[K7Sparky]

I too had thought that there was a reception problem caused with navigation signals so went on a search of LORAN data.  Here is a GREAT read on LORAN development and deployment during WWII http://www.jproc.ca/hyperbolic/loran_a.html

Frequency range of LORAN A was 1750 to 1950 KHz no where close to IF.  The first LORAN A pair Montauk Pt, NY & Fenwick Is, Del went live June 1942

I reread the Rider document given by Ron's link in post #7 and it talks about only IF feedback caused by chassis isolation in the universal radios.  The chassis was not part of common so could propagate the IF and cause feedback.

The cap only would be Rider "How it Works" Figure 1 method A where the one used in the 46-421 is method C.  The trap only conductes close to IF frequency where just a cap conducts any AC / RF and the higher the frequency the lower Xc gets.  Maybe that's why Philco used C.

I am just starting an old Zenith 6R886 universal in a box with a 78 turntable that uses method B.

Didn't even know about this subject till the thread.  Really a great education and just in time.