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Using a 4-square Vertical Phased Array to improve Your 160m signal !

10. listopadu 2006 v 15:50 | Petr, OK1RP |  Antennas

Using a 4 square Vertical Phased Array to improve your 160 meter signal - without a Yagi!

Tom Frenaye, K1KI
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.
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:
  1. 5.5 dB forward gain over a single similar element, for any value of loss resistence
  2. 3 dB or greater forward gain over a 90 degree angle
  3. 20 dB or better F/B ratio maintained over a 130 degree angle
  4. 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 1977 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.
73, Tom, K1KI

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