[462ron]

Hey guys and gals, I was wondering about the benefits of a loop antenna. I have a Philco 37-116 running off a long wire antenna and while it picks up many stations, it seems to also pick up a lot of noise and static compared to my 41-250 with a built in loop antenna! Just about every station on th41-250 is quieter than the same station on the 37-116 except for strong local ones. The long wire antenna is outside  away from power lines and machinery. Would like to build  a loop antenna  for the 37-116.

Ron

[Phlogiston]

The variable IF setting on the 37-116 will make a difference. Set it for narrow to eliminate some of the noise.

[462ron]

Thanks Phlo, yes the variable IF does help some but my set with the loop antenna still seems quieter. I know Philco had a special loop antenna for the 37-116 so I would like to try a fabricate something similar if I had the specs and dimensions of one.

[Ron Ramirez]

I know Philco had a special loop antenna for the 37-116...

No, they didn't. They had a special outdoor doublet antenna for the 37-116 and other 1937 Philco models. It was called the Philco High Efficiency Aerial.

http://www.philcorepairbench.com/mystery/40-6112.htm
http://www.philcoradio.com/phorum/showth...hp?tid=297

[462ron]

Thanks much Ron! My mistake, thought they had a loop antenna for consoles. Interesting threads on these antennae. I will need to do some experimenting, I was just surprised to hear how much quieter my 41-250 was. A guy at K-town a few years ago said something to me about it being a low impedance  antenna that made it less susceptible to external noise and interference.

Ron

[David]

Joe Carr has written several books on the subject one is free on line as a pdf. Several of his books can be purchased from amazon lots of fun projects! David

[462ron]

Thanks David,  Found the Book in PDF format and downloaded it. Now to get the time and read it.

[Alan Douglas]

A shielded loop can be insensitive to electrostatic fields (local RFI), but an unshielded one acts like a short vertical antenna.

The other useful property of a loop is nulling a signal broadside to it (the signal generates equal voltages in the two vertical sides of the loop, which cancel out). Balancing the feed well enough to achieve this is tricky however.

[Mondial]

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

[462ron]

Thanks Mondial, that link looks like something I would like to experiment with. I have the chassis for my 37-116 completed but the cabinet needs work yet. So eventually when it is done and I finally get the radio installed into the cabinet I am going to try a loop on it. Thnks agan.

Ron