Several years ago I did testing of broadband antennas for array use in
an application for DXing on the AM broadcast band.
In the discussion below, numbers in brackets indicate footnotes that
reference web links that follow.
At a salt-marsh site in Rowley, MA [1][2], I set up two verticals
spaced 60 m / 200 ft. on a 82/262 degree axis with the idea of
time-delay phasing to produce a broadband cardioid pattern with a null
at about 262 degrees (roughly towards New York City, 340 km distant).
Then I swapped out the verticals for two figure-of-8 broadband loops,
both positioned for 82/262 deg. peaks, 172/352 deg. side nulls.
The 3 m long active vertical whips were of homebrew design,
functionally similar to MFJ model 1024 [3].
The 2 m per side square single-turn loops, also homebrew, feeding
W7IUV-design amplifiers via balun, were functionally similar to
Wellbrook model ALA1530 [4].
The major difference that was noticed was the loops picked up much
higher levels of short skip at high vertical incidence angles as
compared to low-angle DX and groundwave.
Because the vertical inherently suppresses short skip, it is a better
choice. The problem about high angle skip is that its arrival time at
each array element is closer to being simultaneous, thereby reducing
the effective antenna spacing to perhaps half of what it is for signals
coming in at 30 degrees or less above the horizon. The other tricky
thing about shorter skip is that the phase and apparent direction
bounce around a lot, especially at sunset and sunrise - times that are
often the most useful for DX, whether on 160 m or the AM broadcast
band.
I also did a test with a vertical as one element and the figure-of-8
loop as the other. If phaser-box gain was set to make the strength of
a short to medium skip signal (distance 200-800 km) the same, it was
noted that a long-haul DX or groundwave signal was about 6 dB better on
the vertical than on the loop (assuming the station bearing was in/near
the middle of one of the loop's two maximum-pick-up lobes).
For instance, if WPHT Philadelphia (1210 kHz, about 500 km) was
step-attenuator-set to S-9 on both antennas shortly after sunset,
Bordeaux, France (1206 kHz) was S-8 on the vertical and S-7 on the
loop; UK over Spain (1215 kHz) was similar. Also, on 1210 with the
vertical, there was more evidence of co-channel VOAR Newfoundland (at
about 1500 km) competing with WPHT.
The loop-versus-vertical set-up could be used to produce a cardioid
over a narrow bandwidth whereas loop-versus-loop or
vertical-versus-vertical were suitable for desired front-to-back over a
wider bandwidth.
In summation, testing showed that phasing two verticals was superior to
phasing two figure-of-8 loops, largely because of the verticals'
inherent reduction of signals coming in at 45 or more degrees above the
horizon.
EZNEC plots have been done by Dallas Lankford, Neil Kazaross, and
others to show that phasing two or more terminated (elongated) loops
such as Flag, K9AY, etc. can produce excellent front-to-back ratio and
good suppression of high-angle pick-up, perhaps comparable to using
verticals as elements. An array comprised of four terminated-delta
(Kaz) antennas, as used at a Norwegian DXpedition site, is described
briefly at reference [5]. Somewhat more information can be found on
IV3PRK's website [6]. A prior Topband post [7] mentions much other
documentation (including circuit designs) formerly accessible on public
websites. Unfortunately most of it has been migrated to Yahoogroups
file sites requiring moderator access approval. As such, it wouldn't
come up in Google searches.
Mark Connelly, WA1ION
South Yarmouth, MA, USA
[1] http://www.qsl.net/wa1ion/pictures1/rowley_antenna_layout_map.gif
[2] http://www.qsl.net/wa1ion/rowley_ma.htm
[3] http://www.mfjenterprises.com/Product.php?productid=MFJ-1024
[4] http://www.wellbrook.uk.com/ALA1530.html
[5]
http://www.kongsfjord.no/bm/The%20Kongsfjord%20Quad%20Delta%20Flag%20Array.pdf
[6] http://www.iv3prk.it/user/image/..-rxant.prk_qdfa.pdf
[7] http://lists.contesting.com/_topband/2009-10/msg00057.html
<<
Date: Wed, 13 Feb 2013 07:11:47 -0800 (PST)
From: Rudy Bakalov <r_bakalov@yahoo.com>
To: "topband@contesting.com" <topband@contesting.com>
Subject: Re: Topband: New 160M high performance receiving antenna at
W3LPL
Tom,
Thanks for the insightful reply. Looks like there is no free lunch
here- I can't
get better performance by simply using a different circle array
element. Bummer,
I will have to stick with the verticals.
If space is not an issue, will enlarging the circle diameter make any
difference? Note, however, that I am considering the 3-band commercial
solutions
(160, 80, and 40m 8 circles).
Rudy N2WQ
________________________________
From: Tom W8JI <w8ji@w8ji.com>
To: Rudy Bakalov <r_bakalov@yahoo.com>; topband@contesting.com
Sent: Wednesday, February 13, 2013 5:53 AM
Subject: Re: Topband: New 160M high performance receiving antenna at
W3LPL
I have been wondering if the antenna element in phased arrays could
be a loop
rather than a vertical. My thinking is that the loop has some level of
directivity so phasing two of them should result in better side lobe
suppression
compared to a vertical. Is there any merit to this thought?
Specifically, will I
see better RDF numbers if I were to use loop elements in any of the
active 8 and
4 circle systems (e.g., DX Engineering, Hi-Z Antennas, etc.)?
Hi Rudy,
A loop can work in a fixed array, or bi-directional array. My first
antenna
allowing me to work JA's through LORAN from Ohio was a long array of
loops,
although these were elongated loops. I also had long end-fire arrays of
small
inverted delta loops in Cleveland in the 80's, and small active
verticals.
Small loops do not work well when used in things like four squares or 8
circle
arrays. A multiple direction array, like a four square or 8-circle,
requires a
uniform pattern of uniform phase from each element or cell.
With a small loop, phase flips 180-degrees immediately after crossing
the null.
Also, the directivity is generally poor because the small loop has two
very
sharp null points though the loop axis, but a broad response everywhere
else.
Both of these things actually hurt performance of arrays with loops
that depend
on phasing to eliminate side nulls.
Elongated loops are a different story, because (we probably all know)
elongated
loops are not really loops in function. They are really phased
verticals, and
the horizontal part or component of the conductors is simply a phasing
line.
K9AY's, Flags, Pennants, EWE's, and other forms of elongated loops are
really
all just phased verticals in function. They have a wider null and no
sudden
phase shift at the null, and no null cone at the side or "loop axis".
The best element for a traditional 8-circle or four square will always
be a
simple vertical, and even in a broadside array we would want to avoid
small
loops with deep axis nulls. They are OK as cells in an end-fire array,
but not
particularly advantageous for pattern unless elongated. I used small
loops as a
matter of "construction convenience" as deltas in a long endfire array,
but the
deep side null in that array was really created by out-of-phase cells
of deltas
and not the sharp null pattern of the individual delta. It could have
just as
well been verticals with no loss of pattern.
73 Tom
------------------------------
Message: 2
Date: Wed, 13 Feb 2013 07:17:46 -0800 (PST)
From: Rudy Bakalov <r_bakalov@yahoo.com>
To: "topband@contesting.com" <topband@contesting.com>
Subject: Re: Topband: New 160M high performance receiving antenna at
W3LPL
Message-ID:
<1360768666.23050.YahooMailNeo@web163404.mail.gq1.yahoo.com>
Content-Type: text/plain; charset=us-ascii
Hi Tim,
This does look like a viable option. Too bad it is single-band and only
bi-directional, although a star-like arrangement (with lots of relays)
could
work too.
Rudy N2WQ
________________________________
From: Tim Duffy <k3lr@k3lr.com>
To: 'Rudy Bakalov' <r_bakalov@yahoo.com>; topband@contesting.com
Sent: Wednesday, February 13, 2013 1:43 AM
Subject: Re: Topband: New 160M high performance receiving antenna at
W3LPL
Hello Rudy,
I am using a pair of VE3DO loops in a phased array for 160 meters. The
two
loops are spaced 5/8 wavelength (at 1830 KHz) apart at K3LR - aimed at
45/225 degrees (a DPDT relay selects the direction for each loop).
The VE3DO loops are simple to construct and work very well. The in phase
feed for the two loops is simple with equal lengths of 50 ohm coax to a
T
connector and a 25 to 50 ohm UNUN to match to the 50 ohm RX. The VSWR
of the
system is excellent with the 9:1 K9AY transformers at each loop feed
point
up thru 7 MHz. I suggest using a DX Engineering RPA-1 preamp operating
at 16
VDC to feed the receiver for best results.
Details for the inexpensive VE3DO loop receive antenna is here:
http://topbanddinner.com/page_presentations.html
73!
Tim K3LR
-----Original Message-----
From: Topband [mailto:topband-bounces@contesting.com] On Behalf Of Rudy
Bakalov
Sent: Tuesday, February 12, 2013 12:00 PM
To: topband@contesting.com
Subject: Re: Topband: New 160M high performance receiving antenna at
W3LPL
I have been wondering if the antenna element in phased arrays could be a
loop rather than a vertical. My thinking is that the loop has some
level of
directivity so phasing two of them should result in better side lobe
suppression compared to a vertical. Is there any merit to this thought?
Specifically, will I see better RDF numbers if I were to use loop
elements
in any of the active 8 and 4 circle systems (e.g., DX Engineering, Hi-Z
Antennas, etc.)?
Rudy N2WQ
_________________
Topband Reflector
_________________
Topband Reflector
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