[time-nuts] Re: GPS Splitter for L1, GNSS, etc?

[Bob kb8tq]

Hi

Filtering is a good thing. Narrow filtering for GPS/L1 is the only way to get 
a GPSDO running on a cell site. There simply is way to much RF running around.

Once you head down the “triple band / all GNSS” road, the filtering needs to
cover a *lot* of spectrum. Most setups simply drop the filtering from the equation. 
That’s true of home labs and fancier installations. 

My preferred approach is to use eBay / Minicircuits splitters with SMA connectors
on them. They are dirt cheap and pretty much indestructible.  A high gain survey
antenna already has enough signal out to drive a rational length of LMR 400 and 
a fairly large splitter. 

More or less:

Survey antenna has 50 db gain (eBay link does not work so I’m guessing here) 
Most modules / devices are happy with 20 to 30 db gain. They may only degrade a bit at 15 db. 
… You have 20 to 30 db to work with
8 port splitter is ~9 db
16 port splitter is ~12 db
100 feet of LMR 400 at 1.5 GHz is 5.9 db according to:

https://www.timesmicrowave.com/calculator?Product=LMR-400&RunLength=100&Frequency=1500 <https://www.timesmicrowave.com/calculator?Product=LMR-400&RunLength=100&Frequency=1500>

Worst case would be 20 db gain, 12 db splitter, 6 db coax. You still have 2 db to spare.  Less coax
or smaller splitter would give you a bit more margin. 

Bob


> On Jun 2, 2021, at 12:20 AM, W7SLS <w7sls.scott at gmail.com> wrote:
> 
> Hello,
> 
> Looking for group wisdom to avoid newbie mistakes with a GPS splitter.
> 
> For context, I’m a home- not National- or University-Lab.
> That said, I have a non-zero budget.
> 
> Today:
> 	Antenna 
> 	1- CORS RTK GNSS Survey Antenna high gain measurement GNSS GPS GLONASS BDS <https://www.ebay.com/itm/253786590956>
> 	2 - patch antenna - works really well with Time Hat, even a few meters way from window
> 	
> 	Splitter
> 	1 - Symmetricom 58536A
> 
> 	Devices
> 	1 - Auction Site GPSDO
> 	2 - Leo Bodnar GPSDO
> 	3 - Time Hat <— wow!  a fan!
> 	4 - (on the way) 2nd Time Hat
> 
> 	Site
> 	- suburban, forest to the S, hill to the N
> 
> Challenge:
> 
> 	Existing  splitter is L1 only (I think), which blocks the many newer GPS satellites.
> 	With my compromised (for GPS) location, that’s not so good.
> 
> I need / want a wider band GPS Splitter
> 
> 	1 - some posts talk about removing the bandpass filters in an existing splitter
> 		OK, but (a) it nukes any value of that splitter, and (b) those filters also eliminate other interference (yes?)
> 
> 	2 - new choices seem to be in the $1000 and way above, outside of my budget
> 
> 	3 - more interested in ‘ready to use’ than ‘have to add on bypasses' to power the antenna (e.g., Cable TV splitter)
> 
> 	3 - auction site has numerous options, but I’m not sure how to 'separate wheat from chaff’
> 
> 		LOL, some of you may be the sellers :)
> 
> 		several items $500+  <— more than I want to spend
> 		several items $30 -   <— I’d rather not get  aTV antenna splitter and a hobby to make it work
> 	
> 		324575653743  GPS Source S14 $175
> 
> 		153359161105  GPS Antenna Splitter GPS/GLONASS L1 GALILEO E1 BEIDOU B1- FedEx Fast Ship SV1AFN $120
> 
> 
> Thoughts?   Thanks for the group bandwidth.
> 
> Scott W7SLS
> 
> PS:  yes the Symmetricom 58536A will be for sale after I replace it.
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