The big problem is that the Vbe of the transistors change with temperature. If you are after crystal like performance (100 ppm per deg C). Then it will be impossible for an amateur to do unless you have a temperature controlled oven to test it in and a stable oscillator to compare it with. Why not build a crystal oscillator and divide its output down to the correct frequency. Another thought put it and its PSU regulator in a low temperature oven set to say 50 degs C in use.
Frank
I need a very stable audio oscillator circuit that operates at a single frequency somewhere at 30Hz.
Square wave is preffered and stability is the key point, since it will be used as a reference to lock a higher frequency oscillator.
You need to specify what you mean by very stable.
Theoretically speaking, a square wave is not a single frequency. By convention, the sine and cosine functions form the basic of all periodic functions.
Most likely you will need to have an oven for keeping the temperature constant to 0.1C or better.
Usually we use an accurate high frequency clock (Rb or Cs) or NMR signals (D2 lock) as reference lock- they can provide 1e-9 stability or better.
In any case, drift will be your only enemy.
This is the correct answer. The 4060 fits the bill perfectly.Hi,
HC4060 and a crystal and come Cs, maybe Rs.
Klaus
This is the correct answer. The 4060 fits the bill perfectly.
If for some reason you're opposed to using a crystal+divider, linear technology sells some precision astable oscillators capable of very low frequency operation.
That is absolutely correct.I suspect this is part of a 'huff n puff' stabilizer, perhaps Neazoi can confirm.
Brian.
It is a method of locking a higher frequency oscillator to a low frequency reference without using a PLL. It uses the LF reference to open a gate, allowing the HF to reach a counter. Depending on whether it overflows or not, you raise or lower an analog voltage to 'pull' the HF oscillator one way or the other. Essentially it produces a modulo 30 count of the HF and through a long time constant network, locks it to a multiple of 30Hz.
I suspect this is part of a 'huff n puff' stabilizer, perhaps Neazoi can confirm.
That is absolutely correct.
I need to investigate if the stability of the multivibrator circuits is enough for producing this audio reference.
Two crystal oscillators mixed down would be too difficult to keep unlocked when they operate 30hz apart.
You are putting the cart before the horse here....
Trying to build a stable 30 Hz discrete component oscillator to stabilize a much higher frequency VFO is a complete waste of time.
Just build a stable VFO, it will not be any more difficult.
The very best basis for a home brew VFO is a Collins Permeability Tuned Oscillator (PTO).
These were built by Collins Radio in the 1950's when valves were the go, and well before the age of integrated circuits and digital synthesis.
Distortion will not be your problem, frequency stability will be.
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