KCNN (ex-KAVV) just filed an L2C amendment to their proposed upgrade to C3 at 97.7 showing the antenna proof and surveyor's statement . Instead of the originally-planned H/V arrangement it will be 25 kw directional Horizontal-Only. Typically, H-only polarization is done as a power saving mechanism. In this amendment, Sierra Vista is no longer under the 60 dBu contour, in fact there exists a 9.6 dB null in that direction However, the contour still stretches west to the "exburbs" of metro Tucson.
Supposedly the station already operates in HD mode.
Antenna Proof is here:
Supposedly the station already operates in HD mode.
Antenna Proof is here:

