US patent 2598857, filed on January 29, 1949
This patent specifically talks about a "front end" receiver in the sense of a block diagram.
Moreover, it is apparent that a considerable saving in cost of a wide range television receiver "front end" make be realized through the use of the present invention. For example, in a television receiver RF "front end" incorporating a push-pull RF amplifier, ...
This usage is already older than am I. I think it's considerably older than that.
US patent 1795397, filed on Dec 29, 1927.
This patent uses the terms "front end" and "back end" extensively. A couple of example uses:
Fig. 5 corresponds with Fig. 4 but has the receiver at the "front end" instead of at the "back end".
It is known that a single wave-antenna can be "compensated" to secure null reception from any specufued angle of incidence of the radio waves, by suitably combining a small portion of the front-end current with the back-end output current. (See, for instance, Fig. 19 of the above-cited paper by Beverage et al.)
The referenced article is by Harold H. Beverage, published in the March, 1923 issue of the "Journal of the A.I.E.E." (Good luck finding that on the internet.) I looked at patents by Beverage, and he doesn't appear to use the term "front end" or "back end" in his patents.