Forums :: NEW! Web Resources :: Features :: Photo Gallery :: Vintage Radio Shows :: Archives
Support This Site: Contributors :: Advertise


It is currently Oct Tue 20, 2020 3:45 pm


All times are UTC [ DST ]





Post New Topic Post Reply  [ 9 posts ] 
Author Message
 Post subject: Am Loop antennas
PostPosted: Aug Fri 21, 2020 3:15 pm 
New Member

Joined: Aug Fri 21, 2020 3:02 pm
Posts: 1
I'm restoring a Delco R 1218 the loop antenna is just fine. but being the curious person I am I got to poking around on the net and I know you can purchase Loop antennas. And I found plans to build large loop antennas. But has anyone tried to build one of the small Loop antennas like the ones that come in the All American 5 and All American 6? I don't need one for my set I would just like to see if I could. And what it would take. Thank you.


Top
 Profile  
 
 Post subject: Re: Am Loop antennas
PostPosted: Aug Fri 21, 2020 7:33 pm 
Member

Joined: Oct Sat 03, 2009 2:25 am
Posts: 397
Location: Louisville, Ky
I'm sure people have built their own loop antennas to replace missing ones on radios that originally had one. I'm equally sure that there are plans on the internet for building them.. I just cut a pattern of the size I needed out of cardboard, then cut out an odd number of tabs around the perimeter. Then I wound magnet wire around the perimeter and in and out of the tabs until I got the appropriate inductance. An inductance meter is really handy for this. I just used trial and error until I got it to work with the tuning capacitor. There are formulas out there for calculating the inductance of a coil, but there are also a number of variable.


Top
 Profile  
 
 Post subject: Re: Am Loop antennas
PostPosted: Aug Fri 21, 2020 7:38 pm 
Member

Joined: Nov Tue 14, 2017 5:09 am
Posts: 3064
Location: Austin, Texas
You can find the instructions for building spider coil antennas on this site: http://makearadio.com/coils/spider.php
You will need something like one of the $20 capacitance meters to measure the range of the tuning capacitor you will be using.
https://www.ebay.com/itm/Capacitor-Test ... 2762693353
For about $15 more, you can get a meter that also measures inductance.
Litz wire gives the best performance and can be found on Ebay.
Regular solid wire is used on most AA5 loops and works OK.

Jay


Top
 Profile  
 
 Post subject: Re: Am Loop antennas
PostPosted: Aug Fri 21, 2020 9:48 pm 
Member
User avatar

Joined: Jan Thu 01, 1970 1:00 am
Posts: 5906
Location: Beautiful Downtown Burbank CA
Spacing helps I found out.


Attachments:
antenna.jpg
antenna.jpg [ 329.02 KiB | Viewed 635 times ]
Top
 Profile  
 
 Post subject: Re: Am Loop antennas
PostPosted: Aug Fri 21, 2020 9:59 pm 
Member
User avatar

Joined: Jan Thu 01, 1970 1:00 am
Posts: 36177
Location: SoCal, 91387
Leno Pederson wrote:
An inductance meter is really handy for this.


JnTX wrote:
You will need something like one of the $20 capacitance meters to measure the range of the tuning capacitor you will be using.

A Heathkit RLC bridge will do both.
https://www.ebay.com/sch/i.html?_from=R ... =1&_sop=15

_________________
\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\He Who Dies With The Most Radios Wins/////////////////////////


Top
 Profile  
 
 Post subject: Re: Am Loop antennas
PostPosted: Oct Sun 11, 2020 11:45 pm 
Member
User avatar

Joined: May Wed 20, 2020 5:06 pm
Posts: 214
Mike Toon wrote:
Spacing helps I found out.

I see the loop you built has a winding for an external antenna and I was wondering how you wound it. Did you add it after you had finished the main winding or did you wind it along with the last few turns of the main winding? Seems like it would be hard to add afterwards. How many turns did you add for the external winding?


Top
 Profile  
 
 Post subject: Re: Am Loop antennas
PostPosted: Oct Mon 12, 2020 12:23 am 
Member
User avatar

Joined: Jan Thu 01, 1970 1:00 am
Posts: 5906
Location: Beautiful Downtown Burbank CA
I copied an AA5 antenna with wire I had on hand on Masonite I cut on my bandsaw.
It didn't receive quite as well as the original so I figured it was wire size and spacing being the only difference. I'm sure I could have adjusted the var cap to compensate but I left it as it was. I did wind an additional loop but it wasn't needed on the original. It was just an experiment for another radio.


Top
 Profile  
 
 Post subject: Re: Am Loop antennas
PostPosted: Oct Mon 12, 2020 7:02 pm 
Member
User avatar

Joined: May Wed 20, 2020 5:06 pm
Posts: 214
Thanks Mike. Here's one I built using the formulas at http://makearadio.com/coils/spider.php and was thinking about adding a few turns for an outside antenna hookup.

I used 20 gauge magnet wire (.0334" dia). The inner diameter of the loop is 5". And I wound 29.5 turns. The formula said that would result in an inductance of 224uh. Messy as my attempt looks, it actually came out to 228 uh's.

The var cap in the radio I installed it on has a range of 22 to 470pf. I figured a 224uH loop might be about right. The radio plays really well. It ended up with a range of 533 to 1498khz. So, a little low at the high end. Might be able to raise it enough when I align it, otherwise maybe add a turn to the coil.

C4 Wire diameter Input this value
C5 Number Turns Input this value
C6 Inside Diameter Input this value
C7 Coil Depth (C4*C5)
C8 Mean Radius (C7+(C6*0.5)+(C6*0.5))/2
C9 Outside Diameter (C7*2)+C6
C10 Inductance (((C8*C5)^2)/((8*C8)+(11*C7))) [The main formula]
C11 Wire Length (C5*C8*2*3.14)/12

I found a round loop was easy to lay out, although it might be too tall to fit some cabinets. You need an odd number of cutouts so each winding alternates tabs with the previous winding.
Attachment:
IMG_0159.JPG
IMG_0159.JPG [ 169.39 KiB | Viewed 131 times ]


Top
 Profile  
 
 Post subject: Re: Am Loop antennas
PostPosted: Oct Mon 12, 2020 7:43 pm 
Member
User avatar

Joined: Jan Thu 01, 1970 1:00 am
Posts: 5906
Location: Beautiful Downtown Burbank CA
Using a CD plastic protector.


Attachments:
spider.jpg
spider.jpg [ 141.98 KiB | Viewed 130 times ]
Top
 Profile  
 
Post New Topic Post Reply  [ 9 posts ] 

All times are UTC [ DST ]


Who is online

Users browsing this forum: No registered users and 7 guests



Search for:
Jump to:  


































-->


Privacy Policy :: Powered by phpBB