I was reminded today that some yagi antenna's at 50 Mhz (and probably other frequencies) exhibit a stronger LOWER resonance off the BACK of the yagi than off the front if the frequency you are trying to hear is lower than the yagi is actually resonant at.
For example years ago we used to use listen to 45 Mhz video from New Zealand by turning the 50 Mhz Yagi's we used to 180 degrees of the direct azimuth. In other words, the back end of the beam was pointing towards New Zealand when listening for 45 Mhz TV video.
Today I experience this same phenomena and remembered "Oh yeah, I've seen that before!"
In this case I'm using my 10 Element LFA Yagi and was listening to BOTH 50 Mhz and 44 Mhz at the same time. I noticed that when pointed directly at the noise source I was hunting that the 50 Mhz graph I was watching was very high. But the the 44 Mhz was at least 4-5 db lower! Doh! I rotated the antenna 180 degrees and lo-and-behold the 44 Mhz came up and the 50 Mhz dropped. (Just like the days of old).
Just thought I'd mention this in case anyone ever wonders the same thing, or is trying to figure out a similar issue, or maybe just to remind MYSELF !
Take Care, and be careful out there!