Will it work? Probably. Up to a point. Is is best practice? Not even close.
Each device will (should?) generally present a 50Ω termination. In the case of instruments that provide their own ref output which is then looped back in, they may be different, but I don't recall seeing any that said anything other than nothing or 50Ω. That being said, I've daisy chained a few together to get quick results without trouble. Bob On Mon, Oct 23, 2017 at 1:49 PM, Jeremy Elson <jel...@gmail.com> wrote: > I was about to ask a related question of the list: when do you need a > distribution amplifier, and when is it sufficient to just have a single > (linear) run of coax? > > I have a GPSDO (Nick Sayer's device) that I want to use to feed a few other > pieces of equipment in my lab (an HP5335A, John Ackermann's beautiful TICC, > and a Rigol signal generator). Is it safe to have RG174 coming out of the > GPSDO, tapping into it with a BNC T-junction that plugs into the back of > each device that needs the 10mhz input, and then terminating the strand > with a 50 ohm terminator? (In other words, the way thinnet Ethernet was > wired back in the day.) As long as the signal goes in a straight line, not > a "Y" (i.e. no cables attached to the t-junction taps, just a direct input > into a high-z input) it seems like it should work. Do I need a distribution > amplifier? Or is that, say, if the signal needs to split off in multiple > directions and you don't want to fill your lab with a space-filling curve > of coax? > > -Jeremy > > On Mon, Oct 23, 2017 at 10:26 AM, Bob kb8tq <kb...@n1k.org> wrote: > > > Hi > > > > The correct answer to any real question like this is “that depends”. > > > > For anything that I normally run as test gear, noise outside a very > narrow > > bandwidth really > > does not matter much. The test gear *assumes* (by design) that the > > reference signal going > > into the “ref in” jack is not very clean. It does various tricks with > > filters and PLL’s to “scrub” > > the input. > > > > If we are talking about the reference into one side of a phase noise test > > set, then > > the situation is a bit different. The test set is simply going to tell me > > what the combined > > noise is on the two inputs. If one is significantly more noisy than the > > other, that’s pretty > > much all I will see. In this case, my answer is “don’t use a distributed > > signal”. Use a > > stand alone source as your reference and isolate it from the rest of the > > world. > > > > In any case, making a super duper distribution gizmo and feeding it with > a > > noisy signal > > is not going to make the signal any better. Most GPSDO’s have relatively > > noisy outputs. > > Some are better than others. None that I have seen on the surplus market > > are what > > I would call quiet at the output jack of the GPSDO. They either have an > > ocean of spurs > > or a lot of phase noise. Some have both …. > > > > Any time you boost a bunch of signals up to high levels, you create > “crud” > > running around your > > lab / shack. One of the most basic questions should always be “do I > really > > need this signal?”. Next > > should be “how can I have a shorter run?”. I have many pieces of gear > > that are rarely used. > > They use odd references. When I need to use them I rig a reference. That > > gets shut down > > once the gear goes back to storage. …. no more birdies every 100 KHz …. > No > > need for > > tripple shielded coax …. > > > > Simple answer: > > > > Square up the 10 MHz (or whatever) by matching it into a 5.5 V powered > > high speed CMOS > > gate. The NC7SZ series is one of many families you can use. A NC7SZ125 is > > not a bad gate > > to pick. Distribute the square wave to however many output amps as you > > need. Each one > > is another of the same gates with the output matched via a 50 ohm to 50 > > ohm lowpass Tee network > > with a low Q ( < 2). Likely pad down the output a bit to keep it at a > > rational level. Build up however > > many you need for however many frequencies you require. Very normal > linear > > regulator chips > > are fine for the power. Careful bypassing and solid ground planes are > > always a good idea. > > Parts cost wise, postage is likely to cost you more than the components. > > There are …. errr… > > many thousands …. of multi output amps of this basic design out there …. > > they seem to > > work pretty well. > > > > Yes, there are *lots* of possible twists and turns to this. I’m only > > guessing about the gear you > > are trying to run and what you are trying to do with it. > > > > Bob > > > > > > > > > > > > > On Oct 23, 2017, at 12:45 PM, Tom Van Baak <t...@leapsecond.com> wrote: > > > > > > List -- Don is having email trouble, but here's his posting: > > > > > > ---------- > > > > > > From: donaldbcol...@gmail.com > > > Date: Tue, Oct 24, 2017 at 1:38 AM > > > Subject: Distribution divider/amplifier for 10MHz GPSDO > > > > > > Hello group. I`m intending to distribute, via 50 Ohm coax, frequency > > > reference signals to my test equipment in my test bay [no relation to > > eBay, > > > except that most of the equipment came from there]. I`ll be using > RG58/U > > > coax, and 50 ohm terminations, with the highest reasonable signal level > > > reticulated. Given that the name of the game seems to be to avoid any > > > severe reduction in SNR of the 10MHz signal comming out of the GPSDO, > by > > > the logic dividers, and impedance lowering buffer amplifiers, what > > > considerations should be made regarding the choice of logic families, > and > > > transistors to be used? The frequencies required by the test equipment > > vary > > > from 500kHz to 10MHz, and amplitudes from 100mV P-P sinewave, to 5V > peak > > > squarewave. How good must the PSU be to stop the rot getting worse, and > > is > > > 1/f noise in the active devices important? Your thoughts will be > > > appreciated. > > > > > > P.S.: How accurate is the Trimble Thunderbolt for this > > > application?.............................................. > > Thankyou,............Don > > > Collie. > > > > > > ---------- > > > > > > _______________________________________________ > > > 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. > > > > _______________________________________________ > > 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. > > > _______________________________________________ > 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. > _______________________________________________ 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.