Re: [time-nuts] HP 5335A Question

[Jeremy Elson]

I think single shot is only 9 digits. Press "mean" on the left side to get
a 100 sample average that gives you more digits.

On Oct 31, 2017 1:01 PM, "Richard Mogford"  wrote:

> I have an HP 5335A and I am measuring the output of a Suzler 2.5.  I have
> a GPSDO 10 MHz input into the back of the 5335A.
>
> There is mention in the manual that the counter can display 11 or 12
> digits (in addition to the two Exponent digits).  I presently have it
> displaying nine digits.
>
> Does anyone have one of these and could help me figure out how to get 12
> digits displayed?  The manual is not very helpful here.
>
> Richard
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Re: [time-nuts] Distribution divider/amplifier for 10MHz GPSDO

[Jeremy Elson]

On Mon, Oct 23, 2017 at 1:49 PM, Bob Bownes  wrote:

> 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.
>

I'm confused: I thought most inputs were relatively high impedance.

The manual for the 5335a specifies its external timebase input as being
1000Ω
(http://www.dennlec.com/images/manuals/hp-5335a-op-manual.pdf). Maybe not
"high",
but it's certainly not 50.
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Re: [time-nuts] Distribution divider/amplifier for 10MHz GPSDO

[Jeremy Elson]

Is there an easy way to measure the per-device load, or do you typically
just go by whatever the datasheet says?

I suppose I could just hook everything up and then check the amplitude of
the signal at the far end.

On Mon, Oct 23, 2017 at 1:43 PM, John Ackermann N8UR <j...@febo.com> wrote:

> To some extent, it depends on the load presented by each device.  The "EXT
> REF" input on many pieces of test equipment is fairly high impedance (maybe
> 10k?) and you can drive several of those with a single output, putting a 50
> ohm load at the end of the line to provide a reasonable termination.*  I
> seem to recall that three HP boxes worked nicely off one line, but when I
> added a fourth things got flaky.
>
> But if any of the EXT REF are low-z inputs, that won't work so well.
>
> FWIW, Spectracom had a distribution system (8140 series) that had
> amplified "tap" boxes that were daisy-chained together on a single coax
> run.  The driver put 12 volts DC on the cable along with 10 MHz, and that
> powered the taps.  You could put several taps on a single line.  I once
> measured the phase noise of the system and while it wasn't up to a really
> good distribution amplifier, it was perfectly adequate for normal RF
> testing.
>
> John
>
> * Mismatch causes reflections, which can screw up square wave edges or
> sine wave zero-crossings, increasing jitter.  SWR is usually a bigger issue
> for RF distribution than amplitude loss.
> 
>
> On 10/23/2017 01:49 PM, Jeremy Elson 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 us

Re: [time-nuts] Distribution divider/amplifier for 10MHz GPSDO

[Jeremy Elson]

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  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  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.