[time-nuts] Re: Composite sky GPS - with an added digression

[glen english LIST]

Thanks for the replies so far. and very Interesting Jim !

application is improve the GPS fix for field portable installed 
TABS/conspicuity in experimental aircraft with metal skins or carbon 
fibre skins. In a nutshell they broadcast a 1 sec intervals on ADSB 1090 
MHz the posiiton, and info) . they are usually suction cup fitted.

There are conspicuity units that suction cup to the inside rear window 
and they are terrible for fix, +/- 300m in H, +/- 200m in V.  even worse 
if a high wing and a wing in the way that is full of fuel .

It's passable on the front of the instrument panel at the forward end 
where it can see a fair bit of the sky through the windshield, but not 
great for vis, and also affects compass swing . The units are very 
popular with recreational experimental, and assist to avoid traffic.

Real TSO GPS require GPS antenna on the top of the skin to get an all 
sky view.  (like my PA28)

Possible solution is 2 or 3Â  antennas looking at different parts of the 
sky but my feeling is most likely just one antenna on either side window 
left and right would eb a substantial improvement. I am yet to 
QUANTIITIVELY see exactly why it is so poor- I need to put one of my 
UBLOX radios there in the device's place and get some data.

sidenote - As an RF guy, I would have thought combining the signal from 
both GPS antenna (downstream of their LNAs)Â  would lead to a fair bit of 
infighting, and be highly sub optimal  . maybe not as bad as I imagine.

-glen

On 1/07/2023 8:35 am, Lux, Jim via time-nuts wrote:
> On 6/29/23 10:36 PM, glen english LIST via time-nuts wrote:
>> talking about GNSS, someone here might know....
>>
>> I have a problem which I can see either one hemisphere or the other, 
>> but not both simultaneously  - from the one antenna.
>>
>> It takes two antennas. Consequently, my 3D fixes are in the toilet.
>>
>> Is there a mode where two receivers  separately correlate all the 
>> sats they can see independently and then talk to each other to use 
>> the sats from the 'other' receiver to get a better all sky 3D fix ? 
>> or get  enough raw data out of them and post process elsewhere ?
>>
>> glen.
>
>
> Not easily - you might be better off just running the two antennas 
> into a power combiner.
>
> But, there's a variety of software that will take raw observables and 
> combine them to make a single fix.  GipsyX at JPL does this, but it is 
> non-trivial to do.
>
> There's also RTGx (Real Time Gipsy) which can probably do it on the 
> fly (RTGx is part of GIPSYx). Or, at least, I know it can combine 
> observables from the signals from multiple antennas at the same time.  
> Granted it's all one receiver, usually, with multiple input channels, 
> but I'm pretty sure that RTGx doesn't care - it would help if both 
> receivers share a common clock.  (isn't that a particularly Time-Nuts 
> kind of statement in general)?
>
>
> https://gipsyx.jpl.nasa.gov/
>
> In theory, if you've got a research application, you can get a free 
> non-commercial license from JPL.
>
>
> You can get a pdf from here:
>
> https://www.sciencedirect.com/science/article/pii/S0273117720302532
>
> Willy Bertiger,