[ARC5] VLF Nav

[Bruce Long]

Differential GPS was useful in cancelling the effects of SA   but it is also useful in getting better correction for ionospheric delay and as such is still useful even with SA turned off.

I have been part of some instrument development efforts where we got sub cm resolution out of standard $60 GPS receiver modules by getting the raw psuedo range  information out of more than one receiver and doing an averaged differential GPS measurement.  We only got several such data points a day but as we where measuring Antarctica ice movement that was pretty much good enough.  We did determine at the cm level ice shelf movement was stick and slide and the actual movement happened in a series of short jumps.

For our present set up the accuracy limitation comes from the cheap $10 gps antennas we are using because their phase center location depends upon the signal angle of arrival.  We are thinking of fixing that in software by measuring the exact antenna phase center vs arrival angle, carefully placing and orienting the antenna in the field and recording the GPS satellite positions in the sky during measurement.  Either that of figure out how to make a cheap precision GPS antenna.




On Tuesday, November 26, 2013 7:12 PM, D C _Mac_ Macdonald <k2gkk at hotmail.com> wrote:
 
Before the US turned off the Selective Availability (SA) function of GPS, multiple US Coast Guard stations along the coasts and also in the Great Lakes regions had LF stations that were capable of providing local augmentation and accuracy to the GPS receivers of that era to correct the errors intentionally introduced by SA. 

And I suspect that the USAF still relies more on Inertial Navigation, Astro Trackers, and RADAR for navigation and bombing! 

* * * * * * * * * * * 
* 73 - Mac, K2GKK/5 * 
* (Since 30 Nov 53) * 
* Oklahoma City, OK * 
* USAF, Ret (61-81) * 
* * * * * * * * * * * 



> From: releazer at earthlink.net
> To: arc5 at mailman.qth.net
> Date: Tue, 26 Nov 2013 18:53:53 -0500
> Subject: [ARC5] VLF Nav
> 
> The USN uses VLF Navigation stations - and communications stations as well - because those frequencies penetrate water well and thus the subs do not have to surface to receive the data.
> 
> The NDB Station on Cape Canaveral AFS at around 400 KHZ used to broadcast data to augment GPS as well as the Morse signal - and if you drove by it with your car AM radio on, you knew it, too.  But in any case that approach was not adopted.  In Norway they use a subcarrier on FM radio stations to provide GPS data augmentation.  
> 
> GPS was designed to help the USAF drop bombs - period - not much need for it to work inside a building.
> 
> Wayne    
                          
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