[time-nuts] GPS antenna splitters

[Nick Sayer]

I just went through this exercise. You can use DC blocking on all ports and an injector, but they also have splitters where one port is a DC-pass and the rest are DC block. You use the pass port for a device you’re just always going to have hooked up. In my case, it’s the GPS module on a Raspberry Pi I use for an NTP server.

If it’s a GPS splitter, the DC block ports most likely also present 200 ohm DC loads. This lets auto-switching GPS receivers and modules “feel” the presence of the external antenna. Mine is an amplified splitter, with the amplifier also powered by the pass port. Gain in the distribution splitter is a good idea, but your remote antenna should also be an active one, otherwise by the time the signal gets down the long cable it’ll be down in the mud by the time it’s amplified.

> On Sep 28, 2015, at 3:32 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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