On 8 January 2015 at 10:03, Charles Steinmetz <csteinm...@yandex.com> wrote: > Dave wrote: > >> Yes, but I was aware of this, and that's why I got two different isolation >> figures. > > > What I was pointing out is that there will be *4* different isolation > figures from any one output port, not just two. The lowest will be to the > one electrically adjacent output, next (a bit higher) will be to two outputs > at one remove, then (a bit higher yet) to four outputs twice removed, and > finally (the highest) to eight outputs thrice removed (these eight are the > ones you are calling "on the other 1:8 splitter"). > > Perhaps a diagram is in order (see below). Each dot represents a 1:2 > splitter. (I've drawn only 1:8. A 1:16 is just this plus another 1:8, > connected to the two outputs of another 1:2 splitter.) > > To find the worst case output-to-output isolation, you need to identify two > electrically adjacent output ports -- either by measurement or from the > manufacturer's published data. > > Best regards, > > Charles
The Minicircuits data sheet http://194.75.38.69/pdfs/ZFSC-16-3.pdf basically shows there are two different isolation values, which it calls "adjacent" and "opposite". These are typically 32 and 48 dB @ 10 MHz. I had a quick play yesterday, almost randomly putting the two BNC connectors in different sockets, and there does appear to be only two values of isolation values. What I did notice though is that if the common port is not terminated properly, that dramatically changes the isolation. That might be an issue, as I don't know what the return loss (S22) of the amplifier will be, although that is something I can measure. I need to order up a keyboard and mouse, and then I can use this Agilent N3383A VNA properly. Then I'll be able to make measurements at 10 MHz. (I bought the thing, then sold it a week later to a friend's company. He is working in Singapore, so he said I can borrow it until he gets back. His contract ends in July, but it might be extended, so this is a semi-permanent fixture here! Where else could you hire a 9 GHz VNA for 9 months for free?) If there was a design for an isolation amplifier around with a PCB available that worked well, I would build it. But for now at least, this might be good enough for what I want, which is basically to ensure my spectrum analyzer, signal generators have a common frequency reference. I don't think I have a need for great isolation, as I don't intend this to be used for the sort of precision measurement time-nuts do. BTW, I was looking at the design someone posted for one which used a discrete transistor and transformer. I forget which transistor it was, but I could get 100 delivered from China for £1.00 (about $1.60)!! I would not buy from China via eBay however, as the chances of them being original transistors are pretty remote, so I doubt their characteristics would be like those used to model that design. The transistors are only £0.07 from Farnell, so buying them is easy & cheap enough. I just don't fancy the hassle of making a PCB if this 16-way splitter will do. Dave _______________________________________________ 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.
