Re: [time-nuts] distribution amp question + hp 59309A
> What is the general feeling here about this issue? I confess that if the amp > output is transformer coupled, I see exactly zero benefit in a grounded > connector as the feed from the amplifier. This question comes up every so often. It comes down to whether you want your test setup to look like a loop antenna or a dipole antenna. Usually the loop is better if you're forced to accept one condition or the other. You shouldn't break, lift, or otherwise mess with coax shields without a very good reason. If you need a balanced connection, use a balanced medium. Obviously if you're setting up a commercial 10base2 installation the rules are different. :) But for sensitive work with low signal levels in coax, you will most often be better off if all of your gear looks like a series of monolithic metal bricks. Ground loops are not the worst thing that can happen to a precision T&F measurement. -- john, KE5FX Miles Design LLC ___ 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.
Re: [time-nuts] distribution amp question + hp 59309A
Walter said: "Also on an unrelated topic, I found an HP 59309A HPIB clock on a forgotten shelf and looked at it, and was surprised to see such a poor primary time standard oscillator inside, just a 1Mhz crystal using a cmos buffer oscillator. It can accept an external standard, but it did feel odd for a device that is meant to provide coordinated system time to be so modestly executed. it's like an uncorrected PC desktop clock." Doesn't this policy actually help prevent the "two clocks problem"? If every piece of equipment has its own frequency standard, then how do you compare anything? OTOH, if you buy one piece of equipment with a 10811 (or Rb or Cs or GPSDO) and use that to feed the rest, then even it's wrong, they're all wrong by the same amount. Bob From: walter shawlee 2 To: time-nuts@febo.com Sent: Saturday, January 28, 2017 11:29 AM Subject: [time-nuts] distribution amp question + hp 59309A I notice that in the distribution amp being discussed at the moment, the BNC output connectors are grounded, and tied to the chassis, which in turn has a grounded emi line filter. this seems like an unavoidable noise pathway to me. I notice that some commercial amps are grounded, but more advanced and transformer coupled units have floating connectors. it makes the most sense to me to be floating, since this frees the return from line noise and spurious, and avoids the significant problem of shifted AC voltages on the return from distant units connected to the amp which are on other ac line circuits. What is the general feeling here about this issue? I confess that if the amp output is transformer coupled, I see exactly zero benefit in a grounded connector as the feed from the amplifier. Also on an unrelated topic, I found an HP 59309A HPIB clock on a forgotten shelf and looked at it, and was surprised to see such a poor primary time standard oscillator inside, just a 1Mhz crystal using a cmos buffer oscillator. It can accept an external standard, but it did feel odd for a device that is meant to provide coordinated system time to be so modestly executed. it's like an uncorrected PC desktop clock. This same issue pops up in many hp/agilent counters, signal generators and related objects. I have always been puzzled by the decision to make such marginal instruments that have time/frequency as their primary parameter, when so little additional effort would have dramatically improved them. I do get the concept of an external standard reference, but it's a pretty weak argument for making a $5K generator or counter with poor performance. Just curious to know everybody's thoughts on this. all the best, walter -- Walter Shawlee 2, President Sphere Research Corporation 3394 Sunnyside Rd., West Kelowna, BC V1Z 2V4 CANADA Phone: (250) 769-1834 walt...@sphere.bc.ca WS2: We're all in one boat, no matter how it looks to you. Love is all you need. (John Lennon) But, that doesn't mean other things don't come in handy. (WS2) ___ 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.
Re: [time-nuts] distribution amp question + hp 59309A
> Also on an unrelated topic, I found an HP 59309A HPIB clock on a forgotten > shelf > and looked at it, and was surprised to see such a poor primary time standard > oscillator inside, just a 1Mhz crystal using a cmos buffer oscillator. It can > accept an external standard, but it did feel odd for a device that is meant > to > provide coordinated system time to be so modestly executed. it's like an > uncorrected PC desktop clock. Walter, The hp 59503A was intended as a GPIB "system" time of day clock in the days before PC's had their own clocks, or before NTP or GPS existed. Imagine a 19" rack with 2 or 3 or 10 HP-IB instruments all on the same bus doing some complex experiment yet and no instrument knows the date or time-of-day that the data is collected, or maybe the controller needs to synchronize events across several instruments. Well, just add a 59503A and you're all set. It even has a battery backup option. To their credit, and unlike a PC, there is an external frequency input, so you have control over the accuracy. It's a beautiful little instrument (lots of discussion in the archives). /tvb ___ 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.
Re: [time-nuts] distribution amp question + hp 59309A
Hi The gotcha with transformer coupled coax is keeping it terminated over a wide range of frequencies. If the coax is miss terminated and the end of the cable is floating, you have a pretty good opportunity for noise to get into the system. Floating shields are also a pretty good way to get crosstalk. In many situations, isolation between outputs is a pretty big deal. Bob > On Jan 28, 2017, at 12:29 PM, walter shawlee 2 wrote: > > I notice that in the distribution amp being discussed at the moment, > the BNC output connectors are grounded, and tied to the chassis, > which in turn has a grounded emi line filter. this seems like an unavoidable > noise pathway to me. > > I notice that some commercial amps are grounded, but more advanced and > transformer coupled units have floating connectors. it makes the most sense > to me to be floating, since this frees the return from line noise and > spurious, and avoids the significant problem of shifted AC voltages on the > return from distant units connected to the amp which are on other ac line > circuits. > > What is the general feeling here about this issue? I confess that if the amp > output is transformer coupled, I see exactly zero benefit in a grounded > connector as the feed from the amplifier. > > Also on an unrelated topic, I found an HP 59309A HPIB clock on a forgotten > shelf and looked at it, and was surprised to see such a poor primary time > standard oscillator inside, just a 1Mhz crystal using a cmos buffer > oscillator. It can accept an external standard, but it did feel odd for a > device that is meant to provide coordinated system time to be so modestly > executed. it's like an uncorrected PC desktop clock. > > This same issue pops up in many hp/agilent counters, signal generators and > related objects. I have always been puzzled by the decision to make such > marginal instruments that have time/frequency as their primary parameter, > when so little additional effort would have dramatically improved them. I do > get the concept of an external standard reference, but it's a pretty weak > argument for making a $5K generator or counter with poor performance. Just > curious to know everybody's thoughts on this. > > all the best, > walter > > -- > Walter Shawlee 2, President > Sphere Research Corporation > 3394 Sunnyside Rd., West Kelowna, BC > V1Z 2V4 CANADA Phone: (250) 769-1834 > walt...@sphere.bc.ca > WS2: We're all in one boat, no matter how it looks to you. > Love is all you need. (John Lennon) > But, that doesn't mean other things don't come in handy. (WS2) > > ___ > 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] distribution amp question + hp 59309A
I notice that in the distribution amp being discussed at the moment, the BNC output connectors are grounded, and tied to the chassis, which in turn has a grounded emi line filter. this seems like an unavoidable noise pathway to me. I notice that some commercial amps are grounded, but more advanced and transformer coupled units have floating connectors. it makes the most sense to me to be floating, since this frees the return from line noise and spurious, and avoids the significant problem of shifted AC voltages on the return from distant units connected to the amp which are on other ac line circuits. What is the general feeling here about this issue? I confess that if the amp output is transformer coupled, I see exactly zero benefit in a grounded connector as the feed from the amplifier. Also on an unrelated topic, I found an HP 59309A HPIB clock on a forgotten shelf and looked at it, and was surprised to see such a poor primary time standard oscillator inside, just a 1Mhz crystal using a cmos buffer oscillator. It can accept an external standard, but it did feel odd for a device that is meant to provide coordinated system time to be so modestly executed. it's like an uncorrected PC desktop clock. This same issue pops up in many hp/agilent counters, signal generators and related objects. I have always been puzzled by the decision to make such marginal instruments that have time/frequency as their primary parameter, when so little additional effort would have dramatically improved them. I do get the concept of an external standard reference, but it's a pretty weak argument for making a $5K generator or counter with poor performance. Just curious to know everybody's thoughts on this. all the best, walter -- Walter Shawlee 2, President Sphere Research Corporation 3394 Sunnyside Rd., West Kelowna, BC V1Z 2V4 CANADA Phone: (250) 769-1834 walt...@sphere.bc.ca WS2: We're all in one boat, no matter how it looks to you. Love is all you need. (John Lennon) But, that doesn't mean other things don't come in handy. (WS2) ___ 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.