I suppose you are right, SWR doesn't matter that much in the grand
scheme of things with short coax runs and a "tuner" near the rig.
As others have pointed out, SWR contributes to line loss and on long
runs of coax at high frequency this can be quite a bit. 3 dB takes
your 100W down to 50W delivered to the antenna but even worse it takes
half the signal level on the receive side too. When you get up into
the VHF and UHF world, it's very easy to get more than 3dB loss, even
on really good coax (LMR400 is just under 3 dB/100'). Higher SWR will
just make that 3 dB even worse. Then if you add that most solid state
rigs will "fold back" and reduce power output if faced with SWR's
above 3 or less, it can be quite disappointing to figure out that your
100W rig only delivers a few watts to the antenna. SWR is an good
thing to watch.
"Good" antennas usually have a lower SWR when properly "tuned" but
that doesn't mean that a lower SWR makes a better antenna than
another. The issue is how much energy does the antenna radiate in the
desired direction which may include SWR as a factor, but it doesn't
give you the whole picture. A 10 Meter beam 40' up that has a 2.1 SWR
and 12 dB gain would be a much better long distance performer than a
loaded dipole 2' off the ground that showed 1.8 to 1. There are a
number of common antennas that don't show low SWR when in operation,
yet they work just fine. Usually they are fed with ladder line and
not coax to avoid the losses and requre a tuner to couple your
transmitter to the feed line.
However, all that aside, SWR "changes" can be a good thing to watch.
Keeping a record of SWR at specific frequencies can be helpful in
alerting you that something is wrong or something has changed. If all
of a sudden your SWR jumps up and stays high, it might be time to take
a look at things and find out why.
-= bob =-
On Sep 17, 9:59 pm, (Rockinghorse Winner) wrote:
Looking at charts of cable loss due to SWR I note that any swr less than
8
or 9 to 1 results in hardly more than 1 dB of loss due to SWR using even
1/4" coax. So, really, why the FUD on this subject?
Lee
--
Powered by Linux
2.6.32.14-127 Fedora 12
In rotation:http://www.jamendo.com 2.6.31.12-0.2 OpenSU
SE 11.2
"Hug your cat today" 2.6.
24-16 Mint Elyssa