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Tower Height Question
- Thread starter semoochie
- Start date
A
Andy_Brown
Guest
> Is there any way to determine an AM station's actual tower
> height based on its electrical height?
>
No, because antennae of different electrical wavelengths are used,
(5/8 wave, 1/2 wave, etc.) and reactive loading is also used to fine tune them
for performance (e.g. a 5/8 wave antenna might not be exactly 5/8 of a wave
at the frequency in question).<P ID="signature">______________
Electricity is really just organized lightning.
~George Carlin</P>
> height based on its electrical height?
>
No, because antennae of different electrical wavelengths are used,
(5/8 wave, 1/2 wave, etc.) and reactive loading is also used to fine tune them
for performance (e.g. a 5/8 wave antenna might not be exactly 5/8 of a wave
at the frequency in question).<P ID="signature">______________
Electricity is really just organized lightning.
~George Carlin</P>
M
MaiTKwinn
Guest
It's very easy to determine the actual tower length of an AM tower
from its electrical height in degrees and the FCC can assist. You need
two pieces of information: #1) the station's frequency in kilohertz
and #2) the tower's electrical height in degrees. Both of these
items can be found in the FCC data base listing for the particular
station. The easiest way yo get the answer is to use the calculator
on the FCC website for exactly that purpose.
Go to www.fcc.gov, then scrolldown on the right side & click on
"Media Bureau". When the MB homepage appears, look on the left for the
MB Shortcuts box. Click on and scroll to "Elec Degrees<=>Meters and
click on. When it comes up just enter your data and you'll immediately
have your answer. Remember, the answer will be in meters so you'll
have to convert that to inches/feet. (39.36 in/meter I think).
> Is there any way to determine an AM station's actual tower
> height based on its electrical height?
>
from its electrical height in degrees and the FCC can assist. You need
two pieces of information: #1) the station's frequency in kilohertz
and #2) the tower's electrical height in degrees. Both of these
items can be found in the FCC data base listing for the particular
station. The easiest way yo get the answer is to use the calculator
on the FCC website for exactly that purpose.
Go to www.fcc.gov, then scrolldown on the right side & click on
"Media Bureau". When the MB homepage appears, look on the left for the
MB Shortcuts box. Click on and scroll to "Elec Degrees<=>Meters and
click on. When it comes up just enter your data and you'll immediately
have your answer. Remember, the answer will be in meters so you'll
have to convert that to inches/feet. (39.36 in/meter I think).
> Is there any way to determine an AM station's actual tower
> height based on its electrical height?
>
> Is there any way to determine an AM station's actual tower
> height based on its electrical height?
Maybe.
Electrical height is measured in degrees. 360 degrees = one wavelength. The speed of light divided by the station's frequency in KHz also = one wavelength.
Do all the algebra, and the formula:
h = 2734 * (d/f)
where:
h = physical height in feet
d = electrical height in degrees
f = station's frequency in KHz
--------------------------------
As other replies have mentioned, certain loading and sectionalization techniques will cause the actual physical height to vary from this formula.
> height based on its electrical height?
Maybe.
Electrical height is measured in degrees. 360 degrees = one wavelength. The speed of light divided by the station's frequency in KHz also = one wavelength.
Do all the algebra, and the formula:
h = 2734 * (d/f)
where:
h = physical height in feet
d = electrical height in degrees
f = station's frequency in KHz
--------------------------------
As other replies have mentioned, certain loading and sectionalization techniques will cause the actual physical height to vary from this formula.
> > Is there any way to determine an AM station's actual tower
> > height based on its electrical height?
>
> Maybe.
>
> Electrical height is measured in degrees. 360 degrees = one
> wavelength. The speed of light divided by the station's
> frequency in KHz also = one wavelength. etc
______________
However the electrical length of a typical, unloaded MW monopole broadcast antenna is about 5% longer than its physical length, due to the so-called "end effect" -- which is produced by the velocity of propagation along the tower structure being about 5% slower than in free space.
> > height based on its electrical height?
>
> Maybe.
>
> Electrical height is measured in degrees. 360 degrees = one
> wavelength. The speed of light divided by the station's
> frequency in KHz also = one wavelength. etc
______________
However the electrical length of a typical, unloaded MW monopole broadcast antenna is about 5% longer than its physical length, due to the so-called "end effect" -- which is produced by the velocity of propagation along the tower structure being about 5% slower than in free space.
W
webcastboy
Guest
> Is there any way to determine an AM station's actual tower
> height based on its electrical height?
>
There are calculations you can do, but since what really matters is the electrical height of the radiating element, it's not a perfect science. For example, you can have multiple AM stations on different frequencies "diplexed" to the same antenna tower(s). It can be a giant pain in the ass to engineer and maintain, but it can be done.
That said, if you know the latitude/longitude of the AM station (usually accessible through www.radio-locator.com) you can then find out the actual height of the tower(s) by going to http://wireless.fcc.gov and clicking on "Registration Search" under "Antenna Structure Registration" on the right side.
Punch in the coordinates and set the radius to 1 km...that should reveal the towers you want.
As long as the tower is over 200ft, it has to be lit, so it'll be in that database. Most AM towers are over 200ft, except for those brand-new ones that only need like 40 or 50 ft of vertical height...just got FCC approval last summer, IIRC, so they're not in widespread use yet.
(note - if you're closer to an airport, a tower under 200ft may have to be lit, too).
> height based on its electrical height?
>
There are calculations you can do, but since what really matters is the electrical height of the radiating element, it's not a perfect science. For example, you can have multiple AM stations on different frequencies "diplexed" to the same antenna tower(s). It can be a giant pain in the ass to engineer and maintain, but it can be done.
That said, if you know the latitude/longitude of the AM station (usually accessible through www.radio-locator.com) you can then find out the actual height of the tower(s) by going to http://wireless.fcc.gov and clicking on "Registration Search" under "Antenna Structure Registration" on the right side.
Punch in the coordinates and set the radius to 1 km...that should reveal the towers you want.
As long as the tower is over 200ft, it has to be lit, so it'll be in that database. Most AM towers are over 200ft, except for those brand-new ones that only need like 40 or 50 ft of vertical height...just got FCC approval last summer, IIRC, so they're not in widespread use yet.
(note - if you're closer to an airport, a tower under 200ft may have to be lit, too).
> Is there any way to determine an AM station's actual tower
> height based on its electrical height?
>
240,000/frequency in kHz gives the height in feet for quarter-wave (90 degrees), approximately
take that figure, divide by 90 and multiply by electrical height in degrees for height in feet
> height based on its electrical height?
>
240,000/frequency in kHz gives the height in feet for quarter-wave (90 degrees), approximately
take that figure, divide by 90 and multiply by electrical height in degrees for height in feet
T
TXengineer
Guest
You all missed the easy way on this one...
> Is there any way to determine an AM station's actual tower
> height based on its electrical height?
>
Go to www.fccinfo.com
on the AM pages site, it lists both the tower height in Electrical Degrees and then in Meters.
If I am wrong, I'll admit it but I think it's a pretty good bet.
> Is there any way to determine an AM station's actual tower
> height based on its electrical height?
>
Go to www.fccinfo.com
on the AM pages site, it lists both the tower height in Electrical Degrees and then in Meters.
If I am wrong, I'll admit it but I think it's a pretty good bet.
> > Is there any way to determine an AM station's actual tower
>
> > height based on its electrical height?
> >
>
> No, because antennae of different electrical wavelengths are
> used,
> (5/8 wave, 1/2 wave, etc.) and reactive loading is also used
> to fine tune them
> for performance (e.g. a 5/8 wave antenna might not be
> exactly 5/8 of a wave
> at the frequency in question).
>
Thank you! I'm actually doing this for a friend. You've all been quite helpful. Thanks again!
>
> > height based on its electrical height?
> >
>
> No, because antennae of different electrical wavelengths are
> used,
> (5/8 wave, 1/2 wave, etc.) and reactive loading is also used
> to fine tune them
> for performance (e.g. a 5/8 wave antenna might not be
> exactly 5/8 of a wave
> at the frequency in question).
>
Thank you! I'm actually doing this for a friend. You've all been quite helpful. Thanks again!
> However the electrical length of a typical, unloaded MW
> monopole broadcast antenna is about 5% longer than its
> physical length, due to the so-called "end effect" -- which
> is produced by the velocity of propagation along the tower
> structure being about 5% slower than in free space.
Darn it. Velocity factor. Forgot all about it.
> monopole broadcast antenna is about 5% longer than its
> physical length, due to the so-called "end effect" -- which
> is produced by the velocity of propagation along the tower
> structure being about 5% slower than in free space.
Darn it. Velocity factor. Forgot all about it.
Download the little DOS program from RFS (www.rfspec.com). Has programs for determining actual length where wavelength in degree & frequency known, and for metric conversions.
Saves wear and tear on the little grey cells.
Saves wear and tear on the little grey cells.
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