"c.foster" wrote:

how do you determine the impedance of an antenna?
is this something i can do with a multi-meter or is it very technical?

thanks
chuck

In electronics there are basically three kinds of signals, DC (direct
current), AC (alternating current) and more recently, digital. DC means
the current flows continuously in one direction but it can change in
value. AC current is constantly changing in value and periodically
reverses in direction. A digital signal can be seen as a kind of pulsing
DC where the signal is either on or off but not somewhere between those
two values or 'states'. In a DC circuit, the relationship between
voltage-V and current-I gives the resistance-R of the circuit. The
formula is V/I=R. However things are not so simple with an AC circuit,
particlarly one involving an RF (high frequency AC) signal. In that
case, the word 'impedance' is used to define a special kind of
resistance for AC signals. The impedance of an antenna is the
relationship between voltage and current at the feed point where the
lead wire is connected. This is not something which can be measured with
a typical multi-meter because it involves RF rather than pure DC or low
frequency AC. However the impedance of an antenna can be measured with
the proper equipment. In the days of vacuum tubes there was a device
called a 'grid dip meter' which could be used to evaluate an antennas
charecteristic impedance at a particular frequency. Today we have more
sophisticated solid state equipment for doing this. The first URL below
shows one of these devices. The other two addresses have more
information about antennas.

http://www.mfjenterprises.com/produc...rodid=MFJ-259B
http://www.ominous-valve.com/antennas.txt
http://digilander.libero.it/iw3sim/antennas.html


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STARMAN,

Nice Answer and Two Very Good Links:

http://www.ominous-valve.com/antennas.txt

http://digilander.libero.it/iw3sim/antennas.html

iane ~ RHF
..
..
= = = starman
= = = wrote in message ...

"c.foster" wrote:

how do you determine the impedance of an antenna?
is this something i can do with a multi-meter or is it very technical?

thanks
chuck


In electronics there are basically three kinds of signals, DC
(direct current), AC (alternating current) and more recently,
digital. DC means the current flows continuously in one direction
but it can change in value. AC current is constantly changing in
value and periodically reverses in direction. A digital signal
can be seen as a kind of pulsing DC where the signal is either
on or off but not somewhere between those two values or 'states'.
In a DC circuit, the relationship between voltage-V and current
-I gives the resistance-R of the circuit. The formula is V/I=R.
However things are not so simple with an AC circuit, particlarly
one involving an RF (high frequency AC) signal. In that case,
the word 'impedance' is used to define a special kind of
resistance for AC signals. The impedance of an antenna is the
relationship between voltage and current at the feed point
where the lead wire is connected. This is not something which
can be measured with a typical multi-meter because it involves
RF rather than pure DC or low frequency AC. However the impedance
of an antenna can be measured with the proper equipment. In the
days of vacuum tubes there was a device called a 'grid dip meter'
which could be used to evaluate an antennas charecteristic
impedance at a particular frequency. Today we have more
sophisticated solid state equipment for doing this. The first
URL below shows one of these devices. The other two addresses
have more information about antennas.

http://www.mfjenterprises.com/produc...rodid=MFJ-259B
http://www.ominous-valve.com/antennas.txt
http://digilander.libero.it/iw3sim/antennas.html


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-----== Over 100,000 Newsgroups - 19 Different Servers! =-----