[Milsurplus] More FCC foolishness

[Peter Gottlieb]

  I haven't dug too far into it but I was told that the data modulation used 
made it difficult to use the doppler DF that you are referring to unless the 
modulation is factored out by decoding.  This is apparently what the Becker DF 
units do.

I was thinking that there could be an interface between the Becker and the GPS 
nav moving map where vectors could be drawn on the map as you fly and quickly 
the area of interest narrowed down to start getting the ground teams moving in 
the right direction very early on.  The more you flew the less uncertainty on 
location until you had it nailed.  Right now it's pretty much change heading so 
the signal is dead ahead and fly to it but you don't know where it is until you 
pass it.

Peter


On 9/16/2010 9:59 PM, J. Forster wrote:
> UHF is very different than HF.
>
> I assume the 406 MHz DF system uses the 4 diode switched antenna system
> like cop cars use for LoJack. I know there were accessories sold for
> standard 121.5 MHz aircraft radios a couple of decades ago. A friend had
> one in his plane in CA.
>
> It'd be trivial to add latching of direction to system like that. But my
> understanding is that those were used on mobile platforms like cars and
> planes. Long range, terrestrial based DF 406 MHz is not workable, IMO.
>
> -John
>
> ===============
>
>
>>    The fun part is the new 406 MHz ELTs which transmit a 500 msec burst of
>> data
>> every 50 seconds.
>>
>> Old style DF techniques just don't work well with that system.
>>
>>
>>
>> On 9/16/2010 4:11 PM, J. Forster wrote:
>>> The further you get away from the DF station the larger the uncertainty.
>>>
>>> arc = radius x angle.
>>>
>>> The search triangle area grows as the square of the distance.
>>>
>>> -John
>>>
>>> ================
>>>
>>>
>>>> de WB2CPN
>>>> You don't DF with only one receiver unless you're within
>>>> yards of the transmitter.  Real DF is done with three DF
>>>> stations.  The plot will produce a triangle.  There are two
>>>> ways to reduce the triangle to a point, and all this is
>>>> not new.   Most DF I've seen, or done, is guiding an
>>>> aircraft to the DF station, crooked as the path may turn
>>>> out to be.
>>>> 73  Clete
>>>>
>>>>
>>>>
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