[time-nuts] Building a DC Block Thingy....

John Ackermann N8UR jra at febo.com
Fri Jul 27 16:09:20 EDT 2007


I actually did just that on one of the HP 8 port splitters that was on 
eBay a few months ago.  It was configured for external DC but simply 
passed the input voltage through untouched.  A 78L05 regulator on a 
piece of perfboard mounted fairly easily inside the case and allows me 
to drive the splitter from my 13.8 volt bus.

John
----

Rob Kimberley wrote:
> ); SAEximRunCond expanded to false
> Errors-To: time-nuts-bounces+jra=febo.com+jra=febo.com at febo.com
> 
> My first thought here would be to use a small 3 pin 5V regulator to drop the
> DC down, and then capacitively couple in and out to let the RF through.
> 
> Interesting to see what other comments you get.
> 
> Rob K 
> 
> -----Original Message-----
> From: time-nuts-bounces at febo.com [mailto:time-nuts-bounces at febo.com] On
> Behalf Of Jason Rabel
> Sent: 27 July 2007 20:12
> To: 'Discussion of precise time and frequency measurement'
> Subject: [time-nuts] Building a DC Block Thingy....
> 
> ); SAEximRunCond expanded to false
> Errors-To:
> time-nuts-bounces+rk=timing-consultants.com+rk=timing-consultants.com at febo.c
> om
> 
> I have a NTS-200 on the way, but one thing about them is their GPS power
> output is 12V instead of the usual 5V. I really didn't want to modify the
> board any in an irreversible fashion so I was hoping to build an inline
> coupler that I could block / sink the 12V current.
> 
> I have a Symmetricom SmartSplitter, and I know that *should* do the job as
> long as a lower numbered port is supplying power, but I really don't want to
> take the accidental risk of sending 12V to my antenna.
> 
> Doing the math to sink 25ma of current would require a 480 ohm resistor...
> That should make the receiver happy and think all is well. But that's as far
> as my knowledge goes. What size capacitor would I need to use? Do I need to
> add an inductor in series with the resistor?
> 
> 
> Jason
> 
> 
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