In the process of finishing up a restoration of a Philco 40-145 and am trying to build the missing loop antenna usually attached to the back cover. Have already reproduced the back cover and the frame for the loop antenna, but don't have enough details regarding the directions to loop the wire, the number of loops, or how they connect to the terminal board and variable cap mounted to the frame of the antenna. Used several videos and still images available online to get a basic idea, but there are some specific details missing regarding the path of the wire loops. Would greatly appreciate any assistance, i.e. photos of an original antenna or maybe a hand-drawn schematic. I've attached a pic showing my progress so far.
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.
Nice job!
As a mental exercise I was looking over the diagram to see how I might solve the problem. The large coil "L1" needs to resonant at the bcb with a 350mmfd vari cap in parallel. Top tap to the bottom resonant to the police band. Bottom tap to bottom don't think particularly critical as it's used for coupling the antenna energy into the set. "L2" Just has to be resonant at the top band with the 350 mmfd tuning cap.
Although I could be way off base.
I recently got a capacitance/inductance meter and there are online calculators to sort frequency vs capacitance and inductance. On the other head I rarely buy mulit band sets missing loop ant. Life is short!
When my pals were reading comic books
I was down in the basement in my dad's
workshop. Perusing his Sam's Photofoacts
Vol 1-50 admiring the old set and trying to
figure out what all those squiggly meant.
Circa 1966
Now I think I've got!
Terry
(This post was last modified: 01-21-2023, 06:50 PM by Radioroslyn.)
Hello percyjd,
Wow that looks great and you have put a lot work into this antenna !
I have a nice General Electric Model J-64 missing it's Back and Antenna I made a back but I am looking for the same answers you were with this build .
The Utube channel, jimsradioshop, just posted several videos on this very antenna. He goes into detail on how the antenna was built and how it connects to the radio. He also attempts to "test" the validity of the design, but without much success. It does improve the reception but the receiver had not been re-capped and I don't believe the tubes were verified as being good. So try watching it, I usually fast forward through the slow parts. I think it's quite a coincidence to see two radios the same week that have this antenna. But his is a Philco and the patent owner worked for Philco.
(This post was last modified: 01-22-2023, 09:45 AM by RodB.)
Just watched Jim's videos about this particular antenna. I'm a fan of Jim's channel, but hadn't realized he had just uploaded a video on this antenna. Would have been nice to have found that a few weeks ago, but still, the challenge of figuring something out is part of the fun. I noticed the format of his antenna is rather unique even though it follows the same general principle as outlined in the schematic. Unlike Jim, I noticed a considerable difference when attaching this antenna instead of using a length of wire attached to the back. Almost all of the distortion of the signal this set was experiencing (like being underwater) was eliminated.
percyjd,
Nice work! Did you get all the info you needed? Set working OK? I'm working on a 40-145 now (just finishing it), and the "antenna system" is all intact, wires are more or less the colors they are supposed to be. I'd be happy to send you or post pictures of the "system" before I button it up. Quite a bunch of antennas and trimmers! Just let me know.
Thanks for the offer. Yes, this set is working fine now. Prior to adding the antenna system, had serious problems with reception as this set apparently needs the tuned antenna. Nice set once it was refurbished.
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