[time-nuts] GPS ANTENNA

jimlux jimlux at earthlink.net
Sun Apr 1 20:11:35 EDT 2018


On 4/1/18 3:29 PM, Azelio Boriani wrote:
> An unusual attenuator with a DC pass.
> 

A few feet of RG-174 (or any 0.1" diameter coax) would probably work.




> 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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