[time-nuts] Close-in phase noise measurements

[Bruce Griffiths]

Bruce Griffiths wrote:
> John Miles wrote:
>   
>>> A dual mixer time difference system can have a lower noise floor than a
>>> single mixer system.
>>>     
>>>       
>> I wonder if those are still covered by patents in various corners of the
>> world, the way the TSC's dual-ADC architecture appears to be...
>>
>> -- john, KE5FX
>>
>>   
>>     
> John
>
> Unlikely, the dual mixer time difference technique has been around so 
> long that most patents like:
>
> United States Patent 5128909 (issued  7 July 1992, expired on 7 July 2004).
>
> which is an extension of the technique to multiple channels, have expired.
>
> Bruce
>
>   
Addenda

US patent 4,425,543 issued (JPL NASA) on Jan 10, 1984 has also passed 
its expiry date.
This covers the 1Hz beat frequency system developed at JPL.

Since NIST and others were using the technique well before 1984 its 
likely that any other relevant patents have long since expired.

However the new JPL system using a 123Hz beat frequency may have some 
associated patents, although its hard to see much justification for a 
patent.

Bruce