Recently I have been improving my 160 meter antenna system. I made a few changes to the Inverted-L antenna by spacing it farther off of the tower and getting the end wire out of the tree. I still need to get the end wire higher up in the tree. The wire is around 134 feet long. 80 feet go up the tower and the remainder horizontally toward a tree to the south. The end of that wire is only about 25 feet above the ground. It should be more horizontal. That tree is much taller but I can't get up in it any higher without a bucket truck or a man-lift.
I also added eleven radials fanned out over the back yard. The radials are 67 feet long. There is a reason for that which I should document in a future post.
The 160 meter band is just above the AM broadcast band. I live with in 2 miles of the big three Dayton, Ohio AM radio stations: WING, WHIO, and WONE. These are 5000 watt stations running omni directional antenna during the day and directional at night. The inverted-L picks up a log of RF during the day when the stations are running an omni pattern. At night the directional pattern appears to be away from me as the signal level drops for all three stations.
For example, looking at WHIO (1290 KHz) using a frequency selective volt meter I see +16 DBm during the day on the inverted-L. At night it drops below 0 DBm.
Today I hooked up four 1N4148 signal diodes in a full wave bridge configuration. I hooked that to the inverted-L antenna. I get 38 volts open circuit from the diode bridge. Short circuit current is 8 ma. I placed an LED across the diode bridge output. It lights the LED right up!
During the day I also have intermod problems from the high power stations combining together. One 3rd order mix fall right on the 160 meter FT8 frequency. Of course, 160 meters is dead during the day and the intermod mix disappears once the stations go to their directional pattern at night. This has not been a problem but it would be nice to eliminate the issue.
At first I tried putting high-pass filters on the receiver. Thinking the intermod was from overloaded receiver front end. That did not work so that tells me the intermod mix is coming from something external. That could be anything. Mixing in one of the transmitters, mixing from a rust bolt somewhere. I am going to try to find it. I am thinking a ferrite rod antenna built to resonate on 1.840 KHz might work. Those rod antennas have a sharp null off of the end. If it on my property maybe I can find it. Snowball's chance in hell, but I will give it a try.
