"Telamon" wrote in message
...

In a simple sentence; why would grounding be different than in the US.
Another: why would the terrain be different than in the US?

The pacific side of central America is similar to Florida but not the
west or south America. I don't understand why you are keying on central
or south America. I don't know why grounded towers are not used in most
place most of the time.

The Pacific side of Central America consists of a variety of terrain. It is
soft loamy soil in most places, with mountains farther inland. The
conductivity is high, and it is like the gulf coast of Texas for the most
part, as is the Caribbean coast... although that is more tropical rain
forrest like, with lower conductivity. In both places, the soil is easy to
plow, and it is simple to put in a ground. Unipoles are costly, have to be
imported in kit form, and are often not built to fit locally built metric
dimensioned towers. In addition, few broadcast engineers know the system.
Finally, unipoles, as proven in Puerto Rico and Florida, do not hold up well
in hurricane territory.

South America has as much variety of land as the continental US does. Most
medium and smaller AMs use shorter towers... I had below quarter wave on all
but two of mine in Ecuador due to costs; when I built my first tower in 1964
the only other station with a tower was the government station and the one
owned by the two daily newspapers... it was hard to find a crew to rig it
and all the sections, then, were imported. With spots at less than a dime at
the time, importing anything was a luxury we could not afford. Other
stations used longwires between phone poles.... all 40 of them.

You said that Latin America is "where (it is) expensive to install..."
And
I do not see that it is expensive at all, and where a unipole would be
less
expensive.

Ground systems are expensive to install. The grounded towers don't
eliminate them they just make them less critical.

Grounds in Latin America, where much of our copper comes from, are dirt
cheap. Labor is typically a tenth or less of US costs, the society is not as
litigious, so there is no need for insurance, and it is generally very cheap
and low tech.

I don't understand where you are going with this. A grounded tower does
not eliminate the ground system it just makes for an easier to tune and
more broad band antenna. The antenna is easier to load properly.

Unipoles, like shunt fed towers, are hard to tune. That is why in the US the
kits are also accompanied by a visit from a trained engineer who knows how
to find the right feed point. While a station engineer can easily tune a
series fed tower with simple principles using an OIB, a shunt fed system
like a unipole, requires special riggers and special tuning techniques. and
is very susceptible to damage in high wind zones.

The broadband aspect is not at all of interest, since almost 100% of Latin
American AMs (save a few in Mexico and one or two athat are intentionally
directional do cover better the market, not for protection) are single
towers, and single towers can easily be tuned to decent characteristics,
there is no need for broadbanding and never was one.

You obviously have not measured may, if any, AM vertical radiators.
Untill
they get very wide, like the old towers of the 20's and 30's which were
built like scaffolding, there is no appreciale benefit in width, and the
cost at any optimum point is prohibitative and likely will get no zoning
clearance. The problem with bandwidth can be solved by ATU design, and
VSWR
reduced to less than 1.09 to 1 at 10 kHz with ease.

I haven't tuned any AM broadcasting towers but I have tuned higher
frequency antennas and I know theory and there are companies that build
kits I described to broaden the towers bandwidth as I described.

If you read the websites, like the Kintronics one, you will see the
principal point of purchase is for bad grounds and to enable renting tower
space to other customers. It's so hard today to get a tower built, and
smaller market radio is such a poor business that the revenue from tower
rental is a very important item in most places. Very few single tower AMs
are really worried about andwidth a they are so easy to tune with easy to
adjust ATU's.

As metioned, the cost of importing (duties of as much as 100% and huge
shipping costs) plus the cost of bringing in a specialized antenna is way
too much for the perception of minimal gains.

So for you to be right the theory as I understand it is wrong, I didn't
understand what was really happening in my past antenna tuning
experience and there are companies out there selling radio stations crap
for antenna modification kits.

I did not say that. The unipole is 90% of interst for enabling existing
towers to be used for other purposes without isocouplers. The remaining 10%
is for situations where the ground system is deteriorated and difficult to
replace, or the station is on a rooftop and uses a conutnerpise ground, etc.
The slight, and barely perceptable bandwidth issue is a tiny sidebar
benefirt... the added bandwith on any tower in use in the US is so minimal
compared to a well tuned series fed tower that this can not alone justify
the change from a standard series fed tower; the time off air is also a
major consideration.

The purpose of a unipole is to allow the tower to be at ground potential
so
we can get point to point and other antenna rentals without isocouplers.
It
is also to compensate for bad grounds, like where a parking lot and
shopping
center now sit on the ground system. Bandwidth is mostly enhanced below
1/4
wave, and the FCC only licences such towers under extreme
circumstances...
very few towers under 90 degrees exist in the US. I've seen a bunch of
non-licensed stations, such as AFRTS facilities using them though....
1040
at Ft. Brook used one to tune a roughly 75 foot tower and it did not
sound
too dreadful, either. Rame, on 780, used one on a 50 foot tower, also.

The purpose you state may your reason to use a ground tower.

But those are not licensed stations... they are AFRTS staitons on military
bases. US and Latin American commercial stations do not use unipoles
commonly or, in the later case, at all.

The ATU will generally create a 52 ohm match at carrier, and j 0. At
plus
or minus 10 kHz, we would look for well under 1.1 to 1 VSWR with a good
ATU.
They can be designed to give even less than that, but considering the
amount
of entergy under NRSC at 10 kHz is minimal, that is often good enough.

The ATU can not improve the tower bandwidth. The ATU can only make it
worse.

And tower bandwidth at quarter wave and above is adequate for the AM
service. An ATU can take a short tower, using one example of 60 meters high
at 570 AM, that measures 11 ohms -j 110 and make it 52 ohms at carrier,
with only +/- 5 ohms at 10 khz and similarly tolerable reactance... and
pretty decent bandwidth that can be compensated for by a minor amount of
equalization. There is no need to go off the air for days to install and
tune a unipole if there is no perception of gain. In any case, AM is dying
in Latin America much faster than in the US, with many nations like Chile
and Ecuador and most of Central America having fewer stations today than 10
years ago, so any unnecessary investment would be rejected.
..

The kind of network and the network design can make a pretty decent
broadbanding within licensed bandwith possible. In any case, you are not
going to get a shunt fed tower in the US, and you are not going to get
shunt
fed directionals anywhere.

The ATU's and antenna networks do not improve antenna bandwidth.

The only place where bandwidth within the NRSC mask is an issue on AMs that
are directional. and the towers are generally 5% of the issue while the
phasor is 95%. Phasor redesign requres relicencing the directional, and,
gnerally, an antenna proof or partial proof... the time may be many months,
depending on how much air time the station can afford to lose.


1. I was posting about grounded towers not Uniploes.
2. Grounded tower are more stable that isolated ones.
3. I don't where a Unipole would be more of a mechanical design problem
over an isolated tower.

Shunt fed towers in the US are not licensed; I don't know if one could even
get a waiver to use one. Outside the US, the tuning requires riggers on a
live tower, and that is much more complicated than a simple series fed
system that does everything for less money. There are few who even know how
to find a match point on a shunt fed tower while anyone with an OIB can tune
by trial and error a series fed tower.

AM broadcast towers zero. I have tuned many other types of antennas and
RF circuits. AM towers tune like any other antenna of its type.

Due to the wavelengths involved the huge amount of land needed for the
ground, etc., AM antennas are rather unique... and when you get to
multi-tower directionals, even more so. Doing a full FCC directional proof
may take weeks, and adjusting a critical array months. One construction
permit, for 10 kw night operation of WISN in Milwaukee, took nearly 2
decades to build and adjust and get tuned to operate legally.


You may be looking at this a little to simplistically. I don't know what
the response time of the transmitter fallback circuitry is and I don't
know when the transmitter modules failed. Did they fail at the turn on
of the IBOC exciter? Did they fail after a while? I don't know the
details.

No, they failed due to an improper instruction in installation instructions
regarding the interface between the transmitter and the HD exciter which,
basically, caused the power modules (there are 128 for 50 kw operation) to
overdrive and literally burn out. In this case, the problem was not
corrected by the fialsafe circuitry as it essentially defeated it rather
than interfacing a second system with it.


In that case, I do apologize. I may have mistakenly thought you were one
of
the multitude that thinks that all of Latin America consists of terrain
that
can only be found in an Indiana Jones movie; the fact is that the land
anywhere there is comparable to some place in the US. Towers tend to cost
less, as they are locally fabricated and the labor costs are lower; ATUs
and
such can be made from off the shelf caps and coils you can wind from
automotive AC tubing if the need arises.

From what I have seen the coils don't look to hard to fabricate out of
tubing but you have to buy the high voltage vacuum capacitors. The
connections look like hardware store nuts and bolts would do most of the
time. You would most likely need to buy sense transformers for the
metering.

Most metering today is an RF ammeter at the doghouse and, for directional
stations, an RF sampling system which allows phase and current to be
detected for each tower. Neither is very expensive. With pretty simple
components, even things like diplexers can be built, too. Remember that most
directionals and even ATUs in use in the US were built before computers
could assist in the design. The diplexer shown on my website, built in 1966,
was entirely calculated and designed using a slide rule and a notepad...
this is one of the reasons why highQ networks were preferred as they were
easy to design and tune in the field.

"Telamon" wrote in message
...

That's a good point. I didn't think about flying objects breaking the
tower wires on the extenders. Every engineering solution has its down
side.

Then you will appreciate this: after one of the major gulf coast hurricanes,
in the 70's, an engineer from Miami was hired to settle some tower
destructions. One, which failed at about 80 feet and collapsed was examined.
The measurements on the damaged section that caused the failure exactly
matched the shape and mass of a cow which had been picked up and hurled into
the tower 80 feet over the ground. You can not designee for the occasional
flying cow.

On Oct 11, 10:41 pm, "David Eduardo" wrote:
"Telamon" wrote in message

...



That's a good point. I didn't think about flying objects breaking the
tower wires on the extenders. Every engineering solution has its down
side.

- Then you will appreciate this: after one of the major gulf coast
hurricanes,
- in the 70's, an engineer from Miami was hired to settle some tower
- destructions. One, which failed at about 80 feet and collapsed was
examined.
- The measurements on the damaged section that caused the failure
exactly
- matched the shape and mass of a cow which had been picked up and
hurled into
- the tower 80 feet over the ground. You can not designee for the
occasional
- flying cow.

Gives new meaning to "When Cows {Pigs} Fly"

am'er - watch-out for that tower ~ RHF

On Oct 12, 1:41 am, "David Eduardo" wrote:
"Telamon" wrote in message

...



That's a good point. I didn't think about flying objects breaking the
tower wires on the extenders. Every engineering solution has its down
side.

Then you will appreciate this: after one of the major gulf coast hurricanes,
in the 70's, an engineer from Miami was hired to settle some tower
destructions. One, which failed at about 80 feet and collapsed was examined.
The measurements on the damaged section that caused the failure exactly
matched the shape and mass of a cow which had been picked up and hurled into
the tower 80 feet over the ground. You can not designee for the occasional
flying cow.

What have you been listening to on shortwave lately?

"Telamon" wrote in message
...

Well, thanks for the replies. I learned a few things. It was an
interesting discussion.


Agreed. Thanks.