[time-nuts] Absolute phase

Magnus Danielson magnus at rubidium.se
Fri Nov 17 15:20:05 EST 2017


Hi,

The reason I mention sharing antenna is that it takes out the difference 
that is natural from having different antennas and the difference in 
multipath.

Sharing antenna has its own set of problems, so a suitable antenna 
splitter was assumed. Effectively you need to bypass DC to power the 
antenna, you need to amplify the signal to compensate for the loss due 
to the splitter, and it needs to look like an antenna to the GPS 
receiver, so the antenna alarm does not goes off.

Cheers,
Magnus

On 11/17/2017 09:01 PM, Jerry Hancock wrote:
> Thanks, understand completely.
> 
> You mention “sharing an antenna”.  Is there a problem with connecting the same antenna to two units?  I am referring to my REF0/REF1 pair.
> 
> Thanks
> 
>> On Nov 17, 2017, at 11:39 AM, Magnus Danielson <magnus at rubidium.dyndns.org> wrote:
>>
>> Hi,
>>
>> First of all, the receiver varies around some average phase.
>> The average of two receivers may not be the same, even if sharing antenna.
>> Their average can be offset from "absolute phase" because of offsets in the receiver, antenna cables and antenna.
>>
>> If you are not to careful, a GPSDO will do nicely for many applications. The more you care, the more hassle.
>>
>> Oh, and two GPSDOs next to each other can have significant common mode disturbance, so you can't really evaluate a GPSDO by measuring up to another GPSDO.
>>
>> Cheers,
>> Magnus
>>
>> On 11/17/2017 08:05 PM, Jerry Hancock wrote:
>>> Granted I expect someone on this list to reply with something that makes me feel stupid, if you have two GPSDO units running side by side, should the phase delta on the 10Mhz output be zero (ideally)?  Is there an absolute phase standard kept between GPSDO units as all it would take is one extra inverter in the chain to flip the phase, no?
>>> Thanks
>>> Jerry
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