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[aprssig] Marrying Doppler & APRS, Was: Reading APRS becons w/Dopplers?

Steve Noskowicz noskosteve at yahoo.com
Thu Mar 16 22:09:22 UTC 2006


  Date: Wed, 15 Mar 2006 12:37:42 -0800 (PST)
From: "Curt, WE7U" 
Subject: Re: Reading APRS becons w/Dopplers?

On Wed, 15 Mar 2006, Steve Noskowicz wrote:
> I'm very familiar with the Doppler system as well as other DF
> tools as I was professionally in it some time ago (and have kept
> up on many of the new developments).
> I also have two new ideas I want to try (after all these years of
> thinking and not doing much)....snip...
   
  
Please let us know what you find out, if you're able. I've heard
that doppler scanning systems can lock on with as little as 250ms of
carrier. Is that true?

We want to do RDF'ing of transmitters in the 200MHz range by using
coordinated APRS mobiles. ...snip...  Curt, WE7U. 
  ..............................................................................
   
  Curt,
  Well...  There are many variables.  The Doppler type system is not the "ideal" DFing system.  Every DF tool has advantages and disadvantages.
     With a strong, direct signal (and enough bandwidth in the Doppler-tone filter), 250 ms sounds perhaps possible, but I'd have to see what mine will do.  Mine looks like a pretty good design and it has a variable bandwidth band-pass filter for the Doppler-tone, but I don't know what the limits are.  I have the main unit finished, am in final stages of assembling a dual-mode display (direct and Heads up - perhaps a bit over zealous, but I thought of it and it was easy) and the antenna system is next.
  I suppose I could run a test on the main unit to see if it has enough BW to capture in 250ms.  In the narrow limit, I think mine has less than 1 Hz of BW.
   
  While I know that the technology is here for a fully automatic Doppler and APRS system to do the triangulation and provide a best guess (weighted average) of  the foxes Lat & Lon, (I have all the calculations already coded), the automation part is quite a sophisticated undertaking, so there are several intermediate solutions I'll be toying with.  I'm an RF Engineer and while I do some pretty sophisticated SW, getting this all together is quite a job and needs a real software-head  --  which I'm not.  Not to mention the Maping and getting everything to talk via APRS.
  I want to get close to VK3ZPF's Vector-Fox system of plotting all the fixes on a local map.
  http://www.qsl.net/vk3zpf/index.html
    Doing the best guess for Lat/Lon is trivial after that.  I couldn't get him to release the code or even a copy of his application, over a year ago.  He's got some pretty neat features such as automatic third harmonic tuning and the quieting signal strength extension.
  With multiple APRS mobiles, Dopplers and a command center with a map, you can get pretty good, but the guy with the map can easily be replaced with a little code...Well, maybe a lot..
   
  73, Steve, K9DCI
  P.S. I am aware of the APRS bearing reporting capability.
  P.P.S. I'm doing everything in VBA in Excel...Yup, Excel - Serial I/O and all.
  =====================================================

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