First, get some kind of portable receiver out and put it on 1820 and verify you are hearing the harmonic. I doubt it is being generated in your gear. You will probably hear it because you are only 2 miles from the tx site and if the station is running 5 or more KW they're likely suppressing the harmonic adequately -- you're simply too close. What we often hear in our own stuff like preamps is products generated by a pair of broadcast stations mixing. This doesn't mean that a broadcast station is never at fault. Investigation shows your problem station is a 5 KW directional with 3 or 4 towers depending on the pattern. https://radio-locator.com/info/KRIO-AM
There's more to go wrong there. You should look at the night pattern and determine if your station is in a lobe or null. You can observe if the harmonic strength varies from day to night. It's true that AM stations aren't getting maintained as well as they once were. Problems can crop up in the station's phasor, and tower matching networks. The pattern may not be in specification or they may not even be changing to the night pattern. A lot of high pass filters do not attenuate well near the top of the broadcast band so as to not compromise 160 m. performance. So fellows with stations nearby that are on 1500 or higher: Choose your filter with care. In the case of 910 you have a wider selection from which to choose because just about all of them will knock a low frequency like that down. Even if the problem is a harmonic, putting in one or more filters is worthwhile. What about the harmonic? If it's coming from the station, all is not lost because it is a point source. You can receive with small loop antennas oriented to put the harmonic in the loop's null, or better, employ a phasing network using inputs from two separated receive antennas that can throw a null on 1820 at the offending broadcast station. Or you can use both methods. If you are happy with your current receive antennas, I'd try a phasing network if all else fails. 73 Rob K5UJ _________________ Searchable Archives: http://www.contesting.com/_topband - Topband Reflector
