[Milsurplus] Japanese Air - Ground Communications

[Hue Miller]

I looking at an ONI manual showing Japanese aircraft radios and noticed that 
one model
of 44-50 MHz voice radio had a "second receiver" mounted to the top of it. 
This "second
receiver" was a smaller unit HF receiver with a spectrum of about 3 - 12 
MHz.
I realize this is only speculation, but any ideas why the provision of an HF 
receiver
with no HF transmit equipment?
Tnx-- Hue Miller