GPS Antenna

[150flivver]

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?

[[email protected]]

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 *
************************************************** ***********************

[RST Engineering]

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

[Tauno Voipio]

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

[RST Engineering]

"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")

[David Lesher]

{Splitting a GPS Antenna}

I'll say the same thing I said re: 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

[john smith]

> 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.

[Darrel Toepfer]

john smith wrote:

> 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.

And lets build a Level3 instead and pocket the difference for artsee
projects...

[J. Severyn]

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

[RST Engineering]

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.

[Matt Whiting]

john smith wrote:

>>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.

The real world is that the politicans controlling the money won't
approve enough for either.


Matt

[Newps]

john smith wrote:

>>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.

Don't forget about the explosives to make them fail at the right time.

[David Lesher]

john smith > writes:

>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.


Not quite... See, Level 5, unlike those below it, has no upper limit...

--
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

[J. Severyn]

Trivial for you and trivial for me.... as long as we both know the receiver
designs to let us know where the direct and AC ports of the hybrid should be
located. But without further knowledge of the receivers it takes a little
more testing to get the information. I doubt the original poster had that
information.

John Severyn
"RST Engineering" > wrote in message
.. .
> 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.
>
>

[George Patterson]

Darrel Toepfer wrote:

> And lets build a Level3 instead and pocket the difference for artsee
> projects...

And let's just drive the pilings 1/3 the way down and pocket the difference.

George Patterson
Coffee is only a way of stealing time that should by rights belong to
your slightly older self.