[time-nuts] GPS ANTENNA

Bruce Griffiths bruce.griffiths at xtra.co.nz
Sun Apr 1 21:21:28 EDT 2018


Just use a standard attenuator between a pair of bias T's with their dc ports connected together.

Bruce

> 
>     On 02 April 2018 at 10:29 Azelio Boriani <azelio.boriani at gmail.com> wrote:
> 
>     An unusual attenuator with a DC pass.
> 
>     On Sun, Apr 1, 2018 at 10:21 PM, David C. Partridge
> 
>     <david.partridge at perdrix.co.uk> wrote:
> 
>         > > 
> >         Or use a choke ring survey antenna and an attenuator :)
> > 
> >         Dave
> > 
> >         -----Original Message-----
> >         From: time-nuts [mailto:time-nuts-bounces at febo.com] On Behalf Of Bob kb8tq
> >         Sent: 01 April 2018 14:43
> >         To: Discussion of precise time and frequency measurement
> >         Subject: Re: [time-nuts] GPS ANTENNA
> > 
> >         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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> > >         > > 
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