Hi Hitting the inductance required is relatively easy. Doing so and not hitting self resonance is a bit more tricky. Even a zero ohm reactance likely will work ok (in series with a 150 ohm resistor). It’s tough to know what you have done without a network analyzer. It is even possible that your resistor has enough stray C to mess things up. Of course it might also have enough stray L to get you back in business.
A somewhat less critical approach is to use ferrite beads on both sides of the resistor. They generally are a bit less critical (= more likely to do what the data sheet claims). The trick there is to find some that are set up to work at L band …. they aren’t common in my junk box. Bob > On Jun 21, 2017, at 4:16 PM, Attila Kinali <att...@kinali.ch> wrote: > > On Wed, 21 Jun 2017 15:03:54 -0400 > Bob kb8tq <kb...@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 > http://www.microwavejournal.com/articles/3912-design-of-bias-tees-for-a-pulsed-bias-pulsed-rf-test-system-using-accurate-component-models?v=preview > > [2] "Wideband Bias Tee". by Johnson, 2008 > http://wb9jps.com/Gary_Johnson/Bias_Tee_files/Bias_Tee_Design_V2R.pdf > > -- > 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 > _______________________________________________ > time-nuts mailing list -- time-nuts@febo.com > To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts > and follow the instructions there. _______________________________________________ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.