Bob wrote:
For a reasonable standard distribution, you probably want one input and many outputs. One in / eight out or one in / 12 out are fairly common. At least the video gizmo we've been dissecting has trouble past one in / 4 out.
It has 6 CLC409s, each of which drives 3 BNCs, for 18 outputs. Even if you have all 50 ohm loads and only use 2 outputs per op-amp, that's still 12 outputs.
If you cascade them you are at one in to 3 useful outputs. to get to eight you do a lot of jumping from here to there. Each op amp adds it's noise in a cascade.
You don't need to cascade anything, because you hardwire the inputs in the configuration you want (1x18, 1x12 + 1x6, or 1x6 + 1x6 + 1x6) (which becomes 1x12, 1x8 + 1x4, or 1x4 + 1x4 + 1x4, assuming again that all of your loads are 50 ohms so you use only two outputs per op-amp). Since most of us have few 50 ohm loads and lots of ~1k ohm loads to feed, the current limit of the CLC409s will not matter as long as we distribute the 50 ohm loads among the op-amps. When I used the Extron, I had it set up to be switchable between 1x18 and 1x12 + 1x6.
If you are going to run -185 dbc/Hz phase noise signals, none of these solutions will work. For that stuff you want a totally different approach. The same is true if you are after ADEV at 1x10^-15 at 1 second.
Agreed. Also, if you need >120 dB of isolation from output to output or output to input. All of these solutions are for feeding the external reference inputs of various test equipment, radios, etc., not for buffering and isolating signals for serious phase noise or ADEV analysis.
All I'm really trying to say here is that the alternative isn't all that tough. You can do it cheap with common parts and not a lot of effort. The time to hack up an existing video box (and do it right) may not be much less than the time to do something much simpler from scratch.
One person's "not that tough" is another person's "I don't know how I'd do that." I hacked up a video DA (and did it right, within the limits of re-using the CLC409s) in a couple of hours. I have since built my own DA that has much lower phase noise and ADEV than any source I have or am likely ever to have. By the time you design a PC card and have it made, you are way, way beyond "not a lot of effort" for lots of people, to say nothing of the metalwork (even if it is just making new front and back plates for an existing Extron box). I can do all of that, and I did, but it appears from the on-list interest in video DAs that a lot of time nuts would rather not be bothered.
Best regards, Charles _______________________________________________ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
