[time-nuts] GPS ANTENNA

Björn bg at lysator.liu.se
Mon Apr 2 03:32:35 EDT 2018


Or find an Arra “level set” variable attenuator. 3844 and 3854 models can often be found cheaply, have dc-pass and attenuate at both L1 and L2.

/Björn 

Sent from my iPhone

> On 2 Apr 2018, at 03:43, David C. Partridge <david.partridge at perdrix.co.uk> wrote:
> 
> just use a bias tee to feed in the antenna volts :)
> 
> -----Original Message-----
> From: time-nuts [mailto:time-nuts-bounces at febo.com] On Behalf Of Azelio Boriani
> Sent: 01 April 2018 23:29
> To: Discussion of precise time and frequency measurement
> Subject: Re: [time-nuts] GPS ANTENNA
> 
> 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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