Jim,
The problem with your question is that the answer really is "it all
depends".
If the feedline from the antenna is short and relatively low loss, then
the ATU in the shack is fine.
Or if the feedline is very low loss (say open wire line, well supported
and away from conductors), then the length of the feedline does not
matter much at all, and again the ATU in the shack is the more
convenient answer.
OTOH, if the feedline is coax, and the length is for instance 150 feet,
then you would want to consider something at the antenna. Whether that
is a remote ATU, or some type of fixed matching section to bring the
antenna feedpoint impedance down to a range of 30 to 150 ohms would be
in order. With the fixed matching section (antenna loading), you would
also want to have an ATU in the shack.
I have generalized on the antenna type - but the answer remains the same
no matter what the antenna type. Look at a beam with a matching section
at the driven element - that is one example of a fixed matching section,
it will not likely be flat SWR over the entire band and an ATU in the
shack can keep the PA transistors working into a 50 ohm load as you QSY.
Another example of a fixed matching section is a matching inductor (and
possibly capacitor) that is used on many of the popular 43 foot
verticals - but you still need an ATU in the shack.
One solution for a vertical antenna is to feed it with low loss parallel
feedline. Before you scream 'heresy' because the vertical is
unbalanced, there is nothing wrong with using a parallel feedline for a
vertical, the RF will figure it out - the radials are merely the "other
half" of the monopole. If your feedline run is long, consider using
open wire line if you can, or ladderline as a close second. Yes, you
need a current choke at the vertical antenna, and that takes care of the
'balance' situation - use a 1:1 choke, you are simply choking common
mode current and not trying to match the impedance of the feedline.
73,
Don W3FPR
73,
Don W3FPR
On 4/26/2016 4:09 PM, Jim Rodenkirch wrote:
Don: requiring a wide ranging ATU is half of the question, Don!! What is
truly "significant" is this - many hams, new or otherwise, fail to
understand whether they really need an ATU in the shack or do they really,
REALLY need an ATU out at the antenna. For me, THAT's the mystifying piece
of the "ATU question" that always shows up.....
71.5/72 de Jim Rodenkirch K9JWV
Don Wilhelm wrote
Wunder,
The only reason I can understand is that they can get away by stating
that they have an internal ATU. Sadly many hams (particularly newer
hams) gloss over the significance of the need for a wide range ATU.
They don't discover that they need an external tuner for their
"multiband" antenna until after they buy the transceiver and discover
that it is inadequate.
73,
Don W3FPR
On 4/25/2016 7:25 PM, Walter Underwood wrote:
On Apr 25, 2016, at 4:08 PM, Wayne Burdick <
n6kr@
> wrote:
- *Wide-range ATU (> 10:1 at 100 W; > 20:1 at low power) and two
antenna jacks
I am really mystified about why transceivers include a 3:1 range ATU. It
adds $150-200 to the end cost to get an external ATU. It might add $50-75
to make the internal ATU wide-range. It is especially odd for an
entry-level rig, where people are likely to be using a low-slung dipole.
OK, it is very strange for the IC-7851, too.
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