ANTENTOP- 01- 2014 # 018

Bridge Effect

Figure 3 Area of decreasing reception under the Arch

Generally speaking it is possible to find explanation for the "arch effect."

 It could be assumed that the arch is a closed loop, which in its zone of influence produces local shielding, or shift in direction of propagation of radio waves. Both of this effect could result to decreasing in receiving of the MW radio. Automatic Gain Control cannot stand the fast decreasing of the signal level.

 The arch, which does not affect the reception of MW signals, is not a closed loop which can screen or modify locally direction of propagation of radio waves in MW Band.

 BRIDGE

The bridge influences to radio reception in MW Band in more complicated way compare to the arch. It is possible describe three typical cases and four untypical ones. Bridge does not affect to station at FM-Band.

Three typical cases of the bridge behavior

First typical case is shown in Figure 4. It is the most typical case in influence of the bridge to radio in MW Band. Level of volume is drop down when car is driving under the bridge and after the car driving up to 20- 50- meters out of the bridge. Then the volume goes back to usual level.

Second typical case is shown in Figure 5. Level of volume is drop down when car is driving strictly under the bridge. When car is driven out of the bridge the volume goes back to usual level.

 Third typical case (but rare compare to the first two cases) is shown in Figure 6. Level of volume is drop down when car exits out of the bridge.

That is interesting that picture of attenuation of the radio reception lay in the direction of the driving. If a car would drive under the same bridge in the opposite direction the picture (Figure 4, 5, 6) would be the same. In my opinion the picture of attenuation of MW reception may be explained by various degrees of shielding of the MW radio by bridge and inertia in the receiver's AGC. .

 Behavior of bridges (to influence to MW radio) is unstable. It is oddly enough but any bridge may behave differently. One day, its behavior is consistent with Figure 4, in another day its behavior is consistent with Figure 5, and the next day its behavior is consistent with Figure 6.

 Four untypical cases of the bridge behavior

First untypical case of the bridge behavior is that the bridge has no effect on the reception in MW Band.

For the Second, Third and Fourth untypical case I take inversion in the influence to the MW reception. It means that instead of decreasing in level of volume of MW reception there are increasing in level of volume of MW reception.

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