25 - Equipment Review: A first look RF Signal Frequency Counter

 Equipment Review: A first look

RF Signal Frequency Counter

0.1MHz to 2.4GHz as seen on EBAY! By Ian, MI5AFL

I do have a couple of frequency counters that are 30 years old that will read to 550MHz but need 10
seconds to read to one hertz accuracy. I found the unit above on Ebay, there are a lot of frequency
counters on Ebay! But some have only 6 digits or use an LCD. It can be difficult to be sure of the
actual function of these units as the English description is often Chinglish and a bit inscrutable. I
wanted to measure crystals to one hertz accuracy for some Crystal filters I am building and wanted a
second (or third!) way of checking parameters; I have to admit my NanoVNA doesn’t drift much
when measuring the frequency of crystals but I like to have 2 or 3 different ways of measuring
things. In any case at under a tenner including postage it was worth taking a chance to see if it would
work. I am pleased to report it works very well! I paid £7.62 for mine plus postage from the Seller
“Alimodule” but there are over 20 sellers offering what looks like an identical or nearly identical
module. I got an email saying it might take 40 days and not to report the seller to Ebay however it
arrived in 25 days.

The connections to the unit are not too difficult to work out – there are two identical 2 pin plugs
mounted on the board (in white in the first photograph) and two leads are supplied, each with red
and black wires. You need to know that the lead near the two metal capacitors is for DC power (9 to
15V@60 to 160mA I think) and the input is applied to the end with all the SMT components (right
hand side in the top photograph).

There are also two pushbutton switches on the front of the unit, marked with a sideways U and a solid triangle, these “SET” or “CHANGE” values. Finding out what these do took some searching on the web for a manual, I am glad to say I succeeded although blind experiment would have worked eventually. I can email the manual to any who want it.

The “user interface” allows for 6 functions;

A single depression and release of the SET button brings up the words IF000000. If you hit the CHANGE button, it repetitively alters the first digit, hitting SET moves to the next digit and hence you set an offset between measured and displayed frequency. A final SET moves to the next menu item.

If after hitting the first SET button, you then hit SET again you arrive at the second menu item immediately - the message changes to “IF N” or “IF U” with the CHANGE button toggling between these, you exit this mode by hitting SET again. This mode allows you to either subtract or add the offset. Useful to retrofit into a radio and get a read out of the received or transmitted frequency when the Radio’s VFO is above or below the desired frequency by the IF frequency – often 9MHz or so. I may eventually fit this unit into my BitX 40, my 80m Epiphyte or a RF50 6m SSB transceiver kit I built from Hands Electronics a long time ago, though I might go back to EBAY and get a 6 digit as the VFOs in these rigs are probably not that stable to need 1 Hz accuracy.

The third menu item sets the channel mode to “A”, “L” or “H” and this selects the measured frequency range to 0.1MHz to 60MHz (the “LOW” band) or 20MHz to 2.4GHz (the HIGH band). These bring in a pre-selector and affect resolution. The LOW band can display to 1 Hz resolution whereas the HIGH band can display to 64Hz accuracy. The display on my unit refreshes every second.

The manual I downloaded has a next menu item that allows setting a filter; “DF ON” or “DF OFF” is the message. Did not do much for me – but my test signals were clean. The next menu item was marked as “Move a bit to the right” in the manual and “] on” and “] Off” on the display. I believe this toggles my unit between 0.1 second and 1 second sample time, which makes the unit read to 10Hz or 1Hz resolution on the LOW band. There is a further menu item that sets the LED brightness between “L 1” and “L 8”, from an easy to read dim to an overly bright level 8 display (I left mine on “L 1”). Do note however that I came across a diagram on the net (in Russian!) that showed a further menu item to set more options on gate time so your purchase might be slightly different to mine.

Once you have set the menu items the mode is stored and remembered the next time you switch on. So you only have to configure the unit once, and it might just work out of the box.

I connected the unit up to a Marconi 2022 signal generator which I believe is stable and accurate and also to my old frequency counter (a GW GFC 8055G). I did have to experiment quite a bit to set the signal generator output level to get a stable reading on the Ebay unit. On the low band any value from 200mV to 500mV worked ok but not above or below this value. The manual said 60mV sensitivity on the LOW band which seems optimistic.

At 11,000,000 Hz output the unit displayed 11,000,013 Hz so is a bit high, there are a couple of presets on the board but so far I have left it alone – it will suffice for my needs because it is remarkably stable. Left overnight in an outside shack, albeit above my garage and well insulated, the display read 11,000,014 the next morning so I can declare it as being stable, if not quite calibrated. The specification in the manual mentions a 2.5ppm TCXO and mine seems much better than this. I applied a 1GHz signal and set the mode to H, it read correctly with occasional readings jumping up 64Hz. It stayed stable for the hour that I ran this test. Not bad for a tenner!