Is minimum Z, across a frequency scan, 'resonance' on a 1/4 wave vertical?

Is it resonance on a center loaded vertical?

Thanks - Dan kb0qil

dansawyeror wrote:
Is minimum Z, across a frequency scan, 'resonance' on a 1/4 wave vertical?

Is it resonance on a center loaded vertical?

Thanks - Dan kb0qil


resonance is defined as XL = XC

dansawyeror wrote:
Is minimum Z, across a frequency scan, 'resonance' on a 1/4 wave vertical?

The Xc=XL frequency is not always minimum Z and
is also not always minimum SWR according to my
MFJ-259B.
--
73, Cecil http://www.qsl.net/w5dxp

The point of minimum Z (that is, minimum magnitude of Z) will probably
be close to resonance. Resonance is the frequency at which the reactance
is zero. In a typical antenna near resonance, the reactance changes much
faster than resistance with frequency. This causes the magnitude of the
impedance, and the SWR, to be minimum near the resonant frequency. It
should be true for the antennas you asked about. It isn't true for all
antennas, however.

Roy Lewallen, W7EL

dansawyeror wrote:
Is minimum Z, across a frequency scan, 'resonance' on a 1/4 wave vertical?

Is it resonance on a center loaded vertical?

Thanks - Dan kb0qil

Isn't it necessary to define an impedance against which the antenna input
impedance and SWR is referenced? It may not always be 50 ohms or some other
"standard" impedance.

For example, a self-resonant 1/2-wave dipole in free space has an input Z of
about 65 +j0 ohms, but will not constitute a 1:1 SWR to an r-f system that
otherwise is 50 ohms, even though antenna reactance is zero.

RF
_________


"Roy Lewallen" wrote:
The point of minimum Z (that is, minimum magnitude of Z) will probably be
close to resonance. Resonance is the frequency at which the reactance is
zero. In a typical antenna near resonance, the reactance changes much
faster than resistance with frequency. This causes the magnitude of the
impedance, and the SWR, to be minimum near the resonant frequency. It
should be true for the antennas you asked about. It isn't true for all
antennas, however.

Roy Lewallen, W7EL

dansawyeror wrote:
Is minimum Z, across a frequency scan, 'resonance' on a 1/4 wave
vertical?

Is it resonance on a center loaded vertical?

Thanks - Dan kb0qil

SWR is the dimensionless ratio of two voltages, a maximum and a
minimum, which may be measured along a transmission line, spaced apart
by 1/4-wavelength of line.

Or it can be the ratio of two similarly displaced currents.

It is fully described without reference to line impedance, source
impedance, terminating impedance, line length, or where the max and
min volts are located.

Incidentally, before it can be used for anything, extra information is
needed.

========================================

"Richard Fry" wrote in message
...
Isn't it necessary to define an impedance against which the antenna
input
impedance and SWR is referenced? It may not always be 50 ohms or
some other
"standard" impedance.

"Reg Edwards" :
SWR is the dimensionless ratio of two voltages, a maximum and a
minimum, which may be measured along a transmission line,
spaced apart by 1/4-wavelength of line.
It is fully described without reference to line impedance, source
impedance, terminating impedance, line length, or where the max and
min volts are located.
___________

SWR may be calculated as (A+B)/(A-B), where A & B are square roots of
expressions containing both the complex load impedance, and the reference
impedance against which the SWR is referred.

RF

Reg Edwards wrote:

SWR is the dimensionless ratio of two voltages, a maximum and a
minimum, which may be measured along a transmission line, spaced apart
by 1/4-wavelength of line.

Or (|Vfor|+|Vref|)/(|Vfor|-|Vref|)

Or it can be the ratio of two similarly displaced currents.

Or (|Ifor|+|Iref|)/(|Ifor|-|Iref|)

Or at an (antenna feedpoint) impedance of (R +/- jX) and a resistive Z0

SQRT[(R+Z0)^2+X^2] + SQRT[(R-Z0)^2+X^2] divided by
SQRT[(R+Z0)^2+X^2] - SQRT[(R-Z0)^2+X^2]

Or (1+rho)/(1-rho) if the reflection coefficient is known.

Or it can be [SQRT(Pfor)+SQRT(Pref)]/[SQRT(Pfor)-SQRT(Pref)]
which is the indirect one a typical MFJ dual-needle SWR meter
uses.
--
73, Cecil http://www.qsl.net/w5dxp

Richard Fry wrote:
SWR may be calculated as (A+B)/(A-B), where A & B are square roots of
expressions containing both the complex load impedance, and the
reference impedance against which the SWR is referred.

I have an EXCEL spreadsheet that calculates SWR seven different
ways, if I remember correctly.
--
73, Cecil http://www.qsl.net/w5dxp

"Cecil Moore" wrote in message
om...
Richard Fry wrote:
SWR may be calculated as (A+B)/(A-B), where A & B are square roots of
expressions containing both the complex load impedance, and the
reference impedance against which the SWR is referred.

I have an EXCEL spreadsheet that calculates SWR seven different
ways, if I remember correctly.
--
73, Cecil http://www.qsl.net/w5dxp


What does the spreadsheet do if you don't remember correctly?

73,
John