Using a 4 square Vertical Phased Array to improve your 80
and 160 meter signal - without a Yagi!
Tom Frenaye, K1KI
frenaye@pcnet.com
Below is the handout I used for my 4 square presentation at
the June 1st YCCC meeting.... 73 Tom
What's the history?
The 4 square was originally developed by W1FC and W1CF and
described in QST. A commercial version of the hybrid coupler was
marketed by ComTek Systems, owned by K8UR, and then sold a few
years ago to KF4HK (x-KZ5JM). DX Engineering on the west coast
sells a similar product.
Who else has 4-squares?
KY1H/80 W3LPL/160 AA6TT/80+160 AA0RS/160 Many others. WW2Y
has a four-element rectangular array (also in Antenna Book),
with slightly more gain in two directions.
Comparison
Cushcraft 40-2CD 2L 40 5.5 dBd gain, 20 dB max F/B, 24'
turning radius, list $625.95, approx $410 street, should be
mounted at 60' or higher. Tribanders and monobanders such as the
HyGain 204BA, 155BA or TH6DXX are all marketed saying 20-25 dB
F/B
From ARRL Antenna Book:
- 5.5 dB forward gain over a single similar element, for any
value of loss resistence
- 3 dB or greater forward gain over a 90 degree angle
- 20 dB or better F/B ratio maintained over a 130 degree
angle
- symmetry that allows directional switching in 90 degree
increments
ComTek claims 6.0 dB gain and F/B of >25 dB.
How much space is needed?
1/4 wavelength (33' on 40, 66' on 80, 132' on 160)
1/4 wavelength vertical, spacing and radials
the vertical can be loaded, or a T shape
use 1/4 wavelength of RG-11 foam to feed it (246/F x VF)
W3LPL suggests a 4-square should be 1/2 wavelength away from
other towers
Total area needed for 40m, 105'x105', for 80m, 200'x200', and
for 160m, 400'x400'
How carefully does it have to be constructed?
Most people suggested that I make each vertical/GP exactly
the same. I didn't, on 160m one is full length, base only 50'
from tower, others are in a tilted-T shape, base 100' from
tower, vertical 90' with 45' top, tilted in towards the tower.
How many radials?
W4BZ did a presentation at Dayton that basically said 4
raised radials equal 120 buried radials. Mine have 4-8 raised
radials (raised 6-8', tied to trees, etc).
How do you tune it up?
Build each ground plane so you can easily connect 50 ohm coax
to it. Test each one individually, making sure to short out each
of the other three while testing to avoid mutual coupling. Trim
each vertical to the desired frequency. Connect the RG-11 coax
to the matching box.
If each antenna is constructed and matched well, when you
transmit through the 4-square there will be little left over
power to be shunted towards the dummy load. The SWR should
appear pretty flat across the band (under 1.5:1). If there is a
matching problem it results in extra power being shunted towards
the dummy load. Because the match looks good at the transmitter
you can operate away from the matching frequency and lots of
power will end up in the dummy load. I fried an MFJ 300w dummy
load early on....
Put an SWR bridge between the matching box and the dummy
load. Where the SWR is lowest is your matching frequency. Some
people actually run a piece of coax back into the shack so the
dummy load is inside and the amount of power being wasted can be
measured.
How much does it cost?
The biggest cost is the matching box (hybrid coupler), if you
have the time and knowledge to build one, you should. Comtek
sells them for about $320. You'll have to add about $100 worth
of RG-11 for an 80-meter version, a 3-wire control cable back to
the shack, plus the wire and rope needed for the verticals
themselves plus radials. Total? about $500. Compare that to the
price for an 80m Yagi, the necessary rotator and tower of
reasonable height, and the stressful New England weather. It
isn't even a close choice!
How well does it work?
In last February's ARRL CW DX Contest, the K1KI multi-multi
beat W3LPL badly on 160m (250 to 150 QSOs) and beat their 2L 80m
quad at 200' (barely) on 80m. The front to back ratio is as
advertised - 20 dB or more, sometimes 30! The 1100' Beverage
towards Europe is still usually the better receiving antenna,
though the 4-square is as good some of the time. Having the
capability to instantly switch to in a different direction is
great, no time wasted while a rotator turns.
References: 4-square phased vertical arrays
"A Switchable Four Element 80-Meter Phased Array",
by Fred Collins, W1HKK/W1CF, March 1965 QST, page 48. (N6BV:
though the feed system was less than totally satisfactory, the
system provided gain and some pattern)
"360 Degree Steerable Vertical Phased Arrays", by
Fred Collins, W1CF(and others), April 1976 QST. (N6BV: this used
the now-discredited Wilkinson divider system, see pp 8-12 to
8-13 of the ARRL Antenna Book, 17th edition [current]).
"Phase Adjustment Techniques for a 4-Element Square
Phased Vertical Array", by Lahlum, March 1991 QST, page 39.
"The Square-Four Receiving Array", by Gary Nichols,
KD9SV, John Goller, K9UWA, and Roy Lewallen, W7EL, ARRL Antenna
Compendium, Volume 3 (1992), published by ARRL.
The ARRL Antenna Book, edited by R Dean Straw, N6BV, 17th
edition, pages 8-25 to 8-30, published by ARRL. Theory and
construction details.
Low-Band Dxing, by John Devoldere, ON4UN, pages 11-35 to
11-48 and 11-55 to 11-63, plus optional software with a tutorial
and engineering detail, second edition, published by ARRL. Good
detail for building your own matching and switching system.
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