[time-nuts] GPS antenna??

[Magnus Danielson]

On 04/09/2013 04:02 AM, Jim Lux wrote:
> On 4/8/13 9:59 AM, Alan Melia wrote:
>> Hi all an interesting problem you may have encountered, I want to use a
>> GPS frequency standard inside a building with no opening windows
>> (opening windows are known as air conditioning in the UK :-)) )
>> This is part of a two day amateur microwave conference so we should have
>> the expertise.
>>
>> I intend to try and pass the signal through a a double glazed glass
>> window unit (hopefully not metalised) using a couple of patch antennas.
>> The outer GPS antenna is active so will need a 5v supply via an
>> inserter. Inner patch active, outer patch passive to avoid problems of
>> feedback. Main antenna can be shielded from the "coupling" either
>> physically or with a slab of absorber.
>>
>> Has anyone tried this?.... does it work?.....any gotchas?
>
> we do this all the time at JPL and other places..
>
> I think, though, that your statement "inner patch active, outer patch
> passive" is backwards..
>
> You have the outside antenna with the LNA, then you reradiate inside.
> you might want some pads in the line to knock the signal level down (not
> all GPS receivers do well with stronger than normal signals)
>
> (you could also partly cover the reradiator with something that absorbs)

You need to get power to the outside, then you might just as well pull 
the antenna coax through.

Agree that the external system should be active, but care must be made 
to keep the re-radiator sufficiently distant from the actual antenna, or 
you have yourself a nice feedback-loop with ehm... not favourable GPS 
reception conditions.

Cheers,
Magnus