To receive digital TV signals from all stations, it is important that your antenna be able to receive both VHF channels (channels 2-13) and UHF channels (channels 14- 51). Some antennas only provide good reception of VHF or UHF channels, but not both.
Greeting Card Envelope Size: 5.25 x 7.25 Note Card Envelope Size: 4.375 x 5.75. When creating your design file, make the page size equal to the size of the envelope. The text for your return address should not be closer than 5/16 or .3125 from the edge of the envelope. U.S. Mail Layout Guides. Greeting Card Envelope Note Card Envelope.
As Allmer notes (p. 17-18), postcard size can also be a clue.  If the card is old and is larger than 3.5 by 5.5 inches, it may date from before 1898.  If the card is old and is slightly smaller than 3.5 by 5.5 inches, it may date from 1898-1902.