[time-nuts] GPS antenna splitter recommendation?

[Larry McDavid]

This InStock Wireless 4-Way splitter is a *passive* device, meaning no 
amplification is included. The headline spec of "Insertion Loss 0.4 dB 
typical" may be true but does not tell the whole story. Below that spec, 
is the column heading of "Insertion Loss Above 6.02 dB" explaining that 
each output is down 6 dB due to the 4-way power split without 
amplification. Thus their Marketing Department is emphasizing the low 
insertion loss but downplaying the loss due to power splitting without 
amplification.

This may be adequate if you have enough gain in your GPS antenna and low 
enough loss in the coax down feed but it may not be what you expect when 
casually reading the InStock Wireless spec. Power splitting is splitting 
power; if you divide power 4 ways, each output has to be 6 dB down.

On the good side, this splitter does work on other GNSS systems.

And, they offer (SMA in this case) 50 Ohm terminators, which should be 
used on any port that is not connected to a receiver.

Very few GPS splitters need a Bias-T because they typically have one 
port that passes through the antenna voltage provided by a receiver, 
usually the one connected to Port 1. The other ports are dc blocked.

The GPS Source S14WI 4-Way splitter (as configured) I described here 
previously is amplified and has a more sophisticated method of deriving 
the source for the antenna voltage, detecting which port, starting at 
Port 1, has source voltage available and using that port while dc 
blocking the other output ports. When I bought my NOS units several 
years ago on eBay, I paid $65 each plus some modest international 
postage; I considered that a great price!

Output ports connected to a receiver but not the one powering the 
antenna should present a dc load to each receiver so that the antenna 
failure detector in the receiver does not falsely report an antenna 
failure. Most GPS splitters include a dc load, often 200 Ohms, to output 
ports not powering the antenna.

I do have Type N 50 Ohm terminators but currently each output port on my 
splitter is connected to a GPS device.

There is a GPS Source 4-Way multi-GNSS splitter offered on eBay now as 
Item 401835679864. However, I don't have a data sheet explaining the 
model number letters shown to know if this is an amplified splitter or 
not; both passive and amplified versions of the S14 splitter are 
available. The eBay listing title reads, "GPS Source 1x4 Stamdard 
Amplified Splitter - S14 (S14S-E-SF)" but I would not take that as a 
guarantee this particular model is amplified since both versions are 
offered with that same basic model number. Am I a bit cynical? Well, 
maybe...

Larry

On 4/30/2020 2:38 AM, Chris Burford wrote:
> I use a 4 port splitter from InStock Wireless, all with SMA jacks. You can
> view the specs here as well as browse for other configurations. To help with
> the attenuation factor use the lowest loss coax between the splitter and the
> GPS antenna. I'm using Times Microwave LMR-400 for just that reason.
> 
> https://www.instockwireless.com/gps-splitter-4way-SMA-gps410.htm
> 
> Chris Burford...

-- 
Best wishes,

Larry McDavid W6FUB
Anaheim, California  (SE of Los Angeles, near Disneyland)