[time-nuts] GPS antenna splitter

[Bob Camp]

Hi

With an 8 port splitter, each of the 7 GPS's sees 50 x 7 = 350 ohms. That's pretty close to the "typical" 330 ohm load that gives you around 15 ma of sense current. The antennas pull a wide range of currents, so there is not a "one size fits all" sort of load. 

If your antenna has 36 db of gain, an 8 port should use up about 9 db of that. There's still a lot of gain left to have >=10 db past the loss. If your receiver is a modern one it should have a 1 to 2 db noise figure. If the antenna is at 0.3 db (pretty good antenna) then 10 db is plenty. 

Bob

On Jun 29, 2013, at 8:14 PM, Magnus Danielson <magnus at rubidium.dyndns.org> wrote:

> Hi Bob,
> 
> On 06/30/2013 01:50 AM, Bob Camp wrote:
>> Hi
>> 
>> From what I've seen, a 50 ohm load on the 8th port of an 8 port splitter does a pretty god job of doing the DC correction. No need for an inductor, everything matches up just fine.
>> 
>> Since you have an amp in the antenna, you don't *always* need an amp in front of the splitter. A lot depends on how much cable loss you happen to have (and the gain of the amp in the antenna). With a modest amount of cable (<  50') eight port splitters seem to work pretty well.
> 
> From my experience, what is needed depends on the GPS receiver and it expectance of the antenna current. Some may need that extra load.
> 
> The DC load may not match 50 Ohm.
> 
> For an antenna-splitter to be gain-neutral it needs an amplifier. If you have good conditions, you do not need it. But I have been fighting gain problems and seen how it limits my ability to lock-up.
> 
> Cheers,
> Magnus
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