Re: [time-nuts] distribution amp question + hp 59309A

[John Miles]

> 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 measurement.  

-- john, KE5FX
Miles Design LLC


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Re: [time-nuts] distribution amp question + hp 59309A

[Bob Stewart]

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 <walt...@sphere.bc.ca>
 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)

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Re: [time-nuts] distribution amp question + hp 59309A

[Tom Van Baak]

> 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

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Re: [time-nuts] distribution amp question + hp 59309A

[Bob Camp]

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)
> 
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> time-nuts mailing list -- time-nuts@febo.com
> To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
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[time-nuts] distribution amp question + hp 59309A

[walter shawlee 2]

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)

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