Variable Square Wave to Sine Wave
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From: Robert Baer on 9 Mar 2010 04:17 FyberOptic wrote: > Hiya folks. I've been interested in trying to build myself a radio > receiver for various bands, primarily as a learning experience. The > thing is, though, I've heard that it's kind of hard to build a stable > VFO above 50mhz. One of the bands I'd eventually like to receive is 2 > meters (144-148mhz). Might be fun to receive television audio, as > well. Not to mention, standard FM. > > Since I'm more familiar with digital electronic components rather than > analog, I've seen that there are programmable frequency oscillator > ICs, which can be set via a microcontroller. This sounds like an easy > solution for tuning, and would open the door to setting station > presets and the like as well. The problem is, I'm fairly sure that > these would output a square wave. > > I've read about how you can basically use a low-pass filter to tune > out harmonics of a square wave and get a sine wave output. But from > the way I understand it, an RC filter would just filter out a specific > frequency, defeating the purpose of the variable oscillator. > > So that's pretty much my question: How does one turn a variable > square wave into a sine wave? > > Or, alternatively, what are more reliable ways to produce higher > frequency sine waves to begin with? Though I'm still interested in > the former question as well, for curiosity's sake. > > Thanks! > > - Jeff > > Plain RC filters have a "rolloff" thus work on a range of frequencies. A simple low pass filter would have lower output amplitude as the input frequency goes up. Now why do you think you need a sine wave?
From: Nial Stewart on 9 Mar 2010 08:30 > Two, with all due respect to my learned colleague, instead the of ARRL > handbook, try > > Experimental Methods in Radio Frequency Design, by Campbell, and > Hayward, its more geared to modern, simple, home made gear then the > ARRL handbook is , sadly... I've just had a look at amazon.co.uk (not available) then amazon.com. 4 Used available from _$498.97_ (up to $937.87). It would need to be good at that price! Nial.
From: osr on 9 Mar 2010 09:29 Lets see,mine was 29.99 when they switched from the first edition to the second. Steve
From: George Herold on 9 Mar 2010 10:28 On Mar 9, 8:30 am, "Nial Stewart" <nial*REMOVE_TH...(a)nialstewartdevelopments.co.uk> wrote: > > Two, with all due respect to my learned colleague, instead the of ARRL > > handbook, try > > > Experimental Methods in Radio Frequency Design, by Campbell, and > > Hayward, its more geared to modern, simple, home made gear then the > > ARRL handbook is , sadly... > > I've just had a look at amazon.co.uk (not available) then amazon.com. > > 4 Used available from _$498.97_ (up to $937.87). > > It would need to be good at that price! > > Nial. That's crazy! They had them on Amazon in the US for $49.00 to $41.00. George H.
From: Muzaffer Kal on 9 Mar 2010 11:55
On Tue, 9 Mar 2010 13:30:21 -0000, "Nial Stewart" <nial*REMOVE_THIS*@nialstewartdevelopments.co.uk> wrote: >> Two, with all due respect to my learned colleague, instead the of ARRL >> handbook, try >> >> Experimental Methods in Radio Frequency Design, by Campbell, and >> Hayward, its more geared to modern, simple, home made gear then the >> ARRL handbook is , sadly... > >I've just had a look at amazon.co.uk (not available) then amazon.com. > >4 Used available from _$498.97_ (up to $937.87). > > >It would need to be good at that price! > > >Nial. > It seems to be available at ARRL for $49.99: http://www.arrl.org/catalog/?category=Circuit+Design#9239 -- Muzaffer Kal DSPIA INC. ASIC/FPGA Design Services http://www.dspia.com |