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-----Original Message-----
From: Gary Breed [mailto:gary@noblepub.com]
Sent: Wednesday, January 06, 1999 7:45 PM
To: n2tk@idsi.net
Subject: 160M Small Antennas
Tony
Saw your post on Tower Talk (I'm not a subscriber, just read
the archives periodically). Feel free to forward all or part of
this to the Reflector.
I am working on several arrays of K9AY loops. Their small size
and the fact that they already have a cardioid pattern makes them
ideal for an array. Their inefficiency reduces mutual coupling to nil,
so phasing and matching is very straightforward.
I have thoroughly modeled many different options. Arrays of these
loops can deliver outstanding directivity, but at the cost of some
fairly complex switching and phasing networks. They still need
a good preamp to bring signal levels up to where a receiver is
operating within the optimum portion of its dynamic range and
AGC range. Here are a couple notes --
The smallest practical array is two loops in-line, spaced 70 to
100 feet, and fed with the "rear" antenna at -135 to -145 degrees.
This adds two deep side lobes to the single rear lobe of the
cardioid for substantial rejection around the back side. The
small size of this array is, however, even less efficient than a
single loop, due to field cancellations. It needs 2-3 dB more
preamp gain than one loop, but that's the price of small size.
On the large side, a broadside pair spaced a half-wave (270 ft)
is another way to get front-to-side. Phasing is done with a tee
connector, as they are fed in-phase and one pair can be reversed
for two directions. The pattern is similar, maybe better, than a
500-foot Beverage, in half the space. Put six loops in a circle
to get three two-direction pairs and you can cover all azimuths.
There are many variations on this idea, including three-inline,
rectangles and so on. Each has some performance advantage
and some phasing complexities. All of them achieve directivity
that can't be beat with less than a set of 1000 ft Beverages.
The best small antenna (and the one I will be building first) is
a half-size 4-square. With phasing modified for the short
spacing, the pattern is the same as a regular 4-square.
This array, tuned properly, can have immense front-to-back
of 30-50 dB across more than 180 degrees span. With a
transmission-line phasing network, it can work on 160 and 80
with no bandswitching -- it'll even have a useful pattern on 40.
This antenna has four crossed-loop pairs (like my article) at
the corners of a square 70 feet on a side. The main lobe
is about the same beamwidth as a 500-ft Beverage, but with
the front-to-back noted above. That's right -- a pattern shape
better than a typical 500-ft Beverage in a 70x70 space.
I will let the low band community know what I find when I get
the array built and checked out later this year. (Time is hard
to find, as I have a very busy job these days...) I will be
delighted to share notes and ideas with anyone who wants
to build an array of K9AY loops.
73, Gary
K9AY
P.S. Your findings on the termination resistance is exactly
what it should be -- 390 or 430 ohms on 160M, 560 or 620 on
80M. This is one of ways I verified the EZNEC model with the
as-built loop.
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<DIV> </DIV>
<DIV class=3DOutlookMessageHeader><FONT face=3D"Times New Roman"=20
size=3D2>-----Original Message-----<BR><B>From:</B> Gary Breed=20
[mailto:gary@noblepub.com] <BR><B>Sent:</B> Wednesday, January 06, 1999 =
7:45=20
PM<BR><B>To:</B> n2tk@idsi.net<BR><B>Subject:</B> 160M Small=20
Antennas<BR><BR></FONT></DIV>
<DIV><FONT color=3D#000000 size=3D2>Tony</FONT></DIV>
<DIV><FONT color=3D#000000 size=3D2></FONT> </DIV>
<DIV><FONT color=3D#000000 size=3D2>Saw your post on Tower Talk (I'm not =
a=20
subscriber, just read</FONT></DIV>
<DIV><FONT color=3D#000000 size=3D2>the archives periodically). =
Feel free to=20
forward all or part of</FONT></DIV>
<DIV><FONT color=3D#000000 size=3D2>this to the Reflector.</FONT></DIV>
<DIV><FONT color=3D#000000 size=3D2></FONT> </DIV>
<DIV><FONT color=3D#000000 size=3D2>I am working on several arrays of =
K9AY loops.=20
</FONT><FONT color=3D#000000 size=3D2>Their small </FONT><FONT =
color=3D#000000=20
size=3D2>size </FONT></DIV>
<DIV><FONT color=3D#000000 size=3D2>and the fact </FONT><FONT =
color=3D#000000=20
size=3D2>that they already have a cardioid pattern makes </FONT><FONT=20
color=3D#000000 size=3D2>them</FONT></DIV>
<DIV><FONT color=3D#000000 size=3D2>ideal for </FONT><FONT =
color=3D#000000 size=3D2>an=20
array. Their inefficiency reduces mutual </FONT><FONT =
color=3D#000000=20
size=3D2>coupling to nil, </FONT></DIV>
<DIV><FONT color=3D#000000 size=3D2>so </FONT><FONT color=3D#000000 =
size=3D2>phasing and=20
matching is very straightforward.</FONT></DIV>
<DIV><FONT color=3D#000000 size=3D2></FONT> </DIV>
<DIV><FONT size=3D2>I have thoroughly modeled many different =
options. Arrays=20
of these </FONT></DIV>
<DIV><FONT size=3D2>loops can deliver outstanding directivity, but at =
the cost of=20
some</FONT></DIV>
<DIV><FONT size=3D2>fairly complex switching and phasing networks. =
They=20
still need</FONT></DIV>
<DIV><FONT size=3D2>a good preamp to bring signal levels up to where a =
receiver=20
is</FONT></DIV>
<DIV><FONT size=3D2>operating within the optimum portion of its dynamic =
range=20
and</FONT></DIV>
<DIV><FONT size=3D2>AGC range. Here are a couple notes =
--</FONT></DIV>
<DIV><FONT size=3D2></FONT> </DIV>
<DIV><FONT size=3D2>The smallest practical array is two loops in-line, =
spaced 70=20
to</FONT></DIV>
<DIV><FONT size=3D2>100 feet, and fed with the "rear" antenna =
at -135 to=20
-145 degrees.</FONT></DIV>
<DIV><FONT size=3D2>This adds two deep side lobes to the single rear =
lobe of=20
the</FONT></DIV>
<DIV><FONT size=3D2>cardioid for substantial rejection around the back =
side. =20
The</FONT></DIV>
<DIV><FONT size=3D2>small size of this array is, however, even less =
efficient than=20
a</FONT></DIV>
<DIV><FONT size=3D2>single loop, due to field cancellations. It =
needs 2-3 dB=20
more</FONT></DIV>
<DIV><FONT size=3D2>preamp gain than one loop, but that's the price of =
small=20
size.</FONT></DIV>
<DIV><FONT size=3D2></FONT> </DIV>
<DIV><FONT size=3D2>On the large side, a broadside pair spaced a =
half-wave (270=20
ft)</FONT></DIV>
<DIV><FONT size=3D2>is another way to get front-to-side. Phasing =
is done=20
with a tee</FONT></DIV>
<DIV><FONT size=3D2>connector, as they </FONT><FONT size=3D2>are fed =
in-phase and=20
one pair can be reversed </FONT></DIV>
<DIV><FONT size=3D2>for two directions. </FONT><FONT size=3D2>The =
pattern is=20
similar, maybe better, than a</FONT></DIV>
<DIV><FONT size=3D2>500-foot Beverage, in half the space. Put six =
loops in a=20
circle</FONT></DIV>
<DIV><FONT size=3D2>to get three two-direction pairs and you can cover =
all=20
azimuths.</FONT></DIV>
<DIV><FONT size=3D2></FONT> </DIV>
<DIV><FONT size=3D2>There are many variations on this idea, including=20
three-inline,</FONT></DIV>
<DIV><FONT size=3D2>rectangles and so on. Each has some =
performance=20
advantage</FONT></DIV>
<DIV><FONT size=3D2>and some phasing complexities. All of them =
achieve=20
directivity</FONT></DIV>
<DIV><FONT size=3D2>that can't be beat with less than a set of 1000 ft=20
Beverages.</FONT></DIV>
<DIV><FONT size=3D2></FONT> </DIV>
<DIV><FONT size=3D2>The best small antenna (and the one I will be =
building first)=20
is</FONT></DIV>
<DIV><FONT size=3D2>a half-size 4-square. With phasing modified =
for the=20
short </FONT></DIV>
<DIV><FONT size=3D2>spacing,</FONT><FONT size=3D2> the pattern is the =
same as a=20
regular 4-square.</FONT></DIV>
<DIV><FONT size=3D2>This array, tuned properly, can have immense=20
front-to-back</FONT></DIV>
<DIV><FONT size=3D2>of 30-50 dB across more than 180 degrees span. With=20
a</FONT></DIV>
<DIV><FONT size=3D2>transmission-line phasing network, it can work on =
160 and=20
80</FONT></DIV>
<DIV><FONT size=3D2>with no bandswitching -- it'll even have a useful =
pattern on=20
40.</FONT></DIV>
<DIV><FONT color=3D#000000 size=3D2>This antenna has four crossed-loop =
pairs (like=20
my article) at</FONT></DIV>
<DIV><FONT color=3D#000000 size=3D2>the corners of a square 70 feet on a =
side. The=20
main lobe </FONT></DIV>
<DIV><FONT color=3D#000000 size=3D2>is about the same beamwidth as a =
500-ft=20
Beverage, but with</FONT></DIV>
<DIV><FONT color=3D#000000 size=3D2>the front-to-back noted above. =
That's=20
right -- a pattern shape </FONT></DIV>
<DIV><FONT size=3D2>better than a typical 500-ft Beverage in a 70x70=20
space.</FONT></DIV>
<DIV><FONT color=3D#000000 size=3D2></FONT> </DIV>
<DIV><FONT color=3D#000000 size=3D2>I will let the low band community =
know what I=20
find when I get</FONT></DIV>
<DIV><FONT color=3D#000000 size=3D2>the array built and checked out =
later this=20
year. (Time is hard</FONT></DIV>
<DIV><FONT color=3D#000000 size=3D2></FONT><FONT size=3D2>to find, as I =
have a very=20
busy job these days...) I will be </FONT></DIV>
<DIV><FONT size=3D2>delighted to share notes and ideas with anyone who =
wants=20
</FONT></DIV>
<DIV><FONT size=3D2>to build an array of K9AY loops.</FONT></DIV>
<DIV><FONT color=3D#000000 size=3D2></FONT> </DIV>
<DIV><FONT size=3D2>73, Gary </FONT></DIV>
<DIV><FONT size=3D2>K9AY</FONT></DIV>
<DIV><FONT size=3D2></FONT> </DIV>
<DIV> </DIV>
<DIV><FONT size=3D2>P.S. Your findings on the termination =
resistance is=20
exactly</FONT></DIV>
<DIV><FONT size=3D2>what it should be -- 390 or 430 ohms on 160M, 560 or =
620=20
on</FONT></DIV>
<DIV><FONT size=3D2>80M. This is one of ways I verified the EZNEC =
model with=20
the</FONT></DIV>
<DIV><FONT size=3D2>as-built loop.</FONT></DIV>
<DIV><FONT color=3D#000000 size=3D2></FONT> </DIV>
<DIV><FONT color=3D#000000 size=3D2></FONT> </DIV>
<DIV><FONT color=3D#000000 size=3D2></FONT> </DIV></BODY></HTML>
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