The date when the first encounter across time occurs is October 21st and is a homage to the Back to the Future franchise. October 21st is the date Marty McFly and Doc Brown travel to in 2015 in Back to the Future II and this date is now "Back to the Future Day". The date of the first encounter is her birthday. The opening of the episode has her boyfriend telling her happy birthday...on oct 20
Toby Emmerich, one of the producers of this series, wrote the original movie it is based on. Toby's brother, Noah Emmerich, had a supporting role in the film.
The abbreviation CQ that is heard numerous times in the show by Raimy Sullivan and her father Frank, is an invitation for any operators listening on that frequency to respond. It derives from the French word sécurité which means "safety" or "pay attention". (The letters CQ, when pronounced in French, resemble the first two syllables of sécurité). In English-speaking countries, the origin of the abbreviation was popularly changed to the phrase "seek you".
"Frequency" (2016) is using the same effect in its opening titles as the original film Frequency (2000) which resembles the distinct yellow-ish glow of the vacuum tubes inside a ham radio.