03-23-2015, 08:34 PM
Yes, the shielded loop can be very effective in reducing pickup from locally generated interference. That may be the effect you are noticing when comparing the long wire of the 37-116 to the low impedance loop of the 41-250.
In the 1940 models, Philco used a loop antenna with an electrostatic shield. This was a Faraday shield composed of a large number of grounded wires imbedded in the cardboard covering of the rotatable loop.
In the 1941 and later models, Philco used a different approach. They designed the loop with only a few turns of very heavy wire, and used a tuned antenna matching transformer to step up the impedance to the grid of the front end tube. Because of the low impedance of the actual loop antenna, it was relatively insensitive to the electrostatic fields of locally generated interference, yet still responded directionally to the transmitted electromagnetic field of the more distant broadcast radio signals.
https://docs.google.com/viewer?url=paten...322126.pdf
In the 1940 models, Philco used a loop antenna with an electrostatic shield. This was a Faraday shield composed of a large number of grounded wires imbedded in the cardboard covering of the rotatable loop.
In the 1941 and later models, Philco used a different approach. They designed the loop with only a few turns of very heavy wire, and used a tuned antenna matching transformer to step up the impedance to the grid of the front end tube. Because of the low impedance of the actual loop antenna, it was relatively insensitive to the electrostatic fields of locally generated interference, yet still responded directionally to the transmitted electromagnetic field of the more distant broadcast radio signals.
https://docs.google.com/viewer?url=paten...322126.pdf
