[time-nuts] Dist Amps Questions

[W2HX]

Hi all,

 

I am close to closing in on a video distribution amp for a GPSDO for use in
10 MHz reference signals for various test equipment and had a few questions.

 

1.       50/75 ohm question.  I know that putting 50 ohm source into a 75
ohm device will cause SWR. I know that the total power delivered to the
device will be the difference between forward power and reflected power.  So
that doesn't seem bad, just might have a lower power input into the DA.
However, what about distortion? Will the sine wave be distorted somewhat?
And what if any adverse effect could a distorted sine wave have on various
instruments using the 10 MHz reference?

2.       Many of these amps have LOOP through connections to expand the
number of outputs (in ->loop->in).  I often see 75 ohm terminators at the
end of the loop.  Since we are mostly using 50 ohm sources (GPSDO) would
there be any benefit in terminating these loops with 50 ohm terminators? I
realize that the output of the DA's are still 75 ohm, but I am thinking if a
50 ohm source terminated in 50 ohms might have less distortion (question
above) going into the amp.

3.       Some of these video distribution amps can be loaded with different
cards. Some cards are straight VDA cards. Others have some form of "EQ."
According to one description the card comes ".with the addition of
equalization to compensate for attenuation and phase errors associated with
long cable runs."  And I was wondering, could some form of this EQ
compensation be useful in a 10 MHz ref distribution system? What are the
effects of long cables runs around a lab when distributing the reference
signal?  What is the effect of not maintaining the same phase across all
instruments in a lab? 

 

73 Eugene W2HX