xmsn angle of incidence

[sam critter]

Here in Tucson AZ at night I normally hear KOA Denver 850kHz and KSL Salt Lake City 1160kHz 5by5. (range @600 miles each)
There is usually no background QRN, no QRM and normally little if any fading. If I didn't know any better I'd assume they were local AM stations.

My question is: do MW stations xmit their signal at a more or less specific take off angle?

I've played around with this and I assume the typical angle is @45 degrees. If true, this would allow me to receive KOA/KSL on the second skywave down bounce and account for the solid 5by5 reception.

I realize that there are a number of factors influencing propagation, but none the less, do most have a specific take off angle?

 

[[email protected]]

For AM stations the take off angle is normally not a concern for daytime operation however for night time it is. However, a low angle of radiation does favor increased coverage during the daytime.

Nightime operation is usually restricted due to co-channel station protection so a higher take off angle is usually preferred.

 

[rfry]

do MW stations xmit their signal at a more or less specific take off angle?

This is a good question.

Just to note that the elevation pattern field actually "launched" by a vertical monopole of 5/8-wavelength and less always is maximum in the horizontal plane, day and night.

So if "takeoff angle" refers to the angle having the highest relative field launched by such monopoles, rather than the peak, far field radiation existing at an infinite distance from it over an infinite, flat (non-real) ground plane, then that angle always will equal zero degrees.

The relative field radiated by an unloaded monopole having a physical height of about 1/4 wavelength is about equal to the cosine of the elevation angle. The cosine of zero degrees = unity. The cosine value for angles greater than zero degrees is less than unity.

RF

 

[kenglish]

Right after this thread started, I tried to look for the FCC Part 73 stuff that included charts and graphs that talked about wavelengths vs takeoff angles.
Where they went, I do not know! ???

 

[rfry]

Right after this thread started, I tried to look for the FCC Part 73 stuff that included charts and graphs that talked about wavelengths vs takeoff angles

Just to note again that vertical monopoles of 5/8 wavelength and less in electrical height all radiate maximum relative field [E/E(max)] in the horizontal plane. This is true regardless of the frequency, and the r-f resistance of the ground plane against which the monopole is driven.

The link below leads to a NEC4.2 analysis showing this for three different earth conductivities at the antenna site, including "sea water."

It can be seen that the elevation fields for the two conductivities plotted other than for sea water show the same essential radiated shapes as that for sea water, but with reduced fields.

However the highest radiated field for all three conditions remains in the horizontal plane.

http://i62.photobucket.com/albums/h85/rfry-100/Monopole_Low_Angle_Radiation.jpg