01-21-2023, 09:31 AM
Just thought I'd provide an update on the 40-145 loop antenna. I ended up locating the patent diagram for this particular antenna (see image below) and was able disearn enough of the details to make a reproduction.
Based on these details, I wound the loop antenna using 20 awg enameled magnet wire. The schematic for the 40-145 showed four wires attached to various points on the loop; one at each end of the wire, and two taps. I made a total of 21 windings on the loop and tapped into the loop at what I felt were the appropriate locations based on my analysis of a loop antenna for a different model: at 11 loops and 16 loops. One of the interesting descriptions in the patent info was that this loop should wind around the back half of the antenna frame, further away from the receiver. This is shown in the patent diagram.
One end of the loop connects to a 75-350pf Arco variable trimmer cap (part 465) mounted on a Bakelite terminal strip (with terminals removed) and goes to the back of the receiver (#1). The other end of the loop connects to the opposite side of the same variable trim cap. This is the antenna ground and hooks to the back of the receiver (#4).
The tap at 11 loops connects directly to the back of the receiver (#2). The tap at 16 loops actually connects to a 250pf mica cap and 10k resistor run in parallel from a separate external antenna connection on the back panel. This then runs to the back of the receiver (#5).
Note: The #3 terminal on the back of the receiver is for the shortwave antenna (which I previously reproduced using instructions found on the Antique Radio forum): https://antiqueradios.com/forums/viewtop...6&t=300441
The shield wire has a total of 26 loops of 24 awg enameled magnet wire, 13 on each side with a center tap running to the ground on the variable trimmer cap. The center tap was done according to the description in the patent.
After winding the loop antenna and shield, I secured the wires using some beeswax and double-sided tape mounted on the interior of the loops where they are less obvious.
Once I had the antenna hooked up and the receiver turned on, I had to go back and conduct another alignment. I actually found that I had to adjust the trimmer cap on the antenna first before I could make any further adjustments to the radio. Afterwards, the radio reception is much better with most of the noise and distortion that was occurring without this style antenna attached cleared up.
Hope this helps anyone else that finds they may need to reproduce a similar style antenna.
Based on these details, I wound the loop antenna using 20 awg enameled magnet wire. The schematic for the 40-145 showed four wires attached to various points on the loop; one at each end of the wire, and two taps. I made a total of 21 windings on the loop and tapped into the loop at what I felt were the appropriate locations based on my analysis of a loop antenna for a different model: at 11 loops and 16 loops. One of the interesting descriptions in the patent info was that this loop should wind around the back half of the antenna frame, further away from the receiver. This is shown in the patent diagram.
One end of the loop connects to a 75-350pf Arco variable trimmer cap (part 465) mounted on a Bakelite terminal strip (with terminals removed) and goes to the back of the receiver (#1). The other end of the loop connects to the opposite side of the same variable trim cap. This is the antenna ground and hooks to the back of the receiver (#4).
The tap at 11 loops connects directly to the back of the receiver (#2). The tap at 16 loops actually connects to a 250pf mica cap and 10k resistor run in parallel from a separate external antenna connection on the back panel. This then runs to the back of the receiver (#5).
Note: The #3 terminal on the back of the receiver is for the shortwave antenna (which I previously reproduced using instructions found on the Antique Radio forum): https://antiqueradios.com/forums/viewtop...6&t=300441
The shield wire has a total of 26 loops of 24 awg enameled magnet wire, 13 on each side with a center tap running to the ground on the variable trimmer cap. The center tap was done according to the description in the patent.
After winding the loop antenna and shield, I secured the wires using some beeswax and double-sided tape mounted on the interior of the loops where they are less obvious.
Once I had the antenna hooked up and the receiver turned on, I had to go back and conduct another alignment. I actually found that I had to adjust the trimmer cap on the antenna first before I could make any further adjustments to the radio. Afterwards, the radio reception is much better with most of the noise and distortion that was occurring without this style antenna attached cleared up.
Hope this helps anyone else that finds they may need to reproduce a similar style antenna.
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