zener noise source as a "wideband local oscillator"
I was wondering if a simple zener-based noise source can be used as a local oscillator to a single diode mixer, so that this diode can demodulate ssb signals.
I interest only on CW not voice SSB. Will this configuration be able to demodulate an SSB modulated CW signal?
I know the output tone may be very noisy though, but not "tuning" of this weird local oscillator is needed.
Can't work!
If the noise contains a random frequency and amplitude content, so will the output of the mixer, no matter what kind of signal you try to resolve.
Brian.
All you are going to hear will be wide band noise.
And lots of it.
I read the other day that you can use Zener noise to make a random number generator.
You mean that all the signal generators on my bench are useless, and I have to replace them with Zener diodes?
Noise sources are not local oscilaltors. Depending on the type of noise, you may have all frequency components at all frequencies (white noise, thermal noise and their cousins) but a diode mixer cannot select one frequency over another.
You may get something with digital filtering. But I am not so sure.
Sorry Vfone, yes, they are all useless. I'll send you my address so I can dispose of them for you.
Brian.
Yes I thought so, after an afterthought...
What if I connect a single crystal after the zener noise source?
Will the high Q of the crystal make the noise appear as a single frequency signal?
You will get a narrower band of noise but even if you made a really sharp filter with say 10Hz bandwidth, the amplitude would be extremely small and still variable. The energy in the noise would be spread across the spectrum so the narrower the filter, the more of it you reject and the less remains.
Can I ask what prompted you to ask the question in the original post? I'm just curious.
Brian.
I was thinking of a very broadband simple receiver, with a diode envelope detector and a "local oscillator" that would be able to output power at all frequencies (noise) without need for tuning. Then only the front end filter would determine the frequency of reception. Obviously this can't be done that way.
A way would be to use a fixed low frequency square wave oscillator at the lowest ham band, then filter each of it's harmonics and use it as a local oscillator. It sounds more complex than a broadband vfo.
There are plenty of simple receivers, even a crystal set will work.
The internet is full of simple radio projects, have fun !
I can only hazard a guess!
The total power of the noise source is distributed over a large range of frequencies. I presume that the distribution is 1/f noise type (most common). In any given narrow range, the actual power input to the single crystal (acting as a filter) is extremely small and is within the noise threshold.
If the filter noise threshold is much lower, your idea may work. In any case, you will face the Maxwell's demon.
The object of a radio is to tune to high carrier to noise ratios, not the reverse
SSB requires filter shape to be matched to one side of carrier center and down converted.
That method does work but I would forget the 'noise' solution you proposed.
The usual way to do it is to use a quartz crystal oscillator at say 1MHz, square it's output with a limiting amplifier then use it to generate lots of harmonics. Your receiver then tunes the gap betwen the harmonics and mixes with a single selected harmonic frequency to produce an IF for filtering and detection. It is a basically a superhet receiver where the local oscillator is derived from a narrow range VCO and one of the harmonics, for example:
VFO tunes 1MHz to 2MHz (easy to make stable)
Harmonic generator produces 1MHz, 2MHz, 3MHz, 4MHz..... (a 'comb' spectrum)
To tune 160m band you us ethe VFO alone.
For 80m you filter the 2MHz harmonic and mix with the VFO to tune 3 - 4MHz.
For 40m you filter the 6MHz harmonic and mix with the VFO to tune 7 - 8MHz.
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For 10m you filter the 27th or 28th harmonic and mix with the VFO to tune 28MHz - 29MHz and 29MHz to 30MHz.
The actual frequencies you use are up to you. It combines the stability of the harmonic frequency with the simplicity of a single small range VFO but has the serious drawback of making the harmonic filter difficult to design, especially if you want to make the receiver 'general coverage'. Any leakage of unwanted harmonics will produce 'ghost' signals from stations spaced at multiples of crystal oscillator away from your intended tuning spot. There was a commercial receiver on the market back in the 1980's that had two tuning controls, you set the MHz on one knob and the KHz on the other. The MHz knob was selecting the crystal harmonic and the KHz knob tuned the VFO.
Brian.
A square wave of 1 MHz will have only the odd harmonics, (i.e., 3, 5, 7... MHz) and the intensity drops off markedly.