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Re: [digsstv] Any ideas

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  • jdow
    From: David Rogers ... If the images need to be updated every minute or so then HF Amateur Radio is probably not a suitable medium as it
    Message 1 of 2 , Jul 29, 2005
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      From: "David Rogers" <kd4kob@...>

      > .... on how to capture a radar image, I guess you would call
      > it "slow scan" (that has no outputs) by placing a transmitting
      > camera in front of the screen and sending live feed to a central
      > point within a 25 mile range to be viewed. This would be a
      > mobile/moving radar (like in a car/van/SUV). I would need the
      > transmitters, receivers, camera's, repeaters, routers or whatever
      > would be required. Once captured, I would want to not only view it
      > but convert it to digital to save/record/store/route .....maybe
      > someone has some ideas?
      > Here's what I know. I'm working at trying to balance two
      > variables...bandwidth of the network versus quality of video
      > passed. For the sake of argument, let's say I have 8 mobile systems
      > with from one to three CRTs each. Ideally, I need to pass: 1. the
      > highest quality video (it is probably possible to capture this prior
      > to the CRT in some way) I can, 2. a data channel with system info
      > (time stamp, pointing angles, target range, firing command, some
      > binary switch positions) and 3. a voice channel. I think I have a
      > handle on the requirements for the last two so I am balancing the
      > quality of the video channels with the bandwidth of the transmission
      > media to create a flexible robust mobile network. I know it can be
      > done. I'm just ignorant of how to do it.
      > I know there are some bandwidth saving algorithms around...often
      > times a fairly large part of a video image does not change from
      > frame to frame. But maybe this doesn't matter. Maybe there is (or
      > soon will be) enough bandwidth in a "cell phone-like" system that I
      > don't need to worry about this.
      > Anyway, I'll link my 8 mobile systems to a remote node, then put
      > data from the systems on the internet in a secure fashion and send
      > it back to central location for processing. The processing consists
      > of taking the time stamped system data (radar pointing angles and
      > range...a point in space) and comparing it to time stamped lat/long
      > and altitude from "aircraft of interest" data received through a
      > separate data channel. The video data gets displayed so that local
      > experts can analyze what's taking place in the engagement and at the
      > same time it is also stored for future playback. The voice channel
      > allows monitoring of radar operator actions and some coordination
      > among all the mobile systems, although they have an existing channel
      > for this. The voice channel will also provide a broadcast system
      > from the remote location for test/training organization.
      > This is the stressing case. A slightly different one is when the
      > systems are not mobile and situated on fixed concrete pads within a
      > few hundred meters of each other. For that case, I just run fiber
      > and I can get all the bandwidth I want.
      > Thanks for the help,I look forward to your reply's
      > David Rogers, KD4KOB

      If the images need to be updated every minute or so then HF Amateur
      Radio is probably not a suitable medium as it is presently constituted.
      Both amateur radio digital and analog SSTV modes are too slow even for
      such low update needs. Therefore you need to get clever, seriously clever.

      Amateurs are allowed to use high power on at least one of the 802.11b
      frequencies. This is your backbone as a network carefully isolated from
      the Internet. (You may also want to use various forms of amateur legal
      security on the network to avoid break-ins that might be damaging. Such
      techniques are selecting which MAC addresses are allowed to connect to
      your amateur radio powered and antennaed access point. Encryption is
      right out without special authorization from the FCC. Such might be
      forthcoming for certain forms of projects, such as tornado or hurricane

      The access point could be tweaked to amateur radio power levels. The
      mobile units may be problematic unless you find some PCMCIA Wireless
      cards that permit external antennas. Then you can play some games with
      higher gain antenna arrays. A collinear array can be omnidirectional
      by getting its gain by restricting the vertical pattern. You'd want
      such antennas on both ends. Mobile power may be your limiting factor.
      (You may have to find someone clever with Linux and use that on the
      mobiles. The source code for the drivers may be available at a level
      that will allow you to squeeze just that little bit more power, illegal
      for non-hams, out of the mobile cards.

      Then you can run any of a number of video streaming tools out there.
      The Windows Movie Maker is (or at least was) available for the hub
      station for free for XP machines as a streaming video source. Other
      such tools exist for Linux with the advantage that the OS and software
      part is free. On the other hand it may require more talent to get it
      setup and operational.

      This is only one example of thinking of this problem outside the box.
      In actuality you will need to define the project better before any
      definitive answers are possible.

      1) What resolution do you need? (What is the minimum you can survive?)
      2) How often do you need to update?
      3) Can you get funding from some source to generate any custom software
      that might be needed? (And is there a sufficiently talented ham for
      designing such a tool?)
      4) Push comes to shove you might look at broadcasting the radar display
      via Ham TV in the 430 MHz video band. If you pick a suitable frequency
      simple video converter boxes that tune cable channels can give you a
      nice display, two way communications are not required so the demands
      on mobiles are reduced from the Wi-Fi solution above, power is in no
      way restricted over what is legal for the frequency for your area, and
      you get very high update rates. Resolution is somewhat limited. The
      Wi-Fi solution might be able to use much higher video bandwidths.

      However, if once every five to ten minutes image update rates are OK
      then SSTV over ham FM repeater boxes might be a really mode. Both
      analog and digital should work nicely as long as voice copy is adequate.

      {^_^} Joanne, W6MKU, on a fun "idea riff".
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