[time-nuts] GPS ANTENNA
Bruce Griffiths
bruce.griffiths at xtra.co.nz
Mon Apr 2 01:21:28 UTC 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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