4 Advice to Choose a Universal Frequency Counter

Introduction

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Counters can be a plug-and-play instrument and seem fairly simple from the outside. You connect a signal to the input, and a digital readout tells you the frequency or some other parameter. However, to achieve the best results, whether that means speed or quality, attention to how you set up the counter measurement is important.

Choosing the Best Counter

Selecting which counter will best meet your needs is the first step. There are several related products that perform a variety of tasks at various frequencies:

• Universal counters

Both frequency and time interval measurements, as well as a number of related parameters.

• RF frequency counters

Precise frequency measurements, up to 3 GHz and beyond.

• Microwave frequency counters

Precise frequency measurements, up to 40 GHz and beyond.

• Time interval analyzers

Optimized for precision time interval measurements.

• Modulation domain analyzers

Designed to show modulation quantities, such as frequency versus time, phase versus time, and time interval versus time.

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Hint 1: Recognize the difference between resolution and accuracy 

Assuming a large number of digits equates to a very accurate measurement may not be correct. It is a common mistake to equate resolution and accuracy. They are related, but different concepts. 

The resolution of a counter is the smallest change it can detect in closely spaced frequencies. All other things being equal (such as measurement time and product cost), more digits are better—but the digits you see on the display need to be supported by accuracy. Digits can be deceptive when other errors push the counter’s resolving ability away from the actual frequency. In other words, it’s possible for a counter to give you a very accurate reading of an incorrect frequency. 

Random and systematic errors both determine a counter’s accuracy. Random errors are the source of resolution uncertainties and include: 

• Quantization error 

When a counter makes a measurement, a ±1 count ambiguity can exist in the least significant digit. This can occur because of the non-coherence between the internal clock frequency and the input signal. 

• Trigger error 

Noise spikes can be triggered by noise on the input signal or noise from the input channels of the counter. 

• Timebase error 

Any error resulting from the difference between the actual time base oscillator frequency and its nominal frequency is directly translated into measurement error. 

Systematic errors are biases in the measurement system that push its readings away from the actual frequency of the signal. This group includes effects on the time base crystal such as aging, temperature, and line voltage variations. 

Compare the two counters in Figure 1. Counter A has good resolution but a serious systematic error, so its displayed result in most cases will be less accurate than those of Counter B, which has poorer resolution but a smaller systematic bias error.

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jim111

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Frequency Counter advice

« on: March 02, , 07:49:06 pm » I am looking for a good frequency counter. Budget is around $500.
The primary use is for aligning 2 way radios.

All suggestions are welcome.

jonpaul

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Re: Frequency Counter advice

« Reply #1 on: March 02, , 08:46:54 pm » accuracy needed # digits, % ? Freq range min max?

2 way radios can be anywhere from low band SW, FM, VHF, or UHF bands, to name a few.

Jon The Internet Dinosaur..
passionate about analog electronics since s

jim111

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Re: Frequency Counter advice

« Reply #2 on: March 02, , 09:59:37 pm »

accuracy needed # digits, % ? Freq range min max?

2 way radios can be anywhere from low band SW, FM, VHF, or UHF bands, to name a few.

Jon

Frequency range 1.8 MHz to 500 MHz,
accuracy would like +/- .1 ppm, may not get that in this price range,
at least 9 digits on the counter.

Will be using it to align PLL/VCO's so it needs to be able to work with very low input voltages.

bob

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Re: Frequency Counter advice

« Reply #3 on: March 02, , 10:34:41 pm » My venerable HP A can do all that.  They are available for not too much money.  Try to get one with the oven oscillator I think it is.  There are various options and mine will go to about 700 MHz and can resolve 0.1 Hz with 10-second count time.  The VHF coverage is with one of the high frequency options.

xmo

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Re: Frequency Counter advice

« Reply #4 on: March 02, , 11:40:42 pm » Your frequency counter budget might be better off applied toward a service monitor or spectrum analyzer.  Both of these are essential for servicing two-way radios.

I have been aligning two-way radios for many years and although I have several frequency counters, I find that I never use them.   I always set a radio's frequency using a service monitor (aka communications system analyzer or RF test set).

For measuring low level signals, such as your VCO example, many modern spectrum analyzers have a built in frequency counting function, which - when enabled - stops the sweep at the center and actually counts the input signal frequency with the same accuracy as a frequency counter would have. (based on the respective instrument's time base accuracy)  Plus, with the spectrum analyzer, you can measure the precise level of the VCO and observe it's stability and settling characteristics.

With the capabilities of a modern spectrum analyzer, I find it hard to envision an application for a standalone frequency counter.

Electro Fan

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Re: Frequency Counter advice

« Reply #5 on: March 03, , 02:06:11 am » Maybe one of these....

https://www.ebay.com/itm/BG7TBL-FA-2-6GP-6G-Frequency-Counter-Power-detection-frequency-meter-11-bits-SEC/?hash=itemf2dd:g:eYYAAOSwi8pfJSF5

... taking a 10 MHz reference signal from one of these....

https://www.ebay.com/itm/BG7TBL10MHz-LCD-GNSS-DISCIPLINED-OSCILLATOR-Support-GNSS-GPS-BDS-GLONASS-GALILEO/?hash=item1cefbf:g:ZeQAAOSw99hfJSF8

... and keep ~$100 for beer

jim111

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Re: Frequency Counter advice

« Reply #6 on: March 03, , 09:19:58 pm » Thanks for all your suggestions.

Electro Fan

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Re: Frequency Counter advice

« Reply #7 on: March 04, , 04:35:14 am »

accuracy needed # digits, % ? Freq range min max?

2 way radios can be anywhere from low band SW, FM, VHF, or UHF bands, to name a few.

Jon

Frequency range 1.8 MHz to 500 MHz,
accuracy would like +/- .1 ppm, may not get that in this price range,
at least 9 digits on the counter.

Will be using it to align PLL/VCO's so it needs to be able to work with very low input voltages.

BG7TBL FA-2 spec’d to work down to -20bBm up to ~5GHz, and down to -50dBm up to 550MHz

—-

CH1 Frequency Accuracy:
0.1s Gate Time: 0.001Hz@10M
1s Gate Time: 0.Hz@10M
10s Gate Time: 0.Hz@10M
             
CH1 Test Speed: 11 bits/second@10MHz
CH1 Power Test Range: -50dBm~+20dBm, 1M~550M@50 ohm
CH1 Power Test Accuracy: 0.5dB@10MHz
CH1 Connector Type: BNC

Introduction of CH2:
CH2 Frequency: 30MHz-6GHz
CH2 Input Impedance: 50 ohm
CH2 Power Accuracy: 1dB@2.45GHz

CH2 Frequency Accuracy:
0.1s Gate Time: 1Hz@1GHz
1s Gate Time: 0.01Hz@1GHz
10s Gate Time: 0.001Hz@1GHz
           
CH2 Input Power: -20dBm~+13dBm@0.5~5G
CH2 Connector Type: SMA

CH1 Frequency Accuracy:
0.1s Gate Time: 0.001Hz@10M
1s Gate Time: 0.Hz@10M
10s Gate Time: 0.Hz@10M
             
CH1 Test Speed: 11 bits/second@10MHz
CH1 Power Test Range: -50dBm~+20dBm, 1M~550M@50 ohm
CH1 Power Test Accuracy: 0.5dB@10MHz
CH1 Connector Type: BNC

Introduction of CH2:
CH2 Frequency: 30MHz-6GHz
CH2 Input Impedance: 50 ohm
CH2 Power Accuracy: 1dB@2.45GHz

CH2 Frequency Accuracy:
0.1s Gate Time: 1Hz@1GHz
1s Gate Time: 0.01Hz@1GHz
10s Gate Time: 0.001Hz@1GHz
           
CH2 Input Power: -20dBm~+13dBm@0.5~5G
CH2 Connector Type: SMA

fourfathom

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Re: Frequency Counter advice

« Reply #8 on: March 04, , 06:00:05 am »

BG7TBL FA-2 spec’d to work down to -20bBm up to ~5GHz, and down to -50dBm up to 550MHz

—-

CH1 Frequency Accuracy:
0.1s Gate Time: 0.001Hz@10M
1s Gate Time: 0.Hz@10M
10s Gate Time: 0.Hz@10M
             

To get that accuracy you need an external 10 MHz reference with zero frequency error.  Otherwise that's just resolution.
Fortunately, a GPSDO can be pretty inexpensive.  I use the Bodnar Mini GPS Reference (http://www.leobodnar.com/shop/index.php?main_page=product_info&cPath=107&products_id=301).  Since it uses a VTCXO it doesn't have as good holdover as a GPSDO with an OCXO, but as long as you have a stable GPS signal it does the trick. We'll search out every place a sick, twisted, solitary misfit might run to! -- I'll start with Radio Shack.

Electro Fan

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Re: Frequency Counter advice

« Reply #9 on: March 04, , 09:10:38 pm »

BG7TBL FA-2 spec’d to work down to -20bBm up to ~5GHz, and down to -50dBm up to 550MHz

—-

CH1 Frequency Accuracy:
0.1s Gate Time: 0.001Hz@10M
1s Gate Time: 0.Hz@10M
10s Gate Time: 0.Hz@10M
             

To get that accuracy you need an external 10 MHz reference with zero frequency error.  Otherwise that's just resolution.
Fortunately, a GPSDO can be pretty inexpensive.  I use the Bodnar Mini GPS Reference (http://www.leobodnar.com/shop/index.php?main_page=product_info&cPath=107&products_id=301).  Since it uses a VTCXO it doesn't have as good holdover as a GPSDO with an OCXO, but as long as you have a stable GPS signal it does the trick.

That's why I suggested both....

---

https://www.eevblog.com/forum/testgear/frequency-counter-advice/msg/#msg

Maybe one of these....

https://www.ebay.com/itm/BG7TBL-FA-2-6GP-6G-Frequency-Counter-Power-detection-frequency-meter-11-bits-SEC/?hash=itemf2dd:g:eYYAAOSwi8pfJSF5

... taking a 10 MHz reference signal from one of these....

https://www.ebay.com/itm/BG7TBL10MHz-LCD-GNSS-DISCIPLINED-OSCILLATOR-Support-GNSS-GPS-BDS-GLONASS-GALILEO/?hash=item1cefbf:g:ZeQAAOSw99hfJSF8

... and keep ~$100 for beer

---

I think the BG7TBL GPSDO uses an OXCO rather than a VTCXO.

BG7TBL makes a variety of products.  This one might be a cost-effective solution for a 10 MHz reference signal to drive a counter (if the counter has a 10 MHz ref input).  But it might or might not work for the OP as it has a 13 dBm spec - although this would drive the counter, and the counter would be used with the radio gear, so it might be ok.

https://www.ebay.com/itm/By-BG7TBL-10MHz-OCXO-Frequency-Standard-Sine-Wave-Output/?hash=item28ac73:g:3ZUAAOSwrXhfrmRy

jim111

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Re: Frequency Counter advice

« Reply #10 on: March 05, , 12:56:48 am » How about the B&K Precision A Universal Frequency Counter 
with a Leo Bodnar Precision GPS Reference Clock?

Electro Fan

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Re: Frequency Counter advice

« Reply #11 on: March 05, , 02:10:16 am »

How about the B&K Precision A Universal Frequency Counter 
with a Leo Bodnar Precision GPS Reference Clock?

from the A manual...

INT/EXT TIME BASE SELECTOR:
Selects the source of the time base. EXT.STD. IN sets up BNC as a nominal 600 Ω input impedance path for an external 10 MHz time base signal. INT. STD. OUT sets up BNC to monitor the internal time base signal.
INT/EXT TIME BASE BNC:
Provides a connector through which the internal time base signal can be monitored or through which an external time base signal can be applied (see item above). The external signal should have a voltage range of 1.5 V~5 V rms.