[time-nuts] Re: GPS antenna distribution???

[Stewart Cobb]

The companies "GPS Source" and "GPS Networking" make so-called "networked"
splitters which have very high isolation between ports and which, as a
bonus, do not require unused outputs to be terminated.

How does this work? The incoming signal is amplified by roughly 25 dB, then
split several ways through a Wilkinson divider or equivalent. Each of the
splitter outputs then passes through an attenuator of roughly 15 dB on the
way to its output jack.

This provides > 40 dB isolation between ports (15 dB + 15 dB + whatever the
Wilkinson divider gives) and 30 dB broadband termination for the ports of
the divider even if the output port jack is left open.

The amplifier gain is typically adjusted so that the overall gain from
input to output is around 3 dB, to compensate for typical cable loss from a
roof-mounted antenna.

Splitters from these companies show up frequently on auction sites,
occasionally at attractive prices. The nice thing is that all the optional
features including the "networked" option seem to be implemented by loading
different components on the same PCB. If you can read microstrip circuitry
and solder 0805 parts, you can change an "amplified" splitter into a
"networked" splitter, tweak the overall gain, add or remove DC blocks, and
so forth.

Cheers!
--Stu