[FOSS-GPS] Recommended receivers for precise fixed relative measurements

[Danny Miller]

Bullet-shaped, is that the helical?

What I saw as a problem was the helicals are designed to accept signal 
from all directions.  This helps get a basic fix for consumer use, where 
the cellphone may be physically left on its side or kept in any other 
orientation.

However, for RTK, there are increased problems with multipath, a signal 
reflected off something so the pseudorange distance seen is off by that 
extra distance.  If there's a metal building 25ft behind you and the 
satellite is in front, it gets a signal 50ft later than it should be 
which blends in with the correct direct path.

An antenna ideally would be guaranteed to be oriented a particular way 
and have barriers to physically obscure reception of anything but the 
sky-facing direction, like a choke-ring antenna.  Most multipath 
approaches the antenna from the side and a choke ring will attenuate 
signals from the side so much that it is not seen on the output cable.  
But if a choke ring antenna was on a cellphone, if it was held in a 
different orientation 90 deg off, it would primarily receive the 
multipath and attenuate out the direct-path signal.

Danny

On 9/10/2015 3:33 PM, Model A wrote:
> For the best accuracy I have found that a good quality antenna makes all the
> difference.   I am using a couple of L1/L2 GPS antennas that I bought used
> on eBay for under $100 each.   My system uses L1 only.   I have also tried
> some bullet shaped L1 GPS Timing antennas that were used on cell phone
> towers, they worked just as good.   More information will follow within a
> few week’s time.
>
>
>
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