[time-nuts] To use or not to use transmission line splitters for GPS receivers

Tom Knox actast at hotmail.com
Tue Oct 9 13:06:43 EDT 2012

I believe it is possible for splitters to be invisible to your system. My first choice would be multiple Antennas. But if you have multiple GPS receivers and require outputs to your test bench, splitters are the logical choice. That said the splitter adds complexity to the system and exponentially multiplies your potential for problems.  I have found that equipment placement, grounding, lightning protection can all affect the signal at the receiver and contribute to problems. Although you always want sound theory the complexity of splitter set-up quickly goes beyond what is reasonable to mathematically model. It sound like you are approaching this the way I would by testing different system configurations starting with a simple antenna and coax. You have already seen the difference just antennas can make. Coax model, length, and run will also have a substantial effect.  Now is where MATS law kicks in. (More Art Then Science). When you add the splitter the best performing Ant and Coax may no longer the best combination. But applying best practices, logic,  and a few hours of trial and error and you will begin to understand your system. If over time you set up a number of systems you will start to know from experience what will work. You see this experience based knowledge in many NIST researchers and dare I say a number of Time-Nuts. I am still on the steep part of the learning curve myself. If I can only learn a little from each of my mistakes.

Thomas Knox

> To: time-nuts at febo.com
> From: johncroos at aol.com
> Date: Tue, 9 Oct 2012 12:10:15 -0400
> Subject: Re: [time-nuts] To use or not to use transmission line splitters for GPS receivers
> Hello All -
> I do not believe there is a hard Yes or No answer for this question.
> It depends upon the performance specification of the system elements
> and the system requirements.
> For instance if the leakage of noise and discrete signals from each 
> receiver out
> of the antenna port combined with the port to port isolation of the 
> power divider
> is below the level of harm to the associated receivers then the answer 
> is yes.
> Otherwise NO.
> The issue of antenna power is simply solved by placing a DC block in 
> the line from the splitter to
> all but one of the receivers. It then powers the antenna for all of 
> them. I use this system with
> a 3 way splitter and 3 T bolts. More elaborate and redundant schemes 
> are possible with a bit of engineering.
> I have several of the receivers developed by Novatel for the early WASS 
> project experiments.
>  These boxes used 3 receivers as both L1 and L2 were involved.
> A standard Mini Circuits power splitter was employed to feed the 
> antenna to all 3. Apparently that
> sufficed for what was a pretty demanding requirement.
> Finally - Anyone advocating a hard Yes or No to this question without 
> first considering the performance
> numbers for the system elements has been smoking their view-graphs. 
> With proper design it is totally
> feasible to feed a number of receivers from one antenna.
> -john k6iql
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