[time-nuts] Frequency Distribution Design Basic Module

timeok at timeok.it timeok at timeok.it
Sat Aug 29 05:24:02 EDT 2015


Hi Charles,



On Fri 28/08/15 19:53 , Charles Steinmetz <csteinmetz at yandex.com> wrote:

Charles  wrote:

> I'm not aware of any instrument that needs a reference signal of more 
> than +13dBm (= 1Vrms), and most will happily accept much less than 
> that with no reduction in performance -- so I see no reason why a DA 
> with a maximum undistorted Po of +13dBm should be considered inadequate.

I didn't write that any instrument needs a reference signal of more  than +13dBm (= 1Vrms) as you write, but a DA must be able to handle the signal levels of the standard on the market.
I rely on facts and not words. I have measured the outputs level of some standard I have in my lab:

Nr 3 HP5065A     +15dBm
HP105B             +13.62dBm
Efratom MRT-L     +13.60dBm
Efratom MRT-H    +14dBm
HP Z3815             +9.40dBm

As you can see  the HP GPS only is below + 13dBm. 

 If you need to power a devices that need 1A, you not buy a 1A max power supply but you want to ensure a margin and will buy one from A 1.5 or higher.Don't you think?

Charles wrote:

> What does seem inadequate for this century is the distortion 
> specification of your amplifier. -45dBc is pretty poor by today's 
> standards, and such high distortion generates additional phase noise 
> when the signal is AC-coupled and/or DC-restored, and when the client 
> instrument uses a zero-cross detector or other circuit that is 
> sensitive to the symmetry of the waveform. These days, it is not 
> difficult to build a 1-10MHz DA with distortion products more than 
> 65dB below a +13dBm output signal, either discrete or integrated.

Unfortunately,even in this case what you say does not conform to reality. I am attaching to this mail a comparison I made by taking from  the web some characteristics about DA on the market  or prototypes  built by people far more expert than me.
As you will also see, what we can consider top, made by NIST, has the same harmonic distortion of mine. With rare exceptions that should be evaluated more carefully, harmonic distortion is about 30dBc.

To get as you claim 65dBc, you must insert an output band pass filter or a low pass/notch filter which, as everyone knows, is  phase sensitive  as a function of temperature. For this reason, most of the DA currently on the market are broad band as the one I designed.

   Best regards,
 
    Luciano

P.S. : Please if you have found the web a DA admittedly broad band with features you write (-65dBc)  can you give us the link?




On Fri 28/08/15 19:53 , Charles Steinmetz <csteinmetz at yandex.com> wrote:

> Luciano wrote:
> 
> >As for the amplifier the big job was finding the balance between the
> >polarization parameters, harmonic distortion and output power.
> >Many distribution amplifiers on the market have a Po max of + 13dBm
> >and this limit does not seem appropriate for this century.
> 
> I'm not aware of any instrument that needs a reference signal of more 
> than +13dBm (= 1Vrms), and most will happily accept much less than 
> that with no reduction in performance -- so I see no reason why a DA 
> with a maximum undistorted Po of +13dBm should be considered inadequate.
> 
> What does seem inadequate for this century is the distortion 
> specification of your amplifier. -45dBc is pretty poor by today's 
> standards, and such high distortion generates additional phase noise 
> when the signal is AC-coupled and/or DC-restored, and when the client 
> instrument uses a zero-cross detector or other circuit that is 
> sensitive to the symmetry of the waveform. These days, it is not 
> difficult to build a 1-10MHz DA with distortion products more than 
> 65dB below a +13dBm output signal, either discrete or integrated.
> 
> Best regards,
> 
> Charles
> 
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