I'm an amateur radio operator (K7AAY) specializing in emergency services work, seeking a way to loft a repeater for fire fighting support and other emergency services work. We get wildfires and the state rado net has big gaps in canyons and the boonies.Any design would compete with current state of the art, i.e., a weather balloon, a tank of helium and the tether with a wire carrying 500ma at DC voltage adequate to deliver 8.4VDC to the transceiver (an HT or Handheld Transceiver and a controller board) on the weather balloon.How much mass can I squeeze into a UAV?What's the optimum design?1) Solar cells on fabric to also run an electric motor for sterage on a lighter-than-air craft2) a larger LTA burning hydrogen from the envelope to run a motor with a small generator set as well as an engine for steerage, or3) a multi-engine heavier-than-air craft with larger than ususal fuel capacity?
Just another note, you were saying something about antennas in the wings, don't forget to consider the possibility of cross polarization and resulting attenuation. You may need to have your stick pointed up. And...something else that we have done is simply put the repeater in the basket of a 100' aerial or platform truck. 100' up sure beats anything on the ground and is in line with KISS.
-dave
I believe I may be the fire fighter that was mentioned earlier in this thread. I work for Miami Dade Fire Rescue and I have proposed the idea to our department. Although there were high levels of optimism, ultimately it boiled down to the CoA. As far as I know, the only programs that have obtained the elusive CoA is Houston PD, LA County Sheriff, and Miami Dade PD. I am in contact with Miami Dade PD and thier Honeywell MAV program. Currently, with the fire department, we are looking at a small scale low altitude tethered aerostat to test the concept. Perhaps once found to be feasible, the FAA restrictions will loosen slightly and the CoA will be easily obtained. I agree that not a lot of power is needed. Since it would be nearly LOS, 5 watt handhelds wired like a repeater should do the trick. No need for heavy multi-hundred watt transmitters. The key (I believe) is in selecting the proper antenna(s). Also keep in mind the amateur radio police who may say using your 'amateur' frequencies for fire is not allowed and/or using fire frequencies by an 'amateur' is not allowed. I seem to get many many comments on the legalities of proper license use when posting questions to various amateur radio sites.
-dave (KI4HVT)
The University of Colorado at Boulder is already doing this, and have been doing optimized radio node research for nearly a decade now. I suggest checking recuv.colorado.edu or augnet.colorado.edu to review the work done. We are doing things with heterogeneous fleets, large aircraft, mother/daughter combos, etc. This is some fascinating work and has involved a lot of individuals in controls, aircraft design, and communications. Again, check out what is out there, its actually quite a problem but being worked on now.
Genesis Factor: We're on the scene ANYWAY. This is support to firefighters on the ground in the west, and command get decidedly itchy if they don't have close-in support. We use HF with NVIS (Near Vertical Incidence System) to relay back to a command center anywhere in the state on 40, 80 or 160 meter bandwidth depending on time of day/night as to what the MUF (Minimum/Maximum Usable Frequency) is.
400' AGL gets us s = sqrt(2rh+h^2) optical LOS, with no benefit from atmospheric diffusion, where
s = line of sight distance
r = radius of sphere (Earth = ~20,903,520)
h = height viewed from
s = sqrt(2*20,903,520*400+400*400) = sqrt (16,722,976,000) = 129,317' = 25 miles radius range
So, it's easy to position the UAV relay airchine outside of the strike zone and the path in and out for water bombers and observation craft, or to let it do double-duty if we add a video camera for observation.
Now, that's if we were using UHF handhelds for the grunts with shovels. For the low end of the VHF band, instead factor for ground effect and atmospheric diffusion:
Ah, perhaps, but Noth666, you don't understand the mission... hams are on the scene anyway, so no need for anything long distance. Therefore, we can work within the restrictive rules currently imposed by the FAA.
Also, it would not even need a control crew anywhere near the area, there could be one nationwide control center somewhere, and all that has to be present on local level is ground support in terms of refueling and some small service.
I think a fixed wing uav would be superior mainly because it can fly to the zone of interest from a long distance away on its own power - it does not need to be dropped or raised on the spot by something else.
Also a UAV can be very quickly repositioned and does not need any ground support in the immediate area of operation, it can just fly off to the closest support base for refueling and carry on the mission for a long time if you have rotating crews like they use on the predator.
Comments
Page 130 of the old fashioned paper version, not online.
-dave
-dave (KI4HVT)
400' AGL gets us s = sqrt(2rh+h^2) optical LOS, with no benefit from atmospheric diffusion, where
s = line of sight distance
r = radius of sphere (Earth = ~20,903,520)
h = height viewed from
s = sqrt(2*20,903,520*400+400*400) = sqrt (16,722,976,000) = 129,317' = 25 miles radius range
So, it's easy to position the UAV relay airchine outside of the strike zone and the path in and out for water bombers and observation craft, or to let it do double-duty if we add a video camera for observation.
Now, that's if we were using UHF handhelds for the grunts with shovels. For the low end of the VHF band, instead factor for ground effect and atmospheric diffusion:
miles = sqrt (2*400') = 28.4 miles radius range
Also a UAV can be very quickly repositioned and does not need any ground support in the immediate area of operation, it can just fly off to the closest support base for refueling and carry on the mission for a long time if you have rotating crews like they use on the predator.
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