Pocket
Loop
The
Pocket Loop is a small magnetic loop antenna designed
for a carry anywhere operation, it disassembles in 33
centimeters pieces that can be carried even on an attaché
handbag.
The Pocket Loop is made on 2.80 centimeters of coaxial
cable. The loop diameter is 90 centimeters and the excited
loop diameter is 18 centimeters.
The capacitor is a split one and the capacitance is variable
between 5 to 50 Pico farads.
The
most sensitive component on the loop is the variable capacitor
and I was looking for a case to accommodate the split
capacitor and four banana female connectors.
A burned AC adapter was the perfect solution for the capacitor
case.
I took off the AC pins from the adaptor and soldered the
banana females in parallel with the variable capacitor
to receive the fixed capacitors plug in mini boxes.
The
reader can see on the following photos sequence technical
solutions that came from recycled materials.
1) The burned AC adaptor case.
2) The variable capacitor adjustment
stick is made on promotional mini flag plastic poles.
3) The pressure joints between the adjustment
stick parts are made on used pen ink containers.
4) The rubber knob on the adjustment
stick came also from the used pen.
5) The antenna handle is made on a sparkling
“C vitamin” container covered by bicycle bars
foam handle.
6) A watch gift case was adapted with
foam on the watch compartment to organize and protect
the fixed plug in capacitors mini boxes.
There
are three acrylic custom made parts for the antenna, two
of them are L shaped pieces that works joining the wood
main structure pieces and guiding the frequency adjustment
plastic stick.
The other one is a pressure piece that keeps in place
the main loop and the excited loop.
The
male banana connectors were deformed to be introduced
with pressure to avoid a minimum as possible electro mechanical
contact losses.
I do not recommend this loop for the beginners. It is
better to start with the loops that you need soldering
the loop extremes to the capacitor.
To
mount the wood pieces together an L shaped acrylic part
was designed. On the right photo can be seen the plastic
stick passing trough the hole and the excited loop resting
between the acrylic and the wood structure.
The other acrylic
piece acts pressing the coaxial cable loop (marked on
the middle), against the excited loop cable to the wood
structure.
The Pocket
Loop covers continuously from 30 MHz to 14 MHz. To lower
the operation frequency I use fixed capacitors in parallel
with the variable capacitor.
To calculate the value of the add on capacitor we must
go to the website link pages and download a loop design
program and find out the capacitor value to be added to
the loop capacitor to cover lower bands.
We can use an approximately 400 Pico farads variable capacitor
in parallel with the loop variable capacitor positioned
on the middle of the coarse and carefully rotate with
a plastic stick on the aisle to avoid the hand capacitance
influence.
An increase on the hash sound on the receiver will indicate
the new resonating frequency and the new capacitance value.
A capacitor meter will be needed to read the capacitance
from the temporally installed add on variable capacitor.
The fixed capacitors are critical and some time you need
serial or parallel associations to achieve the right value.
On
the next photos the plug in capacitors ready to be plugged
on the back of the AC adapter enclosure and the plug in
capacitors organizer made on a wrist watch gift case.
