Radio Tuning

[Roy Ingham]

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

 

[Rich Grise]

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

 

[John Fields]

On Wed, 25 May 2005 18:21:36 GMT, Roy Ingham <brif8@hotmail.com>
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 "0-365ľľF" 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 (0ľľF) 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

 

[Roy Ingham]

Thank You all

To build a simple radio, is is better to have a variable
capacitor or a variable inductor?

Thanks in advance

 

[John Fields]

On Mon, 30 May 2005 18:41:19 GMT, Roy Ingham <brif8@hotmail.com>
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

 

[Gar]

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) )
Where:
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" <brif8@hotmail.com> wrote in message
news:Qm3le.68814$IO.35140@tornado.tampabay.rr.com...

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

 

[Rich Grise]

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