The Loop My Dad Built
This is the loop aerial my dad built in 1958.
Although I was only 8 years old at the time, I knew what this was for
and how it worked. The radio is a Fairbanks Morse that my dad bought
new in 1936, when he was a teenager. This loop measures 33 inches (84cm) on
a side and has 8 turns of wire connected to a 365 pf variable capacitor.
There is a band spread capacitor and a switch with a fixed
mica capacitor that is switched in to cover the low end of the band.
There is a single turn that is connected to the antenna and ground
of the radio.
This is the original red paint. I never knew why he painted this red.
After thinking about it I realized that the trim on our house was
red and this was leftover paint.
This loop is still in very good condition
and one of my prized possessions. I have always been fascinated with this
device and enjoyed tuning the radio and turning the loop. I never built
a loop when I was a kid, but I was very influenced by it.
2004 Loop Update
I was not sure I was going to do this change to the loop. After all
my dad built it and for me to modify it, was not taken lightly. But I had some good
ideas. I wanted to make this loop into a crystal set for the upcoming contest, but
I still wanted it as a loop. Not a problem. I took off the original front panel, which
will be put away and labeled. I then made the new crystal radio tuner, complete
with a "Hobbydyne" type detector and a Bogen audio matching transformer. The only
change I had to make that would show, is two holes to mount the transformer.
I used a vernier drive, a dual 365 pf Jackson Brothers variable capacitor.
The dial is calibrated in khz. Now I have true one control tuning when using this
as a conventional loop. No band spread capacitor, no switch to change to a lower
frequency range either.
I think my dad would be proud of me.
This is the original 1958 tuner.
My Dads BCB Loop Antenna Updated 2004
Top down view of the new tuner.
The "New Loop"
Loop Schematic
Update - September 2008
The 50th anniversary of the construction was in early 1958. Since this
loop also serves as my DX loop crystal set, I decided to replace the 50 year old windings.
The wire insulation was getting a little bad. The wire was starting to have that gummy
feeling. Some red 660 strand, 46 gauge wire recently came on the market. While this Chinese
wire was not of real high quality, one thing it had was a very nice double silk covering.
The problem with the litz wire that I have is the covering was not rough and tough and would
like fray while on the loop, or even while winding it. But the covering on this other wire
is good enough to stand up on the litz. I now have reasonably low loss wire on my dad's loop
antenna. I tested it by connecting the headphones and seeing what I could hear. The volume
was impressive, compared to what I remember it being. I am planning on entering some of
the winter DX contests using this loop.
The new wire didn't make that much difference in the normal loop mode, it gave my loop
crystal set a new breath of life. I have enjoyed improving one of my fathers favorite toys.
Here are the specs as measured on my HP Q Meter:
L = 160µH
Q 1.6 mHz = 140
Q 1.0 mHz = 250
Q 0.6 mHz = 290
Distributed Capacitance = 35.5pF
Length per side = 33 inches (84 cm)
Turns = 8
Distance between turns = ½ inch (12mm)
Here is the map of stations heard during the 2008 October crystal set sprint contest.
Links
Other projects with loop antennas on this site:
Crystal Radio Loop Set #19
Crystal Radio Loop Set #30
Homemade Tube Loop Radio
Homodyne Regen Loop Radio
External Loop Antenna Links
Rahmenantenne (frame antenna) in german.
Rahmenantenne (frame antenna) construction in german.
Loop information is abundant here.
Minnesota DX Club Loop page
Yahoo! Loop Antennas group
Javascript Loop Calculator. This is for loops with a constant diameter windings.
Loop antenna calculator. Works neat but it is for a different kinds of loops than is shown on this page.
Loop Builder
Michael Thompson is a loop builder and has offered to make custom loops for
visitors of makearadio.com. Please contact him directly for details and prices
at this address: mltube@yahoo.com
