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Old 19-Feb-2015, 1:39 PM   #4
Tower Guy
Senior Member
Join Date: Dec 2009
Location: Delmar, NY
Posts: 1,234
WPSU is running two transmitters on channel 15 simultaneously. When running such a distributed transmission system there are areas where the two signals interfere with each other. You are in one such location. For you, the two signals are 47 degrees apart.

For reliable reception of WPSU you will need an antenna that has at least 10 db gain at one or the other of the two signals and a rejection of the other signal of roughly 25 db. Two widely available high performance antennas are the 91XG and the DB8e, both of them have side lobes in the -10 db range at 47 degrees on channel 15. That won't work.

To get 25 db rejection at 47 degrees you'd need to stack two identical antennas at the critical distance to null the interfering channel 15. You can find that distance on the chart here The first null occurs on two antennas 17.5 inches apart. The second null occurs with antennas 50" apart.

I would not stack a pair of DB8e antennas due to cost and windload considerations. A pair of 91XGs could be stacked 50" part. For a smaller, more reasonable antenna, a pair of 43XG antennas stacked 18" apart with the two reflectors touching would reject the second transmitter roughly the same amount as a pair of 91XG antennas.

The key to the installation is a rooftop installation with the fewest number of trees in the direction of the transmitter that you would like to pick up. The small difference in the two NM values for the two WPSU transmitters says that either one could be best for you.
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