Your diagram shows three crystals in parallel; they are tightly coupled. You should expect to see the sum and difference frequencies, in addition to harmonics. Most high frequency crystals are designed to be run at 2nd or 3rd overtones and for that you need to keep them lightly loaded.
WWV broadcasts beeps spaced one second apart, on several shortwave frequencies (2.5 MHz, 5, 10, etc). Maybe your circuit could create something similar? Not sure if you'd have trouble with overtones in case you use frequencies which are integer multiples.
No that wont change anything....one can achieve a very stable oscillator without an oven, by mixing these two frequencies. If the crystals have quite close characteristics their up-converted or down-converted frequency should be extremely stable, since they drift at the same amount prior to mixing..
Mix them to their sum and you get 21.000 021 MHz with is the same stability - 1ppm.
Mix them to their difference and you get 1.000 001MHz and that is 1ppm all over again.
Hi,
I can´t see HOW one could mix two independent clock signals as sum or difference.
I assume when you somehow join both signals you will always get 21.000 012 MHz as well as 1.000 001 MHz
Klaus
I've seen this post, and Barkhausen told me: let's give a try and replicate the phenomenon.
I am afraid that somewhere is a misunderstanding.
Whatever crystals I used (various frequencies, various packages, various manufacturers) never ever the oscillator oscillate on two SIMULTANEOUS frequencies.
I used various JFETs (J309, J310, BF245, BF256, MPF102), with various bias currents, but never got two simultaneous oscillation frequencies.
Always I get only one oscillation frequency, most probably the priority is given by the crystal with higher Q.
Sometimes (when perhaps the Q of the crystals are appropriate) I get a free running oscillation, which doesn't match any crystal frequency.
I used various crystal combinations, for example: 4MHz and 10MHz, 9.6MHz and 10MHz, 14MHz and 10MHz, 5MHz and 14MHz, 11MHz and 12MHz, and many other combinations.
I found in my box also a J108 and retest the circuit with mentioned crystals, new series capacitors, and different loads.
But again, I NEVER get two SIMULTANEOUS oscillation frequencies.
Barkhausen oscillation criterion mention that a feedback amplifier can sustain a steady oscillation if the loop gain is equal to unity in absolute magnitude, that is, | β A | = 1, AND the phase shift around the loop is zero or an integer multiple of 2π: ∠ β A = 2 π n , n ∈ 0 , 1 , 2 , …
For the same given feedback amplifier, to get at 2 different frequencies a phase shift necessary to obtain 2 different steady oscillation frequencies, is practically impossible.
Doesn't matter what type of crystals I use. I do have many high quality low ppm crystals that behave the same.
Here is about basic oscillator theory. It's impossible to get the necessary phase shift at two different frequencies and get two simultaneous steady oscillations.
Anybody else who want to try this experiment, it will not take more than 15 minutes to arrive to the same conclusion.
if you actually TRY to make an oscillator with three parallel frequency resonators, you most likely will have it oscillate at only ONE of those frequencies. It is because the gain of your active device might favor one frequency slightly over the others, and as oscillations build up and the active device gets gain compression, only the one In the sweet spot keeps sustained oscillations. The other two will snuff out.
Doesn't matter what type of crystals I use. I do have many high quality low ppm crystals that behave the same.
Here is about basic oscillator theory. It's impossible to get the necessary phase shift at two different frequencies and get two simultaneous steady oscillations.
Anybody else who want to try this experiment, it will not take more than 15 minutes to arrive to the same conclusion.
Are you sure you don't use separate oscillators?
The screenshot picture of the spectrum analyzer have good resolution and contrast, but the picture of the breadboard circuit looks like was taken by the inventor of photography, Nicéphore Niépce.
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