Re: How transmitters work.
Jason wrote:
> 1. DC current flows through a crystal.
Crystals, like capacitors, don't pass DC.
> 2. The resonance of the crystal causes the current to form waves
around
> the frequency of crystal
> 3. This new "pulsating" current is then amplified and then sent
through
> the crystal again. (This is called positive feedback)
The oscillator is an amplifier with a freqyuency-selective positive
feedback network around it. Oscillation starts by amplifying noise.
> 4. The pulsating current is sent through a low-pass filter to "filter
> out" unwanted frequencies. (That's why I said "around the frequency"
> of the crystal)
The crystal is a band-pass filter not a low pass filter. A low-pass
filter is also required on the output to remove harmonics.
.
Relevant Pages
- Re: About a narrow filter at 10.7 MHz
... I'm suddenly blank about the name, but it was a balanced transformer ... phasing crystal filter, which I suddenly was blank about when I posted. ... I'm not sure I've ever seen it called a "Lamb filter", ... : "Filters employing crystals were first ...
(rec.radio.amateur.homebrew) - Re: resonators/crystals as filters ?
... >> resonator is possible, as i cant seem to get hold of proper ceramic ... >> was quite low, i gues becuse the ESR of low F crystals is high, and the ... >> what is the diference between a ceramic filter and a ceramic ... >> worth getting a proper ceramic filter and if so where cld i get one ...
(sci.electronics.design) - Re: About a narrow filter at 10.7 MHz
... Certainly it was described first by Lamb, or he actualy came up with ... in that famous 1930's article about improving receivers. ... phasing crystal filter, which I suddenly was blank about when I posted. ... in the SSB column in the fifties that had two serial crystals and one ...
(rec.radio.amateur.homebrew) - Re: resonators/crystals as filters ?
... >> ladder filter design on my web site. ... > using parallel cut crystals in series with the signal and series cut ... > also i note the parasitic capacitance is an issue as i was wondering about ...
(sci.electronics.design) - Re: Receiver bandwidth .. dayton filter find!
... >>>For filters I use microprocessor crystals in the ladder configuration. ... >>the radio since I can program the DDS to function as a sweep generator ... Then I can use the same osc to sweep the filter later to test ...
(rec.radio.amateur.homebrew) |
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