MEL’S

DOG & PONY SHOW

RADIO FREQUENCY FILTERS

A radio frequency filter

is an electronic circuit that

will allow or not allow a

band of frequencies to

pass thru it

RADIO FREQUENCY FILTERS

There are 2 basic

types of filters

SERIESOR

PARALLEL

RADIO FREQUENCY FILTERS

Today we will be discussing

SERIES FILTERS

More commonly called

The Series Resonant Circuit

RADIO FREQUENCY FILTERS

The purpose of a

SERIES RESONANT CIRCUIT

is to allow a specific band of

frequencies to pass thru it

RADIO FREQUENCY FILTERS

The simplest

SERIES RESONANT CIRCUIT

looks like this

RADIO FREQUENCY FILTERS

RADIO FREQUENCY FILTERS

Now, to design our Series Resonant Circuit we will need to do some math

These are the formulas we will need

RADIO FREQUENCY FILTERS

PRIMARY ASSUMPTION

The antenna is a standard Half-Wave Dipole

The antenna is tuned to the center of a band

RADIO FREQUENCY FILTERS

RESONANCE AND REACTANCE FORMULAS

2 * pi * L Cf =

1

4 * pi * f2 2LC =1

4 * pi * f * L22C =1

XL = 2 * pi * f * L2 * pi * f * C

1XC =

F

BWQ =

4 * pi * f * CL =

12 2

Inductance

in Henries

Capacitance

in Farads

RADIO FREQUENCY FILTERS

VSWR EQUATIONS

P = 1 2Z Z

Z1 Z2

VSWR = 1 P

1 P

RADIO FREQUENCY FILTERS

COIL WINDING FORMULASL = self inductance in microhenrys

N = total number of turns

r = mean radius of the coil in inches

l = length of coil in inches

9r + 10lL =

(r N) 2

L(9r +100l)

rN =

l

r

TIME FOR THE

SPREAD SHEET

RADIO FREQUENCY FILTERS