[time-nuts] Advanced 5 to 10 MHz doubler

[Bruce Griffiths]

Paramithiotti, Luciano Paolo S wrote:
>
> http://www.timeok.it/files/5_to10_mhz_advanced_doubler.pdf
>
> Best regards, Luciano
>
> Luciano P. S. Paramithiotti
>
>
>    
The claimed 50 ohm input impedance is incorrect except perhaps for small 
signals.
For large signals the input impedance will be much lower essentially the 
input transformer equivalent series resistance plus the transformed 
large signal emitter resistance.
The key to low phase noise is low base to collector dc gain and local RF 
feedback (largely due to the source impedance in this case).
The circuit is essentially the BJT equivalent of the NIST common gate 
JFET doubler.

Common emitter variants are also useful especially since the input 
impedance can easily be 50 ohms if a suitable termination resistor is used.

As pointed out by NIST decades ago, using traps for the unwanted 
harmonics improves the phase stability and phase noise over the 
alternative of using a high Q bandpass filter.

NIST have recently explored the possibility of using an all digital 
implementation of the DMTD at least for clock comparisons.
The mixers are replaced by undersampling ADCs to produce an aliased beat 
frequency signals from which phase differences can be extracted by DSP 
techniques:

http://tf.boulder.nist.gov/general/pdf/2442.pdf


Bruce