RadioBanter - Smith Charts

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"gareth" wrote in message ...

I wonder if anyone takes a more scientifc approach by measurement and then
calculation, such as by Smith Chartification?

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Yes, the world's Navies do. I worked for the US Navy for many years so I
know much of what they do.

On HF, a few transmissions are made on whips with base-mounted couplers to
bring the whip to resonance.

The remainder are by broadband antennas (2 - 6, 4 - 12, 10 - 30 MHz) These
broadband antennas are fed through matching networks that had to bring them
within the 3:1 circle on the Smith Chart. During inspections, we had to
sweep them and we reported any that failed. (Some of our tasks were
find-and-fix, most were not.)

We used an Anritsu something-or-other as the sweeper. It had ten memories,
so we could store profiles for multiple antenna ranges. Although I want one
for home, they're far too expensive for me. I have an AA-54 from RigExpert.
It's the Poor Man's Anritsu.

"Sal"
(KD6VKW)

"Sal M. O'Nella" wrote in message
...

The remainder are by broadband antennas (2 - 6, 4 - 12, 10 - 30 MHz)
These broadband antennas are fed through matching networks that had to
bring them within the 3:1 circle on the Smith Chart. During inspections,
we had to sweep them and we reported any that failed. (Some of our tasks
were find-and-fix, most were not.)

Interesting. I wonder if that could be the solution to amateur
installations,
a set of broadband dipoles, but perhaps swept smithchartwise to better
than 2:1?

"gareth G4SDW GQRP #3339" wrote in message
...

"Sal M. O'Nella" wrote in message
...

The remainder are by broadband antennas (2 - 6, 4 - 12, 10 - 30 MHz) These
broadband antennas are fed through matching networks that had to bring
them within the 3:1 circle on the Smith Chart. During inspections, we had
to sweep them and we reported any that failed. (Some of our tasks were
find-and-fix, most were not.)

Interesting. I wonder if that could be the solution to amateur
installations,
a set of broadband dipoles, but perhaps swept smithchartwise to better
than 2:1?

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

Quite on target.

Apropos of that, I fielded an inquiry last week from a fellow in our club
who wants some help putting up a 125' long-wire for 30m operation. I've
tried to convince him that random-length wires are tricky and any end-fed
antenna can be a matching nightmare but he insists he still wants to try it.
I've never tried long-wire for transmit, so ... might as well play. He
would like to go coax from the shack to an end-feed about 25 feet aloft.

I've been debating with myself whether I could do a Smith chart at the feed
point and calculate the required component(s) to be placed at the feed. If
he's only going to use it for one frequency (essentially, since that band is
so narrow), I just have one point on the chart to move with one or more
reactive component(s). The big drawback, as I see it, is there is no ground
for the shield. I have not yet investigated matching techniques for this,
although I do recall reading about a so called 9:1 balun. More research
needed.

Although I sure as heck can read a Smith Chart and tell you whether the
tested frequencies fall within the 3:1 VSWR circle, I've never gone the
other way -- taking a "bad" antenna and bringing it to good health, IRT its
feed-point impedance. At work, as described above, we merely validated the
continuing suitability of each antenna for its intended freq range.

"Sal"
(KD6VKW)

On Monday, February 22, 2016 at 9:41:30 AM UTC-8, gareth wrote:
ATU setting up seems to be a matter of suck-it-and-see, even
on the part of the auto ATUs (which are made for for
CBers-masquerading-as-radio-amateurs
because _REAL_ radio amateurs have no qualms about twiddling knobs
themselves)

I wonder if anyone takes a more scientifc approach by measurement and then
calculation, such as by Smith Chartification?

Sure, I use a nice Smith chart program (unfortunately no longer available) to figure out optimized matching networks for antennas and other things. I'd add, there's an old "Ham Radio" article (actually two articles), "The Antenna-Transmission Line Analog," from April+May, 1977, that can help you understand what's going on in wire antennas (if you can manage to digest the article, anyway). Some people pooh-pooh Smith charts, perhaps saying that computers can figure all that out for you, but I find the visualization quite helpful.

73, Tom