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front end modification of the 50 MHz crystal Frequency Counter kit
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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?  :-/O
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. \/
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