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Radio Road Which tuner to get and getting the most from it. Thank God, for the radio! |
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Radio Road Which tuner to get and getting the most from it. Thank God, for the radio! |
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In Reply to: " No tuner made can reject multipath." Discuss? posted by Timbo in Oz on December 28, 2011 at 16:41:31:
Multipath is really a function of environment/location and the antenna sending the signal to the tuner as you know. Mulitipath does however alter the phase after a "bounce" off of buildings and other objects between you and the signal source. Perhaps a circuit can designed to work from this angle. I doubt it though as this has been known for a long while.
Having adjustable sensitivity and selectivity has always helped me in the past. My location is so bad now I don't even try. I'm almost at the base of a narrow valley only 300 yards wide.
I found this:
"""From David Mann Audio:
""Multipath" is a phenomenon that, to a degree, affects all radio communications. Radio frequency energy travels through space at the speed of light. The figure shows a common radio communications situation. The line A-B represents energy traveling straight from the transmitter A to the FM receiver B. Unfortunately, energy bouncing off building C, is causing a problem. Some of the energy travels the line A-C-B to the receiver. Since all of the energy travels at the speed of light, the energy traveling along A-C-B takes longer to arrive because the path length is longer. Hence the name "multipath". Multipath can be caused by a variety of sources including: buildings, mountains, bridges, tall towers, passing airplanes or clouds, and windmills.
On a TV set this late arriving energy will cause a second, distinct picture (Ghost image) offset to the right of the direct picture. Knowing a few details about how TV pictures are transmitted and the speed of light, one can measure the image displacement with a ruler on the face of a TV set and calculate the path difference between A-C-B and A-B. For FM reception, the late arriving signal is not late enough to perceived as an echo, but the recovery of FM Stereo information is disrupted and listening to the station can be an unpleasant experience.
The tuner's plight under a barrage of multipath is similar to your own while trying to understand voice announcements in a large transportation terminal filled with echoes.
Certain FM tuners perform better under severe multipath conditions. The relevant tuner specification is "capture ratio". A fortunate characteristic of FM technology is its ability to ignore a weak station arriving at the tuner on the same channel as a strong station. The stronger station is said to "capture" the tuner. A lower capture ratio usually results in better immunity to multipath problems. A very low capture ratio implies that the weaker station could be almost as strong, yet be completely rejected by the tuner. "Better", however, is not always satisfactory. One should not expect the multipath information to behave nicely and always arrive below the capture threshold.
Your best ally for preventing multipath distortion is a highly directional antenna. If the antenna does not respond to the off axis signal, multipath distortion cannot occur. Unfortunately, directional antennas at FM broadcasting frequencies, come in one size -- large. Unless the diagonal dimension of the antenna is approximately 120 inches, it will not be very effective for eliminating multipath." """
ET
ET
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