[time-nuts] Using commercial video amplifier for 10MHz clock distribution.

[paul swed]

I have used the amplifiers for years. Good grade GVGs and extrons. They
just work.
Though like everyone I considered shifting to 50 ohms it never seemed worth
the effort.
In fact most of my distribution is 75 ohms.
Cable and connectors are cheap well shielded and easy to install.
They make very fine 75 ohm crimp bnc connectors also. Not so cheap.
Also many of the amps will pass square wave signals just fine. Think of the
60 Hz sync pulse.
They would not be good for 1 PPS.
I did do something recently that turned out well. Convert the reference to
a 110 ohm balanced signal using AD8131 amplifiers and drive cat6 cable. Far
end mini ckt 110-75 ohm xformer.
Works very well and allows 4 signals on one cable. No emissions I can
easily detect. 100 watt transceivers do not upset things. My cable run is
150'. Loss is expected and the far end amp makes up for it. Now the
basement equipment is locked to the upstairs equipment without additional
divider chains.
Crazy silly I know.
Regards
Paul
WB8TSL

On Fri, Oct 18, 2019 at 3:09 PM Bob Bownes <bownes at gmail.com> wrote:

> I have a few of the 2 in 5 out video distribution amps. I took one apart
> and converted it to 50Ω from 75Ω, and to be honest, I can't really see a
> difference.
>
> Bob
>
>
> On Fri, Oct 18, 2019 at 8:08 AM Charles Steinmetz <csteinmetz at yandex.com>
> wrote:
>
> > Taka Kamiya wrote:
> >
> > > I am using Extron MDA 3V for distributing 10MHz at several places in my
> > lab.  MDA3V is a one port in - 3 port out device made for VIDEO market
> and
> > rather low end at that.  Input and output is 75 ohm and bandwidth extend
> to
> > 150MHz or so.  Looking at 10MHz sine wave through it, it looks good.  No
> > visible distortions.  Gain is unity between input and one of the ports.
> > >
> > > Couple of questions though.  This device is 75ohm.  It's easy to add
> > 150ohm in parallel to a matching resister and make it 50ohm.  However,
> I'm
> > guessing 50 ohm / 75 ohm mismatch is not really a big deal that I'm not
> > doing anything about it.  Input and output cables are RG58 (50 ohm)  VSWR
> > is 1.5, For external sync port, many equipment is not exactly spec'd for
> 50
> > ohm, but often only spec'd for voltage or at db level without any
> specific
> > impedance mentioned.  Recommended cable is 50 ohm though.  I typically
> shy
> > away from consumer grade gear but looking inside, it's just an op-amp and
> > registers.  If I use square wave which contains higher frequency
> > components, would this be inadequate?
> > > There are many web pages by people doing exactly what I'm doing with
> > usually bigger Extron devices.  I'd like to consult the Time-Nut
> community
> > of sanity in what I am doing.
> >
> > I published a doc with recommended mods to the opamp-based Extron video
> > DAs for use as 1-10MHz clock/timing DAs:
> >
> > <
> >
> http://www.ko4bb.com/getsimple/index.php?id=download&file=02_GPS_Timing/Extron_ADA_6_modifications_for_use_as_10MHz_distribution_amp_STEINMETZ.pdf
> > >
> >
> > Whether you make the changes or not, you may find some helpful
> > information there.
> >
> > Best regards,
> >
> > Charles
> >
> >
> >
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