Hi Ram,
Do you have an oscilloscope? If so look at the waveform from your
crystal test oscillator--I bet it's more of a square wave than a
sine wave and if so your counter is looking at the stronger 3rd
harmonic component and reading that instead of the fundamental.
73,
Steve AA7U
On 11/11/2019 9:52 AM, Ramakrishnan
Muthukrishnan wrote:
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I am very early into the
project. As a first step, I thought of building a G3UUR
crystal tester to select crystals for the filter and the
oscillators. I have got about 100 4.9152 MHz crystals that I
got from aliexpress. Last weekend I built the G3UUR Colpitts
Oscillator (straight out of the EMRFD book and also described
in many other webpages). I also have a counter with a 1 Hz
resolution, again obtained from Aliexpress specifically to
hook up into the Oscillator.
Unfortunately, when I plug in the
4.9152 MHz crystal, I get a reading of 14.742475. Looks like it
is 3x the frequency of the crystal. I tested many from the lot
of 100 crystals, which came in lots of 50 from two different
vendors and they all read the same. I had a 28.04 MHz crystal
which seem to be oscillating at the correct frequency. I don't
know what to make out of these readings. Is the crystal, a 3rd
overtone crystal? Or is it that the colpitts oscillator is
designed to operate at a higher frequency and the 3rd harmonic
is where the tuned circuit that comprise the crystal (which is
inductive?) and the two capacitors are getting tuned?
73
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