Frequency counter. Do you really need one? - Page 1
Forum section: electronics / testgear

author: Unknown
author_rank: Unknown
timestamp: June 07, 2013, 05:12:27 pm
content: I am saking myself, why should you buy FC if every dig. scope nowdays have one build in.Yes. Thats a question.

author: nctnico
author_rank: Super Contributor
timestamp: June 07, 2013, 05:22:34 pm
content: Frequency counters are often more accurate. I have an old HP5334A and I have used it about 10 times over the past 10 years but when I use it, it serves its purpose well.

author: Lightages
author_rank: Unknown
timestamp: June 07, 2013, 05:22:55 pm
content: The need for a frequency counter depends on the individual's interest or need. If you need to measure frequencies less than 20-40MHz, there are many multimeters that have this capacity to measure within their display limits and accuracy.If you need to measure higher frequencies or have higher accuracy or more resolution, then yes there is a need for a dedicated meter.In other words, if you don't know if you need a dedicated frequency counter, then you do not need one.

author: ve7xen
author_rank: Super Contributor
timestamp: June 07, 2013, 05:33:27 pm
content: A 'universal' counter can also measure many other timing parameters of a signal that may be awkward or inaccurate to measure on a scope. For example A->B interval, A/B frequency ratio. It will also have adjustable trigger thresholds and usually the option of using an external gate and time reference. And of course much higher resolution.And it doesn't require any 'scope channel(s).

author: hgg
author_rank: Frequent Contributor
timestamp: June 07, 2013, 05:36:32 pm
content: Hi, by the way, do you know if you can use a frequency counter like the one below (RF)http://www.409shop.com/409shop_product.php?id=104535and convert it somehowso that you can measure the frequency of signals with higher voltages peak to peak?e.g. 10V peak to peak.

author: dfmischler
author_rank: Frequent Contributor
timestamp: June 07, 2013, 06:07:27 pm
content: Quote from: nctnico on June 07, 2013, 05:22:34 pmI have an HP 5315B and it's just about the same deal for me. At one time I worked for a company that did a bunch of microwave stuff and they had guys with some serious counters and a cesium frequency standard to calibrate them to. They needed their counters every day.

author: jpb
author_rank: Super Contributor
timestamp: June 07, 2013, 06:10:05 pm
content: I've been wondering about this myself. Frequency counters, compared to other equipment, are quite cheap and the ones provided with scopes are limited.For example, the one on my scope is 6 digits (many are just 5) and is limited by the bandwidth of the scope (350MHz). It is also confined to the trigger channel, though I know other scopes allow you to choose. It is also tied to the accuracy of the scope, there is no external 10MHz input. For a typical scope this may be only a few 10s of ppm. I tested mine with a GPS 1pps signal and it measured it as 999.997 mHz so was within 3 ppm which I was pleased about (my scope timebase should be within 10ppm).I wouldn't buy an 7 or 8 digit counter as that wouldn't be sufficient a step up, but a 9 or 10 digit counter allows you to check frequencies very accurately if you can make use of an external GPS or Rubidium source. (A counter that doesn't allow the use of an external frequency standard might only be accurate to 1ppm so is the same order as the scope's counter.)I don't really need such accuracy as I'm not a radio enthusiast, but I'd like to have it. And there are lots of experiments I might do which would be helped by a counter. It also provides a means of checking the timing aspects of other equipment (such as a scope).

author: G0HZU
author_rank: Super Contributor
timestamp: June 07, 2013, 09:05:08 pm
content: For servicing of ham/CB radio gear a decent counter is an essential piece of gear to have on the bench because this type of equipment tends to use numerous crystal oscillators that each need to be adjusted for accuracy using a counter that should typically offer 0.5ppm accuracy.When I was a student I used to use an old Marconi TF2430 counter for stuff like this. Its very basic internal reference is typically within 2Hz of 10MHz after a 30 minute warmup which isn't bad.However, if you don't need to service radio gear then I think a decent counter probably isn't needed by many people.I also have a couple of reciprocal counter/timers from Philips and Anritsu and these are very useful for measuring lower frequencies with very high accuracy and very fast update rate and also they can time events very accurately. The old TF2430 can't really do this.Note that you can buy a decent counter on ebay for very little money if you are patient. I would avoid the cheapo chinese counters on ebay and instead look for the usual vintage makes such as Racal or Philips and always choose one with an external 10MHz option.

author: vk6zgo
author_rank: Super Contributor
timestamp: June 08, 2013, 05:51:05 am
content: I have a cheapo Chinese counter---I couldn't pass it up for $A99 at the local Hamfest!Apart from being a bit flimsy,it is good enough for most work I will do,& probably better than some of the very early RACALs & such!It certainly counts a lot higher in frequency.My Tek 7613 has a vertical amp output on the back,so if I stick the FC on that output,I can accurately determine the frequency of whatever signal I am probing.This is useful when checking through Ham Transcievers of which many have multiple oscillator circuits.Obviously,I could do the same with a DSO with a built in frequency display,but from what I have seen,they have quite limited resolution.

author: EEVblog
author_rank: Unknown
timestamp: June 08, 2013, 06:19:41 am
content: Quote from: Lightages on June 07, 2013, 05:22:55 pmI concur. Although when you do need a good one, there is no substitute.Some counters have meany features, like actual counting (input pulses) and other stuff which can be handy.

author: G0HZU
author_rank: Super Contributor
timestamp: June 08, 2013, 10:59:04 am
content: I still think there are better bargains for the patient purchaser if you buy a used counter.eg for £65 I bought a 3GHz Anritsu MF1603A counter on ebay. It came with all the top options including the option 3 oven that has 0.005ppm stability over temperature and 0.0005ppm per day. Also GPIB to allow logging of measurements remotely.It's probably 17 years old but it was one of the finest (and fastest) counters on the planet in its day. eg it can display 10MHz to 0.1Hz with several updates a second or it can display 11 digits on the slowest gate time. No $99 chinese counter on ebay can compete with thatIt's outclassed by the best of today's counters from Agilent or Tek etc but you can pick them up very cheaply if you are patient because Anritsu gear tends to get overlooked in favour of HP/Agilent yet the build quality of the japanese counter is arguably better.

author: vk6zgo
author_rank: Super Contributor
timestamp: June 09, 2013, 04:26:19 am
content: Quote from: G0HZU on June 08, 2013, 10:59:04 amAgreed,but my $99 counter was handed to me at a Hamfest brand new----no ebay,or postage cost involved.As it is,I now have a counter,whereas I would still be looking for one,if I went the secondhand route.I am a great booster of Anritsu,though,having used their Spectrum Analysers,which are extremely well made.

author: manticore00
author_rank: Regular Contributor
timestamp: June 09, 2013, 05:28:32 am
content: One exception to cheap(both in price and quality) Chinese imports is probably the VC3165. I wish it had an external timebase input but otherwise, based off of my own experience, and the reviews I read before I bought one, I'm quite impressed given its price point.

author: alex77
author_rank: Contributor
timestamp: June 09, 2013, 01:33:52 pm
content: Quote from: manticore00 on June 09, 2013, 05:28:32 amI have bought one a few months ago mainly for measuring high frequencies that my 100mhz siglent can´t reach. I agree with you, I think that its a great tool for the price.

author: bingo600
author_rank: Super Contributor
timestamp: June 10, 2013, 08:52:06 am
content: I got a cheap China one with a lousy Ref-Xtal , but i was lucky as it used a 13Mhz Reference.And there is a cheap 26Mhz docxo on the *BayGet the docxo , and an AC74. And you have a superstable 13Mhz ref.https://www.eevblog.com/forum/testgear/zhaoxin-hc-f2700l-%28atten-f2700c%29-frequency-counter-un-stable-count/msg205383/?topicseen#msg205383/Bingo

author: Tepe
author_rank: Frequent Contributor
timestamp: June 10, 2013, 02:10:57 pm
content: Quote from: manticore00 on June 09, 2013, 05:28:32 amIs it possible to add such an input so you could use an external 10 MHz signal?

author: Unknown
author_rank: Unknown
timestamp: June 10, 2013, 07:11:36 pm
content: I'm fortunate enough to have Two one is frequency counter, from 5 Hz to 600 Mhz, the other is a universal Counter timer that goes from 0.1 hz to 10 Mhz, both used for my Amateur Radio the !0 Mhz one, is mainly used with my HF transceiver which doesn't have digital readout .

author: bingo600
author_rank: Super Contributor
timestamp: June 10, 2013, 07:33:20 pm
content: I have (by accident) actually used one of my counters to debug some microcontroller programs.I had a 10ms timer irq that i was watching (toggling a pin) , but noticed that once in a while the frequency went off ....I later found out i (once in a while) had a stack/heap collision , and the "counter told me about it" :-)I have lots of them (but i'm addicted ... time-nut)The China Thingy with the 26Mhz OCXOThese are driven by 10Mhz from my Tbolt GPSDO.PM6671PM6674 - TCXOHP5384aRacalDana 1991And the Ref' onePM6680BI actually use the HP384a a lot , for plain measurements.It's so easy to set up , and is quite accurate. (with Ext 10Mhz)/Bingo

author: PA4TIM
author_rank: Super Contributor
timestamp: June 10, 2013, 08:24:27 pm
content: I have several including a few frequency references. My first one was a kit with a pic that went up to 55 MHz. the rest varies from two 60 MHz nixie counters upto a 18 GHz counter. I builded a 1GHz counter last year for use in a signal generator but that became to big and 1 GHz was not enogh so now I made a very simple but very acurate one. Nothing more as a MB506 prescaler, a fet, and a 4013 to it get divided by 512. Then a 4060 with watch Xtal and a 4013 to get 1 Hz as gate. An Arduino programmed ATmega328 does the rest. No calibration needed. It was only 3 Hz high at 512MHz (so in real 3 Hz devided by 512) Did not bother to get is better. But this only reads frequency. Commercial versions can do a lot more. Attenuation, trigger, gatingtime, periode, frequency, delta two channels and some a lot more.But the answer to the question:No, you do not need a counter because if you did, you would have know.

author: bingo600
author_rank: Super Contributor
timestamp: June 10, 2013, 09:04:16 pm
content: Quote from: PA4TIM on June 10, 2013, 08:24:27 pmThat's quite impressive as i don't expect you to have the watch Xtal@BodytemperatureOhh and i do agree , if you really need a counter ... You know .../Bingo

author: PA4TIM
author_rank: Super Contributor
timestamp: June 10, 2013, 09:28:56 pm
content: The 32kHz is divided back to 1 Hz so the Xtal ppm/C does not matter muchI played around with N0P caps and a very small ceramic trimmer to get it adjusted at 1000.0000 ms after the devider (a whole turn is about 500ns adjustment) but later I tested the effect and it does not matter. The fault is below 1 Hz and my resolution stops there. The final version reads only with 1 kHz resolution what more then enough is for my purpose (sweep/signal generator upto 2 Ghz)http://www.pa4tim.nl/?p=2662The schamatics are not yet upto date. I will do that when he is ready. The arduino software is there too, but there is a small bug in it. Not a big thing, i forgot to uncomment a line that closes the string with a zero. I will change that toO.The meter also measures power

author: alank2
author_rank: Super Contributor
timestamp: June 10, 2013, 11:39:21 pm
content: This really is a great ocxo:http://www.ebay.com/itm/Pletronics-26MHz-OCXO-Miniature-Oscillator-NEW-/130718871982?pt=LH_DefaultDomain_0&hash=item1e6f73b1aeI use it in my AVR based reciprocal frequency counter. It is still on a breadboard missing a decent input stage, but works great...

author: Marc M.
author_rank: Regular Contributor
timestamp: June 27, 2013, 08:37:36 pm
content: Quote from: Tepe on June 10, 2013, 02:10:57 pmIf the counter uses a 10MHz internal clock then yes you can. You'll need to add some buffering/impedance matching and there may be some phase issues but for most users they won't matter. I run my 30+ year old B&K 1801 counter off a rubidium standard piped into its xtal oscillator. For most stuff I don't need more than 1Hz resolution and if I slip and contact high voltage, it's less than $1.00 US to repair the front end. Prior to modification it was all over the place, varying in the 10's of Hz and would never stabilize. I have a HP5334a (also running off the rubidium standard) I use for critical or higher frequency measurements (1801 is about 60MHz vs 5334a is 1.3GHz).Marc -

author: alank2
author_rank: Super Contributor
timestamp: June 28, 2013, 12:47:53 am
content: I use mine all the time for calibrating things. It uses one of the Pletronics 26MHz OCXO's from eBay (seen in the lower right). It is based on an ATMEGA328. It uses a MC74AC4040N to handle frequencies from 0-100MHz and a MAX7219 for the LED display. The picture shows an 80 MHz oscillator. It has min/max/avg and is a reciprocal style counter.

author: jpb
author_rank: Super Contributor
timestamp: June 28, 2013, 09:48:34 am
content: I've just bought an ex-demo TTi TF930. It is a reciprocal counter with 10 digits and, importantly for me, goes down to 0.01Hz - most counters I've seen on e-bay start at around 10Hz. It also has no dead zone in counting (i.e. the counters aren't stopped when measurements are taken). It also has remote control via USB.The reason I wanted the lower frequency was to allow me to connect a GPS 1pps whilst at the same time connecting an OCXO to the external reference. I can then adjust the external reference to get exactly 1Hz to 10 figures. A lazy approach to a GPS disciplined oscillator.So far I'm happy with it. With the internal oscillator it reads 1.000 000 020Hz and it is very steady except when I regularly lose the satellites (I've not yet set up my outdoor antenna).12 digits would be nice but the TF930 seems a good compromise between cheap 8 digit counters (which I felt wouldn't add much to the 6 digit one on my scope) and nice Agilent ones which even on their e-bay store are over £1000 (the TF930 as ex-demo cost me just under £200 ex VAT). I'd been looking on e-bay for a while and most 9 or more digit counters were quite old, didn't go down below about 10Hz or above a couple of hundred MHz and often were in the region of £140 to £200 anyway. And buying directly from TTi I get a years warranty and I like to support local (to me) companies though my spending budget will not make much difference to their turn-over!The only negative (so far) is that the display is not backlit so needs good light, but this is partly to keep the power requirement down allowing the counter to be run from its internal rechargeable batteries or from the USB connector.

author: ben_r_
author_rank: Frequent Contributor
timestamp: June 28, 2013, 04:25:32 pm
content: I guess Im a little confused on the matter, but whats the difference between a dedicated frequency counter and the frequency measurement setting in a DMM? Is it just that a dedicated unit usually has a higher and/or lower range? Is a dedicated more accurate?

author: PA4TIM
author_rank: Super Contributor
timestamp: June 28, 2013, 04:57:32 pm
content: The frequency measurement capabilitys of a DMM are very limitted.Most are not very sensitive, no triggering options and low resolution.Most couters are 8 or more digits and even 40 year old models go to 50 or 60 MHz. ( my old HP and Philips both with nixies go to 60 MHz, my old LED Tek is 100 MHz, my Philips is 1 GHz, i have a 17 GHz counter and some homebuild ( 50 MHz and 2,5GHz)It is very easy to build a counter. You need a uP, 2X16 digit LCD, one or two logic ICs and a prescaler and you can measure over 1 GHz.But a commercial one can do much more. External reference connection, period measurement, event counting , frequency, difference between two signals, attenuators, filters. Some can even measure things like rpm.triggerlevel and filters is often needed is signals are not very clean.

author: ben_r_
author_rank: Frequent Contributor
timestamp: June 28, 2013, 05:22:18 pm
content: Quote from: PA4TIM on June 28, 2013, 04:57:32 pmI see. Makes sense. Ive had my eye on picking up a used Agilent 53181A for a bit now. Perhaps Ill grab one the next time I see a good deal. Be nice just to have one around. Thanks.

author: saturation
author_rank: Super Contributor
timestamp: June 28, 2013, 07:23:41 pm
content: A quality frequency counter provides high accuracy, in ppb. Whatever feature it has for measurements e.g. period, frequency, rise time, fall time, etc., can also be made with lower cost counters, or even your DSO, but not with the same accuracy. A good counter will have at least 10 digits of resolution or greater, to give you 1 ppb accuracy, thus it can resolve a 10 MHz signal down to 0.01Hz.< $200 ones go to about 2-3 Ghz easily, accuracy in ppm, stable to 8 digits. You can get many of these handheld.Why you need ppb accuracy is another story!but ppb separates costly from cheaper counters.

author: G0HZU
author_rank: Super Contributor
timestamp: June 28, 2013, 08:44:06 pm
content: I would say a modern quality counter will also have a much faster refresh rate than those TTi counters. The TTI 930 bench meter looks like it needs to wait 100 seconds (!) to display to 10 digits. That is very slow. These days a decent reciprocal counter should be at least 100 times faster than that when displaying 10 digits.QuoteIn my case I need to be able to measure/set the 10MHz ovens in my test gear to a fairly decent accuracy. Eg the spec when aligning the 10MHz reference on one of my analysers is to set it to +/-0.001Hz at 10MHz after a 48hour warm up. Obviously I don't try for that degree of accuracy but I do like to keep the various ovens within 0.1Hz of 10MHz. I try to keep the error below 0.05Hz and some of them manage <0.02Hz error over several months.This may seem OTT to many, but some of the test gear runs up at many GHz so the errors soon mount up especially when mixing two microwave signals down to baseband. eg a 1Hz error at 10MHz means a 1kHz error at 10GHz.

author: dmmartindale
author_rank: Contributor
timestamp: February 12, 2015, 03:43:11 am
content: Quote from: G0HZU on June 28, 2013, 08:44:06 pmActually, the TTi provides pretty good resolution for a reciprocal counter. Reciprocal counters measure for a number of complete input signal cycles, but that period includes one incomplete timebase cycle at the start and another at the end of the gate time. If the timebase frequency is 10 MHz and the gate time is 1 s, then the measured period is always going to be about 10 million cycles plus or minus 1 cycle - and that's good for only 7 digits of resolution. (B&K 1823A or 1856D are examples). The TTI multiplies the 10 MHz timebase up to 50 MHz for counting, and so it manages to do 8 digits of resolution (+- 2 counts in the LSB) in 1 second. But there is still 20 ns uncertainty in the length of the measuring period, and thus 2 parts in 10^8 uncertainty in the frequency.You're probably thinking of counters which also have analog interpolator circuits that measure the length of the first and last incomplete cycles of the timebase when the gate opens and closes. This can provide much better precision for the start and end time, and thus several extra digits of output in 1 second gate time. If you see a counter providing 10 or 12 digits/second, it is likely an interpolating counter - not a reciprocal counter with a really high timebase frequency. But interpolating counters are still rather expensive new.And the TTi does have one rather interesting feature: It is a "capture and continue" counter, where the counting registers are saved but not reset each time they are sampled. With no "dead time" or lost cycles, the counter can provide an update rate faster than the gate time. With a 10 s gate time, the display updates every second, but each value is based on measurements 10 seconds apart using a "rolling window" on saved measurments. With a 100 s gate time, the display updates every 2 seconds, while each value is based on the most recent 100 seconds of measurement.- Dave

author: babysitter
author_rank: Frequent Contributor
timestamp: February 12, 2015, 05:26:24 am
content: Shameless reusing of some advice I gave before regarding counter selection, edited a bit to solve the dependency of what was going on in that thread:Quote from: myself on January 10, 2015, 01:41:24 pm

author: TunerSandwich
author_rank: Frequent Contributor
timestamp: February 12, 2015, 07:52:41 am
content: One could use a frequency counter to verify that their scope count was accurate. If you can afford it I don't see how it could hurt. If you work on designs that use timing critical components....it can never hurt to get a second opinion.

author: dom0
author_rank: Super Contributor
timestamp: February 12, 2015, 02:42:59 pm
content: IF one wants to buy / build a frequency counter here's what I would watch for:- No counters with stupid 10 MHz references. They're slooooow. Remember that in a "modern" reciprocal counter measurement speed is the log10 of the greater frequency (ref / input). E.g. a stupid reciprocal counter with a 10 MHz reference measures a 100 kHz only with 7 digits per second, i.e. 6 digits if you want 10 updates per second.- Many cheap counters are build like this. Most DIY counters do it like this. Mine uses a 20 MHz ref which is only marginally better. Next one (if I ever come around to design it) will probably use some FPGA or CPLD and a synthesized/PLL'd poly-phase reference ; much faster.- Better counters still of course use a standard 10 MHz reference, but generate a much higher internal reference clock from it. See next item in the list...- Good older counters are sometimes still good. For example the HP 5345A (from the early seventies, as seen inDays Of Future Past) uses a 500 MHz reference (check out their schematics - they use resonance amplifiers locked on harmonics of the 10 MHz reference clock, absolutely amazing circuit technique!) and thus achieves something like 8.7 digits/second.- Analog front end matters. For many uses a counter which can't measure low level (<100 mVrms) signals is simply useless.- You want a high-Z input good for at least 50 MHz- You want adjustable trigger levels- You probably want a front end which can trigger on narrow pulses- Consider counters with interpolation, they don't have the usual +-1 gate uncertainty and interpolation usually gives 1 digit/second more meas speed- For some uses a TIA is to much more useful. TIAs are, however, much more expensive and rare and you really wouldn't ask if you didn't need it(but if you do, consider Yokogawa TIAs, they're much cheaper than the HP ones and have excellent performance, just like the HP ones — also, for a DIY TIA you really want a top-notch analog front end with the least amount of trigger uncertainty (i.e. jitter) you can get)- Oh, there's also Spectracom/Pendulum. But chances are that if you find someone selling one of their counters the seller knows what they are really worth ("Worth their weight in gold" - literally). Pendulum split from Philips/Fluke and all their stuff is top-notch.

author: G0HZU
author_rank: Super Contributor
timestamp: February 13, 2015, 12:22:36 am
content: QuoteYes, I'm thinking along the lines of my old Anritsu counter. It's still described by Anritsu as a reciprocal counter but they use reciprocal /vernier techniques to enhance the resolution. It works really well for my needs at 10 digits per second although modern counters outclass it. I assume it uses digital interpolation rather than analogue but I've never really studied its operation due to the lack of a manual...TBH I'm not really that 'into' measuring frequency very accurately. I only bought the Anritsu because it was so cheap on ebay. I saw it with a few minutes left on the auction and put in a low bid and won it for just over £60.Otherwise, I think I would have (happily) just carried on using a scope and my homemade offair standard to align my various 10MHz OCXOs to be in reasonable agreement

author: Lightages
author_rank: Unknown
timestamp: February 13, 2015, 12:36:19 am
content: if you want a frequency counter, cheap, and accurate, then there seems to be a good option. I stuck my neck out and purchased a Victor VC3165. Before I did I checked for reviews and opinions on it. Places like eham.net and some other places had good opinions on it. For around $100 it is a good deal. If you buy one and it arrives in one piece then you get an oven stabilized clock referenced counter that seems to cover most people's needs. The plastics used in the case are really bad and some people have reported receiving something that sounds like everything is trashed inside because the transformer broke loose. Mine arrived in fairly good shape and it seems to be accurate. I would buy one again.

author: Lightages
author_rank: Unknown
timestamp: May 08, 2015, 09:53:56 pm
content: The decision is easy. If you need to measure frequencies over 120MHz, forget the PM6671. If you want a better instrument with more options but don't need over 120MHz, then the PM6671.In reality, most people have some frequency measurement capability with their multimeters. If you have an oscilloscope then you have even a higher range. The VC3165 is probably the best bet for most people IMHO.

author: Smith
author_rank: Frequent Contributor
timestamp: May 09, 2015, 05:46:30 am
content: I once tried to calibrate an old function generator with a 1GHz scope without HW counter. Could only take a bit acurate frequency measurements at high sample memory, so friggin slow. Drove me crazy. Took out an old HP counter, and was done in no time.Unless you have a brand new scope with HW counter a seperate counter is much cheaper than replace your scope. Probably more accurate too.

author: VK5RC
author_rank: Unknown
timestamp: May 09, 2015, 06:12:09 am
content: Some of the good 'interval timer then invert' type frequency counters have no down time between timing cycles improving accuracy considerably, esp if you are getting all time-nut - ish and doing Allan deviation etc.Once you compare the result between a reasonable dso and a good counter locked to a trusted time base, you become pretty sceptical about some dso and also dmm counters.

author: nowlan
author_rank: Frequent Contributor
timestamp: May 09, 2015, 06:23:13 am
content: This guy does a review of some chinese frequency counter thing. Seems to perform very well. Not sure when I'd need out outside of RF.

author: dom0
author_rank: Super Contributor
timestamp: May 09, 2015, 08:45:33 am
content: Quote from: VK5RC on May 09, 2015, 06:12:09 amHow is that? They should have at least one cycle of either reference or signal dead time. The only technology I am aware of that can do measurements with no dead time at all is continuous time stamping.

author: VK5RC
author_rank: Unknown
timestamp: May 09, 2015, 12:09:56 pm
content: If I understand it correctly the HP 5371 was one of the earliest to do this, it doesn't count cycles over a defined time, it times a defined number of cycles, then does the maths to calculate frequency, but can do this while the next timing interval is progressing. See HP Journal below.http://www.keysight.com/en/pd-1000001409%3Aepsg%3Apro-pn-5371A/frequency-and-time-interval-analyzer?cc=US&lc=enghttp://www.hpl.hp.com/hpjournal/pdfs/IssuePDFs/1989-02.pdfAgain if I understand correctly, most good ~ HF range frequency counters e.g. Racal, HP etc (really inverted interval measurement) mostly use this technique since then (~1989).

author: dom0
author_rank: Super Contributor
timestamp: May 09, 2015, 12:18:28 pm
content: That techniqueiscontinuous time stamping.http://www.spectracomcorp.com/Desktopmodules/Bring2Mind/DMX/Download.aspx?EntryId=446&PortalId=0

author: VK5RC
author_rank: Unknown
timestamp: May 09, 2015, 12:36:07 pm
content: Ah Not heard/noted that term before, thanks for the reference, the HP 5371 (1989+) appears bit earlier than the article suggests "2000-ies".I keep learning , ThanksRobert

author: rdl
author_rank: Super Contributor
timestamp: May 09, 2015, 08:49:35 pm
content: Quote from: nowlan on May 09, 2015, 06:23:13 amThere's another thread here somewhere about those frequency counter modules. That one doesn't look bad at all. I guess I'll have to buy one. I haven't been able to find a decent deal on ebay for something used that I like (don't want to spend more than $150 or so).Also, thanks for that youtube link. I hadn't seen that guy's videos before. I've watched a few more of them and they are nicely done and very informative.

author: HarryDoPECC
author_rank: Regular Contributor
timestamp: February 23, 2020, 01:42:30 am
content: Some additional information for this necro-thread.Reciprocal method and interpolation go back further - HP introduced both of these with the 5360A of 1970. Well worth a read of the May69 and Dec70 HP Journals for a detailed description. HP5323A and 5326A offered same technologies for those who did not have the entry price of well over 50k (todays $) for a 5360A.All of these were pre-microprocessor, the maths was implemented in discrete TTL and the digital front end had bleeding edge ECL for maximim speed. I'm wrestling with the 500+ ICs of a 5360A whenever I feel like a challenge....