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Old 27th Jul 2021, 6:41 pm   #1
Gabe001
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Location: Stockport, Greater Manchester, UK.
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Default A cheap Chinese frequency counter, a review

Having been in the market for a signal generator, I have recently acquired a working Heathkit RF1U. It's pretty much all stock, but I've implemented the frequency counter rear socket suggested by David in his write-up, and secured the mains cable properly. Having got this up and running, I needed a good, reliable, and preferably inexpensive frequency counter to complement my purchase. Previous posts on this forum and some private enquiries suggested that the "bare bones" Chinese frequency counters could potentially work reasonably well.

With this in mind, I purchased the "RF Signal Frequency Counter Cymometer Blue/Red/Green 8 Bit Tube LED Digital Tester 0.1MHz to 60MHz 20MHz to 2400MHZ 2.4GHz Meter" (see picture) from AliExpress. It arrived in less than 2 weeks. Total cost including VAT and postage was £9. I also purchased a case as an optional extra, also available on AliExpress.

Specifications (from seller)

Description:

With Microchip's PIC16F648A, 2.4 GHz frequency meter.
Using temperature-compensated voltage controlled crystal oscillator (2.5 ppm VC-TCXO).
Unique gate control and precise time algorithm (non-timed interrupt).
Gate (display refresh) time 0.01 seconds / 0.1 seconds / 1.0 seconds, real-time display frequency value.
Single-ended input design, three-channel frequency measurement (low channel / high channel / Auto Channel).
Dual frequency design, value and IF / down mode can be preset separately.
Using eight 0.56 inches high brightness digital display, eight adjustable brightness.
Circuit is simple and reasonable structure, two-button control, simple operation.
The settings are automatically saved, boot directly call.

Descriptions:

1 Gate time

0.01 秒
0.10 秒
1.0 秒
2 Measurement channels (channels are low impedance)

low channel

Measuring range: 0.1 MHz ~ 60 MHz
Accuracy: ± 100Hz (0.01 1s gate time)
± 10Hz (0.1 seconds gate)
± 1Hz (1.0 seconds when the gate)

Low channel sensitivity:

0.1 MHz ~ 10 MHz: better than 60mVPP
10 MHz ~ 60 MHz: better than 60mVPP
60 MHz ~ 75 MHz: Not tested
high channel (divided by 64)
Measuring range: 20 MHz ~ 2.4 GHz
Accuracy: ± 6400Hz (0.01 seconds gate)
± 640Hz (0.1 1s gate time)
± 64Hz (1.0 1s gate time)

High channel sensitivity:

20 MHz ~ 30 MHz: better than 100mVPP
30 MHz ~ 60 MHz: better than 50mVPP
60 MHz ~ 2.4GHz: not tested


Auto Channel
Automatically selected according to the input signal frequency high or low channel channel, identifying the frequency of 60 MHz. Such as when the input signal amplitude is greater than 60 MHz shortage can not automatically select high channel, the channel should manually select high frequency measurement.


3,IF settings
Independent double-IF design, adjust the minimum frequency step of 100 Hz,frequency range 0 ~ 99.9999 MHz, can be set to increase or decrease the IF frequency mode.

4. Frequency reference
Using 5032 package 13.000MHz Warming voltage controlled crystal oscillator (VC-TCXO), frequency stability of ± 2.5 ppm.

5. Operating voltage
DC Input: DC 9V ~ 15V (with reverse polarity protection)

6 Current

Maximum 160 mA (test conditions: ① DC12V power supply; ② red LED; ③ eight brightness)
7 Eight LED display, the highest display eight digits.
8 Eight LED brightness is adjustable, factory set to maximum brightness.
9 Physical Dimensions,Length × width × height: 125.5 mm × 25.5 mm × 21.5 mm
10. Component quality 46 g (NW)
11. Onboard Interface
DC IN (Power Interface): HX2.54-2P socket
RF IN (signal input): HX2.54-2P socket
ICSP (programming interface): 2.54-6P Pin
Color;Red,Blue and Green


Package included :

1 x 0.1-60MHz 20MHz ~ 2.4GHz RF Singal Frequency Counter Cymometer Tester Meter

First impressions

The frequency counter arrived after just over a week. It appeared solid and well made. Two connectors were included.
I used a wall wart type adapter (12v 3a max) and hooked it up to the signal generator. The result was a very fluctuant reading, making it essentially unusable. The video below illustrates what I mean

https://youtu.be/vgdWyfgDFCs

£10 down the drain, I thought! The oscilloscope confirmed that the output from the signal generator was steady, localising the fault to the counter.

Second attempt

In desperation, I attempted to power it from a new 9v battery. With its high power consumption (150mA), the battery wasn't going to last long, but it would do as an experiment.

I also did some changes to the settings. The unit comes with two buttons, of which the top can be used to toggle a settings menu. The IF offset frequency can be set here. So can the channel (high/low/auto - lower being more accurate) and the brightness. I set the channel to low (range 100kHz to 60MHz) and the brightness level to 1 (lowest).

I was rewarded by a good stable reading, indicating that the unit needs a good stable power source. I rummaged in the "man drawer" and found an old 12v 1a power supply from an old Netgear router. It worked well - the frequency readings remained accurate and stable.

Some finishing touches included a co-ax socket and a DC connector (see pictures). Not particularly pretty but they get the job done and save me having to use a number of crocodile clips.

Finally, this is a video of it working with my heathkit.

https://youtu.be/QGn5ZooKXtI

As you can see the reading appears accurate, and stable. It happily reads between 100kHz and 60MHz on the "low channel". Between 60MHz and 200MHz it will need to be shifted, automatically or manually, to the "higher channel". I have connected the signal input into the frequency counter to the unattenuated signal output from my additional socket on the Heathkit. Of course, you can use the RF out socket, but it won't work if the signal is too attenuated (ie ensure output is at maximum)

Conclusion

With a bit or perseverance, most of it down to locating a suitable power supply, this is a pretty good performer for its price. It is capable of reading anything the heathkit can output, working well from 100kHz to 200MHz. The only downside is that it's probably unsuitable for battery power. The IF offset frequency is a bonus and may increase the breadth of its application. The lowest brightness setting is plenty, and defaulting the channel to "low" increases accuracy and is sufficient for AM alignment.

I hope someone finds this useful. I'm happy to answer any questions. David is testing a similar unit at present too (we've been communicating by email) so I'm very interested for him to add his thoughts to mine.

Gabriel
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Last edited by Gabe001; 27th Jul 2021 at 6:48 pm.
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Old 27th Jul 2021, 6:59 pm   #2
Bazz4CQJ
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Default Re: A cheap Chinese frequency counter, a review

I've bought a number of budget-priced counters over the years, and have generally been happy with them.

The one issue that is sometimes arises is the question of drive level; not too little and not too much. Then there are factors like noise on the input and the waveform.

On my to do list is to knock together a circuit I saw that uses a Schmidt trigger used ahead of the counter to try and ensure it is only fed with clean square waves, and I think it also has a drive limiting feature too. I know I have over-driven one unit to it's death.

B
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Old 27th Jul 2021, 7:00 pm   #3
paulsherwin
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Default Re: A cheap Chinese frequency counter, a review

Not bad for nine quid.
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Old 27th Jul 2021, 7:07 pm   #4
Gabe001
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Default Re: A cheap Chinese frequency counter, a review

Quote:
Originally Posted by Bazz4CQJ View Post
I've bought a number of budget-priced counters over the years, and have generally been happy with them.

The one issue that is sometimes arises is the question of drive level; not too little and not too much. Then there are factors like noise on the input and the waveform.

On my to do list is to knock together a circuit I saw that uses a Schmidt trigger used ahead of the counter to try and ensure it is only fed with clean square waves, and I think it also has a drive limiting feature too. I know I have over-driven one unit to it's death.

B
There's a nice Arduino project that appears to work well too. Had I not got this to work satisfactorily, this is what I would have built.

https://create.arduino.cc/projecthub...-6-5mhz-6b496e
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Old 28th Jul 2021, 2:44 pm   #5
SiriusHardware
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Default Re: A cheap Chinese frequency counter, a review

Most likely the issue with the first PSU was that it had too much stray mains AC leaking to 0V through the low value Y class capacitor which connects DC 0V out to the high voltage side. As an experiment, try measuring the AC voltage between the 0V-out of that PSU and a known good mains earth.

You got lucky with the second PSU but I would suggest that either a linear supply or a better class SMPSU in which the DC 0V-out is connected to mains earth would be a better fit for this type of item.
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Old 28th Jul 2021, 3:35 pm   #6
Gabe001
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Default Re: A cheap Chinese frequency counter, a review

David is currently experimenting with a stable linear bench power supply, I'm sure he will let us know his findings.
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