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

[Charles Steinmetz]

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