[time-nuts] GPS splitter
kb8tq at n1k.org
Sun Jun 18 17:40:12 EDT 2017
One subtle advantage of the simple satellite splitters - F connector based DC blocks are dirt cheap ….
> On Jun 18, 2017, at 4:06 PM, ziggy9+time-nuts at pumpkinbrook.com wrote:
> +1 for satellite splitters as a low cost option. But as others have mentioned, you do need to use a little care. Some are 'DC isolated', but that can mean diode OR’ing for each port (all ports DC pass) and not a DC block. And they often don’t have the frequency response (many satellite splitters only say 1GHz or 1500MHz).
> The Radio Shack 4 way splitter I started with was just such a device. One input, four outputs, DC pass on all ports with diode isolation. It worked OK, as long as all GPS were 5V antenna types. Adding a 12V receiver was suddenly a problem as my antenna is 5V, along with the other receivers.
> The best satellite splitter choice (for me) was a DirecTV SWIM 4 way unit. It’s rated 2-2150, has DC pass on one port. So I could connect my somewhat deaf 12V receiver with an inline amp on one of the DC block ports, and a 5V unit on the DC pass port. Each receiver was happy. A picture of one is at <https://images-na.ssl-images-amazon.com/images/I/41EWn-NoJlL.jpg <https://images-na.ssl-images-amazon.com/images/I/41EWn-NoJlL.jpg>> Easily found and cheap, 2, 4, or 8 port models exist.
> BTW, putting each splitter on the network analyzer proved that the DirecTV unit had lower loss and better port to port isolation than the Radio Shack unit (no surprise really). I ran this way for quite a while until I uh… ran out of ports. I now have a GPS Networking 8 way with ‘proper’ DC block and load on each port which works well too.
> Just as an aside, does anyone have any thoughts on the noise contribution of the diodes in the Radio Shack splitter (or similar)? It’s device dependent of course, but I wonder if it’s enough to be a ‘significant’ contributor.
>> On Jun 17, 2017, at 12:07 PM, Chris Albertson <albertson.chris at gmail.com> wrote:
>> On Fri, Jun 16, 2017 at 8:54 PM, Clay Autery <cautery at montac.com> wrote:
>>> This brings up some interesting questions:
>>> I am assuming since this is a receive only situation, it will follow
>>> approximately the same rules of physics that dealing with satellite
>>> antenna installations.
>> And guess what? Satellite TV splitters work. They even have the answer to
>> "how much attenuation" printed right on the splitter and they come with F
>> type connecters you can use the recommended TV type antenna cable too.
>> You can buy them with DC blockers too. All this stuff is low cost because
>> it is mass produced by the billions
>> Yes, it's 75 ohm not 50 and the splitters a 2+ GHz but it works just fine
>> if your antenna has the right gain. The splitters don't high pass the
>> signal. Trimble actually recommends using the 75 Ohm TV cable and
>> supplies it with their kits.
>> Sometimes a GPS receiver will raise an "Antenna Alarm" if it does not see a
>> DC load but you can turn those off with a serial command
>> Chris Albertson
>> Redondo Beach, California
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