[time-nuts] GPS: ADEV or MDEV?

Dr Bruce Griffiths bruce.griffiths at xtra.co.nz
Sat Apr 14 09:17:17 EDT 2007


Magnus Danielson wrote:
> From: bg at lysator.liu.se
> Subject: Re: [time-nuts] GPS: ADEV or MDEV?
> Date: Sat, 14 Apr 2007 14:46:42 +0200 (CEST)
> Message-ID: <1678.125.24.131.37.1176554802.squirrel at webmail.lysator.liu.se>
>
>   
>> On Sat, April 14, 2007 13:32, Magnus Danielson said:
>>     
>>> From: Peter Schmelcher <nebula at telus.net>
>>> Subject: Re: [time-nuts] GPS: ADEV or MDEV?
>>> Date: Sat, 14 Apr 2007 02:40:57 -0700
>>> Message-ID: <5.2.1.1.2.20070414001036.02afa7d0 at pop.telus.net>
>>>
>>>       
>>>>> Surely its better to detect the pseudorange instability in software (if
>>>>> one has access)  rather than attenuating the signal from all SVs.
>>>>> Another option is to use multiple GPS antennae operating as a phased
>>>>>           
>>>> array.
>>>>         
>>>>> Bruce
>>>>>           
>>>> Of course but I think that approach is part of sub nanosecond time
>>>> transfer
>>>> accuracy. Attenuation is simple and the results are descent. The signal
>>>> is
>>>> less than 6dB above the receiver noise floor to acquire SV.
>>>> Unfortunately
>>>> the SV do not have matched output power so they are acquired and
>>>> weighted
>>>> unequally.
>>>>         
>>> The difference in path-length and thus space attenuation is compensated by
>>> the
>>> antenna pattern such that it emits stronger to the rimb of its earth view
>>> than
>>> central. That evens out power-shifts due to space attenuation for the
>>> viewer.
>>> Otherwise we would have yeat another problem to deal with.
>>>       
>> Do the HP GPSDOs not have a tuneable maskangle?
>>     
>
> Maskangle is indeed setable.
>
> Cheers,
> Magnus
>
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>   
Magnus

But what is really needed, in general, is to be able to vary the mask 
angle with azimuth to account for hills and other obstructions that do 
not extend all the way around the the site.

Bruce




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