FM polarization may be either "clockwise" or "counterclockwise":
Apparently, in addition to Horizontal ONLY, it can also be Vertical ONLY:
Unfortunately, the FCC's FMQ database does NOT require submission of
polarization direction, so you might have to look at the detailed application
requests and engineering data, or investigate the antenna part number or
call the station (hoping to talk to someone who REALLY knows):
PS: If broadcasting a polarized signal, TV is always "clockwise (right hand)":
BTW: A Helix would be preferred vs Crossed Yagi's due to the "quarter-wave"
mis-match across the FM Band (20% bandwidth). K6STI has analyzed several
Circularly Polarized antennas for FM, including a Cubical Quad. Someone might
want to perform further analysis using 4nec2 (or equivalent):
More information re Cir. Pol. Antennas and the quarter-wave transformer:
Some DIY Cir. Polarized Antennas:
Exercise for OTA experimenter who has some FM Yagi's but isn't ready for a DIY project:
Mount one Yagi for horizontal reception and the other for vertical reception and
interconnect using the quarter-wave transformer described in the the first reference above.
It might not be an "optimal" antenna for circularly polarized signals, but it might
surprise you and for sure will receive signals that are predominantly Horiz. OR Vertical,
depending on what the station is transmitting. Not sure if they need to be matched.....
Unfortunately, like all Cir. Pol. antennas, it will also pick up noise & interference from
the "other" antenna when trying to receive a predominately Horiz. or Vertical signal....
Exercise for the 4nec2 student: simulate the above with various vertical stacking and
horizontal stacking heights....which will require figuring out how to REALLY simulate
AND analyze Cir. Pol. signals in 4nec2 (it isn't obvious....) Verify by looking for big drop
in Gain when trying to receive a left-hand signal with a right-hand antenna.