[time-nuts] To use or not to use transmission line splitters for GPS receivers

[Timeok]

I agree,
Luciano
timeok

Il 2012-10-09 10:41 Azelio Boriani ha scritto:
> Is there any difference between what a GPS receiver can receve via
> crosstalk or receive directly from the antenna? In my opinion 
> crosstalk is
> absolutely less than the last argument about GPS antenna splitters.
>
> On Tue, Oct 9, 2012 at 9:58 AM, Timeok <timeok at timeok.it> wrote:
>
>> Hi all,
>>
>> In my shack I have a single antenna with two power splitter in 
>> series
>> because I need several ports for the four GPSDO and spare port for
>> occasional testing.
>>
>>
>>
>>
>>          1.1 They argued that cross talk could happen among ports. I 
>> doubt
>>> it
>>> with the newer models. I have experience with HP and Symmetricom 
>>> units
>>> and they state their products cancel cross talk.
>>>
>>
>> any cross talk depends on the circuit and layout of the splitter. 
>> Some
>> crosstalk can happen with two close antenna cable.
>> I suppose the first question have to be : What is my time stability 
>> target?
>> Important is a stable electrical and mechanical configuration and 
>> port
>> connection.
>>
>>
>>
>>          1.2 They argued that there could be problems from the power
>>> feeding
>>> of the antenna and mismatches at the receiver antenna port 
>>> voltages.
>>> Again I doubt it if one uses receivers in the same voltage range
>>>
>>
>> I have the same dubt and for this reason I have powered my Agilent
>> splitter not from the GPS but from separate port is present (ac and 
>> backup
>> du power).This also for the smart splitter.
>>
>>
>>> 2. I have been experimenting with GPS constellation coverage with
>>> different brands of antennas. I have found different gains, 
>>> different
>>> radiation patterns and as a result different satellites in view for
>>> identical GPS receivers.
>>>         2.1 I have found that using a single antenna and a two port 
>>> HP
>>> splitter I get the same radiation pattern, gain and identical
>>> satellites in view for a set of identical receivers. For comparison
>>> purposes I feel this is an adequate scenario.
>>>
>>
>> I agree, the new receivers have comparable performance.Some more
>> difference are in PLL OCXO and firmware.
>>
>>
>>          It is easier for me to take care of the transmission line 
>> length
>>> and
>>> errors caused by phase differences, attenuation and delays.
>>>         2.2 Two identical GPS receivers each one with it's own 
>>> antenna,
>>> could eventually cause spatial diversity reception for a system of 
>>> two
>>> receivers conceptually set as one for comparison purposes. 
>>> Different
>>> satellites being tracked on
>>>         each receiver if not connected to a common antenna. Even if
>>> antennas
>>> and transmission lines are identical.
>>>
>>> Question is: Am I wrong doing the above mentioned assumptions while
>>> considering the use of GPS transmission line splitters? I which
>>> scenarios are the splitters recommended? In which cases they are
>>> rather not to be considered?
>>>
>>
>> I think a standard calibration lab have to setting up with two 
>> antenna
>> system and two receivers as recovery plan in case of fault. One 
>> system can
>> be single antenna plus GPSDO (recovery reference). The other can use 
>> a
>> splitter connected to second receiver and several more ports for 
>> testing.
>> All my ports are with a blocking capacitors in series to avoid any 
>> antenna
>> or active splitter interaction.
>>
>>
>> Luciano
>> timeok
>>
>>
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-- 
timeok