GPS Antenna

Can a single GPS antenna be used for more than one GPS? For example,
is there a splitter available that allows both a panel mount GPS and a
handheld to use an installed GPS antenna?

150flivver wrote:
: Can a single GPS antenna be used for more than one GPS? For example,
: is there a splitter available that allows both a panel mount GPS and a
: handheld to use an installed GPS antenna?

Although I haven't done so, I'd imagine it's possible. A few things to
consider, however. External GPS antennas for aircraft are usually amplified. The
radio puts 5VDC on the coax and the antenna has a LNA inside it.

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

-Cory

--

************************************************** ***********************
* Cory Papenfuss *
* Electrical Engineering candidate Ph.D. graduate student *
* Virginia Polytechnic Institute and State University *
************************************************** ***********************

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

The answer to the OP's question is that yes, it is possible, fairly easy,
and needs an active antenna to do the job right.

Jim



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

-Cory

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?

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.

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

--

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

"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")

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.

Oh what the heck!!!
Let's make this real world...
A good engineer can build a levy that will stand up to a Level 5
hurricane plus safety factor. An EXCELLENT engineer can build a levy
that will stand up to a Level 5 hurricane plus safety factor JUST BARELY.

And let's add the corillary... for tens of billions of dollars less.

{Splitting a GPS Antenna}

I'll say the same thing I said comm/nav antennas.

You'd adding to your single point of failures. If GPS is important
to you; get separate antennas..

--
A host is a host from coast to
& no one will talk to a host that's close........[v].(301) 56-LINUX
Unless the host (that isn't close).........................pob 1433
is busy, hung or dead....................................20915-1433

As pointed out earlier, you have to determine if the two GPS receivers
supply 5V to the antenna, and if the antenna requires 5V (active antenna).
After determining this, the divider must supply both the RF division and
pass through the 5V from one of the GPS (if the antenna is active and gets
its power from the coax)

This is not quite as simple as just hybrid or resistive RF power divider
because of the 5V for the LNA inside of many GPS antennae. More info is
needed on the receivers and the antenna.

Peace,
John Severyn EE
@KLVK


"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?

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.

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

--

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

It is trivial. You let the one side of the hybrid direct couple the signal
and let the other side of the hybrid capacitively couple the signal. THe
downside is that the DC receiver has to be on and working to let the AC
receiver work. A bit more work with diodes and chokes can be done as a
work-around to let either of the receivers power the active antenna.

Jim




"J. Severyn" wrote in message
news:QsOdncAU7pUX6gbeRVn-

This is not quite as simple as just hybrid or resistive RF power divider
because of the 5V for the LNA inside of many GPS antennae. More info is
needed on the receivers and the antenna.