I totally missed that 73 is only a choice when you select Cable, not Air. 73 is above the available Home Dist range of 21-69. Ch 21 IS a choice on my 722 receiver, but the picture is quite poor for me because that frequency is used for the digital 31.1 ATSC signal.
Dual-Tuner, Two-TV Receiver with Remote Control Antenna Combined with Home Distribution (Ch 21-69 or 73-125) Output
I was thinking otnipj3s was using a channel at the END of the Air range. Cable 73 is very close in frequency, but the TV may have also been setup for HRC / IRC??
OTA 21 513.25 MHz
OTA 22 519.25 MHz
EIA/NCTA, Standard , HRC , IRC
73 , 517.25 , 516.0258 , 517.2625
Cable 73 should work nearly as well as OTA 22 as far as being a lower frequency (my original intent). If there is something OTA on channel 21, Cable 73 would be closer to it than Air 22. Here, there doesn't seem to be a good choice anywhere in the 20s, but an open channel in the 30s is better than an open channel in the 40s, which is better than one in the 50s. otnipj3s could get a better picture on higher channels if there is something in use in the lower frequencies - just takes experimenting.