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

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