Confused about Frequency Counters

Look for something that has a built in prescaler. Something like this: The basic counter goes from 100KHz to 60MHz. The other ranges use a prescaler to divide down the input frequency so that it ends up at less than 60MHz and can be counted.

Or, maybe one of these variations:

You can also use a mixer to take a higher frequency signal, and mix it down to something lower that the counter can handle. I have some HP microwave counters that work like that.

--
Jeff Liebermann     jeffl@cruzio.com 
150 Felker St #D    http://www.LearnByDestroying.com 
Santa Cruz CA 95060 http://802.11junk.com 
Skype: JeffLiebermann     AE6KS    831-336-2558

What good is a frequency counter WITH test leads for television. Where are you gonna connect those leads and what's the signal level there? And how do you measure channel 40 when channel 42 is 10x stronger.

You suffer from test equipment buyer's exaggeration. "I dunno what I want so gimme EVERYTHING, and then some, for cheap."

Take a step back and decide what you need to measure that you didn't need for the last 50 years.

I designed frequency counters for a living back in the day. I have more than a few. I haven't turned one on in more than a decade, and here's why...

FOR CHEAP COUNTERS: They're inaccurate. If you're setting a radio frequency, you want an ACCURATE counter. Most other times, the accuracy is irrelevant. It's go/nogo. The accuracy and stability of the timebase may be the most important parameter. What do you want to do?

They're insensitive. You typically can't go probing around in equipment and learn anything. A counter typically reads the biggest signal it hears. You might find that everything reads 120Hz. Probing around in a radio circuit may detune it. What do you want to do?

I find an oscilloscope to be a more useful tool. You can read the frequency right off the screen with sufficient precision for most troubleshooting tasks. And you can do it in the presence of noise that might render a counter useless.

Expensive counters have a few bucks worth of counting stuff. The majority of the expense is in the timebase and the front end that helps you trigger on what you want to observe. All those knobs are there for a reason.

If you need more accuracy, you probably need a LOT more accuracy.

Draw a frequency chart from 0 to 2.4 GHz. Put an arrow at every frequency where you ever needed to measure a frequency and the specs of the counter you'd have needed to do it. Let that be your guide. You might decide that you still don't need a counter that you can afford. ;-)

You can do audio with a cellphone app. Just be careful what you plug into that microphone jack.

This seems to be closer to what you want. EBAY ID 401196543325 If it has a removable antenna with signal and ground connections, you can make test leads. Just be careful with DC or too much signal breaking it.

I have two of those. I bought the second because I thought I'd broken the first, it performed so badly. They're as bad as each other.

If you have a strong and stable signal, it can work ok, but the input design is poor. The HF and the pre-scaler both have dual-gate mosfets, but there's no gain control (automatic or otherwise) and the inputs are paralleled. I've disconnected the two inputs by cutting a track and soldered on a little bit of RG-158 to an SMA connector for the high range.

I'd love it if Mike is willing to share some of his counter front-end wisdom.

I"m assuming those really cheap portable counters are using prescalers, since they only start counting at 50MHz or something. INtended for two way radio checking I assume, so you don't need the lower frequencies, and a whip or rubber duckie antenna will pick up the output power fine.

I've certainly thought about buying one of those cheap ones, hoping I could bypass the prescaler, though I suspect another issue, the prescaler isn't a decade counter. Back when Heathkit came out with a frequency counter, circa 1971, the prescalers were decade counters, and things got better as they improved, and the frequency counters had higher limits. But that sort of IC seems out of fashion now, so the prescalers are meant for other things, and offer a binary division, so bypassing it in the counter (and maybe adding an input stage) means the clock for the counter is "wrong".

Michael

** Anything using a crystal time base will have good accuracy.

** Yep, RF circuits are very load sensitive and you will need a FET probe to buffer the signal.

But any counter will read the carrier frequency of a transmitter, long as it has a few milliwatts of output.

Radio mics operating in the VHF and UHF bands can be read by placing them close to a short antenna attached to the BNC input.

Analogue mobile phones (remember them) would read from 5 yards away.

..... Phil

I don't think the prescaler is the problem is it? The problem is the inappropriate front end. If you design a decent front end and feed the prescaler with that signal it should work at lower frequencies ok. It may not have timing controls to let you measure below some 10s of Hz or so, but is that really a problem? Or do the prescalers work in some way I'm not familiar with so they just don't operate at lower frequencies?

--

Rick C

I don't expect anything I could say would change your mind. We'll just have to disagree on that.

---------------

** Why I change my mind when what I posted is correct ??

** You must enjoy being wrong.

You have nothing that explains your strange opinion ?

.... Phil

Thanks. I was thinking of buying some of those. I should have known as much of the low cost "modules" that I've purchased seem to have deficiencies as a result of crude design or cost cutting exercises.

To clarify my my comments a little, I was not recommending the purchase of any of the devices I pointed to on eBay. I meant them as examples of devices that have prescalers, which was part of the OP's rant on requiring multiple counters to cover the frequency range. My comment "Something like this:" usually preceeds something that I haven't worked with.

I picked that particular example because it has a drawing of the PCB showing i/o and controls: It has two adjustments labelled "High channel sensitivity adjust" which I guess would help with the tiggering. Do these controls work, or were they deleted in yet another cost cutting exercise?

The OP has not disclosed how he plans to use the counter. If it's a bench instrument, that requires precision, I suggest any of the numerous used HP counters available on eBay. Especially the HP 5300 series: I have accumulated a fair collection of these and find that used counters are a far better deal than the eBay instruments, such as:

Incidentally, since the OP is into tubes, my favorite counter is an HP

5248M with genuine Nixie tubes. Middle right above the spectrum analyzer: The pile of 4 plugins under the Glad bag box are the various mixer type downconverters I previously mentioned. I also have an HP 5245L: Cheap but scarce on eBay:

--
Jeff Liebermann     jeffl@cruzio.com 
150 Felker St #D    http://www.LearnByDestroying.com 
Santa Cruz CA 95060 http://802.11junk.com 
Skype: JeffLiebermann     AE6KS    831-336-2558

It was developed by a good hobbyist who posted everything online.

I think that full schematics of slightly earlier versions are available online. He uses a dual-gate MOSFET before the prescaler and before the main counter, with the inputs paralleled. I think that affects the sensitivity (though I don't have measurements) so for my 2nd module, I cut a track to separate the input paths. I might wind up adding an independent input amplifier with AGC, or even a pot to adjust the 2nd gate bias on the MOSFETs for a manual gain control. A little difficult though, as parts of the circuit are underneath the LED displays, so I'd need to remove those.

The main counter is a PIC.

--------------------------

** Wow !!

Is it just dawning on this total moron that he is one ?

.... Phil

Although I am not willing to spend big money on this, I tend to avoid those super cheap boards with no cabinets. I dont know how they can even sell them that cheap, so obviously they are not quality. Not to mention it costs 5 times the price of the board to buy some sort of box to put those boards in, and for all the connectors and stuff. So, by that time I'd have $25 or $30 invested. I'd rather find a complete unit that is better quality and eliminate all the hours it takes to put them into some sort of box. Making boxes and drilling all the holes and that sort of thing has never been something I am real fond of anyhow.

I am currently looking at a Hickok 380, several HP counters, and a C&C

150. That Hickok is a BID sale, which means I dont have much of a chance of getting it. (Being on dialup, I cant place a bid in the last 10 seconds). Normally I dont even bother with bid sales, and just do the "Buy It Now" items.

The HPs are all over my price range, but I dont need to buy it today or even this week. I can wait till I find a better deal. That C&C 150 seems like a real good deal, (about $39 with shipping), but I have never heard of that brand so I am looking to see if I can find more reviews of it. It appears to be a rather high-end device, with lots of features and a very wide freq range.

My main reason to get a counter is mostly just to check the frequency coming from my Signal Generator. Having one that also checks audio freqs would be kind of nice, since I have a tone generator that I'd like to be able to know the frequencies it's outputting, but that is not an absolute necessity.

I probably got more use from the Freq counter I used in the 70s (which was borrowed). Back then I was doing a lot with CB radios and that counter would check the CB channel output for accuracy. But I dont do much with CBs anymore, since no one uses them now.

YOu really need to buy one of the used service monitors. They can be had for around $ 1000. You get a counter signal generator and many more things.

Like this for example:

--
Jeff-1.0 
wa6fwi 
http://www.foxsmercantile.com

Have you been living under a rock for the past 20 years?

--
Jeff-1.0 
wa6fwi 
http://www.foxsmercantile.com

Can't blame you a bit for not jumping on those "kits" mentioned previously. Often more trouble than they're worth when you consider all the other stuff you have to buy and then all the work to assemble and make work. The C&C 150 seems like a pretty good deal for you. Certainly in your price range, and appears to be a decent entry level counter. You can get a manual from the manufacturer' web site

; (Registration required, but nothing out of reason, like credit card numbers, etc.)

You'll probably find out, if you research "reciprocal counters" (of which, this is one) that they offer much better resolution than other "normal" counters, especially at low audio frequencies. This is a good thing, since you can select a shorter gate time for the measurement than normal counters. If you want to measure an audio tone of, say 123.4 Hz, you'd need to select a gate time of 10 seconds to get the last digit to display. With a reciprocal counter, you can select a gate time of 1 second, or even 0.1 second, and see all the digits the counter can display. It actually measures the period of a signal, and a microcomputer inside the counter does a bit of math to calculate and display the frequency with all the digits the counter is capable of displaying.

Good luck with your choice, Dave M

Or you can just buy something that works.

-- Jeff-1.0 wa6fwi

--- This email has been checked for viruses by AVG.

To get from 2400 MHz to 60 MHz requires dividing by 40. However, that doesn't seem to be how this one works.

Checking the prescaler chip from the photos, I find a Fujitsu MB501L prescaler: That's a 64/65 or 128/129 prescaler for a dual modulous synthesizer. I would guess(tm) that the eBay counter would use divide by 64 to get: 2400 / 64 = 37.5 MHz which is too low to utilize the full 60 MHz counter range.

However, there's a problem. The MB501L prescaler is only rated to

1.1GHz. How they claim 2.4GHz will remain a mystery. If I had this counter (and a clean workbench), I would probe it to see what they're really doing. I couldn't find a schematic.

There are some handheld counters that count to 60Mhz, and use a divide by 40 prescaler, which results in the proper frequency ranges: 2400 / 40 = 60 Mhz However, I can't find an example right now. The 40 is achieved with a divide by 4 followed by divide by 10, which I guess qualifies as a decade prescaler of sorts. As I recall, it was usually done with 2 ECL chips, which sucked plenty of power and were not cheap.

Here's another way to use a prescaler: The frequency ranges are: 50MHz, 800MHz, and 2800MHz which correspond to: /1 /16 and possibly /64 Sorry, but no schematic or block diagram found.

--
Jeff Liebermann     jeffl@cruzio.com 
150 Felker St #D    http://www.LearnByDestroying.com 
Santa Cruz CA 95060 http://802.11junk.com 
Skype: JeffLiebermann     AE6KS    831-336-2558

I couldn't find any such project. I suspect that it might have gone the same way as the various M328 component test meters being sold online. The original project was open source. It was then commercialized by various vendors with wildly varying pricing. Much of the stuff I've found was early versions of the board and firmware. Meanwhile, the project has done on to add features and improve the firmware, but the online stuff seems stuck with early revisions. This link includes some history: I can't seem to find the original development site, which was in Germany.

If the amplifier is used to simply produce a square wave out of whatever it fed into the input, low gain might be a big problem. So will noise around 0v which is why a "threshold" adjustment is usually supplied. Getting such a simple amplifier to work from 0.1MHz to

2.4GHz is unlikely, which might explain the lack of sensitivity.

May I suggest that you remove the input amp and setup something that give the prescaler a 50 ohm input. Then, design a broadband RF amplifier that has a chance of working over the frequency range. Something similar to a CATV or OTA TV/FM amplifier might be suitable. However, don't worry about getting a flat frequency response. Just take whatever you can get that produces enough drive to make the MB501L prescaler happy. A collection of communications freq range bandpass filters would be nice to prevent triggering on out of band junk.

I'm not PICky.

--
Jeff Liebermann     jeffl@cruzio.com 
150 Felker St #D    http://www.LearnByDestroying.com 
Santa Cruz CA 95060 http://802.11junk.com 
Skype: JeffLiebermann     AE6KS    831-336-2558