More on
K9AY
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Basics
General
info on the K9AY loop
Performance
Listening test and other observations
Homemade
How to make your own K9AY
Grounding
The importance of good ground
Wires
How to place wires best
Remote
Remote control
of the KPAY |
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Make
your own K9AY transformer
By George Maroti
K9AY
web group, August 7, 2000
Regarding the magnetic matching transformer, some have ordered theirs
from Minicircuits:
http://www.minicircuits.com/
Or, here's how I built mine:
For the 9:1 matching transformer I used an FT140-43 toroid core
from Amidon, and used solid #24 telephone wire for winding the primary
and secondary.
As suggested in the Topband reflector for matching flag antennas,
I didn't overlap the windings.
Rather, I wound the primary on one side of the toroid, and the secondary
on the opposite side of the toroid. This type of transformer is
a great asset in reducing local noise into the antenna.
My notes indicate that I wound 24 turns for the side connected
to the loops, and 8 turns for the side connected to the coax feedline.
Keep
the windings separated
By Johan Bodin
K9AY
web group, November 13, 2000
"9:1" is the impedance transformation ratio (450/50 ohms). The actual
turns ratio is simply the square root of this figure = 3.
I use a 1" toroid from Philips which is made of 3F3 material (blue).
Primary is 45 turns, secondary 15 turns. This gives it enough inductance
to work well down to 15 kHz or so.
I highly recommend using a "real" transformer (galvanically separated
windings) instead of the autotransformer shown in the original K9AY
article.
If you are using a "real" transformer with separate pri and sec
windings, do not connect the coax shield to the antenna ground/counterpoise
as this would allow noise from the shack ground to enter the antenna
system. I went one step further and installed a 1:1 isolation transformer
in the shack end of the coax. It helped a lot in my case. The control
cable is also "floating" since it has no connection to the shack
ground other than via the small pri/sec capacitance in the transformer
in the power supply. |
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