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

[Bob Bownes]

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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