freq counters. Why would you have need to use one. - Page 1
Forum section: electronics / general

author: Ed.Kloonk
author_rank: Super Contributor
timestamp: May 27, 2014, 09:39:07 am
content: Back in the '90's I bought a silicon chip 50mhz Frequency counter. Only for fun really as I never had a actual use for it as my CRO could be used for anything I was tinkering about with. Just wanted to understand the path and design of it's analog - digital - display circuit.Years later, I wonder why a general purpose counter was needed when most of the signals you are probing are random logic not oscillating aren't they?I understand the obvious practical use for a counter that reads 12 digits. But for everything else, how useful is/was a freq counter to you?

author: jeremy
author_rank: Super Contributor
timestamp: May 27, 2014, 09:46:59 am
content: Ok, so you have a 2.4GHz synth in a circuit that isn't working. How do you know it is on? How do you know it is 2.4G? I think they are useful in the same way that cheap multimeters are useful: for when I don't really care about the difference between 3.34V and 3.33V, just that it is ~3.3V

author: GK
author_rank: Super Contributor
timestamp: May 27, 2014, 10:09:07 am
content: A frequency counter is invaluable for any kind of serious radio frequency repair/calibration and design work. However these days everyone has DSO's and synthesized signal generators, so a frequency counter isn't as needed on the test bench as it used to be. Last time I used my fancy, modern frequency "meter" was to check the calibration of my somewhat older ones:

author: jpb
author_rank: Super Contributor
timestamp: May 27, 2014, 10:41:58 am
content: For frequency counting you only need one if high accuracy is required generally as most scopes have a 5 or 6 digit counter.Other uses are perhaps more appropriate to physics than electronics such as counting events at high speed and doing accurate interval timing and gathering statistics on it.I would guess for Ham radio they are important as you don't want to stray out of band.I'm working on a GPSDO at the moment and I find my 10 digit TTi 930 is not accurate enough for doing things like measuring the jitter on the 1pps from the GPS so I have to do it on the scope with the aid of a 10MHz OCXO but it is very tedious. I'd thought of getting a top Agilent counter but I wonder how much use I'd make of it beyond my current project - even second hand from the Agilent store they are more than ten times the cost of my counter.For what they do, interval timing and frequency, counters are a relative bargain as they are much cheaper than a scope with the same resolution.Counters seem to fall into two categories. Either for use simply to measure frequency/period in which case a relatively cheap 8 digit counter is probably adequate. Or to also measure jitter and accurate one-shot timing in which case you probably need a top-of-the-range model that has time stamping and 20psec resolution.

author: Ed.Kloonk
author_rank: Super Contributor
timestamp: May 27, 2014, 11:00:08 am
content: Thanks.

author: Rerouter
author_rank: Super Contributor
timestamp: May 27, 2014, 11:20:33 am
content: Vehicle Calibration, RPM / Speed, both use some form of impulse signal, with a nice front end to cover almost every signal type imaginable, (only has to cover 25Khz so not that hard to make)equally for testing the gauges outside of the vehicles, while our sources are absolutely rubbish, we rely on an accurate counter so it makes no difference,then if you wanted to get more obscure some marine wind direction sensors rely on an oscillation frequency (LC tank) which while being an absolute PITA to set up and correct are simple to test with a frequency counter,to clarify i am playing in the low end of the spectrum of test gear, relying on a reciprocal counter for under 250Hz and a fixed gate counter for greater,

author: Unknown
author_rank: Unknown
timestamp: May 27, 2014, 12:40:18 pm
content: Quote from: Ed.Kloonk on May 27, 2014, 09:39:07 am"Most" depends entirely on what you're doing. Electronics isn't all digital - and, even if it was, anything more than the most trivial needs accurate clocking/timing. 90% of what I play with is RF or timing related, not random logic, and that's why I have a passably decent frequency counter. For the 10% that isn't, I have a cheap logic analyser.FWIW, don't kid yourself about the accuracy of frequency counters in 'scopes, especially cheap Chinese ones. Most are about as accurate as the scope itself (i.e. not very).

author: han
author_rank: Frequent Contributor
timestamp: May 27, 2014, 01:30:38 pm
content: freq counter.1. typicaly : for people need to measure high freq, but not have spectrum analyzer.2. for calibration.3. They can buy

author: olsenn
author_rank: Frequent Contributor
timestamp: May 27, 2014, 01:34:06 pm
content: First of all, fixed oscillators are still used as clocks for most digital circuits. Knowing the precise frequency is important for determining timing characteristics. The counter will count non-periodic signals as well, and tell you the average frequency, which is useful for checking the center frequency of radio signals etc. Lastly, counters can often deploy a reciprocal technique to more accurately determine low frequencies and periods. Counters (at least good ones) will have 9+ digits, making them more precise than the average oscilloscope.

author: nctnico
author_rank: Super Contributor
timestamp: May 27, 2014, 03:20:54 pm
content: Quote from: Ed.Kloonk on May 27, 2014, 09:39:07 amObviously when you need to check whether a frequency is accurate. Every now and then (every few years) I want/have to measure whether the frequency of a signal is accurate to the Hz. That is where a frequency counter comes in.

author: G0HZU
author_rank: Super Contributor
timestamp: May 27, 2014, 04:48:59 pm
content: Quote from: Ed.Kloonk on May 27, 2014, 09:39:07 amBack in the 1980s and 1990s a scope, a sig gen and a counter were considered the three essential items for radio servicing or construction. Back then most radios weren't fully synthesised and so in order to align a radio up properly you had to measure and adjust several crystal oscillators inside the radio to be on frequency. The output from these were typically summed or multiplied to make up the final frequency for the radio. Usually each was set to something like +/- 20Hz and so the total error could easily exceed 100Hz. So to provide a decent service to customers you did really need a fairly accurate counter that could read down to 1Hz and have an accuracy of better than about 0.5ppm.I repaired a lot of radios back in the 1980s when I was a student to gain extra income and a decent counter was a very useful asset. But I stopped doing that stuff back in the 1990s. These days I rarely use a counter. eg I have three counters and they all sit on an equipment storage rack in a spare room. I do dig out and use the best one for checking the accuracy of the 10MHz OCXOs in some of my test equipment but this only happens a few times a year.Like most people here, I can use a scope or a spectrum analyser for measuring frequency to a reasonable accuracy so the counter is fairly redundant. If I started repairing radios again then a counter would be on my bench all the time again.

author: corrado33
author_rank: Frequent Contributor
timestamp: May 27, 2014, 05:33:18 pm
content: My friend uses a highly accurate frequency counter to verify the RPM of a chopper wheel inside of some scientific equipment. Rather it's used for the active feedback I believe. (It's a complicated piece of machinery.)

author: ve7xen
author_rank: Super Contributor
timestamp: May 27, 2014, 06:07:20 pm
content: Quote from: jpb on May 27, 2014, 10:41:58 amA bit offtopic but you might want to look for a time interval analyzer instead, at least for this particular purpose. These are niche devices designed for this kind of analysis. I've seen some going on fleaBay lately for low $100s with 150ps or better one-shot resolution and analysis capabilities built-in.Alternately, thePICTIC IIis a pretty cheap and easy build and gets you a high resolution interval counter for < $100, it's popular with time-nuts to monitor 1pps sources.

author: G0HZU
author_rank: Super Contributor
timestamp: May 27, 2014, 11:58:44 pm
content: To show what even an old (but good) spectrum analyser can do I fed a signal into my old 1980s Advantest spectrum analyser from an ESG-4000D sig gen set to 1.5GHz and 10uV.The analyser is fully synthesised from a very high quality 10MHz OCXO and has a frequency counter built into it. The idea is you place the marker somewhere on the signal you want to measure then press 'frequency counter' and then set the counter resolution to 1Hz.You don't have to select a narrow RBW to get this level of performance as the signal just has to get through the RBW filter to get to the counter section at the low freq IF. I think it does some kind of zero span mode when the counter gate is open (with the Centre Freq set by the marker) and this lets the counter see the signal.It can read and measure signals down to a few microvolts and measured 1.500 000 014GHz for the 10uV signal. However the counter gate time (in the analyser) to get this resolution is several seconds. I have a fairly decent counter here and it measured 1.500 000 0154GHz from the signal generator after I turned up the level to 100mV to make sure the counter would read it easily.So the analyser can quite accurately read down to 1Hz resolution and can measure tiny signals of a few microvolts even if they are right next to huge signals a few kHz away.You can't do this with a regular frequency counter