Click the second line on the page and this will take you to the download page. Scroll down to the blue button.
I loaded the schematic into ELSIE. I just picked some component values for show and tell.
If you examine the circuit you should see the same hookup. Now for the frequency response.
What I want to show is that the circuit is being used to reject the lower frequencies and pass the higher frequencies. The circuit could be modified to be a low pass. With a superhet front end we could have a dual band receiver by selecting the high or low. This is the scheme The chief designer chose in the 40/80. He simply changes the preselector to change bands. It can also provide some RF gain control by tuning the signal to the slope of the curve.