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 Post subject: Loop Antenna - One Connection?
PostPosted: Jan Thu 10, 2019 2:19 am 
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Location: Plymouth, MI
Awhile back I found a Fiat loop antenna in amazing condition. It's the only loop antenna I've bought and I hadn't tried using it until today. I was about to hook it up to my Federal 61 when I realized there was only one wire connection point on the antenna, as least a far as I could see. What am I missing here? Leads end at screws on far left and right.

Attachment:
Fiat 1.jpg
Fiat 1.jpg [ 228.11 KiB | Viewed 984 times ]

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Last edited by atwaterkent1 on Jan Thu 10, 2019 4:58 am, edited 1 time in total.

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 Post subject: Re: Loop Antenna - One Connection?
PostPosted: Jan Thu 10, 2019 3:43 am 
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atwaterkent1 wrote:
...... What am I missing here? .
you are missing one of the connections.......;)

There's no advantage to a loop unless both ends are connected---in fact, the equivalent length of wire run straight should be better that the loop with only one end connected.

Get out your magnifying glass and follow that wire---it has to go somewhere.......

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 Post subject: Re: Loop Antenna - One Connection?
PostPosted: Jan Thu 10, 2019 3:53 am 
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If it's one with a center pole.
Rotating the pole adjusts the antenna... :)

Greg.


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 Post subject: Re: Loop Antenna - One Connection?
PostPosted: Jan Thu 10, 2019 4:59 am 
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Check photo added to 1st post please.

Attachment:
F-1.jpg
F-1.jpg [ 229.71 KiB | Viewed 980 times ]



Attachment:
F-2.jpg
F-2.jpg [ 233.52 KiB | Viewed 980 times ]


Attachments:
F-3.jpg
F-3.jpg [ 226.39 KiB | Viewed 980 times ]

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 Post subject: Re: Loop Antenna - One Connection?
PostPosted: Jan Thu 10, 2019 9:19 am 
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I have seen two arrangements on Fiats from a termination arrangement similar to yours. They both use either one or both of the other two bolts holding the lower assembly together, but not through the face. The gap between the 2 plates has a knurl headed screw that works the same as the one on the face.

Attachment:
Fiat loop attachment.jpg
Fiat loop attachment.jpg [ 37.95 KiB | Viewed 947 times ]


Since it isn't obvious to you, I would guess the knurl headed screw has been lost but that there is a threaded hole on one or both sides.

Some have a lead attached to each of the three points, but most use the one you show plus one of the other two. Sometimes the two plates are wood, like yours, and sometimes are metal with insulators.

It is one of the more attractive loops.

John


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 Post subject: Re: Loop Antenna - One Connection?
PostPosted: Jan Fri 11, 2019 1:46 am 
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Thanks John. Whoever wired this did't know what he was doing. I'll need to find a fitting like the one in your photo and try to figure out a way to make the connections without wrecking the looks of the antenna or I may have to rewind it.

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 Post subject: Re: Loop Antenna - One Connection?
PostPosted: Jan Fri 11, 2019 3:26 am 
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Most loops are 2 wire affairs.

Attachment:
Simple Loop.jpg
Simple Loop.jpg [ 17.96 KiB | Viewed 849 times ]


This image can be construed to show a Fiat with an attachment to each end of the loop:

Attachment:
Fiat Loop Connection.jpg
Fiat Loop Connection.jpg [ 20.06 KiB | Viewed 849 times ]


There are 2 reasons for more wires. Sometimes a tuning cap is tied in with one of the ends and another point. Sometimes 3 wires are for 2 bands. It could be a broadcast band and LF or broadcast and HF. Yours seems to have had 3 connection points, which are the 3 bolts that are shown in your first image. The 2 outer ones tie down the ends. I can't tell where the middle is connected, but you should be able to see. Since we know the connectors have been tampered with, including the middle which is not original, you may or may not be able to know where the middle connector was originally attached. It could be that 1 end is now connected to it.

You have no image of either end, but if those end bolt are original, one of them should provide a clue of a prior attachment and the end of the loop should be electrically connected. If it was rewired, the connection may have been lost if the insulation wasn't removed.

I would be inclined to put a brass collar with a threaded hole for a screw to use to clamp the the antenna lead to it, around the bolts at each end of the plates. Make sure the ends of the loop make connection under the existing nuts. Then you can try all combinations of the 3 leads on the radio and see which work best. and remove the unneeded lead.

John


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 Post subject: Re: Loop Antenna - One Connection?
PostPosted: Jan Fri 11, 2019 4:09 am 
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The reason for the center tap connection is because some superheterodynes require the center tap to be the bias source. One side connection is for part of the tuning and regeneration and the other side connection is for part of the tuning tuning and the incoming signal so the only connection for the bias would be the center tap.

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http://www.duanesradios.info/html/scott ... odyne.html

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http://www.duanesradios.info/html/scott ... per_9.html

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 Post subject: Re: Loop Antenna - One Connection?
PostPosted: Jan Fri 11, 2019 6:10 am 
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I would not attempt to re-wind the loop. The wire is indented and the runs have faded. Rewinding will offset all the points where the wire was originally would be into the runs, it will look awful... Handling the fragile rayon covered loop wire will encourage it to fall off. Authentic looking loop wire is almost unobtainium...

Chas

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 Post subject: Re: Loop Antenna - One Connection?
PostPosted: Jan Fri 11, 2019 6:24 am 
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Indiana Radios,

That's my lesson for the day. I have never seen that arrangement. I'm used to extra lines coming off the loop for other reasons.

Attachment:
Loop With Pickup.jpg
Loop With Pickup.jpg [ 62.56 KiB | Viewed 816 times ]


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 Post subject: Re: Loop Antenna - One Connection?
PostPosted: Jan Fri 11, 2019 7:08 am 
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The ends of the wires at the outside screws check 16 ohms. From either of the outside screws to the "center tap" third connection (photo) where the lone pin connector is checks 8 ohms. For a 20's battery radio I would be using the outer screw connections, the full loop. So now I just need pin connectors. Thanks for the info on the superhet's , now I understand the wiring set up.

Attachment:
Fiat 1.jpg
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 Post subject: Re: Loop Antenna - One Connection?
PostPosted: Jan Sat 12, 2019 8:00 am 
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I think the pins you need are called "phone tips" like these:
Attachment:
Keystone Phone Tips.jpg
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John

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 Post subject: Re: Loop Antenna - One Connection?
PostPosted: Jan Sun 13, 2019 12:46 am 
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Thanks John, but what I need are the proper posts for the pins.

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 Post subject: Re: Loop Antenna - One Connection?
PostPosted: Jan Sun 13, 2019 1:39 am 
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Image

I've got a few pairs of nickle plated battery posts that have side set skews similar to the one in this photo. What is the measurement of the gap between the two sides?

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 Post subject: Re: Loop Antenna - One Connection?
PostPosted: Jan Sun 13, 2019 2:53 am 
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.560 and .602, they are bent in slightly since they have brass spacers that are not the right size. I'm guessing the correct gap would be .625.

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 Post subject: Re: Loop Antenna - One Connection?
PostPosted: Jan Sun 13, 2019 3:44 am 
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OK, what's the gap length near the center or next to the center post. That should represent the antenna's true gap length. Measure it in either true metric or in true inches, not in decimal fractions of an inch.

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 Post subject: Re: Loop Antenna - One Connection?
PostPosted: Jan Sun 13, 2019 4:27 am 
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Hard to get in there with the wires, around 43/64.

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