[time-nuts] GPS ANTENNA

Bob kb8tq kb8tq at n1k.org
Sun Apr 1 13:42:47 UTC 2018


Hi

Indeed, it is *very* easy to put to much gain in front of a timing GNSS receiver. These 
beasts are trying to dig out a signal that you can’t even see with a spectrum analyzer.
It’s way to far below the noise floor to detect that way. They optimize things pretty
tightly to get that done (and to hit a price target ….). Put to much gain in front of 
them and they get unhappy. 

Making this even more crazy, the survey industry standard antenna *does* have
a lot of gain. Survey receivers need way more gain in front of them than timing 
receivers. Put a survey antenna directly on a timing device and trouble will likely be the 
outcome. Equally, a survey instrument probably will not be happy with a timing 
receiver. 

Why all this nonsense? As far as I can tell, it goes back to how the very early L1 / L2
survey boxes were designed back in the 1980’s and early 1990’s. They made a 
basic decision to put a lot of gain at the antenna. Motorola came along with their 
GPS modules later on. They made a *very* different decision about how to distribute
the gain. There are very good arguments on both sides for why they did it this way. 
The bottom line is still - you need to match things up …

Bob

> On Apr 1, 2018, at 2:36 AM, cfo <xnews5 at luna.dyndns.dk> wrote:
> 
> On Sat, 31 Mar 2018 10:58:19 -0500, donandarline-Re5JQEeQqe8AvxtiuMwx3w
> wrote:
> 
>> I found a supplier for high quality GPS antennas at a very reasonable
>> price. PCTEL GPSL1-TMG-SPI-40NCB.
> 
> *** SNIP ***
> 
> I had one of those on 25m cable, and it worked fine on a Tbolt , until
> i got an active antenna splitter that also had some gain.
> Then i had to replace it w. a 26dB version of same type, else the
> "Jackson Lite" was loosing sync.
> 
> What i mean here, is that you can get too much gain too.
> 
> Btw: Good price.
> 
> CFO
> Denmark
> 
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