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#1
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Radio Tuning
Hi All
Where or What is the formula to calculate Radio Frequencies? Variable Capacitor (I assuming) as the tuning dial, then what give you the range of Freq to tune into. Yes I'm wanting to start my first electronics project and would like to build a simple yet effective radio, driven on a 9V battery. Also Automatic tuners or scanners found on modern car radios do, these detect the strongest Voltage / ? to determine that the current frequency is a good channel to lock into. You know you press the button and the radio runs through the stations, and stops at some point. Missing some stations. What makes it stop a detection in strong voltage or what ?? Thanks in advance B |
#2
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On Wed, 25 May 2005 18:21:36 +0000, Roy Ingham wrote:
Hi All Where or What is the formula to calculate Radio Frequencies? f = 1 / (2 * pi * sqrt(L * C)). Also, the frequency of a radio wave is equal to the speed of light times the velocity factor of the medium divided by the wavelength. Variable Capacitor (I assuming) as the tuning dial, then what give you the range of Freq to tune into. Yes I'm wanting to start my first electronics project and would like to build a simple yet effective radio, driven on a 9V battery. Also Automatic tuners or scanners found on modern car radios do, these detect the strongest Voltage / ? to determine that the current frequency is a good channel to lock into. You know you press the button and the radio runs through the stations, and stops at some point. Missing some stations. What makes it stop a detection in strong voltage or what ?? Probably a phase-locked loop. But I'd suggest you learn about inductive and capacitive reactance, resonance, and so on before taking on one of those. Good Luck! Rich |
#3
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On Wed, 25 May 2005 18:21:36 GMT, Roy Ingham
wrote: Hi All Where or What is the formula to calculate Radio Frequencies? --- The formula to calculate _any_ resonant frequency involving a capacitance and an inductance is: 1 f = ---------------- 2pi (sqrt (LC)) where L is the inductance in henrys and C is the capacitance in Farads. --- Variable Capacitor (I assuming) as the tuning dial, then what give you the range of Freq to tune into. --- The range of the variable capacitance and the inductance of the fixed inductor. For example, in the old "All-American 5" 5 tube superheterodyne receivers, what was called a "0-365µµF" tuning capacitor was used to cover the range of frequencies from 540 to 1600kHz. Rearranging the formula to solve for L will give you the value of inductance needed to resonate the 365pF of capacitance at the 540kHz end of the dial and then, knowing that inductance, you can rearrange again and solve for the required capacitance at 1600kHz. At the high frequency (0µµF) end of the band, the tuning capacitors had what are called "padders" (screwdriver adjustable capacitors in parallel with the variable capacitor) which were used to resonate the coil with the variable capacitor in its low capacitance position at about 540kHz. There was some slop on both ends so that as things drifted bothe ends of the range were still available, although stations at the low and high frequency ends of the dial might not appear at exactly where the pointer said they were. --- Yes I'm wanting to start my first electronics project and would like to build a simple yet effective radio, driven on a 9V battery. --- If you're interested in radio, you should get acquainted with the ARRL at: http://www.arrl.org/ --- Also Automatic tuners or scanners found on modern car radios do, these detect the strongest Voltage / ? to determine that the current frequency is a good channel to lock into. You know you press the button and the radio runs through the stations, and stops at some point. Missing some stations. What makes it stop a detection in strong voltage or what ?? --- Strong voltage. -- John Fields Professional Circuit Designer |
#4
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Thank You all
To build a simple radio, is is better to have a variable capacitor or a variable inductor? Thanks in advance |
#5
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On Mon, 30 May 2005 18:41:19 GMT, Roy Ingham
wrote: Thank You all To build a simple radio, is is better to have a variable capacitor or a variable inductor? --- It depends on the frequency and the tuning range, but generally a variable capacitor is better. Easier, anyway. -- John Fields Professional Circuit Designer |
#6
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1) Excepting digital, most modern radios use a tuning diodes such as:
Industry Number : NTE618 NTE Device Number: NTE618 DIODE-AM RADIO TUNING DIODE Simple non-hetrodyne radio application. This nifty diode has about a 10:1 capacitance change effected by applying a tuning voltage. For a parallel tuning circuit you will need to add additional blocking diodes and a bypass cap. Use the simpler series resonant circuit. In either case a biasing network applys a tuning voltage to the diode. If you google this device NTE918 you probably can find examples of circuits. The frequency formulas are the same as for a variable capacitor which is actually what this diode becomes in the circuit. Freq = 1 / ( 2pi * squareroot of ( L*C) ) Whe Freq is in cycles per second L is in henries C is in farads You can use a series resonant circuit, tuning diode in series with your inductance. The NTE 918 works for the AM band. Google the specs, plug in its midrange capacitance in Farads ( picofarads times ten to the -12) and the middle of the AM band freq. (~ 1,200,000 cycles / second) into the formula above to calculate the needed inductance in henries. Here is the mystery. You will also need to fix the bandwidth (Wbw) to 10,000 AM. For a series circuit, Wbw = R / L You do this by fiddling with the source resistance of the network feeding the voltage to the tuning diode. Use the Thevenin equivalent resistance of the source. 2) Phase lock loops can be used to lock onto an adequately strong carrier signal. "Roy Ingham" wrote in message . .. Hi All Where or What is the formula to calculate Radio Frequencies? Variable Capacitor (I assuming) as the tuning dial, then what give you the range of Freq to tune into. Yes I'm wanting to start my first electronics project and would like to build a simple yet effective radio, driven on a 9V battery. Also Automatic tuners or scanners found on modern car radios do, these detect the strongest Voltage / ? to determine that the current frequency is a good channel to lock into. You know you press the button and the radio runs through the stations, and stops at some point. Missing some stations. What makes it stop a detection in strong voltage or what ?? Thanks in advance B |
#7
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On Mon, 30 May 2005 18:41:19 +0000, Roy Ingham wrote:
Thank You all To build a simple radio, is is better to have a variable capacitor or a variable inductor? Depends on how much of it you're building. If you're winding your own coils and building up your own capacitors, then a variable coil is much, much easier - if you can buy them, then a variable capacitor is the way to go. (I'm reminded of the crystal set with the tank coil wound on a toilet paper roll, and a strip cut from a tin can for a wiper...) Good Luck! Rich |
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