[time-nuts] VNA design

Richard (Rick) Karlquist richard at karlquist.com
Mon Jun 2 12:35:41 EDT 2014

On 6/2/2014 7:43 AM, Attila Kinali wrote:

> Also, any good resource on how to build a directional coupler that
> does 10-3000MHz without going to exotic materials would be much

I once had the opportunity to discuss directional couplers with
Julius Botka, then with HP/Agilent.  Specifically, a true directional
coupler he designed that approached the range of 10-3000 MHz.  IMHO,
Botka was one of the greatest experts of all time in this area.
It took extreme attention to detail to get it to work.  It
didn't so much involve exotic materials, but rather expertise.
Don't try this at home kids.  Julius said that he designed it before
the era of cheap calibration.  Now that everyone has calibration,
you don't need a good directional coupler.  You can get away
with a MiniCircuits coupler.  But in fact it is
even easier to just use a resistive bridge.  Four ordinary
resistors will easily go to 3 GHz.  Use a differential amplifier
at the output.  Lots of info on this in the literature.

Another way to make in effect a directional coupler is to use
a 180 degree hybrid.  I also had the opportunity to study Alan
Podell's amazing designs and even have discussions with him.
I dissected one of his 10-3000 MHz hybrids.  (Originally made
by Anzac, now available from Macom Technology for about 5 Benjamins). 
Don't even think about trying this at home.

BTW, you didn't mention software, but that's a big part of
the job.

Rick Karlquist N6RK

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