KG5VK four square
Four Square for 75/80m
I used a Comtek control box last year not with a four square, but a bi-square instead that was wide spaced. While it seemed to work well with our transmit signal it seemed lacking on receiving.
So this year in preparation of Winter and ARRL Sweepstakes (November) I decided to add the other two antennas. However, I did not want to invest a lot of money into placement of insulated towers for each of the radiators and went with wire wire radiators for the verticals. These wires are ground mounted at a treated 4x4 that is 12 feet tall (minus the 3 feet in the ground).
The tops of the wires are supported by my Rohn 55g tower which supports two of my larger beams, and is in the center of the square. While receeiving performance still seems less than expected with respect to steering for signals there is the expected gain of approximately 5dB over a single radiator and an approximate f/b ratio of 20 - 30 dB when steering West versus East.
I say West versus East because the difference in signals is mainly from either West direction (SW or NW) to that of either East direction (NE/SE), while there is relatively little difference in switching from either North or South to either East or West.
However the few contacts had so far indicate better steering for transmitted signal. Of course, all of this is from an operator perspective and little technical or precision measurement. However I did use an MFJ-259B to cut the phasing lines to the right length and to measure the electrical length of each verticals.
My phasing lines were constructed of cable TV hard ine which has a foam dielectric. Measured velocity factor was .83. Dumped power to the dummy load from the Comtek controller is less than 10%, which seems to be within the expected range for those that have built these arrays. The measured dumped power varies from 10 - 5 % dependent on how close to the designed frequency I am operating.
My radial field is still a bit lacking. However, at the base of each vertical I am using galvanized roofing material (tin) 12 feet in length away from the array center. I will be adding radials and notes here as I do.
The tilt angle of my verticals is close to 45 degrees, which is a bit more than that recommended by John ON4UN in his Low Band book This I can not easily fix, so I will concentrate on adding a better ground screen.
Summary - was it worth the work?
Too early to tell for sure but I think so. While I am more geared for stateside Q's for ARRL SS than DX, the antenna does appear to help get a very strong signal to either the West or East coast from my mid-continent qth (I am in the very NW corner of Louisiana)
My goal now is to improve our receive antenna systems since the four Ssuare seems to work better for transmit than receive I am considering adding a DX engineering Receive Antenna Phasing Controller to my East/West Beverage antenna and installing a common mode choke on my K9AY loop.
An Update January 2010 We had great results for ARRL SS Phone in 2009 even with one of my amps dying Sunday morning we did well Mainly because of a great signal on 75m with our Four Square
Here is some more thoughts that were discussed about my 80/75m Four Square in several emails with close friends......
80m Four Square Array some thoughts by KG5VK
Cost of a vertical array versus a beam are substantial a two el beam for 80m requires a substantial investment compared to a vertical array
My 80m Four Square is not installed exactly to specs but close can get you performance way beyound what a low hanging diople will offer......
The Comtek conroller for 80m is $409.95 http://www.dxengineering.com/Parts.asp?ID=2703&PLID=315&SecID=160&DeptID=46&PartNo=COM%2DACB%2D80%2D1
They also sell pre cut phasing lines, but you would probably cut your own, they are aprox $300 http://www.dxengineering.com/Parts.asp?ID=2849&PLID=319&SecID=160&DeptID=46&PartNo=COM%2DH11%2D80%2DP
Layout of a Four Square is of course 4 vertical antennas 1/4 wave length a part from each other forming a square
for 80m (cw and lower freq phone portions of the band) 3.650 mhz the exact spacing would be 67 ft 4 inches between each vertical making the diagonal distance across the square 95 feet
The feed line from each vertical to the center of the square where we would mount the phase controller is aprox 52 ft 6 and one half inches The exact length would be calculated based on the Velocity factor of the feedline (remember the feed line to each vertical must be made from coax that has a velocity factor of at least 78% if you don't the feed line from each vertical will not be physically long enough to reach the center of the square and connect to the phasing box
I used cable TV hardline that I measured (with my LP-100A) to have a VF factor of .91 234 / 3.650mhz = 64.1095 feet that 64.1095 x .91 gave me a feedline length of 58.3397 feet
I cut four lengths of my 75 ohm Hardline to 60 feet and then used the LP-100A to trim these down to exact resonance at 3.650 (a tape measure layed on the ground with Hardline that will never lay perfectly flat or straight would cause a measurement error of at least a few inches, so trimining the length while measureing it with a frequency device is the most accurate)
My Verticals are not perfectly straight up either..... The center of my Four square is layed out with my 90 foot tower in the middle (center) and the four vertical radiators are pulled towards the top of the tower giving the verticals a slant in toward the center of the square, this is not a preffered design but what would work physically with the least cost at my antenna farm ON4UN actually talks about this deviation from 90 degrees for a vertical and how much "slant" one can safely get away with I am on the outside edge of what he suggested was safe but have found my array works quite well.
From the Four square controller I have Two tarnsmission lines back to the shack and one Four conductor control cable Actually only one is the transmit line while the second coax is a line that connects from the Load (DUMP) side of the phase controller to a dummy load in the shack thru a watt meter This is because almost never will we get the swr flat and the interaction of the verticals will rarely be perfect any in balance will cause an unknown amount of power that must be Dumped to a dummy load otherwise the phase control unit will burn up from over heating of power
During some of my research on use of Four Squares for Domestic contesting (ARRL Sweepstakes) I found several mentions of using a low hanging dipole verus a dummy load for that dumped power so I did that, only after I tested my Four Square for several weeks with the wattmeter and dummy load connections that are standard configuration for a Four Square array.
My radial system is not perfect, but may be considered more elabortate that some Half of the antenna farm area that this array is located on has extensive wire mess layed on the soil with grass growing though the mesh and over it, this is from my ground plane mounted under neath my Hy Gain Hy Tower vertical This ground plane is not evenly spaced under my Four Square and idealy we would what this Four Square several wave lengths away from any other 80m antenna, this would have meant removal of my Hy Tower, which I am yet un willing to do.
At each radiator of the Four Square I have one 3 foot by 12 foot long sheet of galvanized roofing tin left over form an old barn and two ground rods, these are electricaly connected to the shield of the Hard line with the center conductor simply solder to the vertical wire, which by the way is 14 gauge copper steel clad These were cut to length using 246 / 3.650 and then prunned to resonance at 3.700
My wires are supported by 12 foot tall 4x4 wood post with three feet of them in the ground giving my radiators 9 feet of straight vertical height before they start their slant towards the high center support (the 90 foot tower) The top of the verticals have a insulator and then a rope to the tower the radiators are not insulated from the 4x4 wood and damp conditions have little effect of the system performance because of the low rf frequency we are at.
Note: The diference of those two Frequncies is intentional....... Comtek cautions us to cut our feedlines for a bit higher in freq because once the four square is all connected the interaction between radiators will drop the frequency 50mhz higher than your preferred operating frequency
During Sweepstakes many said we were the strongest signal on the 75m band so it was worth the effort !
If I was ordering a Phase control unit for a Four Square today I would get the one from DX engineering It is a bit more modern design and it has the added abililty to use the Array 360 degree for receive at the push of a button here is the link to the pdf file on that product http://www.dxengineering.com/pdf/TFS-Rev4.pdf
Yes building your own Phase Controller would save money and the instuctions are available in ON4UN's book, as well as the ARRL Books you must have the right test gear etc
I wanted a more plug and play method Installation alone is a complex enough task without me winding coils, building Un Uns etc
Cheers ! Steve KG5VK