On Tue, 31 Mar 2020 07:04:50 -0700 (PDT), George Herold <ggherold@gmail.com> wrote:>On Monday, March 30, 2020 at 10:56:18 PM UTC-4, jla...@highlandsniptechnology.com wrote: >> On Mon, 30 Mar 2020 19:48:18 -0700, jlarkin@highlandsniptechnology.com >> wrote: >> >> > >> >Anybody have one of these? >> > >> >https://www.digikey.com/products/en/test-and-measurement/equipment-specialty/618?k=&pkeyword=&sv=0&pv335=349388&sf=0&FV=-8%7C618&quantity=&ColumnSort=0&page=1&pageSize=25 >> > >> >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. >> >> 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&qid=1585623243&sprefix=frequency+counter%2Caps%2C206&sr=8-6 >> >> The B+K stuff is usually pretty good. >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."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. Claude Bernard
pretty good frequency counter
Started by ●March 30, 2020
Reply by ●March 31, 20202020-03-31
Reply by ●March 31, 20202020-03-31
On Tuesday, March 31, 2020 at 11:51:33 AM UTC-4, jla...@highlandsniptechnology.com wrote:> On Tue, 31 Mar 2020 07:04:50 -0700 (PDT), George Herold > <ggherold@gmail.com> wrote: > > >On Monday, March 30, 2020 at 10:56:18 PM UTC-4, jla...@highlandsniptechnology.com wrote: > >> On Mon, 30 Mar 2020 19:48:18 -0700, jlarkin@highlandsniptechnology.com > >> wrote: > >> > >> > > >> >Anybody have one of these? > >> > > >> >https://www.digikey.com/products/en/test-and-measurement/equipment-specialty/618?k=&pkeyword=&sv=0&pv335=349388&sf=0&FV=-8%7C618&quantity=&ColumnSort=0&page=1&pageSize=25 > >> > > >> >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. > >> > >> 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&qid=1585623243&sprefix=frequency+counter%2Caps%2C206&sr=8-6 > >> > >> The B+K stuff is usually pretty good. > >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. > > "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.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.> > > > -- > > John Larkin Highland Technology, Inc > > Science teaches us to doubt. > > Claude Bernard
Reply by ●March 31, 20202020-03-31
On 1/4/20 2:51 am, jlarkin@highlandsniptechnology.com wrote:> On Tue, 31 Mar 2020 07:04:50 -0700 (PDT), George Herold > <ggherold@gmail.com> wrote: >>> The B+K stuff is usually pretty good. >> 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. > > "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.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.
Reply by ●March 31, 20202020-03-31
On 31/3/20 8:29 pm, Pimpom wrote:> On 3/31/2020 8:18 AM, jlarkin@highlandsniptechnology.com wrote: >> >> Anybody have one of these? >> >> https://www.digikey.com/products/en/test-and-measurement/equipment-specialty/618?k=&pkeyword=&sv=0&pv335=349388&sf=0&FV=-8%7C618&quantity=&ColumnSort=0&page=1&pageSize=25 >> >> >> 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. >> >> > *Not* offered as a viable alternative to what you're looking at, but has > anybody fooled around with one of these Chinese 2.4GHz 8-digit modules? > - https://tinyurl.com/qv4tfun > > I got one last year with the intention of building a usable counter by > adding input stages, power supply, etc., but so far have never got > around to playing with it.Yes, I have two, one mounted in a little case with a USB power pack. The module is a clone (from multiple suppliers) of a *hobbyist* project, and it shows. The inputs are not very sensitive, and the zero-crossing detector is not very reliable. If you have a clean signal with adequate and fairly constant strength you can get a stable reading, but otherwise the readout will wander around or just lie to you. The 2.4GHz and 60MHz inputs are both wired to the same input. They work better if you separate the two inputs. That's a little awkward, because you have to cut and paste a PCB trace that's sandwiched (near the edge) under the LED. They would be just fine with a better input circuit. Buy one with a TCXO. Clifford Heath.
Reply by ●April 1, 20202020-04-01
On 2020-03-31 20:43, Clifford Heath wrote:> On 1/4/20 2:51 am, jlarkin@highlandsniptechnology.com wrote: >> On Tue, 31 Mar 2020 07:04:50 -0700 (PDT), George Herold >> <ggherold@gmail.com> wrote: >>>> The B+K stuff is usually pretty good. >>> 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. >> >> "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. > > 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.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 ElectroOptical Innovations LLC / Hobbs ElectroOptics Optics, Electro-optics, Photonics, Analog Electronics Briarcliff Manor NY 10510 http://electrooptical.net http://hobbs-eo.com
Reply by ●April 1, 20202020-04-01
On Monday, March 30, 2020 at 10:48:28 PM UTC-4, jla...@highlandsniptechnology.com wrote:> Anybody have one of these? > > https://www.digikey.com/products/en/test-and-measurement/equipment-specialty/618?k=&pkeyword=&sv=0&pv335=349388&sf=0&FV=-8%7C618&quantity=&ColumnSort=0&page=1&pageSize=25 > > 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. > > Claude BernardDoes your oscilloscope have a counter? I do not hink I have actually ever used a frequency counter. Between having a spectrum analyzer and O-scopes that can measure frequency I have never needed one.
Reply by ●April 1, 20202020-04-01
Am 01.04.20 um 18:35 schrieb Phil Hobbs:> The attenuation of course introduces jitter, but you usually don't care > much in a counter.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
Reply by ●April 1, 20202020-04-01
On 2020-04-01 16:06, Gerhard Hoffmann wrote:> Am 01.04.20 um 18:35 schrieb Phil Hobbs: > >> The attenuation of course introduces jitter, but you usually don't care >> much in a counter. > > 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. > > 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 ElectroOptical Innovations LLC / Hobbs ElectroOptics Optics, Electro-optics, Photonics, Analog Electronics Briarcliff Manor NY 10510 http://electrooptical.net http://hobbs-eo.com
Reply by ●April 1, 20202020-04-01
On 2/4/20 3:35 am, Phil Hobbs wrote:> On 2020-03-31 20:43, Clifford Heath wrote: >> On 1/4/20 2:51 am, jlarkin@highlandsniptechnology.com wrote: >>> On Tue, 31 Mar 2020 07:04:50 -0700 (PDT), George Herold >>> <ggherold@gmail.com> wrote: >>>>> The B+K stuff is usually pretty good. >>>> 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. >>> >>> "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. >> >> 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. > > Makes perfect sense. The log amp approach prevents the threshold from > changing on the scale of the AGC bandwidth--it responds cycle-by-cycle.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.
Reply by ●April 2, 20202020-04-02
Am 02.04.20 um 04:08 schrieb Clifford Heath:> 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?Get the service manual of the Stanford SR620 or HP 5473. (not log) cheers, Gerhard
