[time-nuts] Frequency doubler with quadrature hybrid

[Charles Steinmetz]

Some time ago, I said I'd post a description and schematic of an 
excellent frequency doubler using a quadrature hybrid directional 
coupler to drive a diode DBM.  It is now available on ko4bb.com 
following Didier's recent work on the site (Thank you, Didier, for 
this wonderful resource):

<http://www.ko4bb.com/manuals/download.php?file=05_GPS_Timing/4_App_Notes_and_Articles/Frequency_doubler_quadrature_DBM.pdf>

When carefully constructed, this circuit has exceptional inherent 
balance and, consequently, very low feedthrough of the input 
frequency and its harmonics.  It also avoids most of the flicker 
noise created by push-push doublers.  For many uses, no output 
filtering is needed.  (The schematic includes a filter/amplifier, in 
case one needs a signal with even lower harmonics.)

In addition to the frequency doubler (which is drawn for 5MHz/10MHz, 
but can be easily scaled), I included the seminal article on 
lumped-constant quadrature hybrid splitter/combiners.  More 
information on these extremely useful but relatively unknown devices 
can be found in Chapters 3 and 9 of Wes Hayward's "Experimental 
Methods in RF Design," in the discussions of single sideband and 
image-reject mixers.

(EMRFD is a must-have book for anyone playing with RF hardware, IMO, 
the same way Horowitz & Hill's "The Art of Electronics" is for 
general electronics knowledge.  Hayward's "Introduction to Radio 
Frequency Design" is also extremely useful.)

Best regards,

Charles