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Questions tagged [oscillator]

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5
votes
2answers
94 views

Is there a best ratio of L to C in a resonant circuit?

When designing a resonant circuit, for example as a local oscillator, the product of $L$ and $C$ determine the resonant frequency according to $$f_{res} = \frac{1}{2\pi \sqrt{L C}}.$$ This means that ...
2
votes
2answers
245 views

78.5MHz AM receiver self-oscillation

Circuit appears to be working but very easily breaks into oscillation - sometimes just getting up from my desk triggers it, or while tuning, and sometimes after a few seconds with no disturbance that ...
1
vote
1answer
78 views

How does this Pixie circuit produce a beat frequency?

I have two Chinese Pixie kits that I've assembled. I think they are pretty interesting, from a QRP / tinkering stand-point. Looking at the schematic below, where is the beat frequency coming from? ...
1
vote
1answer
114 views

Frequency divider in premix oscillator (PMO)

In his book "Crystal Sets to Sideband", Frank Harris K0IYE describes using premix oscillators (PMOs) to convert signal from low-frequency LO to a particular ham band. Many ham bands are harmonically ...
3
votes
5answers
579 views

“Local oscillator generates a frequency twice lower than received signals”. Why and how does it work?

I would like to construct the following receiver: I have a fair knowledge about a receiver building blocks. I have previously build small receivers. In the description it say: The local ...
4
votes
4answers
1k views

Shaving Quartz Crystal for New Frequency

Back in the 1960s during my Novice days I operated on the 40-meter band only with 4 different quartz crystals that determined my transmitting frequency with my Eico 720 CW transmitter. I had heard ...
3
votes
1answer
326 views

How can I tell the frequency without an oscilloscope, or frequency counter?

Just going through the RF oscillator listed on SM0VPO's web-site. I replaced C1 by a reverse biased 6A8, and used an E-core transformer pulled out of a Compact Fluorescent Lamp instead of an inductor ...
4
votes
3answers
1k views

SSB demodulation

I was building the superhet receiver for ham radio. But I seem to have got stuck at the demodulation stage. As an example: Suppose the person is transmitting SSB signal (20m band) at 14.250 MHz ...
5
votes
1answer
550 views

Doppler Shift Compensation in Inter Satellite Communication

I am currently doing a project in the area of optical inter-satellite communication (GEO-LEO). I am using a optical carrier of 281 THz, and the Doppler shift corresponding to it is ±7 GHz. I ...
6
votes
2answers
208 views

Does the waveform of the VFO necessarily have to be sinusoidal?

Looking around for a VFO online, I see most kits/manufacturers make it a point to mention the waveform. Sinusoidal is a fundamental shape, whereas others (sawtooth, square) are a composite. I recall ...
3
votes
1answer
385 views

Can an external VFO be injected into a commercial rig?

Constraints of various kinds preclude any investment in a rig at present; so I find myself pondering the means to get back on the band piece-meal. Say I were successful in an attempt to throw ...
7
votes
2answers
4k views

Why prefer LC oscillators rather than RC oscillators in RF design?

I don't recall ever seeing an RC oscillator driven RF transmitter or receiver. What prevents people from choosing RC oscillators in RF design?
1
vote
1answer
83 views

Can I filter after modulation when using a square wave oscillator? [closed]

Most designs appear to filter most of the harmonics out of the oscillator before modulation, then apply additional filtering as needed for the specific modulation they are using after modulation. ...