the different issues that degrade the video link quality, and also to be able to cause them, in order to determinate later if the adopted solution corrects the problem.
So, I have built a small test platform, using a Lawmate 2.4GHz transmitter, with standard omni vertical polarization antenna, and a Lawmate receiver, with the same antenna, but using one 18dB SMA attenuator, to simulate long range.
The following video gives examples of all the issues:
1. WIFI INTERFERENCE: When using channels inside the wifi band, if there are wifi networks in the neighborhood, you get this kind of horizontal lines.
2. MULTIPATH: with good quality signal, we get suddenly a video drop out, due to the reflected propagation path cancelling the direct propagation path. This happens in a specific point of the space, and disappears just moving one of the antennas (typically less than one wavelength).
3. PROPAGATION LOSS: when the distance between Tx and Rx increases, the video quality start to slowly degrade.
4. POLARIZATION LOSS: When using vertical polarization, if the Rx and Tx antennas are at 90º, in theory there are infinite losses. So, if we bank the plane, we start adding polarization losses, and at a perfect 90º we lose the video.
5. ANTENNA RADIATION PATTERN NULL: The omni antennas are not isotropic, and typically they have got nulls in their radiation pattern, aligned with the antenna axis. If we point the Tx antenna to the Rx antenna, the effective gain of the Tx antenna is much lower, and the effect is adding suddenly some extra dB loss to the video link. The most common situation is when flying over the ground station.
6. SIGNAL OBSTRUCTION: If we place between the Tx and Rx antenna some conductive elements (a battery in the video), the signal gets partially obstructed, and the effect is adding some dBs loss to the video link. This happens when the camera, motor, batteries, etc. get in the middle of the transmission path in a specific orientation of the plane.
Now that I can replicate all these issues, is time to start playing with Circular Polarization and Diversity, to see how we can solve all these issues one by one.
I will keep posting.