[time-nuts] GPS splitter
brooke at pacific.net
Wed Jun 21 17:44:58 EDT 2017
I just use a resistor.
and here is the Cable TV power divider were Type-F DC blocks are added to all but one of the output ports.
-------- Original Message --------
> 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.
>> On Jun 21, 2017, at 4:16 PM, Attila Kinali <attila at kinali.ch> wrote:
>> 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  and  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
>>  "Design of Bias Tees for a Pulsed-Bias, Pulsed-RF Test System
>> using Accurate Component Models", by Baylis, Dunleavy, Clausen, 2006
>>  "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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