polynomial fitting for COMPLEX data

On Tue, 15 Nov 2016 15:05:36 +0300, Evgeny Filatov wrote:

> On 15/11/2016 03:01, Tim Wescott wrote:
>>
>> (Radio direction finding, BTW, is the reason for those round antennas
>> on top of old airplanes: they were designed so that you'd get a null in
>> reception when the hole of the donut was pointed along a line to the
>> transmitter.  Plot a few of those on a map, and you'd know where you
>> were.)
>>
>>
> Satellite navigation has by now evolved to centimeter-precision Real
> Time Kinematic. I'm a complete ignoramus, but made me wondering whether
> anyone has bothered to upgrade Radio direction finding with modern
> techniques, such as spread spectrum for multipath mitigation or perhaps
> more accurate beamforming with MIMO...
> 
> Gene

I don't pay much attention to that segment any more.  The last I heard 
there was still some debate about whether to scrap Loran or update it.  
I'm pretty sure that RDF is inherently imprecise because it's noncoherent.

-- 
Tim Wescott
Control systems, embedded software and circuit design
I'm looking for work!  See my website if you're interested
http://www.wescottdesign.com

On Tue, 15 Nov 2016 10:47:57 -0600, Tim Wescott <tim@seemywebsite.com>
wrote:

>On Tue, 15 Nov 2016 15:05:36 +0300, Evgeny Filatov wrote:
>
>> On 15/11/2016 03:01, Tim Wescott wrote:
>>>
>>> (Radio direction finding, BTW, is the reason for those round antennas
>>> on top of old airplanes: they were designed so that you'd get a null in
>>> reception when the hole of the donut was pointed along a line to the
>>> transmitter.  Plot a few of those on a map, and you'd know where you
>>> were.)
>>>
>>>
>> Satellite navigation has by now evolved to centimeter-precision Real
>> Time Kinematic. I'm a complete ignoramus, but made me wondering whether
>> anyone has bothered to upgrade Radio direction finding with modern
>> techniques, such as spread spectrum for multipath mitigation or perhaps
>> more accurate beamforming with MIMO...
>> 
>> Gene
>
>I don't pay much attention to that segment any more.  The last I heard 
>there was still some debate about whether to scrap Loran or update it.  
>I'm pretty sure that RDF is inherently imprecise because it's noncoherent.

Even the VOR network will be partially dismantled, leaving just enough
as backup in case something happens to GPS/GLONASS.   Very few
airplanes, even general aviation airplanes, even have ADF or NDB
equipment any more.

Aviation is weird.   Some technologies get adapted quickly while other
critical parts of the system remain in the stone age.

On Monday, November 14, 2016 at 4:01:19 PM UTC-8, Tim Wescott wrote:

(snip on differential GPS)

See: http://www.gps.gov/systems/gps/modernization/sa/

> Actually, I think those frequencies are correct and my memory was 
> faulty.  I just fired up the receiver to check (my thesis advisor gave it 
> back to me about 10 years ago), but some of the LED segments are out -- 
> but as far as I can tell that's the frequency range it supports.  

I remember some of this discussion years ago.  One side of the
government was building GPS with selective availability (such that
only some users got the full resolution), and the other side 
building differential GPS (so that they could get full resolution
even with SA on).

> The USCG transmitters were originally piggy-backed on their radio 
> direction finding beacons (I don't know if they even support that any 
> more); originally there was some thought that it would be nice to also be 
> capable of using aviation RDF beacons as well; those are at higher 
> frequencies, and are probably why I was remembering 400-ish instead of 
> 300-ish.

According to the link above, in 2007 the government decided never
to apply SA again, sounds like about when you got your box back.

The newer satellites don't have the ability to turn it on, even
if someone wanted to change the permanent decision.
(Now, who would go around changing permanent decisions?)

On Tue, 18 Jul 2017 17:07:15 -0700, herrmannsfeldt wrote:

> On Monday, November 14, 2016 at 4:01:19 PM UTC-8, Tim Wescott wrote:
> 
> (snip on differential GPS)
> 
> See: http://www.gps.gov/systems/gps/modernization/sa/
> 
>> Actually, I think those frequencies are correct and my memory was
>> faulty.  I just fired up the receiver to check (my thesis advisor gave
>> it back to me about 10 years ago), but some of the LED segments are out
>> -- but as far as I can tell that's the frequency range it supports.
> 
> I remember some of this discussion years ago.  One side of the
> government was building GPS with selective availability (such that only
> some users got the full resolution), and the other side building
> differential GPS (so that they could get full resolution even with SA
> on).
> 
>> The USCG transmitters were originally piggy-backed on their radio
>> direction finding beacons (I don't know if they even support that any
>> more); originally there was some thought that it would be nice to also
>> be capable of using aviation RDF beacons as well; those are at higher
>> frequencies, and are probably why I was remembering 400-ish instead of
>> 300-ish.
> 
> According to the link above, in 2007 the government decided never to
> apply SA again, sounds like about when you got your box back.
> 
> The newer satellites don't have the ability to turn it on, even if
> someone wanted to change the permanent decision.
> (Now, who would go around changing permanent decisions?)

I got the box done around '99, so it had a few years of potential 
usefullness.

I asked my thesis advisor about the whole defeating SA thing, and he said 
the DoD was fine with it because it only worked in a fairly well-defined 
area around the reference point -- the further away you got from that 
point, the less that corrections to the satellite signals were useful.

-- 

Tim Wescott
Wescott Design Services
http://www.wescottdesign.com