info about frequency counter, Introduction, construction, counter types, counter schematic, AVR Frequency Counter, High-Performance counters, FC frequency Counter, Frequency Counter History

frequency counter Introduction

A frequency counter is an electronic instrument, or component of one, that is used for measuring frequency. Since frequency is defined as the number of events of a particular sort occurring in a set period of time, it is generally a straightforward thing to measure it.

If the thing to be counted is already in electronic form, simple interfacing to the instrument is all that is required. More complex signals may need some conditioning to make them suitable for counting - most general purpose frequency counters will include some form of amplifier, filtering and shaping circuitry at the input. Other types of periodic event that is not inherently electronic in nature will need to be converted using some form of transducer. For example, a mechanical event could be arranged to interrupt a light beam, and the counter made to count the resulting pulses.

Frequency counters designed for radio frequencies (RF) are also common, and operate on the same principles as lower frequency counters, but often have more range before they overflow. For very high frequencies, many designs use a high-speed prescaler to bring the signal frequency down to a point where normal digital circuitry can operate. The displays on such instruments take this into account so they still read true. If the measured frequency is too high for any prescaler, a mixer and a local oscillator can produce a suitable frequency to measure.

The accuracy of a frequency counter is strongly dependent on the stability of its timebase. Highly accurate circuits are used to generate this for instrumentation purposes, usually using a quartz crystal oscillator within a sealed temperature-controlled chamber, known as a crystal oven. Where the frequency does not need to be known to such a high degree of accuracy, simpler oscillators can be used. It's also possible to measure frequency using the same techniques in software in an embedded system - a CPU for example, can be arranged to measure its own frequency of operation provided it has some reference timebase to compare with.

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AVR Frequency Counter

A simple, inexpensive and versatile frequency counter with LCD display and some special extra features.

Introduction

How would you like a 40 MHz frequency counter for under $50? What if I told you it also had an 8 digit LCD display, optional offsets for use in a receiver or transceiver, 10 Hz (even 1 Hz!) resolution, and also a six channel digital voltmeter built in? Direct reading with prescalers in the VHF version? Oh, and optional PC telemetry so you can watch the output on a PC, log the results, or graph drift? Well, read on!

Counter Specifications

The VHF version can select divide by 10 or divide by 64 prescalers and provide direct reading.
Maybe all you are looking for is a low power digital display for your homebrew QRP rig? Well the receiver software version of the counter has programmable IF offsets and an S-Meter display thrown in!

The counter contains only three inexpensive ICs (well, add a regulator and three transistors), and operates from 6 - 15V DC at about 25mA. The most expensive single item is the LCD display, which is an industry standard 16 x 2 dot matrix module, which can often be found used or at bargain prices. This isn't a kitset, but the parts are easily obtained, and the circuit can be built using any prototyping technique, or you could design your own PCB. The prototype was built on a small commercial strip board.

Some of the features of the unit are:

Four ranges, with 10 Hz and 1Hz resolution to at least 40 MHz.
High sample rate (5 samples/sec or more) with averaging to remove jitter.
Programmable ?offsets and S-Meter display for receiver or transceiver.
Binary and BCD maths to provide direct reading of frequency with prescalers.
Low current single supply operation. Can be operated from a small battery for portable use.
Optional high speed PC telemetry.
Well documented source code is available, so the design can easily be adapted.
Features of the PC telemetry application provided are:
Six A-D channels and high resolution counter channel.
Graphical colour display on the PC, with digital display, bar-graphs and a trend graph.
PC display completely configurable independently on each channel.
Channel data type, gain, offset, and measurement units can all be preset.

Source about frequency counter from qsl.net

construction of frequency counter

I will here by explain my easy construction of a frequency counter.
This counter is supposed to be working with a computer or a micro-computer like the PIC16F84.
All contribution to this page are most welcome!

Background
The reason why I built this frequency counter is becasue I need a (easy to build) HF-counter to my tuner project. This counter has no display showing the frequency. The frequency information is supposed to be fethed by a computer or a micro-computer and then it can be displayed on the screen or a LCD-screen module.

I have been using CMOS chip to my counter wich makes it kind of slow. The max frequency is about 20MHz. This is not much for a counter, but I will add a prescaler to it wich will make the max frequency 1.1GHz.

This frequency counter will not bet a precision instrument, but the resolution will still be 250Hz from DC upp to 1.1GHz. This counter will be easy to build and to control. Personally I like radioequipment with nice fronts and what better can you add to your radio projects if not a green LCD-display module, showing the frequency.

Block diagram
The counter is 24 bit and the 24 output are connected to shiftregisters. There is a timer wich produce 2 frequency 2 Hz and 0.2Hz. This two frequency is the measuring time. (The time under wich a measurement should take plase.) In the logic is a divider so the actual measure time will be 1 sec or in the other case 10sec.
The "start" signal activates the logic wich let the Fin be connected to the counter. after 1 sec the logic disconnect the Fin from the counter and the "Ready" signal is activated by the logic. If you want higher resolution you can let the 0.2 Hz control the logic. In this case the logic will let the Fin be connected to the counter for 10sec. If you want other measure times you can easy change it.
Mostly often i use 0.5 s and I use a prescaler wich divides with 250. This gives me the resolution of 500Hz and I get 2 measurement per second. I find this good enough.

When the "Ready" has ben activeted you can simply shift out the result from the counter via the shiftregister. The counter-data will be at serie out and the "Clock" will shit out each bit until all 24 bit are shifted out. The counter can be reseted by activeting the "Reset" input.

The whole construction can be made very compact and easy to build. One important thing is the timer that produce the measuring time. This timer is build around a 32768 Hz Crystall oscillator wich needs to be calibrated if you want accurate measurements.

Details about the frequency counter schematic

The 24 bit counter consist of two 12 bit counter 4040. Three (8-bit Parallell in - serie out) shiftregisters 4014 are connected to the counters.
When the "ready out" signal goes high the value in the counters can be loaded into the shiftregisters by holding P/S high and send a rising clock-puls. The 24-bit value can then be shifted out by lower the P/S to ground and pulsing the clock.

A crystal oscillator 4060 creates a frequency of 2 Hz. This frequency is then divided by 10 in the circuit 4017, the resulting frequency is 0.2Hz. One of these two frequencies can be send to the first 4013 by 2 control signals. The reason of this option, is to be able to increase the measuring time by a factor of ten. The first flip-flop works as a divider by 2. The output frequency will be 1 Hz or 0.1Hz. Flip-flop number 2 works also as a divider by 2, so the output frequency will be 0.5Hz 0.05Hz.
0.5 Hz means that the positive flank is 1 sec and the negativ flank is 1 sec, and 0.05Hz gives 10 sec positiv flank and 10 sec negativ flank. During the positiv flank the 4093 nand gate opens so the Fin can reach the counters. When flip-flop 3 aktivates it will lock (turn off) flip-flop 1 so there can not be any more measuring time.
The result will be that when the Reset goes low the counter will start counting during 1 sec or 10 sec. When the end of the measuring time is reached the "Ready out" goes high and no more counting can be done. The value in the counter can be fethed via the shiftergisters.

The prescaler

There are several prescalers you can use to this frequency counter. One disasvantage with lot of prescalers is that they only divide with 64 or 128.
I have grown fond in the LMX2337 Frequency Synthesizer. This circuit has a very sensitive input (10mV). One part of this circuit is a programmable divider. It can be programmed from 192 to 33538175 by a serie interface with a computer or microcomputer. Most often I divide the input frequency with 250 and set the frequency counter to measure under 0.5 sec, wich gives me the resolution of 500Hz and the uppdate will be 2 times/second.
The LMX2337 circuit is serially programmed. You can read the datasheets to find out how to set the divider.
I have added a preamplifier to the LMX2337 so there will not be any load of the measuring object.

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High-Performance Frequency counters

We have developed two high-performance frequency counter models for every need and budget. Choose from the basic 300 MHz frequency counter CNT-85 or the ultimate portable frequency calibrator CNT-85R with built-in Rubidium time base.

Both counters can be equipped with optional HF-inputs to 2.7 GHz and a GPIB-interface, for use in automatic test systems, or in PC-controlled instrument clusters on the lab bench or workshop bench. A new option - the 8 GHz Prescaler input - extends the frequency measuring range.

The CNT-85 is a compact portable high-performance frequency counter ideal for portable frequency calibration. It is very easy to use, thanks to an advanced and intelligent Auto Set function, which ensures perfect triggering on any type of input signal. Compared with other frequency counters, the CNT-85 has a lot extra to offer, like an input signal level meter (analog bar graph), pulse width and duty cycle measurements.

The CNT-85R is an excellent portable calibrator for calibration of the master clock in GSM base stations. Its built-in atomic clock never needs to be adjusted during the lifetime of the network.
Easy-to-use and accurate frequency calibrators
Ultimate stability with integrated atomic clock
Versatile and portable. One counter fits all needs
NEW! 8 GHz Prescaler input, extending the frequency measuring range of the CNT-85/85R and the CNT-81/81R

Source from pendulum.se

Frequency Counter History

In the early 1950s, the frequency counter was developed. The device could measure and accurately indicate frequencies up to 10 MHz. Present-day frequency counters can accurately read frequencies as high as 40 GHz. In addition to direct frequency measurement indication, some types of frequency counters can measure the WAVE PERIOD, which is the inverse of frequency; RATIO, which compares one frequency against another; and TIME INTERVAL, the time between two events or the time between two functions of an event. In addition, frequency counters can totalize event indications. This is similar to measuring the frequency except that a manual or an electronic start-stop gate controls the time over which the measurement is taken. Frequency counters can also provide scaling in the form of a digital output signal from the frequency counter that represents a frequency-related division of the input frequency.

All of the above functions have useful applications. For pulse timing, the period function is used; totalizing is used in digital applications; and ratio is used in comparing harmonic-related signals. Scaling is used for triggering other test equipment used in conjunction with the frequency counter; and time-interval capability is used in measuring the interval between two pulses or between two sets of pulses. Because of the wide variety of frequency counters in use, the technical manual for a specific frequency counter should be consulted to determine the instrument's full capabilities.

Frequency Counter Accuracy

All frequency counter measurements are measured with 1 part in 108 of accuracy. However, frequency counters have provisions for input from external frequency standards. This extends the accuracy of the frequency to that of the standard. A frequency self-check capability is provided to determine if the counting and lighting circuits are operating properly.

For more info about frequency counter from tpub.com

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Frequency Counters theory

The frequency counter is probably one of the most useful radio monitoring tools ever made. It has the ability, when used in the proper manner, to snag frequencies out of the air. This is much more preferable work, as opposed to sifting through FCC databases and personal webpages, finding outdated info, sitting in your car and scanning different frequency ranges, etc. The catch here is that many people see the frequency counter as this magical device that will instantly tell them the frequency of that agency or group that they want to monitor. It's a lot more complex than that, both logistically and technically. First, let's look at (or drool over, your pick) equipment.

The first frequency counter you'll probably notice is the one sitting on the shelf of your local Rat Shack. This is about standard for what you'll see available. Range is AF (audio frequencies) to 1.3gHz. Hold function, selectable gate times, and a backlight
are included. This is an alright counter, available, and not too expensive (around $100 last time I checked).

When shopping for counters, there are counters, and then there is the Opto Scout. It has 400 memories, each with a hit counter capable of counting 255 transmissions on each received frequency, CI-V interface, etc. Really nice. Most other frequency counters
were made for testing radio gear to see if it's on frequency, etc.. not so with the Scout. The Scout is the only counter that's made specifically to snag frequencies for monitoring. This may explain the $350 price tag. If you have the cash, it's definitely worth it; however, it's not for everyone.

A frequency counter, in theory, is a very simple device. Flashback to basic electronics and radio class. Radio transmissions oscillate at a certain frequency, in the shape of an AC (alternating current) waveform. What your frequency counter does, basically, is measure the number of times that the waveform's voltage drops from its peak to zero within the given gate time. After that measurement is taken, the number of times that the wave's voltage would drop from its peak to zero in a second is calculated, factoring in the length of time that the counter was counting voltage drops. This calculated value is then displayed, stored into memory, etc. From this, we can determine that the counter's gate time is a setting that will affect the accuracy of the measured signal. In most cases, however, the shortest gate time will prove most beneficial and will give results accurate within 1kHz or so. Remember that frequencies, for police departments and such, are allocated based on a bandplan, with predefined steps. In other words, if you got a reading on your counter of 155.687, one could guess that the actual frequency in use would be 155.685mHz (the closest frequency allocated for police activity). Same goes for a reading of 879.98 - that's in the cellular band, and the cellular band is allocated in 30khz steps, making the closest valid frequency 879.99mHz. Also remember that your frequency counter isn't entirely accurate. And, most likely, neither is the transmitter you're measuring. This inaccuracy should not harm your readings at all - so don't think that your counter is screwed when it reads 155.68592 when counting your local PD.

Source from textfiles.com

Frequency counters Works

The best tool for finding those elusive frequencies is the Frequency Counter. These come in a number of guises with Optoelectronics and Watson being the the more commercially known brands.

So how do they work?

In laymans terms I'll try not to be too technical here, (Maybe because I'm not quite so sure myself) basically a frequency counter is a tool used by radio manufacturers, Programmers etc. to fine tune radio transceivers to check the frequency output of a radio, the frequency counter is constantly "listening" for frequencies being transmitted when it receives (hears) a frequency the frequency received is displayed on the lcd screen. This little tool has now been adopted by Scanner enthusiasts for finding radio frequencies, Imagine you are in your shopping precinct and you see a shoplifter being chased by a security wouldn't it be good to know the frequency that security guard is transmitting on? Well with a frequency counter you will have his frequency logged as soon as he keys up his radio.

What range have they got?

Some owners are a little dismayed at first I know when I got mine I was expecting to pick up all the same frequencies my scanner could receive plus the ones I had missed, but in reality you have to be very close, Why? I hear you ask. Well if it received everything at once it would have great difficulty distinguishing between signals, heres how I had it explained to me. Imagine being in a football ground and everyone shouts at the same time would you be able to distinguish between the voices what was being said? Well it works the same for a frequency counter. Also there are other factors to consider, such as frequency range being monitored some counters work better on different frequency ranges, My Optoelectronics Scout receives over a greater range on UHF than it does on VHF.

You can of course help things in your favour. e.g. Say you want to find the local ambulance station, you know that they operate on VHF you dont want to get to close to the Station as you do not want to sit outside and arouse suspicion so you "plot up" in the pub across the road. Now your best bet would be to attach a VHF ariel to the frequency counter as this will somewhat filter out UHF signals and give your counter a greater receive range than if you had a wideband or UHF ariel attached.

Source from ukmidlandscanner.co.uk