hevans1944
Hop - AC8NS
Clearly, much more investigation is required before jumping into any sort of multiplexed, single-channel, duplex communication scheme. You are absolutely correct in your observations about propagation through vegetation, such as trees, being affected by frequency. I had not considered that a problem if using amateur radio frequencies and allowable amateur radio power levels, but of course it is, especially as you move higher in frequency. You mentioned in another post using lower frequencies (900 MHz) to propagate around or through obstacles, but that isn't always practical either because of size, weight, and power (SWAP) constraints.
I don't think it is either necessary or desirable to separate the command/telemetry functions from the video/still-image functions and use separate frequency spectrum for each, but this is apparently current practice, and it was not by design. Instead, existing control and telemetry technology using one part of the radio spectrum was paired with later video technology that "happened" to use a different part of the radio spectrum. So we are stuck with it for now.
There is a lot of unused bandwidth available "between the lines" of even HD video, and breaking data up into digital packets with cyclic redundancy check characters, and error detection and correction using a duplex communications link, is standard practice for Internet Protocol packets... otherwise you would never be able to transmit files without corruption or loss of data. Of course a "noisy" path with lots of packets that need to be re-transmitted is going to degrade latency and introduce an undesirable delay, but with sufficient power and bandwidth even that can be mitigated to allow real-time radio control. The axe and mop approach, so-to-speak.
I have done some more reading about UAV operations. It appears that FPV control is the wave of the future that some operators or pilots may now be surfing (illegally) as we speak. There are procedures in place to request and obtain FAA exemptions from the line-of-sight visibility, 400 foot ceiling above ground level, and 100 mph speed limitations for those pursuing a non-hobby FAA drone licensing path. Unfortunately, I have no idea how often, or under what circumstances, such exemptions are granted, but it seems like a lot of hoops to leap through just to fly an airplane with FPV visualization. I suspect there are a LOT of UAV pilots that are ignoring the FAA line-of-sight rules. If so, they would certainly need a reliable radio link to do this. If this high-quality link were to be enabled by an FCC licensed amateur radio operator, that operator would have to also abide by the FAA rules and regulations and obtain an exemption to the line-of-sight rule before flying off into the wild blue yonder to escape the surly bonds of Earth, and maybe touch the face of God. (Apologies to John Gillespie Magee Jr.)
I don't think it is either necessary or desirable to separate the command/telemetry functions from the video/still-image functions and use separate frequency spectrum for each, but this is apparently current practice, and it was not by design. Instead, existing control and telemetry technology using one part of the radio spectrum was paired with later video technology that "happened" to use a different part of the radio spectrum. So we are stuck with it for now.
There is a lot of unused bandwidth available "between the lines" of even HD video, and breaking data up into digital packets with cyclic redundancy check characters, and error detection and correction using a duplex communications link, is standard practice for Internet Protocol packets... otherwise you would never be able to transmit files without corruption or loss of data. Of course a "noisy" path with lots of packets that need to be re-transmitted is going to degrade latency and introduce an undesirable delay, but with sufficient power and bandwidth even that can be mitigated to allow real-time radio control. The axe and mop approach, so-to-speak.
I have done some more reading about UAV operations. It appears that FPV control is the wave of the future that some operators or pilots may now be surfing (illegally) as we speak. There are procedures in place to request and obtain FAA exemptions from the line-of-sight visibility, 400 foot ceiling above ground level, and 100 mph speed limitations for those pursuing a non-hobby FAA drone licensing path. Unfortunately, I have no idea how often, or under what circumstances, such exemptions are granted, but it seems like a lot of hoops to leap through just to fly an airplane with FPV visualization. I suspect there are a LOT of UAV pilots that are ignoring the FAA line-of-sight rules. If so, they would certainly need a reliable radio link to do this. If this high-quality link were to be enabled by an FCC licensed amateur radio operator, that operator would have to also abide by the FAA rules and regulations and obtain an exemption to the line-of-sight rule before flying off into the wild blue yonder to escape the surly bonds of Earth, and maybe touch the face of God. (Apologies to John Gillespie Magee Jr.)
Roger, that. Can't legally do FPV flight control over long distances either. Guess I should apply for a drone pilot license and then ask the FAA for a line-of-sight exemption. Ever heard of anyone doing that? I don't want to lose my amateur radio license because I violated an FAA rule or regulation.
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