pretty good frequency counter

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Anybody have one of these?

https://www.digikey.com/products/en/test-and-measurement/equipment-specialty/618?k=&pkeyword=&sv=0&pv33534%9388&sf=0&FV=-8%7C618&quantity=&ColumnSort=0&page=1&pageSize25%

I'll have my new 150 MHz Colpitts LC oscillator test board in a week
or so, and I need a modestly good frequency counter for testing.  

We usually buy some high-end Keysight counter/timer for $5K, but I'd
like a cheap, not so exotic counter for my bench.

The LC oscillator has a driven guard, a small ground plane patch,
under the critical nodes. One experiment will be to measure tempco
with that bit grounded, or driven from the emitter of the follower
transistor.

We're still in lockdown, so I'll have to sneak in to build and test
it. Don't tell anybody.





--  

John Larkin         Highland Technology, Inc

Science teaches us to doubt.

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Re: pretty good frequency counter
On Mon, 30 Mar 2020 19:48:18 -0700, snipped-for-privacy@highlandsniptechnology.com
wrote:

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This looks OK.

https://www.amazon.com/Precision-1823A-Universal-Frequency-Function/dp/B005J6LP72/ref=sr_1_6?crid=1NZZF2EY5O2PI&dchild=1&keywords=frequency+counter&qid15%85623243&sprefix=frequency+counter%2Caps%2C206&sr=8-6

The B+K stuff is usually pretty good.




--  

John Larkin         Highland Technology, Inc

Science teaches us to doubt.

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Re: pretty good frequency counter
On Monday, March 30, 2020 at 10:56:18 PM UTC-4, snipped-for-privacy@highlandsniptechnology.com wrote:
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At PPoE we ditched a (cheaper) B&K counter.  The problem for us was  
that it didn't actually give the number of pulses, (or rising edges)
in the time window.  But it did some sort of unknown averaging, so that  
though the average number was correct, there was not enough scatter in the  
count number.  (This was for a random source... counting pmt pulses.)

For what you want it may be fine.  

George H.  
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Re: pretty good frequency counter
On 2020-03-31 10:04, George Herold wrote:
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I use an HP 5316 for lower frequency and an EIP 578 for up to 18 GHz.  
Both cheap on eBay, but don't come with Prime shipping. ;)

Cheers

Phil Hobbs

--  
Dr Philip C D Hobbs
Principal Consultant
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Re: pretty good frequency counter
On Tue, 31 Mar 2020 07:04:50 -0700 (PDT), George Herold

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"Frequency" counters are often AC-coupled with a zero-volts trigger
threshold. They count sine waves fine but are terrible with pulses.
For pulses, you need DC coupling and a settable trigger level.



--  

John Larkin         Highland Technology, Inc

Science teaches us to doubt.

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Re: pretty good frequency counter
On Tuesday, March 31, 2020 at 11:51:33 AM UTC-4, snipped-for-privacy@highlandsniptechnology.com wrote:
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Yeah.  For pulses it's really nice to have a discriminator where you  
can see the input and output to set the threshold.  

George H.  
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Re: pretty good frequency counter
On 1/4/20 2:51 am, snipped-for-privacy@highlandsniptechnology.com wrote:
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I investigated the input stages of a good HP frequency counter, because  
the cheap one I have is not very reliable, and was quite surprised what  
I saw.

There is a huge amount of attenuation first (presumably mostly for  
protection) followed by lots of amplification - three stages of  
differential ECL or something, I think.

I guess the attenuation ensures that the first amplification stage stays  
linear, and the amp provides progressive compression ala a log-amp,  
which (it seems to me) should be much better than just zero-crossing  
detection. I couldn't see any sign of AGC leading up to the (clamped)  
output.

Does that make sense?

Clifford Heath.

Re: pretty good frequency counter
On 2020-03-31 20:43, Clifford Heath wrote:
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Makes perfect sense.  The log amp approach prevents the threshold from  
changing on the scale of the AGC bandwidth--it responds cycle-by-cycle.

The attenuation of course introduces jitter, but you usually don't care  
much in a counter.

Cheers

Phil Hobbs

--  
Dr Philip C D Hobbs
Principal Consultant
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Re: pretty good frequency counter
Am 01.04.20 um 18:35 schrieb Phil Hobbs:

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I have just sold this one, never used in > 4 years:

https://www.ebay.de/itm/202906918438

It can do a lot of stunts that normal counters cannot.


But I will never ever let the Timepod go or the
Stanford SR620.
12 digits in 1 second gate time and ~ 20 ps for time
interval single shot, with the excellent Wenzel time base.

I still have a HP5473, but it is just an array of
intermittent contacts. Takes up valuable rack space.
I have already removed its 10811A time base oscillator.

cheers, Gerhard

Re: pretty good frequency counter
On 2020-04-01 16:06, Gerhard Hoffmann wrote:
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 >
 > It can do a lot of stunts that normal counters cannot.
 >
 >

Yeah, I have a 5372A with the jitter FFT option.  A great instrument for  
looking at PLL settling and so on, but a big pain to set up, so I don't  
use it much either.

Tally-ho

Phil Hobbs

--  
Dr Philip C D Hobbs
Principal Consultant
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Re: pretty good frequency counter
On 2/4/20 3:35 am, Phil Hobbs wrote:
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Oooh, way to go, I understood something tricky, the first time, without  
bumping my head on it :)

The guy who designed these counter modules went through lots of  
iterations to come up with his dual-gate MOSFET setup that still doesn't  
work very well. I found the Chinese forum where he posted (and got  
feedback on) his earlier versions, and read much of it using Google  
Translate.

Someone should clone the design but replace the input with a log-amp...  
What's the best chip for that these days?

Clifford Heath.


Re: pretty good frequency counter
Am 02.04.20 um 04:08 schrieb Clifford Heath:

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Get the service manual of the Stanford SR620 or HP 5473. (not log)

cheers, Gerhard


Re: pretty good frequency counter
wrote:

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What's wrong with a comparator with hysteresis? Why do all that
agc/log stuff?

Front-end options can include attenuation and lowpass filtering and
ac/dc coupling.



--  

John Larkin         Highland Technology, Inc

Science teaches us to doubt.

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Re: pretty good frequency counter
Am 02.04.20 um 06:40 schrieb snipped-for-privacy@highlandsniptechnology.com:
  cheers, Gerhard
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The Stanford and the HP5370 use comparators, not agc/log.
They rely on exact trigger levels. You can even measure rise/fall time.

The HP type number was wrong.

Re: pretty good frequency counter
On 2/4/20 3:55 pm, Gerhard Hoffmann wrote:
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I found the SR620 schematics. After some FET+BJT buffering, the signal  
goes to a AD96685 comparator (ECL differential output), chosen for its  
low delay dispersion, which the data sheet defines as "a measure of the  
difference in propagation delay under differing overdrive conditions."

Only the tiniest amount of hysteresis though: 1/50th of the ECL swing  
(is that 10mV?), with an extra 1pF (about 200R, tau~10%ns). Hysteresis  
is applied from the negative output to the negative input, so it doesn't  
feed into the signal path.

It's a nice thing. Thanks for mentioning it Gerhard.

Clifford Heath.

Re: pretty good frequency counter
wrote:

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We used to use a bunch of 5370s here. It had 20 ps single-shot
resolution and 30 ps RMS jitter for time measurements. The user
interface was wonderful. Somehow it did all its math with a single
8-bit 6800 (not 68K) CPU, which took 2 us to execute a no-op
instruction and had no multiply.

They eventually died, so we use a Keysight box with about the same
specs, 20 ps LSB and better jitter, 15 maybe. But a brain-damaged user
interface.

The 5370 has a custom IC as the trigger discriminator, and if it gets
zapped it can't be replaced, I think.

Does anybody use the SRS box?



--  

John Larkin         Highland Technology, Inc

Science teaches us to doubt.

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Re: pretty good frequency counter
On Wednesday, April 1, 2020 at 9:40:38 PM UTC-7, snipped-for-privacy@highlandsniptechnology.com wrote:
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So it has good performance with high or low impedance inputs, with
or without attenuation, tolerates a variety of buffers/filters/amplifiers
if you want to process the input.

Comparators have high output but also limited slew rates make 'em
a pain at 250 MHz.

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Yep, you can build a front-end for almost anything.   For taking Hsync
from a video signal, I made a self-biased one-transistor amp that
forced the duty cycle but let the input DC level float (because that's
useful for composite video).   It woudn't be optimal, however, for
general purpose use (the forced duty cycle wasn't 50% and would
have caused unnecessary jitter).

Built-to-order front ends just don't belong inside the box, where switches  
and pots are a signal-path nightmare when they get dirty.

Re: pretty good frequency counter
On 2020-04-02 00:40, snipped-for-privacy@highlandsniptechnology.com wrote:
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Clean limiting amps help a lot in messier situations, e.g. radio links  
with fading.  AGC is bad news in a counter because it's slow, so that  
fast fading causes artifacts.

Cascaded limiters do give a logarithmic response, but that's not the  
essential point--clean limiting is the key.

Cheers

Phil Hobbs

--  
Dr Philip C D Hobbs
Principal Consultant
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Re: pretty good frequency counter
Am 02.04.20 um 13:24 schrieb Phil Hobbs:

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<      https://ieeexplore.ieee.org/document/494304         >

Googling for "Oliver Collins zero crossing" delivers pointers to
more work, most of it on the time nuts list.

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Gerhard

Re: pretty good frequency counter
On 2/4/20 3:18 pm, Gerhard Hoffmann wrote:
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It was the HP5386 I was looking at. I'll see if I can find the section  
again.

The comparator approach is fine until you have a mix of signals.
What should a freq counter do if you have a strong fundamental but a  
spurious signal introduces an extra zero-crossing every 3rd or 4th cycle?

The HP5386 just seemed rock-solid, where the Chinese hobby clone tended  
to be just vague. Well duh... but looking at its input schematic I  
couldn't really see why it wasn't better.

Clifford Heath

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