[time-nuts] Building new pods for the Spectracom 8140 using modern components

[Julien Goodwin]

On 28/4/19 3:25 am, John Ackermann N8UR wrote:
> I have a large box of 8140 pods (well, I call them "taps").  They are
> quite handy for stringing distribution points around a large room,
> provided ultimate phase noise performance isn't required.
> 
> You *don't* need an 8140 main box to use these.  All the 8140 does is
> put 12V DC bias on its output connectors, and the taps couple their
> power off the coax with an RC choke.  When I was using my setup, I built
> a bias-tee box that was inserted right after the frequency source and
> that worked fine.
Earlier in the project I just built some test boards with a tee, a DC
block and space for a regulator, which have proven to be handy little
things, allowing me to use whatever source is handy for testing, plus my
precision DC supplies so I can actually meter the power.

> However, one note:  for best performance, you want to terminate the end
> of the distribution line in 50 ohms, but since there's a DC voltage
> present, you need to include a DC block (series capacitor) so you're not
> burning 3 watts in the load.

Building a set of those terminators, and then having them not actually
terminate was one of the reasons I picked up the VNA, for now I'm
running with values I came to using LTspice, but once I get the test
sets I plan to measure and see if I can do better.