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How to Build the K9AY
Loop Receiving Antenna
Gary Breed, K9AY
AY Technologies
E-mail: gary@aytechnologies.com
The AY Technologies AYL-4 K9AY Loop Control system provides the electronic
portion of the K9AY Loop receiving antenna system. Here are the instructions
for constructing the loop itself. If you don't want to make the loop using 'homebrew'
construction, we also offer the AYL-M kit that includes a mast, wire and all
the hardware needed to construct the antenna.
Terminated Loop Basics
The K9AY Loop is one of several published designs that use a terminated loop
to get a directional pattern in a small space. The EWE, Pennant, Flag and
others all operate using the same principle as the K9AY Loop, and they all
provide a cardioid pattern with one deep null. In simplest terms, these
antennas are very small phased arrays, with the vertical (or mostly
vertical) portions being the main elements. The termination resistance
balances the currents to provide the best possible null. It is also possible
to explain the loop's behavior in terms of its response to the E-field and
H-field components of the arriving wave, but this is more complicated than
necessary!
The main advantage of the K9AY
Loop is that the feedpoint and termination are at the same location. Simple
switching lets you instantly reverse the pattern direction by exchanging the
feed and termination. Using the AYL-4 unit and two crossed loops, 4
different directions can be selected, giving you the greatest flexibility in
reducing interference and hearing the signal you want. Switching from one
direction to another can mean the difference between solid copy and a signal
covered up by interfering stations!
Horizontal and vertical radiation
patterns of the K9AY Loop over average ground:
Construction Details
A single loop that will cover the 160 and 80 meter ham bands requires one
25-foot high support and 85 feet of wire. The basic layout is shown here:
Construction of a single K9AY
Loop:
The matching transformer and terminating resistor are located in the AYL-4
relay box, so you only need to install the basic wire loop, its support and
insulators, plus the ground rod. The support can be a tree limb, a strong
mast, or anything else that will hold the loop in place.
The AYL-4 4-way loop control
system uses two of these loops, sharing the same central support, but
oriented at right angles to one another. The relay box changes pattern by
switching the feedpoint and termination connections-front-to-back by
reversing the ends of a loop; 90-degrees by switching from one loop to the
other.
Locating Your K9AY Loops
Since you have chosen a small receiving antenna, it is likely that your
transmitting antenna will be nearby. Transmitting antennas, power lines,
towers and other nearby large conducting objects can re-radiate signals that
are coupled to the receiving antenna. To avoid this problem, locate the K9AY
Loop as far from the transmitting antenna as possible. Because the loop is
small, it is often possible to place it among trees or shrubs in a front or
side yard, while the transmitting antenna is in back. Another way to
minimize the interaction is to locate the loop toward the most important
direction you want to hear. For example, if you are most interested in
hearing Europe from the US, locate the loop Northeast of the transmitting
antenna. When pointed toward Europe, the null will be in the direction of
the transmitting antenna, reducing the pickup of re-radiated signals. Some
European users of the K9AY Loop have chosen single loops, placing one of
them Northwest of the transmitting antenna to hear US stations, with another
East or Northeast to hear Asia and the Far East.
Grounding
A 4-foot ground rod (such as 3/4"
diameter copper pipe) is often sufficient. If the earth is very dry, a
longer ground rod is advised, to reach permanently moist earth-or you may
install four or more 15- to 20-foot long radial wires for better coupling to
ground. The grounded design of the K9AY Loop has several advantages over
ground-independent versions of the terminated loop (Pennant and Flag),
including simpler switching, no feedline isolation problems, and greater
signal capture for the same size loops.
Preamplifier
All terminated loop antennas are
inefficient, which means that signal levels are low. The K9AY Loop requires
about 15 dB of gain to restore signals to levels similar to Beverage
antennas. A preamplifier providing this gain, along with excellent bandpass
filtering for 1.75 to 4.5 MHz, is included with the AYL-4 systems. At 160
and 80 meters, coax loss is very low, so a preamp located at the receiver is
usually sufficient. In normal installations, we recommend against an outdoor
preamp, since it is exposed to greater risk of damage from static discharge
(lightning) or RF from nearby transmitting antennas. The most common
exception is with extremely long feedlines, where a preamp at the antenna
will boost the signal level to overcome coax losses and to increase the
signal relative to any common-mode noise and signals picked up by the long
feedline.
Feedline and Control Line Routing
As with all small receiving
antennas, the low signal levels from the K9AY Loop require careful routing
of the coax feedline and control cables. The best solution is to bury the
cables and take advantage of the natural RF shielding of earth. Second best
is to simply lay them on the ground, which is often done when receiving
antennas are only connected during the Fall and Winter lowband DX season. We
strongly recommend against above-ground installation, but we know it is
sometimes unavoidable. If you believe that your feedline is affecting the
pattern of the loop, it probably indicates that your grounding is
insufficient. In this case, refer to the previous notes and other published
data on grounding.
Using the K9AY Loop on Other
Frequencies
The K9AY Loop keeps its
directional pattern at lower frequencies, making it an excellent antenna for
Medium Wave and Low Frequency DXing. Many Broadcast Band DXers marvel at the
way switching the pattern lets you hear different stations on the same
frequency. In some installations, the antenna may retain some directivity
above 5 MHz, but this should not be expected. The preamplifier provided
includes a bandpass filter that limits its use to approximately 1.75 to 4.5
MHz. A preamp is rarely needed for Broadcast listening or for frequencies
above 5 MHz. For Low Frequency DXers, we can provide the AYL-4 without the
highpass filter (no extra charge for this special order), which allows the
preamp to operate down to 100 kHz or lower.
Installation Checklist (Problems
experienced by some users):
1. The two loops in the 4-way
system are completely separate--not connected at the top
2. The control cable is wired properly between the indoor control unit and
the outdoor relay unit
3. The antenna is properly connected to the ground rod
4. The two loops are connected properly-NOT "one end of loop A and one end
of loop B"
5. Proper control relay voltage
Enjoy your K9AY Loops!
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