[time-nuts] Distribution Amp

Mike Feher mfeher at eozinc.com
Sat Sep 24 16:01:00 EDT 2005

Bill -

This thing does have 18 outputs, so yes, I did mean one piece of equipment
per one/each output. I do not know how that could have been misconstrued.
Since I was talking about frequency the simultaneous fits as I indicated
that a constant phase shift between outputs, to me is not relevant. If I was
using it for a timing reference then I would be more cautious. I am well
aware of mismatches occurring due to paralleling 50 ohm inputs or outputs.
My post was not intended to bring out an academic and non relevant debate. I
simply wanted to alert potential customers for a distribution amplifier to
this one which seemed pretty cheap for what it does. Since it is for HDTV, I
expect that all inputs and outputs are probably 75 ohms. That would explain
the loss I was observing as I was using a 50 ohm instrument to measure the
output power. I can live with the 1.5 to 1 VSWR at 10 MHz just fine. I
wonder if you even looked at the URL, or did you just start your negativism
out of habit. - Mike 

Mike B. Feher, N4FS
89 Arnold Blvd.
Howell, NJ, 07731

-----Original Message-----
From: time-nuts-bounces at febo.com [mailto:time-nuts-bounces at febo.com] On
Behalf Of Bill Hawkins
Sent: Saturday, September 24, 2005 12:54 PM
To: Discussion of precise time and frequency measurement
Subject: RE: [time-nuts] Distribution Amp

Mike Feher said,

" It will be ideal to drive a bunch of test equipment simultaneously
from the same source. "

You mean one equipment per output, right? Paralleling 50 ohm inputs
will result in the wrong termination resistance for a cable. This may
not be a problem for a 10 MHz sine wave, as long as the direct coupled
emitter follower can handle the load.

I have used networks where the devices are high impedance. The cable
sees 50 ohms at both ends. Some test equipment has an optional 50 ohm
terminator, for use as a high impedance device.

Suppose I have 3 frequency synthesizers that have optional terminators.
Are there any ill effects, except phase shift, from putting them all on
the standard's output, if only the end one is terminated?

Has anyone tried the high impedance distribution scheme?

Seems like "simultaneously" would be relative, unless the distribution
cables are all of the same length.

Bill Hawkins

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