Quadrature oscillator 1KHz-30MHz

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neazoi

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Hello,
I am thinking of the attached Quadrature oscillator covering 1KHz-30MHz, and I wonder if this would work and if it will be stable enough to be used on HF ham bands? (as it is, no decreasing of the range)

I do not expect crystal stability, but I have read that the thermal stability of these chips is 40ppm per C!
Also the max freq of the 74f74 will be kept to 120mhz max.

also, can the 74f74 drive directly an SBL-1 mixer at it's +7dbm?
 

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Don't forget you probably need 0 and 270 degree shifts as well but you can get those from the other flip-flop output pins.

The stability should be good but you will have to be extremely careful to prevent any noise or hum pickup on the resistor wiring. If you use a vaiable resistor for tuning, use a good quality one with low temperature coefficient.

Not sure about the SBL-1 drive levels, the spec (which I don't have to hand) probably doesn't mention driving with a square wave. In a situation similar to yours I have used CD4066 switches as mixers and even simple diode switches, they are quite happy with logic level drives.

Brian.
 


Why do I need the other two outputs? To select the other sideband I guess right?

My intention was to use 4066, but can I make this switching mixer bidirectional, like the diode ring? I am not sure about this.

I am impressed you say that the frequency stability will be adequate, I thought it would be poor!
 

Stability should be good *if the tuning resistor is stable* and your layout is OK. My concern is that the resistor itself and the wiring to it will be very prone to drift and interference.

Yes, the 4066 can be made bidirectional, it is a symetrical device so in theory the mixing process should work in reverse if the input and output 'ports' are reversed.

Swapping the phases should reverse the sidebands but some designs (for example polyphase modulators) need all four quadrature phases to work properly.

Brian.
 
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    neazoi

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In my design, I probably need two phases, as this will drive the sound plaster, with a suitable IQ demodulator/modulator.
Thanks a lot, I like the simplicity of the mixer and the oscillator itself (low number of external components).
 

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