"Telamon" wrote in message
...
In article ,
"David Eduardo" wrote:

The folded dipole is also appropriate, like a Franklin, when there is
a bad ground system, such as antennas in marshes and salt flats where
they corrode, or where there are structures on the property.

Yeah. That's why I thought it would be more popular in central and south
America where expensive or difficult to install, due to terrain,
grounding systems requirements could be reduced.

Why would the terrain considerations, grounding requirements and such be any
different than in, say, Idaho or Wisconsin or Arizona or Alabama?

And why would it be more expensive to do in Central and South America? I can
see no logic in any of this set of statements.


A unipois also useful with a shorter than 1/4 wave tower because the
tuning network needed to tune out the capacitive reactance often
narrowbands the antenna (not the tower itself).

That my point. The shunt type coupling is more broadband.

Only for very short towers where a high capacitive reactance is found.
Otherwise, the bandwidth is much more the effect of the Q of the ATU and the
trandsmitter itself.

So a unipole is mostly used to compensate for bad ground systems and
the need to multitask the tower, not to reduce the noxious effects of
a less than conforming tower, as the FCC requires a very special
showing to allow low antennas.

I don't know what you mean by "the FCC requires a very special showing
to allow low antennas" but I wasn't after the shorter tower aspect.

That is the only place where the unipole offers a distinct bandwidth
advantage. It also gets a better field strength at 1 km than a short series
fed tower. But the main reason anyone uses them is either due to a bad
ground or the need to put other antennas on the tower.

A broader cross section will broadband the tower a bit, but the
difference
in a 24" to 30" cross section and a folded dipole is minimal.

That's not my understanding.

Go back to Carl Smith's AM antenna and DA handbooks, Unless you find a nice
old Blaw Knox with a 24 foot center cross section, there is not much gain
except cost, maintenance, etc., in adding outriggers insofar as
broadbanding.

The bandwidth for AM is, by NRSC, 10 kHz in each sideband... actually, a
little less. This is to avoid 10 kHz harmonics with adjacent channels.

You usually make measurements beyond spec to show the trend over the
entire specification. Here the spec is VSWR.

A well tuned tower of 1/4 wave has less than 1.08 to 1 vizwar. And, except
for test situations, a tower measurement is usually done at -10, licenced
frequency and +10 kHz. This is what is often asked for by outside
fabricators of ATUs.

A well tuned ATU, whether high Q or broadbanded, does not create a
significant amount of reflected power. A tower that is mismatched at
carrier does.

Yes that is my point. The tower itself will have a narrow resonant
bandwidth so a method is needed for the tower to not present a high VSWR
+/- 15 KHz around the carrier frequency.

A mismatch is generally considered to be a mismatch of impedance output of
the ATU with the tower itself at the fundamental. Since the audio is
brick-walled right under 10 kHz, there should be little or no excursions
beyond +/- 10 kHz.

ATU's that couple the coax transmission line to the tower using a series
connection to an insulated tower have a stronger tendency to be
narrowband in and of themselves.

Not for the last 40 years or so. High Q was much more common pre-60's when
AMs mostly ran network showsthat came over 5 kHz lines from very far away.
When music took over AM, stations wanted better bandwidth.

An ATU designed to couple the coax
transmission line to a shunt fed tower tends to tune a little less
sharply and the useful resonance range is broader.

Since true shunts are no longer licensed, this point is moot. Most US AMs,
for economy, zoning, FAA, etc. use quarter wave series fed towers. Since a
huge percentage are directional, there are very, very few Unipole
directionals, so in that area series fed is the only way to go.

The FCC no longer authorizes shunt fed towers.

Why?

I don't know. This has been the case for many decades. I suspect part has to
do with the slight directionality the shunt itself introduces, and the fact
that shunts would be very difficult to do with directional stations for this
reason.

The unipole is the closest you get to this; one manufacturer,
Kintronics, who makes kits to order, compares them with shunt fed
systems. So, except for the unipoles, all US towers for AM are
insulated from ground.

I don't understand why the FCC would care how transmission lines are
coupled to the tower or tuned / matched by an ATU.

There is a lot about AM radio in the US you don't understand. The fact is,
shunt fed towers are very seldom used. I suspect that the fact that they are
not particulary easy to tune on short, 1/2 wave towers may be part of it,
but there must be more.

Transmission lines are never couple to the tower (with maybe one or two
exceptions... more later) because so few towers are a perfect impedance
match with the coax and devoid of +j or -j. An antenna coupling unit is
placed between the coax and the tower, using a network to match the tower
to
line impedance and to bring reactance to zero at the carrier. The ATU is
typically attached to the tower with a copper strap, copper tubing or
sometimes even braid. In any case, it is silver soldered to a connector,
which is usually pressure bolted to the output of the ATU and to a leg or
the base plate of the tower.

That's all interesting information but we are mixing and matching
terminology. The ATU doesn't just tune the tower to resonance it is also
a part of circuitry that couples the transmission line to the tower.

An ATU is not necessary if the tower is 52 ohms and not reactive, found
around about 100 to 110 degrees in electrical height.

The ATU is a matching circuit, to make the coax "see" 52 ohms (or some other
impedance) when, in fact, the tower is not of that impedance. In some
senses, a top hat or top loading does the same thing... it makes the tower
change the apparent electrical height. You are trying to complicate
something that is relatively simple... cancelling the reactance and matching
impedance.


Reactance is near zero at resonance and the antenna looks like a
resistive load to the transmission line. The resistive load value also
needs to match the line impedance so there is little or no reflective
power. This is one reason why transmitters are getting damaged when IBOC
is turned on. The reflective power goes up over the increased power
bandwidth IBOC requires.

That is not why the very few cases of transmitter damage have occured. Most
transmitters will simply shut down over reactive or mismatched loads. The
issues reported (and one that took out 80% of the power modules at KTNQ) had
to do with the control interface of the HD exciter and the analog
transmitter.... a design defect in non-rf and non-af circuitry.

Several things happen when the reflected power goes up. Mainly the power
does not go into the antenna to be radiated and instead heats the
transmission line and transmitter finals. Another bad effect is the
reflected power can make the transmitter unstable and generate spurious
energy.

Or, in today's transmitters, it does neither. It detects VSWR and shuts off.
..

This method was used by a few high power AMs in Latin America in decades
past, ones like XEB and XEW. The rest, if they have a tower (many use
inverted L's of wire) use series fed towers. Since many towers are
diplexed
and even triplexed, a rejection network is required and that requires an
ATU. Shunt fed towers are generally half wave or similar, and shunt
feeding
is not and has never been common with quarter wave or less towers.

I have visited every AM in Mexico City, and only 3 had shunt fed towers
in
1963... today, I believe only XEW has one. In Colombia, I have visited
about
20 50 kw or higher sites, and none was shunt fed. In Ecuador, today and
in
the past, no station was shunt fed. Of the several hundred stations I
visited in Central America, none was shunt fed. The most powerful AM in
Argentina, Radio 10 on 710 with 100 kw, with a nice half wave tower, is
series fed.

The only other Latin American shunt fed I know about was CB106 Radio
Mineria
in Santiago. That station, saying AM was no longer viable in Chile,
turned
in its license and turned off the 100 kw transmitter nearly a decade ago.

You sure get around.

Yes, I have worked in every nation in Latin America save Cuba and Nicaragua,
and visited stations in each one. There are pictures of dozens and dozens
stations I took, including some shunt fed ones, on my web page, from trips I
made visiting stations.

The fact is you have said that shunt feeding is common in Latin America
where it is highly uncommon and always has been. You made statements about
costs, land and towers in Latin America that make it sound like you think we
are talking about another planet, not the same Hemisphere. In fact, the
conditions and terrain in South Florida are more difficult and hostile than
in most places in Latin America.

In article ,
"David Eduardo" wrote:

"Telamon" wrote in message
...
In article ,
"David Eduardo" wrote:

The folded dipole is also appropriate, like a Franklin, when there
is a bad ground system, such as antennas in marshes and salt flats
where they corrode, or where there are structures on the property.

Yeah. That's why I thought it would be more popular in central and
south America where expensive or difficult to install, due to
terrain, grounding systems requirements could be reduced.

Why would the terrain considerations, grounding requirements and such
be any different than in, say, Idaho or Wisconsin or Arizona or
Alabama?

They would not and since when is Idaho, Wisconsin, Arizona or Alabama
in south America?

And why would it be more expensive to do in Central and South
America? I can see no logic in any of this set of statements.

Where did I say it was more expensive in SA? The logic is why spend
money you don't have to spend. The problem looks to be reading
comprehension.

A unipois also useful with a shorter than 1/4 wave tower because
the tuning network needed to tune out the capacitive reactance
often narrowbands the antenna (not the tower itself).

That my point. The shunt type coupling is more broadband.

Only for very short towers where a high capacitive reactance is
found. Otherwise, the bandwidth is much more the effect of the Q of
the ATU and the trandsmitter itself.

No.

So a unipole is mostly used to compensate for bad ground systems
and the need to multitask the tower, not to reduce the noxious
effects of a less than conforming tower, as the FCC requires a
very special showing to allow low antennas.

I don't know what you mean by "the FCC requires a very special
showing to allow low antennas" but I wasn't after the shorter tower
aspect.

That is the only place where the unipole offers a distinct bandwidth
advantage. It also gets a better field strength at 1 km than a short
series fed tower. But the main reason anyone uses them is either due
to a bad ground or the need to put other antennas on the tower.

A broader cross section will broadband the tower a bit, but the
difference in a 24" to 30" cross section and a folded dipole is
minimal.

That's not my understanding.

Go back to Carl Smith's AM antenna and DA handbooks, Unless you find
a nice old Blaw Knox with a 24 foot center cross section, there is
not much gain except cost, maintenance, etc., in adding outriggers
insofar as broadbanding.

I don't have that book so I can't do that but general theory would
indicate otherwise and there are companies that offer tower kits to
improve bandwidth performance as I have described.

The bandwidth for AM is, by NRSC, 10 kHz in each sideband...
actually, a little less. This is to avoid 10 kHz harmonics with
adjacent channels.

You usually make measurements beyond spec to show the trend over
the entire specification. Here the spec is VSWR.

A well tuned tower of 1/4 wave has less than 1.08 to 1 vizwar. And,
except for test situations, a tower measurement is usually done at
-10, licenced frequency and +10 kHz. This is what is often asked for
by outside fabricators of ATUs.

Again that is not my understanding of tower VSWR. The levels at 5, 10,
and 15 KHz are much higher than you indicate, which requires mitigation
efforts.

A well tuned ATU, whether high Q or broadbanded, does not create a
significant amount of reflected power. A tower that is mismatched
at carrier does.

Yes that is my point. The tower itself will have a narrow resonant
bandwidth so a method is needed for the tower to not present a high
VSWR +/- 15 KHz around the carrier frequency.

A mismatch is generally considered to be a mismatch of impedance
output of the ATU with the tower itself at the fundamental. Since the
audio is brick-walled right under 10 kHz, there should be little or
no excursions beyond +/- 10 kHz.

For analog +/- 10 KHz sounds reasonable but it looks like IBOC is
going past that number. The testing recommendation I read suggests
testing to +/- 15 KHz.

ATU's that couple the coax transmission line to the tower using a
series connection to an insulated tower have a stronger tendency to
be narrowband in and of themselves.

Not for the last 40 years or so. High Q was much more common pre-60's
when AMs mostly ran network showsthat came over 5 kHz lines from very
far away. When music took over AM, stations wanted better bandwidth.

I don't see how that can be improved. Series feeding the tower will
require a fairly high Q network that is inherently narrow band
compared to a shunt feed method.

An ATU designed to couple the coax transmission line to a shunt fed
tower tends to tune a little less sharply and the useful resonance
range is broader.

Since true shunts are no longer licensed, this point is moot. Most US
AMs, for economy, zoning, FAA, etc. use quarter wave series fed
towers. Since a huge percentage are directional, there are very, very
few Unipole directionals, so in that area series fed is the only way
to go.

I don't see where you keep on this tack about Unipoles as they can just
as easily be part of a directional network.

The FCC no longer authorizes shunt fed towers.

Why?

I don't know. This has been the case for many decades. I suspect part
has to do with the slight directionality the shunt itself introduces,
and the fact that shunts would be very difficult to do with
directional stations for this reason.

I don't see where a Unipole would present a problem in a directional
network.

The unipole is the closest you get to this; one manufacturer,
Kintronics, who makes kits to order, compares them with shunt fed
systems. So, except for the unipoles, all US towers for AM are
insulated from ground.

I don't understand why the FCC would care how transmission lines
are coupled to the tower or tuned / matched by an ATU.

There is a lot about AM radio in the US you don't understand. The
fact is, shunt fed towers are very seldom used. I suspect that the
fact that they are not particulary easy to tune on short, 1/2 wave
towers may be part of it, but there must be more.

Yeah, there must be another reason.

Transmission lines are never couple to the tower (with maybe one
or two exceptions... more later) because so few towers are a
perfect impedance match with the coax and devoid of +j or -j. An
antenna coupling unit is placed between the coax and the tower,
using a network to match the tower to line impedance and to bring
reactance to zero at the carrier. The ATU is typically attached to
the tower with a copper strap, copper tubing or sometimes even
braid. In any case, it is silver soldered to a connector, which is
usually pressure bolted to the output of the ATU and to a leg or
the base plate of the tower.

That's all interesting information but we are mixing and matching
terminology. The ATU doesn't just tune the tower to resonance it is
also a part of circuitry that couples the transmission line to the
tower.

An ATU is not necessary if the tower is 52 ohms and not reactive,
found around about 100 to 110 degrees in electrical height.

The ATU is a matching circuit, to make the coax "see" 52 ohms (or
some other impedance) when, in fact, the tower is not of that
impedance. In some senses, a top hat or top loading does the same
thing... it makes the tower change the apparent electrical height.
You are trying to complicate something that is relatively simple...
cancelling the reactance and matching impedance.

That's fine if the coax and transmitter output impedance is 52 ohms. I
didn't realize I was making it more complicated I was just trying to
explain the dynamics of tuning the tower.

An ATU is usually necessary.

Reactance is near zero at resonance and the antenna looks like a
resistive load to the transmission line. The resistive load value
also needs to match the line impedance so there is little or no
reflective power. This is one reason why transmitters are getting
damaged when IBOC is turned on. The reflective power goes up over
the increased power bandwidth IBOC requires.

That is not why the very few cases of transmitter damage have
occured. Most transmitters will simply shut down over reactive or
mismatched loads. The issues reported (and one that took out 80% of
the power modules at KTNQ) had to do with the control interface of
the HD exciter and the analog transmitter.... a design defect in
non-rf and non-af circuitry.

Wow, I guess the engineering of the IBOC working group really sucks. I
figured something in the way of the application in the field is what
would bring things down. This is far worse that I imagined.

Several things happen when the reflected power goes up. Mainly the
power does not go into the antenna to be radiated and instead heats
the transmission line and transmitter finals. Another bad effect is
the reflected power can make the transmitter unstable and generate
spurious energy.

Or, in today's transmitters, it does neither. It detects VSWR and
shuts off.

And all my equipment has fuses or circuit breakers but I usually apply
effort toward making sure they are not used.

This method was used by a few high power AMs in Latin America in
decades past, ones like XEB and XEW. The rest, if they have a
tower (many use inverted L's of wire) use series fed towers. Since
many towers are diplexed and even triplexed, a rejection network
is required and that requires an ATU. Shunt fed towers are
generally half wave or similar, and shunt feeding is not and has
never been common with quarter wave or less towers.

I have visited every AM in Mexico City, and only 3 had shunt fed
towers in 1963... today, I believe only XEW has one. In Colombia,
I have visited about 20 50 kw or higher sites, and none was shunt
fed. In Ecuador, today and in the past, no station was shunt fed.
Of the several hundred stations I visited in Central America, none
was shunt fed. The most powerful AM in Argentina, Radio 10 on 710
with 100 kw, with a nice half wave tower, is series fed.

The only other Latin American shunt fed I know about was CB106
Radio Mineria in Santiago. That station, saying AM was no longer
viable in Chile, turned in its license and turned off the 100 kw
transmitter nearly a decade ago.

You sure get around.

Yes, I have worked in every nation in Latin America save Cuba and
Nicaragua, and visited stations in each one. There are pictures of
dozens and dozens stations I took, including some shunt fed ones, on
my web page, from trips I made visiting stations.

The fact is you have said that shunt feeding is common in Latin
America where it is highly uncommon and always has been. You made
statements about costs, land and towers in Latin America that make it
sound like you think we are talking about another planet, not the
same Hemisphere. In fact, the conditions and terrain in South Florida
are more difficult and hostile than in most places in Latin America.

I don't see the need to be so defensive about what I posted. I made it
clear it was an assumption and explained my logic for those
assumptions. The reasoning was technical and there is no need to try to
make it into something else.

--
Telamon
Ventura, California

"Telamon" wrote in message
...
In article ,
"David Eduardo" wrote:

Yeah. That's why I thought it would be more popular in central and
south America where expensive or difficult to install, due to
terrain, grounding systems requirements could be reduced.

Why would the terrain considerations, grounding requirements and such
be any different than in, say, Idaho or Wisconsin or Arizona or
Alabama?

They would not and since when is Idaho, Wisconsin, Arizona or Alabama
in south America?

I asked why South or Central America would have conditions of terrain,
grounding or cost any different than those states? I have no idea why you
think a unipole would be of any greater advantage there than in, say, Lake
City, FL? Why?

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

And why would it be more expensive to do in Central and South
America? I can see no logic in any of this set of statements.

Where did I say it was more expensive in SA?

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.

The logic is why spend
money you don't have to spend. The problem looks to be reading
comprehension.

Importing a unipole kit from the US (nobody makes them or uses them in Latin
America) and bringing in an experiienced installer would be much more
expensive than a simple to build and maintain series fed antenna. Every
nation in Latin America has a local tower fabricator and erector or two.

A unipois also useful with a shorter than 1/4 wave tower because
the tuning network needed to tune out the capacitive reactance
often narrowbands the antenna (not the tower itself).

That my point. The shunt type coupling is more broadband.

Only for very short towers where a high capacitive reactance is
found. Otherwise, the bandwidth is much more the effect of the Q of
the ATU and the trandsmitter itself.

No.

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.


Go back to Carl Smith's AM antenna and DA handbooks, Unless you find
a nice old Blaw Knox with a 24 foot center cross section, there is
not much gain except cost, maintenance, etc., in adding outriggers
insofar as broadbanding.

I don't have that book so I can't do that but general theory would
indicate otherwise and there are companies that offer tower kits to
improve bandwidth performance as I have described.

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.


A well tuned tower of 1/4 wave has less than 1.08 to 1 vizwar. And,
except for test situations, a tower measurement is usually done at
-10, licenced frequency and +10 kHz. This is what is often asked for
by outside fabricators of ATUs.

Again that is not my understanding of tower VSWR. The levels at 5, 10,
and 15 KHz are much higher than you indicate, which requires mitigation
efforts.

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.

A mismatch is generally considered to be a mismatch of impedance
output of the ATU with the tower itself at the fundamental. Since the
audio is brick-walled right under 10 kHz, there should be little or
no excursions beyond +/- 10 kHz.

For analog +/- 10 KHz sounds reasonable but it looks like IBOC is
going past that number. The testing recommendation I read suggests
testing to +/- 15 KHz.

The stations for which AM HD is even appropriate are major stations in each
market only... and most of these have nicely designed antennas. The very
directional stations are going to have more problems in the phasor than in
the ATU and tower. Phasors have to be a compromise of tunability (High Q)
and bandwidth... so the bottleneck is in the phasor, the rest of the system
being infinitely more tolerant.

Not for the last 40 years or so. High Q was much more common pre-60's
when AMs mostly ran network showsthat came over 5 kHz lines from very
far away. When music took over AM, stations wanted better bandwidth.

I don't see how that can be improved. Series feeding the tower will
require a fairly high Q network that is inherently narrow band
compared to a shunt feed method.

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.

Since true shunts are no longer licensed, this point is moot. Most US
AMs, for economy, zoning, FAA, etc. use quarter wave series fed
towers. Since a huge percentage are directional, there are very, very
few Unipole directionals, so in that area series fed is the only way
to go.

I don't see where you keep on this tack about Unipoles as they can just
as easily be part of a directional network.

Shunt fed towers tend to have slight directionality, and unipoles have
enormous mechanical instability, making adjusting a unipole directional and
meeting licensing requirements something that might not even be possible.
And the cost of readjusting as the outriggers move about and the wires
strech and age would be huge... most station engineers do not adjust their
own directionals... a consulting engineer does, at great cost.

I don't see where a Unipole would present a problem in a directional
network.

See above. Mechanical stability is the first issue.

An ATU is not necessary if the tower is 52 ohms and not reactive,
found around about 100 to 110 degrees in electrical height.

The ATU is a matching circuit, to make the coax "see" 52 ohms (or
some other impedance) when, in fact, the tower is not of that
impedance. In some senses, a top hat or top loading does the same
thing... it makes the tower change the apparent electrical height.
You are trying to complicate something that is relatively simple...
cancelling the reactance and matching impedance.

That's fine if the coax and transmitter output impedance is 52 ohms. I
didn't realize I was making it more complicated I was just trying to
explain the dynamics of tuning the tower.

How many towers have you tuned?

An ATU is usually necessary.

Always unless there is a perfect match. I chatted with some engineers who
are into this sort of thing, and we came up with one station in the west,
the 1590 in the Victor Valley about two decades ago... it has since moved
and has a doghouse at the tower base, now.

That is not why the very few cases of transmitter damage have
occured. Most transmitters will simply shut down over reactive or
mismatched loads. The issues reported (and one that took out 80% of
the power modules at KTNQ) had to do with the control interface of
the HD exciter and the analog transmitter.... a design defect in
non-rf and non-af circuitry.

Wow, I guess the engineering of the IBOC working group really sucks. I
figured something in the way of the application in the field is what
would bring things down. This is far worse that I imagined.

iBiquity does not design exciters. In this case, the HD exciter was built by
one of the big three transmitter companies, and it had a "design mismatch"
(read "flaw") when mated to one particular transmitter which they did not
even manufacture. It's the price stations pay for being early on the
curve... which is usual in major markets because, problem and all, such
stations have at least one backup transmitter, and many have two.

Or, in today's transmitters, it does neither. It detects VSWR and
shuts off.

And all my equipment has fuses or circuit breakers but I usually apply
effort toward making sure they are not used.

In the case of transmitters, the control circuit performs system shutdown or
power reduction to protect itself without fuses or circuit breakers; a high
VSWR might cause a transmitter to progressively fall back to half power,
half again, and so on until it can operate... or it shuts off.

The fact is you have said that shunt feeding is common in Latin
America where it is highly uncommon and always has been. You made
statements about costs, land and towers in Latin America that make it
sound like you think we are talking about another planet, not the
same Hemisphere. In fact, the conditions and terrain in South Florida
are more difficult and hostile than in most places in Latin America.

I don't see the need to be so defensive about what I posted. I made it
clear it was an assumption and explained my logic for those
assumptions. The reasoning was technical and there is no need to try to
make it into something else.

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.

On Oct 10, 11:17 pm, "David Eduardo" wrote:
"Telamon" wrote in message

...

In article ,
"David Eduardo" wrote:

Yeah. That's why I thought it would be more popular in central and
south America where expensive or difficult to install, due to
terrain, grounding systems requirements could be reduced.

Why would the terrain considerations, grounding requirements and such
be any different than in, say, Idaho or Wisconsin or Arizona or
Alabama?

They would not and since when is Idaho, Wisconsin, Arizona or Alabama
in south America?

I asked why South or Central America would have conditions of terrain,
grounding or cost any different than those states? I have no idea why you
think a unipole would be of any greater advantage there than in, say, Lake
City, FL? Why?

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



And why would it be more expensive to do in Central and South
America? I can see no logic in any of this set of statements.

Where did I say it was more expensive in SA?

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.

The logic is why spend
money you don't have to spend. The problem looks to be reading
comprehension.

Importing a unipole kit from the US (nobody makes them or uses them in Latin
America) and bringing in an experiienced installer would be much more
expensive than a simple to build and maintain series fed antenna. Every
nation in Latin America has a local tower fabricator and erector or two.



A unipois also useful with a shorter than 1/4 wave tower because
the tuning network needed to tune out the capacitive reactance
often narrowbands the antenna (not the tower itself).

That my point. The shunt type coupling is more broadband.

Only for very short towers where a high capacitive reactance is
found. Otherwise, the bandwidth is much more the effect of the Q of
the ATU and the trandsmitter itself.

No.

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.



Go back to Carl Smith's AM antenna and DA handbooks, Unless you find
a nice old Blaw Knox with a 24 foot center cross section, there is
not much gain except cost, maintenance, etc., in adding outriggers
insofar as broadbanding.

I don't have that book so I can't do that but general theory would
indicate otherwise and there are companies that offer tower kits to
improve bandwidth performance as I have described.

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.



A well tuned tower of 1/4 wave has less than 1.08 to 1 vizwar. And,
except for test situations, a tower measurement is usually done at
-10, licenced frequency and +10 kHz. This is what is often asked for
by outside fabricators of ATUs.

Again that is not my understanding of tower VSWR. The levels at 5, 10,
and 15 KHz are much higher than you indicate, which requires mitigation
efforts.

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.



A mismatch is generally considered to be a mismatch of impedance
output of the ATU with the tower itself at the fundamental. Since the
audio is brick-walled right under 10 kHz, there should be little or
no excursions beyond +/- 10 kHz.

For analog +/- 10 KHz sounds reasonable but it looks like IBOC is
going past that number. The testing recommendation I read suggests
testing to +/- 15 KHz.

The stations for which AM HD is even appropriate are major stations in each
market only... and most of these have nicely designed antennas. The very
directional stations are going to have more problems in the phasor than in
the ATU and tower. Phasors have to be a compromise of tunability (High Q)
and bandwidth... so the bottleneck is in the phasor, the rest of the system
being infinitely more tolerant.

Not for the last 40 years or so. High Q was much more common pre-60's
when AMs mostly ran network showsthat came over 5 kHz lines from very
far away. When music took over AM, stations wanted better bandwidth.

I don't see how that can be improved. Series feeding the tower will
require a fairly high Q network that is inherently narrow band
compared to a shunt feed method.

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.



Since true shunts are no longer licensed, this point is moot. Most US
AMs, for economy, zoning, FAA, etc. use quarter wave series fed
towers. Since a huge percentage are directional, there are very, very
few Unipole directionals, so in that area series fed is the only way
to go.

I don't see where you keep on this tack about Unipoles as they can just
as easily be part of a directional network.

Shunt fed towers tend to have slight directionality, and unipoles have
enormous mechanical instability, making adjusting a unipole directional and
meeting licensing requirements something that might not even be possible.
And the cost of readjusting as the outriggers move about and the wires
strech and age would be huge... most station engineers do not adjust their
own directionals... a consulting engineer does, at great cost.

I don't see where a Unipole would present a problem in a directional
network.

See above. Mechanical stability is the first issue.



An ATU is not necessary if the tower is 52 ohms and not reactive,
found around about 100 to 110 degrees in electrical height.

The ATU is a matching circuit, to make the coax "see" 52 ohms (or
some other impedance) when, in fact, the tower is not of that
impedance. In some senses, a top hat or top loading does the same
thing... it makes the tower change the apparent electrical height.
You are trying to complicate something that is relatively simple...
cancelling the reactance and matching impedance.

That's fine if the coax and transmitter output impedance is 52 ohms. I
didn't realize I was making it more complicated I was just trying to
explain the dynamics of tuning the tower.

How many towers have you tuned?

An ATU is usually necessary.

Always unless there is a perfect match. I chatted with some engineers who
are into this sort of thing, and we came up with one station in the west,
the 1590 in the Victor Valley about two decades ago... it has since moved
and has a doghouse at the tower base, now.

That is not why the very few cases of transmitter damage have
occured. Most transmitters will simply shut down over reactive or
mismatched loads. The issues reported (and one that took out 80% of
the power modules at KTNQ) had to do with the control interface of
the HD exciter and the analog transmitter.... a design defect in
non-rf and non-af circuitry.

Wow, I guess the engineering of the IBOC working group really sucks. I
figured something in the way of the application in the field is what
would bring things down. This is far worse that I imagined.

iBiquity does not design exciters. In this case, the HD exciter was built by
one of the big three transmitter companies, and it had a "design mismatch"
(read "flaw") when mated to one particular transmitter which they did not
even manufacture. It's the price stations pay for being early on the
curve... which is usual in major markets because, problem and all, such
stations have at least one backup transmitter, and many have two.



Or, in today's transmitters, it does neither. It detects VSWR and
shuts off.

And all my equipment has fuses or circuit breakers but I usually apply
effort toward making sure they are not used.

In the case of transmitters, the control circuit performs system shutdown or
power reduction to protect itself without fuses or circuit breakers; a high
VSWR might cause a transmitter to progressively fall back to half power,
half again, and so on until it can operate... or it shuts off.





The fact is you have said that shunt feeding is common in Latin
America where it is highly uncommon and always has been. You made
statements about costs, land and towers in Latin America that make it
sound like you think we are talking about another planet, not the
same Hemisphere. In fact, the conditions and terrain in South Florida
are more difficult and hostile than in

...

read more »- Hide quoted text -

- Show quoted text -

Of course, none of this justifies your lying about your academic
background.

"Steve" wrote in message
oups.com...

Of course, none of this justifies your lying about your academic
background.

It's obviously past your bedtime.

But, before you go, there is a Boise 50 kw AM on Craigslist for $800
thousand dollars... why don't you buy it and impress us all with your radio
talent and knowledge? Of course, the potty words you erupt with here will
have to be controlled, perhaps with a muzzle.

On Oct 10, 11:31 pm, "David Eduardo" wrote:
"Steve" wrote in message

oups.com...

Of course, none of this justifies your lying about your academic
background.

It's obviously past your bedtime.

But, before you go, there is a Boise 50 kw AM on Craigslist for $800
thousand dollars... why don't you buy it and impress us all with your radio
talent and knowledge? Of course, the potty words you erupt with here will
have to be controlled, perhaps with a muzzle.

You're much closer to Boise than I am. Why don't you buy it? Perhaps
you can solve all of it's problems by putting a fresh coat of paint on
the station.

In article ,
"David Eduardo" wrote:

"Telamon" wrote in message
...
In article ,
"David Eduardo" wrote:

Yeah. That's why I thought it would be more popular in central and
south America where expensive or difficult to install, due to
terrain, grounding systems requirements could be reduced.

Why would the terrain considerations, grounding requirements and such
be any different than in, say, Idaho or Wisconsin or Arizona or
Alabama?

They would not and since when is Idaho, Wisconsin, Arizona or Alabama
in south America?

I asked why South or Central America would have conditions of terrain,
grounding or cost any different than those states? I have no idea why you
think a unipole would be of any greater advantage there than in, say, Lake
City, FL? Why?

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.

And why would it be more expensive to do in Central and South
America? I can see no logic in any of this set of statements.

Where did I say it was more expensive in SA?

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.

The logic is why spend money you don't have to spend. The problem
looks to be reading comprehension.

Importing a unipole kit from the US (nobody makes them or uses them in Latin
America) and bringing in an experiienced installer would be much more
expensive than a simple to build and maintain series fed antenna. Every
nation in Latin America has a local tower fabricator and erector or two.

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.

A unipois also useful with a shorter than 1/4 wave tower because
the tuning network needed to tune out the capacitive reactance
often narrowbands the antenna (not the tower itself).

That my point. The shunt type coupling is more broadband.

Only for very short towers where a high capacitive reactance is
found. Otherwise, the bandwidth is much more the effect of the Q of
the ATU and the trandsmitter itself.

No.

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.

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.

So that said where do you think things went wrong?

Go back to Carl Smith's AM antenna and DA handbooks, Unless you find
a nice old Blaw Knox with a 24 foot center cross section, there is
not much gain except cost, maintenance, etc., in adding outriggers
insofar as broadbanding.

I don't have that book so I can't do that but general theory would
indicate otherwise and there are companies that offer tower kits to
improve bandwidth performance as I have described.

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.

A well tuned tower of 1/4 wave has less than 1.08 to 1 vizwar. And,
except for test situations, a tower measurement is usually done at
-10, licenced frequency and +10 kHz. This is what is often asked for
by outside fabricators of ATUs.

Again that is not my understanding of tower VSWR. The levels at 5, 10,
and 15 KHz are much higher than you indicate, which requires mitigation
efforts.

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.

A mismatch is generally considered to be a mismatch of impedance
output of the ATU with the tower itself at the fundamental. Since the
audio is brick-walled right under 10 kHz, there should be little or
no excursions beyond +/- 10 kHz.

For analog +/- 10 KHz sounds reasonable but it looks like IBOC is
going past that number. The testing recommendation I read suggests
testing to +/- 15 KHz.

The stations for which AM HD is even appropriate are major stations in each
market only... and most of these have nicely designed antennas. The very
directional stations are going to have more problems in the phasor than in
the ATU and tower. Phasors have to be a compromise of tunability (High Q)
and bandwidth... so the bottleneck is in the phasor, the rest of the system
being infinitely more tolerant.

Not for the last 40 years or so. High Q was much more common pre-60's
when AMs mostly ran network showsthat came over 5 kHz lines from very
far away. When music took over AM, stations wanted better bandwidth.

I don't see how that can be improved. Series feeding the tower will
require a fairly high Q network that is inherently narrow band
compared to a shunt feed method.

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.

Since true shunts are no longer licensed, this point is moot. Most US
AMs, for economy, zoning, FAA, etc. use quarter wave series fed
towers. Since a huge percentage are directional, there are very, very
few Unipole directionals, so in that area series fed is the only way
to go.

I don't see where you keep on this tack about Unipoles as they can just
as easily be part of a directional network.

Shunt fed towers tend to have slight directionality, and unipoles have
enormous mechanical instability, making adjusting a unipole directional and
meeting licensing requirements something that might not even be possible.
And the cost of readjusting as the outriggers move about and the wires
strech and age would be huge... most station engineers do not adjust their
own directionals... a consulting engineer does, at great cost.

I don't see where a Unipole would present a problem in a directional
network.

See above. Mechanical stability is the first issue.

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.

An ATU is not necessary if the tower is 52 ohms and not reactive,
found around about 100 to 110 degrees in electrical height.

The ATU is a matching circuit, to make the coax "see" 52 ohms (or
some other impedance) when, in fact, the tower is not of that
impedance. In some senses, a top hat or top loading does the same
thing... it makes the tower change the apparent electrical height.
You are trying to complicate something that is relatively simple...
cancelling the reactance and matching impedance.

That's fine if the coax and transmitter output impedance is 52 ohms. I
didn't realize I was making it more complicated I was just trying to
explain the dynamics of tuning the tower.

How many towers have you tuned?

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.

An ATU is usually necessary.

Always unless there is a perfect match. I chatted with some engineers who
are into this sort of thing, and we came up with one station in the west,
the 1590 in the Victor Valley about two decades ago... it has since moved
and has a doghouse at the tower base, now.

Many amateur radio operators don't understand the necessity of tuning
the antenna at the antenna and not in the shack. Usually this is done
for convenience though.

That is not why the very few cases of transmitter damage have
occured. Most transmitters will simply shut down over reactive or
mismatched loads. The issues reported (and one that took out 80% of
the power modules at KTNQ) had to do with the control interface of
the HD exciter and the analog transmitter.... a design defect in
non-rf and non-af circuitry.

Wow, I guess the engineering of the IBOC working group really sucks. I
figured something in the way of the application in the field is what
would bring things down. This is far worse that I imagined.

iBiquity does not design exciters. In this case, the HD exciter was built by
one of the big three transmitter companies, and it had a "design mismatch"
(read "flaw") when mated to one particular transmitter which they did not
even manufacture. It's the price stations pay for being early on the
curve... which is usual in major markets because, problem and all, such
stations have at least one backup transmitter, and many have two.

Or, in today's transmitters, it does neither. It detects VSWR and
shuts off.

And all my equipment has fuses or circuit breakers but I usually apply
effort toward making sure they are not used.

In the case of transmitters, the control circuit performs system shutdown or
power reduction to protect itself without fuses or circuit breakers; a high
VSWR might cause a transmitter to progressively fall back to half power,
half again, and so on until it can operate... or it shuts off.

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.

The fact is you have said that shunt feeding is common in Latin
America where it is highly uncommon and always has been. You made
statements about costs, land and towers in Latin America that make it
sound like you think we are talking about another planet, not the
same Hemisphere. In fact, the conditions and terrain in South Florida
are more difficult and hostile than in most places in Latin America.

I don't see the need to be so defensive about what I posted. I made it
clear it was an assumption and explained my logic for those
assumptions. The reasoning was technical and there is no need to try to
make it into something else.

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.

--
Telamon
Ventura, California

"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
...

I don't see the need to be so defensive about what I posted. I made it
clear it was an assumption and explained my logic for those
assumptions. The reasoning was technical and there is no need to try to
make it into something else.


By the way, thank you for an interesting and civil discussion. Your
technical knowledge is obviously extensive, and some of my anecdotal or
field experience may be unknown to you. Goes to show... we can learn from
each other. I hope...

On Oct 10, 11:33 pm, "David Eduardo" wrote:
"Telamon" wrote in message

...



I don't see the need to be so defensive about what I posted. I made it
clear it was an assumption and explained my logic for those
assumptions. The reasoning was technical and there is no need to try to
make it into something else.

By the way, thank you for an interesting and civil discussion. Your
technical knowledge is obviously extensive, and some of my anecdotal or
field experience may be unknown to you. Goes to show... we can learn from
each other. I hope...

I'll bet you could also learn from on-topic posts. You might want to
give it a shot. Maybe start off slow, with one or two on-topic posts,
and see how it goes.