GPS Antenna

"Tauno Voipio" wrote in message
...
RST Engineering wrote:

Also, to keep impedances correct, the splitter will likely either have to
be lossy, or active.

google "Wilkinson" "hybrid power divider" and "IRE Transactions" before
saying stuff like this.

What's the matter?

The "matter" is defining "loss". In general, we do not say that a device is
lossy unless the incoming power is greater than the outgoing power. In the
case of the Wilkinson (or any variety of hybrid) splitter, the "loss" (if
any) is measured in tenths of a dB for any decent design.

There are a series of truly "lossy" resistive splitters that are not
acceptable for this particular application.



To divide the antenna power to several receivers
always means some loss to a single receiver. In
an ideal case, a passive divider to two branches
will show a loss of 3 dB to both branches, and
this means no power loss in the divider.

An active divider can compensate for the losses
with an amplifier.

With something on the order of 26 dB active gain in the typical external GPS
antenna, and with a loss of something on the order of 8 to 10 dB in the
normal run of coax from antenna to receiver, you are still something like
16-18 dB ahead of the game over a stock passive antenna. A 3 dB reduction
in signal level (30% in voltage) will not be noticeable.

Why would you go to the hassle of an active splitter at 1.7 GHz. when it is
not necessary? Remember, a good engineer can build a bridge that will stand
up to maximum design loads plus safety factor. An EXCELLENT engineer can
build a bridge that will stand up to maximum design loads plus safety factor
JUST BARELY.



The division losses always exceed zero if the
impedances are not properly matched, which will
show more than 3 dB in divide to two.

Like I said, in a properly designed hybrid, losses are measured in feathers,
not bricks.



--

Tauno Voipio, avionics engineer
tauno voipio (at) iki fi

Jim Weir

Avionics Technician at 16

Avionics Engineer at 22

Avionics Engineer Emeritus after 40 years in the 'biz with any kind of luck
at all in a couple more years.
(Emeritus = "on the shelf")