[ash]

Some speculations:

I suspect FCC simply allowed Raytheon to use whatever frequency its "Radarange" oven used. After all, Raytheon was the main radar producer for the US military. Presumably the military had a strong influence on FCC. Remember, it all happened in 1947, just 2 years after World War II.

http://www.raytheon.com/ourcompany/history/leadership/

[anotherhue]

Indeed, I strongly suspect the answer will be something along these lines. I have tried to research the operating frequency of the radarange, but have come up empty. If you click the 'contact us' link on the page you've referenced, you find this section:

Academic Research Assistance

We do not entertain requests for academic research assistance. Our web site is rich in both historic company information and current product material. Explore the links from our home page, Our Company, History, and search engine.

Which is disappointing, but perhaps I can reach an ex employee.