Build your own K9AY
firstname.lastname@example.org list, February 12, 2000
I've had my homebrew K9AY loop up now for 2 weeks, and
decided it was time to pry myself away from the radio to share
my results and impressions thus far.
All listening was conducted in Mount Kisco, NY, 40 miles north
of New York City on a Drake R8B.
short, performance of the K9AY is miraculous.
I can easily and consistently separate two co-channel stations
on a given frequency.
Some of the best examples are 530, 780, 860, 1000, and 1020, where
I can switch between a stateside station (usually to the north)
and a station in Central or South America.
As far as Transatlantic DX goes, I've only detected carriers;
Spain 684 and Morocco 1044 appear regularly.
I have no other MW antenna to compare it to, but judging from
the K9AY loop's performance, I don't really need any other antenna
One observation here is that sometimes I can obtain a better null
when switching to the East-West loop for stations to the North
and South and vice-versa.
It really pays to try all 4 directions to see which works the
don't know code, so can't give any specifics on which CW stations
I was hearing, however the loop can null most of them.
I didn't observe any co-channel activity, so I can't say if the
loop would be effective at separating two co-channel signals.
able to null WWV on 2500 kHz.
on 90 meters and up is not as dramatic as that on MW.
My main goal was to try to separate R. Maya de Barillas in Guatemala
on 3324.8 and R. Bougainville in Papua New Guinea on 3325, but
I'm not able to null the Guatemalan.
On other occasions however, I have noticed strong directional
characteristics of the loop; as an example I'm able to null Sierra
Leone on 3316.
90 meters, my best performing antenna is a half wave dipole 45
meters in length. Compared to the K9AY loop, the 45 meter dipole
is about 2 S-units stronger. However, the loop's strength is its
ability to reduce or eliminate sources of noise.
Most recently, there was a nice opening to India between 0015
and 0145 UTC, and the K9AY loop was my preferred antenna as the
signal-to-noise ratio was much better. I was able to hear Lucknow
3245 and Bhopal 3315.
Again, the optimum loop and direction for the most readable signal
didn't necessarily follow the great circle path.
this band, my T2FD cut for the 90 meter band outperforms my 30
and 45 meter dipoles. RRI Merauke 3905 is usually audible during
my local sunrise.
Although the T2FD's signal strength is stronger than the loop,
the loop wins out at times, as it can reduce the ARO QRM on LSB,
expected, the 30 meter dipole's signal strength is 2 S-units higher
than the K9AY loop.
Again, depending on the noise, the loop can usually reduce it
so that the signal is better on the loop.
Trying to null the noise in the tropical bands is not as easy
or pronounced as finding the null on MW, you really have to try
all 4 directions, and slowly adjust the terminating resistance.
able to observe directionality with the loop on 5950 kHz, where
on the south loop I can receive the WYFR transmitter in Florida
at S9/+20 dB, while reversing the loop direction drops the signal
Constructed with 85 foot loops as in the original QST article
by Gary Breed (K9AY), the K9AY loop is a very good "compromise"
or broadband antenna for all shortwave frequencies.
It should definitely be the antenna of choice for those with small
In my case, the loop is not always the best performer, so I'm
keeping my dipoles and T2FD.
Compared to a flag antenna, I definitely prefer the K9AY
loop. For me, the flag was "deaf" on the tropical bands. I can
usually live with the 2 S-unit reduction of the K9AY.
On MW, the flag exhibited a nice front-to-back ratio, similar
to the K9AY. The K9AY is simpler to build than an equivalent four
direction flag or pennant array, and requires less space.
I'd like to see more work in the area of optimizing loop size
and dimensions for even better shortwave performance. Once you
are able to cleanly separate two co-channel stations on MW, it
is easy to get greedy and hope for similar performance on 90 or
I hope others will share their experiences in this area.
Another area for discussion might be the different techniques
for grounding the antenna.
I'm wondering if anyone has tried using elevated radials with
their loop, essentially suspending everything in the air, and
not connecting anything to a ground rod.
I may be forced to do this during the warm weather months as how
I have my loop mounted now will hinder the use of my backyard.
design borrowed elements from the original K9AY loop, Al Merriman's
loop and the Wellbrook Communications design.
My loops are 85 feet in length, and are roughly equal on all sides.
The horizontal portion of the loops are only 1 foot of the ground.
My ground rod is a half inch four foot copper pipe driven 3 feet
below ground. In addition I have one ground radial directly under
each loop to supplement the ground rod connection.
For the controller box, I used a 9 volt Radio Shack AC/DC
adapter, two toggle switches for selecting the loop and direction,
a 1k ohm potentiometer that controls the Vactrol terminating resistance,
and a four conductor telephone cable was wired to the relay box
to control the two relays and the Vactrol.
feature of the relay box is that I used a Vactrol (Type VTL5C2)
in place of the terminating resistor. This is an absolute must
for getting the best nulls in any given situation.
I've observed that different values of terminating resistance
is required when going from band to band, and even day to day
the resistance varies for the same frequency. Thanks go to Al
Merriman for coming up with this essential design modification.
Also mounted in the relay box is a 9:1 impedance matching transformer,
two 12 VDC relays for switching the feed point and termination
of the loops, and an SO-239 connector for the 50 ohm coaxial cable
connection to the radio.
9:1 matching transformer I used an FT140-43 toroid core from
Amidon, and used solid #24 telephone wire for winding the primary
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. With this I'm actually able to DX even while
working on the computer, even with my radio directly next to the
go to Gary Breed, K9AY for his original design, and Al Merriman
and Andy Ilkin for their modifications.
Thanks also to Guy Atkins, John Bryant, and Tony Ward for sharing
their successful experience with their K9AY loops, which served
as motivation for me to build one and try it for myself.