front end modification of the 50 MHz crystal Frequency Counter kit

[jonovid]

I'm interested in using the cheap 1 Hz to 50 MHz  crystal Frequency Counter kit as audio /ultrasonic Frequency Counter.
this unit is sold as a cheap & simple crystal Frequency test oscillator DIY kit.
so has anyone any ideas for adding a 1 Hz to 2 MHz preamplifier to the input of this Frequency Counter kit?
anyone constructed front end circuit? or made preamplifier modifications? 
the original Frequency Counter circuit http://www.qsl.net/dl4yhf/freq_counter/freq_counter.html
just seeking second opinions on this Frequency Counter kit.  I would appreciate any advice.

[Kleinstein]

It looks like the counter is a direct counting type with a more or less fixed gate time. So it will not work really good with low frequencies. The resolution is limited to so something like 1 Hz or 10 Hz (at best). So not much use below about 1 kHz and thus capacitive coupling at the input should be acceptable.

The is a preamplifier circuit in the link (it might want an extra diode for protection). Another option would be a preamplifier from a CD40xx series inverter or maybe an old 74LS00. With an 2 MHz upper limit an LM311 comparator should work too. Triggering on audio signals is really difficult - this is more something send to a sound-card and using software to determine the frequency.

[rstofer]

One version of the board, commercially available, measures to 1 Hz on a 1 kHz range.  Decent...

http://www.qrpproject.de/Media/pdf/DL4YHFcounterEnglManual.pdf
http://www.qrpproject.de/UK/DL4YHFcounter.html

It has a preamplifier that will probably be adequate.

[jonovid]

thank you 
-hope others post modifications here, \/  if any useful improvements can be made? 
my ordered package of this kit is still in the post, being delivered.  so I have no modification images to show.
I do thank you for your advice. 

post update
found this video
Fairly Easy - Frequency Counter - Electronic Kit Build (part 3)

review of this frequency counter kit clone, as seen in this yt video.
the original frequency counter had a preamplifier for the input. & was intended for amateur radio use.
but the crystal oscillator was added later in the clones of this frequency counter. as a substitute for the preamplifier circuit.
it seems that the frequency counter circuit is good, but the crystal oscillator circuit is poor and unstable.

[jonovid]

preamplifier circuits for this Frequency Counter I was looking for. \/

[tocsa120ls]

Hi,

just bought 2 of these sets -> DL4YHF is right, they pretty much reduced it to a crystal tester (unless your source is okay driving into the crystal tester output)
See picture. Left is the original circuit as delivered by the happy little Chinese people (I think someone just googled "single transistor crystal oscillatoru") but thankfully the supplied 2SC9015 transistor is an IF mixer supposedly good up to 1GHz, so it is suitable to use as an input buffer (right hand drawing)

Do not install the pictured components (3 caps, 2 resistors and the tranny) unless you want to use the kit just as a crystal tester.

For a really good frequency meter, build the right side drawing (taken directly from DL4YHF's homepage) - I drilled 3 new holes for the C9015, cut the trace going to the PIC's 3rd leg - as the designer states, the less distance between the buffer stage and the uC, the better - what could be better than a mm?

I have  to say, this mod really "wakes up" the circuit, before I had to hit the input with almost an 1Vpp signal to wake it up, with the buffer it shows 60kHz  as soon as switched on (my lights PSU, if I'm not mistaken) and only goes to zero if I short the input 330 resistor.

-my 2 cents

[StuartA]

I bought one of those kits and it worked extremely well...for 2 days and then it died. I had killed the PIC, almost certainly by static discharge or spikey connections to the input. I hadn't mounted it in any sort of a box and I was messing with the inputs while it was powered up.

I replaced the PIC and all is well, but I added a resistor (47k ?) across the RF input and another across the crystal connections. I think I added a resistor and a small cap across the DC input too. Once you inserted the PIC, try avoid touching the PCB with you hands, unless wearing an earthing strap.

The problem with pretty much all the DFC modules you can buy is that, too little drive and they don't work and too much drive can fry them.

S

[ledtester]

The youtube user HWCave has done a number of videos on modifying this kit including making the front-end more sensitive and mods to the firmware to improve measurements and to add functionality.

Changing the hardware:  https://youtu.be/0BxpMm6SLoE
Changing the firmware: https://youtu.be/8rOCmhPWLWw
Improving resolution and adding RPM mode:  https://youtu.be/0D6EcgTQtNw
Using the RPM mode: https://youtu.be/QlIv1DEAvQw
Adding up-counting: https://youtu.be/3imEpm_zztQ