On Tue, 28 Jun 2005 21:01:52 -0700, "Steveo"
wrote:

if you have over a 2:1 standing wave you can do damage to your finals
or linear

*****

Only if you are exceeding the power dissapation of the devices.
Considering the way most CBers use radios and amplifiers, your
statement maybe more ture than false.

Generaly if the power disapation of the finals is not exceeded and
there is sufficient margin to handle the reflected power, it will just
dissapate as heat in the output circuits and the fianls. Then this is
only true if the reflection coefficient of the radio is zero. If other
than zero then there will be some of the antenna power reflected back
to the transmitter reflected back to the load. Then the rest is
dissapated as heat. Then you get all kinds of funny things happening
inside the coax. But that is another subject.

james


"Frank Gilliland" wrote in message
.. .
On 28 Jun 2005 17:51:10 -0700, "K7ITM" wrote in
. com:

snip
But there's a real problem in communicating this. If you hook a 50
ohm
SWR meter to the input of a 75 ohm, 300 ohm, or line of any
impedance
other than 50 ohms, the meter reading won't be the SWR on the
transmission line. That can mislead people into thinking that the
SWR is
changing with line length when it actually isn't.


In addition, most hams (and other non-professionals -- and even many
professionals) don't bother to check that their SWR meter is
properly
calibrated to the impedance they think it is. Most are nominally 50
ohms, but they can be built for any practical line impedance.
Checking
calibration is not all that difficult, if you take the time to do
it.
In addition, your nominally 50 ohm line (or 75 or whatever) can have
an
actual impedance 10% or more from the nominal value. If you have
properly calibrated your meter to 50 ohms, and your line is 60 ohms,
you would read 1.2:1 SWR when your line is actually 1:1. And if the
SWR on the 60 ohm line is 1.2:1, that 50 ohm SWR meter can read
anything between 1:1 and 1.44:1, depending on the line length and
its
load. Finally, though you may have checked that the meter to reads
1:1
with a 50 ohm load and infinity to 1 with a short or open load, the
construction of inexpensive meters may cause them to have
significant
errors at other load impedances.


Impedance matching of an SWR meter is generally unimportant since
most
SWR meters used for HF have a directional coupler that is much
shorter
than the operating wavelength. Regardless, I'm not a big fan of SWR
meters -- they are good for detecting a major malfunction but that's
about it. Antenna tuning/matching is best done with a field strength
meter.







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