[time-nuts] GPS splitter

Attila Kinali attila at kinali.ch
Wed Jun 21 16:16:42 EDT 2017

On Wed, 21 Jun 2017 15:03:54 -0400
Bob kb8tq <kb8tq at n1k.org> wrote:

> The typical answer is: The largest one I could that 1) Would handle the short circuit current expected and
> 2) was self resonant at or above 1.6 GHz.

I found out, by experiment, that any "large enough" inductance is ok.
A simple "a few dozen windings of AWG30, air core and a tiny bit of
epoxy to keep the windings apart, yet stable" does the trick quite well.
At least it does for the bias-T I used it in. As a rule of thumb,
at the frequency you are using it, the inductor should have an
impedance much larger then the 50Ohm. And for 1.5GHz you get there
pretty quickly. E.g. 20-30 windings on 3mm spread to a length of 20mm
give you something in the order of 150 to 350nH, which translates
to 1k5 to 3k5 impedance at 1.5GHz.

I recommend reading [1] and [2] for the design of bias-T's
(there are probably better sources, but these are those
that I stumbled upon, some time ago)

			Attila Kinali

[1] "Design of Bias Tees for a Pulsed-Bias, Pulsed-RF Test System
using Accurate Component Models", by Baylis, Dunleavy, Clausen, 2006

[2] "Wideband Bias Tee". by Johnson, 2008

You know, the very powerful and the very stupid have one thing in common.
They don't alters their views to fit the facts, they alter the facts to
fit the views, which can be uncomfortable if you happen to be one of the
facts that needs altering.  -- The Doctor

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