LOOP ANTENNAS OF 20s RADIO VINTAGE
Anyone have a real loop antenna of that vintage?
If so please describe it.
Anyone know what was used or an information site?
Thanks for the help.
Many of these were home-made, and I expect a degree of experimentation was required. You see descriptions in the literature like "20 inches diameter". The majority were square or diamond shaped. This just reflects the simplest mounting method in use... two crossed sticks. Rectangular versions were also made, requiring an additional lateral supporting arm.
Here's a description from page 10 of "The Wireless Manual", 14th edition, undated, which was actually a catalog from Manhattan Electrical Supply Co.:
"This loop generally takes the form of a coil of wire wound on a wooden frame about three feet square. Six or eight turns wound in a continuous coil with the wire spaced about 3/8 of an inch apart will be satisfactory. The ends of this coil can be treated as the aerial and ground wires respectively, and may be connected directly to the terminals of the receiving set."
I believe you'll find some information in the book entitled "Radio For The Millions" which can downloaded online from somewhere??? I expect Google can be of help here.
These loops were resonated by the input tuning cap, and thus must be of the correct inductance to work with a particular radio. You can calculate the inductance if you know (or can measure) the minimum and maximum values of the tuning cap.
I can post a photo of a zenith 40a antenna from 1928.
I have been cleaning and restoring the guts and have this out right now for reglueing and general cleanup. This is an interesting one as it is hooked to a shaft and linkage that comes out the front of the wood console in front and sliding the lever from the front rotates the antenna. I think it has 10 settings on the lever. Pretty creative for 1928 I thought.
I'll try to remember to take my camera home tonight and shoot some shots for posting here inthe gallery.
Just how effective were these loops back in the 1920's? I know I have seen lots of pictures of them in ads and a lot of sales hype, but lets be honest here. How did they compare to the standard longwire antenna in use in most homes?
(Connoisseur of the cold 807) CW forever!
I've used loops in various configurations versus outdoor random-wire antennas.
First let me say that some "20s loops" were specific to a certain model of radio by virtue of their tuning cap range or a whole nuther bag of snakes in 20s superhets. That eludes a generic answer.
On the whole, an outdoor wire is going to capture more signal than an indoor loop. Period. No 25-mile restrictions if you are comparing a 50kw station vs a 1kw station although older texts occasionally skipped over the details in this way so as to not to confuse a beginner.
In generic terms the external loop antenna played the same role as the loop antenna glued on the back of your 1960s clock radio. It served as the inductance part of the tuned circuit at the input of the radio. Just as back panel "loop antennas"are not all the same, neither are just anyole 20s loop antenna.
Now, with technical minituae in tow...whats the question?
Heres a link for just about anything you need to know about loop antennas
"AC volts and DC volts and little lamps and lities..."
I have used my Western Electric 4D receiver with a loop antenna and with the 2B tuner with long wire.
Sensitivity was comparable, but something that seemed missed here- I was able to tune out some interfering stations by carefully directing the loop to the nulling position for the interfering station (in this case, it was fortunate it didn't also null the intended station).
Here's a few photos of the 40-a from 1928. The chassis is the same in the 39-a also. These look pretty much like the late 30's and early 40's ones.