AM DA Basics Questions...

[TXengineer]

On the AM license.
It indicates 'field ratio', Phase Degree, Spacing Degree, Orientation, and Electrical height...

What are the field ratio, phase degree and spacing degrees calculate out to?

I assume that orientation is how tower # is associated with tower #1 ?

The electrical height is the amount of the tower is electrically charged and how high that is?. (So if you have a 56 meter tower with 52 meters electrically charged, you have a 52 meter electrical height)

Am I off or right on?

[tpt]

> On the AM license.
> It indicates 'field ratio', Phase Degree, Spacing Degree,
> Orientation, and Electrical height...
>
> What are the field ratio, phase degree and spacing degrees
> calculate out to?
>
> I assume that orientation is how tower # is associated with
> tower #1 ?
>
> The electrical height is the amount of the tower is
> electrically charged and how high that is?. (So if you have
> a 56 meter tower with 52 meters electrically charged, you
> have a 52 meter electrical height)
>
> Am I off or right on?
>
Field ratio: One tower is designated the reference tower in the design, the field ratio is, in effect, the ratio of the amount of power provided to the other towers compared to the reference tower.

Phase degree also is in relation to the reference tower. The combination of the power ratios between towers and the phase difference determine the basic shape of the pattern (as seen on a polar plot), the depth of the nulls and the size of the major and minor lobes.

Spacing degrees enters into this equation as well, and refers to the separation of the towers in electrical degrees, and of course the orientation indicates the direction each tower is from the reference tower, compared to true north. "Dogleg" configurations, where one tower is offset to the other two, may be used to take a basic figure eight pattern (for example)and shift one of the lobes off at an angle.

Finally electrical height is as you guessed the electrical height of each tower. Since electrical height determines the efficiency of the radiator (standing alone) as well as vertical radiation angle (important at night), designers may use the height of the towers, or varying heights, to design a nighttime pattern that places skywave signals into areas that won't interfere with protected stations.

Of course, tower heights, spacing and orientation of the towers are not going to change.  Unless you have a tornado come through the site.

However, field and phase ratios can vary as measured on the station's monitor. For some arrays, this is a common summer to winter change, and the shift is minor.  Sometimes it is not the array that is shifting, but the monitoring system drifting.  So if readings change, the first step is to grab the FIM and see if the monitor points are still in. BEFORE you begin to crank anything.

[TXengineer]

> Field ratio: One tower is designated the reference tower in
> the design, the field ratio is, in effect, the ratio of the
> amount of power provided to the other towers compared to the
> reference tower.

OK Makes sense.

> Phase degree also is in relation to the reference tower. The
> combination of the power ratios between towers and the phase
> difference determine the basic shape of the pattern (as seen
> on a polar plot), the depth of the nulls and the size of the
> major and minor lobes.

OK, so in a situation of a multi-tower array, what is the reference tower's phase degree in relation to? I'll give an example. WHYN (AM) Springfield has three towers. According to the license, tower #2 is the reference tower.
#2 tower has a phase of 3.8° (Towers 1 & 3 have a phase of -143.1°/143.1° respectfully). Is that phase of 3.8° in relation to the +/- = 0 phase of towers 1 & 3?
 
> Spacing degrees enters into this equation as well, and
> refers to the separation of the towers in electrical
> degrees,

This makes sense...

> However, field and phase ratios can vary as measured on the
> station's monitor. For some arrays, this is a common summer
> to winter change, and the shift is minor.  Sometimes it is
> not the array that is shifting, but the monitoring system
> drifting.  So if readings change, the first step is to grab
> the FIM and see if the monitor points are still in. BEFORE
> you begin to crank anything.
>
Thanks,

This is very interesting to me. I've always done work with FM and TV, but never AM...

Is there a recommended read to further explain AM arrays?

[Les]

> This is very interesting to me. I've always done work with
> FM and TV, but never AM...

Fewer and fewer competent AM directional engineers survive each year.
I only ever messed with one two-tower rig and it was stable year after
year, so I never got much real experience with it.  

Working around others with multi-tower arrays I reached my own
conclusions:  1.  If you want job-security work for a station with
a 3-tower array so you can chase the pattern all over the place.
2.  Directional AM antenna science is an oxymoron.  It's all black
magic.

> Is there a recommended read to further explain AM arrays?

I won't say there are none; just that I have never seen one that
did not have extremely advanced mathematics as prerequisite!

______________

Due to continuing underwhelming popular demand...

[wkbam1690]

> > This is very interesting to me. I've always done work with
>
> > FM and TV, but never AM...
>
> Fewer and fewer competent AM directional engineers survive
> each year.
> I only ever messed with one two-tower rig and it was stable
> year after
> year, so I never got much real experience with it.  
>
> Working around others with multi-tower arrays I reached my
> own
> conclusions:  1.  If you want job-security work for a
> station with
> a 3-tower array so you can chase the pattern all over the
> place.
> 2.  Directional AM antenna science is an oxymoron.  It's all
> black
> magic.
>
> > Is there a recommended read to further explain AM arrays?
>
> I won't say there are none; just that I have never seen one
> that
> did not have extremely advanced mathematics as prerequisite!
>

John Cunningham's book (I forget the title) is an excellent book on the subject, but long out of print. They come up occasionally on EBay, but expect to pay around $100 per copy at the end of bidding.

[RadioDoc]

> > This is very interesting to me. I've always done work with
>
> > FM and TV, but never AM...
>
> Fewer and fewer competent AM directional engineers survive
> each year.
> I only ever messed with one two-tower rig and it was stable
> year after
> year, so I never got much real experience with it.  
>
> Working around others with multi-tower arrays I reached my
> own
> conclusions:  1.  If you want job-security work for a
> station with
> a 3-tower array so you can chase the pattern all over the
> place.
> 2.  Directional AM antenna science is an oxymoron.  It's all
> black
> magic.
>
> > Is there a recommended read to further explain AM arrays?
>
> I won't say there are none; just that I have never seen one
> that
> did not have extremely advanced mathematics as prerequisite!
>

I've got a 5 tower DA-2.  You are correct, it is ALL black magic!  

The other thing to remember about DA's - a slight change in one tower can change the parameters of all the rest!  I would say an infrared thermometer, FIM, and a very good knowledge of the DA you're working on are major requirements!!

I've become pretty good at DA's over the years, but I've had real smart guys who taught me.

______________

[TXengineer]

> John Cunningham's book (I forget the title) is an excellent
> book on the subject, but long out of print. They come up
> occasionally on EBay, but expect to pay around $100 per copy
> at the end of bidding.

Is that the title?

[rfburns]

> > John Cunningham's book (I forget the title) is an
> excellent
> > book on the subject, but long out of print. They come up
> > occasionally on EBay, but expect to pay around $100 per
> copy
> > at the end of bidding.
>
> Is that the title?
>

That's the book.  I was given a copy about 15 years ago and it is the best reference book I've seen for AM antennas.

RFB

[k9ez]

> > > John Cunningham's book (I forget the title) is an
> > excellent
> > > book on the subject, but long out of print. They come up
>
> > > occasionally on EBay, but expect to pay around $100 per
> > copy
> > > at the end of bidding.
> >
> > Is that the title?
> >
>
> That's the book.  I was given a copy about 15 years ago and
> it is the best reference book I've seen for AM antennas.
>
> RFB
>


I found a copy at a regional library using the following URL:

http://www.worldcatlibraries.org/

[am_directional]

There is another excellent book that is currently published about directional antennas - it's called Dirctional Antennas Made Simple by Jack Layton.  I know the SBE bookstore sells it - probably some others have it as well.

The title is a bit deceptive: I don't beleive directional antennas can ever be "simple" but this book does an excellent job on the topic without tons of math.    

Regards,
Joe


> > > > John Cunningham's book (I forget the title) is an
> > > excellent
> > > > book on the subject, but long out of print. They come
> up
> >
> > > > occasionally on EBay, but expect to pay around $100
> per
> > > copy
> > > > at the end of bidding.
> > >
> > > Is that the title?
> > >
> >
> > That's the book.  I was given a copy about 15 years ago
> and
> > it is the best reference book I've seen for AM antennas.
> >
> > RFB
> >
>
>
> I found a copy at a regional library using the following
> URL:
>
> http://www.worldcatlibraries.org/
>