[time-nuts] GPS antenna splitters

[Bob Camp]

Hi

Mini-Circuits will happily sell you DC injectors with a variety of connectors on them. For a basement lash up, there are satellite TV splitters at your local big box store that have DC inputs. Some of the lightning protection interfaces from people like PolyPhaser have DC bias inputs. 

Gain wise, a lot depends on the GPS units you have and the real gain of the antenna. The splitter should dump 3 db each time you double the number of outputs. An 8 output splitter will have a bit over 9 db of loss, 4 outputs will loose 6 db. If 8.5 db is the total system loss, you have about 20 db of gain in the system. 

For most GPS devices 20 db of gain is a lot. If you have survey grade units, they will need more than that. If you have really old GPS modules that may be close to the limit
they will take. If your GPS devices are modern (designed in the last 10 years) they likely are happy at 6 db or maybe even less. 

Bottom line, I would not put a 20 db amp in your system ….

Bob  

> On Sep 28, 2015, at 6:32 AM, Martin A Flynn <maflynn at theflynn.org> wrote:
> 
> Hi folks,
> Need a bit of advise:   I have a project underway that requires multiple GPS receivers.   They all provide 3V power to the antenna.    My existing antenna is a generic KS-24019L112A (26dB) that needs 5V.    There's about 75' of 1/2 heliax between the receiver location and antenna.
> 
> Best fix I can come up with is using a re-purposed  Spectracom 8224* splitter  with an external power supply for the antenna, and DC blocking at the receiver ports.
> 
> Two questions
> 
> 1. Is there another vendor I should be looking at?
> 2. Do I need to add gain at the splitter (options are -8.5 dB or +18
>   dB).  Heliax chart says 2.771 dB loss per 100' @ 1.5 GHz, with
>   another dB loss in the connectors and protector.
> 
> Cheers,
> 
> Martin Flynn
> 
> *http://spectracom.com/ProductsServices/TimingSynchronization/GPSAntennasAccessories/8224GPSAntennaSplitter/tabid/147/Default.aspx 
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