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## [TowerTalk] RE: 80 meter 4 square array notes from N0AH

 To: [TowerTalk] RE: 80 meter 4 square array notes from N0AH Dinsterdog@aol.com (Dinsterdog@aol.com) Mon, 30 Aug 1999 18:31:56 EDT
 ```Greetings All- I have recently constructed a 4 square for 80 meters. It has performed wonderfully so I thought I would share some notes about it- First, a disclaimer- I'm not an engineer- my data is from what I remember reading from others and what I've experienced from putting one of these antennas together- If you want to put one together, here are some notes I hope you will find helpful- Ok, so whats a four square?? A four square earned its name by the way it is put together. It consists of 4 verticals, placed 1/4 wave apart, in a square pattern, that together, act as an array. You can aim your signal in 4 directions, diagonally across the radiators, using a phasing system (I use Comtek's hybred coupler). The phasing system should provide power distributing and phasing to obtain a directional pattern. Two verticals can be used but you get much improved front to back, front to sides, and forward gain using four verticals. The antenna designed was formulated by Fred Collins, (W1FC) and Dana Atchely (W1CF) in the 1980's. Steve Davis, K1PEK helped and the three designed a way to phase the array so that it would work well- and be available for others to use. Through various reports, the array provides a reported front to back gain of around 20-25db. The forward gain claims I have read about range from 4-8 db. A lot of factors go into these reports such as phasing methods, materials used for radiators, full size verticals vs. shortened verticals, radials systems etc...So needless to say, it is not balck and white on exact gain but needless to say, it has a punch- There are a lot of ways to construct the radiators. A lot of hams use wire hanging from long side arms off the top of towers. Others, like me, use aluminum radiators while others still use commercial verticals and/or insulated towers. Ok, so now some notes on how I put mine together- Based on a design in the Com Tek manual, I used 44 foot tall aluminum radiators with three 20 foot long top hats connected at the 39.5 foot level. The first aluminum section had a diameter that started at 2 1/8 inches, and is tappered down 1/8 of an inch every 6 feet so that the last element has about a 1 1/4 diameter. I used black nylon cord to guy each vertical. They are guyed at 20 feet, 35 feet, and at the 39.5 foot level using the tophats pulled out with nylon rope. Each antenna uses about 600 feet of nylon rope- I used 2,400 feet in all to guy the antennas. I used 60 1/4 wave radials per antenna using insulated 16AWG wire. About 15,000 feet all together. My radials lay on top of the ground and are pinned in place using landscape pins. I considered using raised radials to conserve wire but other 4 square users suggested a minimum of 60 ground radials- Lots of data on rasied radials but none of seem conclusive that a 1-4 wire raised radial system would be better than a 60 ground radials per vertical system used for an array- The radials that criss cross inside the square are spliced onto a bus line made up of 4AWG copper wire. This is said to prevent unwanted currents from developing as a result of criss crossing radials- It is a common practice in commercial arrays- (Although several 4 square owners I spoke to just lay the radials accross one another- and a few radial guru's told me that it was ok to just lay them out) The antenna array takes up about 1 acre of land, apprx 46,000 sq ft, and I use another 40,000 sq feet to keep everything at least a full wave length away from the tips of the array's radials- Thus a total of 76,000 sq feet were used to accomodate the system. To get the antenna to work properly, it is important to phase the system so that your signal goes where you want to and unwanted signals are rejected by a strong F/B, and power put into the array is properly distributed with little wasted. There are a lot of ways to set up phasing on the antenna. ON4UN's 3rd edition on Low Band DX'ing addresses several ways. But to save time, and to go with what had already been a proven product, I went with the Com Tek hybred coupler to control the phase relationships. The hybred coupler sits right in the center of the array, on a small post. It has 6 coax ports. One for the rig's input, 4 for each of the verticals, and one for the dummy load which dissapates unused power resulting from resonant issues. Because of the dummy load, the SWR of the antenna is masked by the coupler- So how do you check the antenna's performance? You simply insert a watt meter between the dummy load and the dummy load port and measure the power being dumped by the system. For example, if you run 500 watts into the array, and the dummy load shoiws 50 watts being dumped by the array, you have 10% of your power not making it out- Not bad- But most 4 squares owners, including me, try to get the minimum power dump not to exceed 3%. The antenna will work well with less than 10% of the power being dumped. Once you start going up from there- your signal will still radiate well but you will notice a decrease in your front to back gain. To feed the verticals using the hybred coupler, you need to use 1/4 wave 75 ohm feedlines. The feedline should have a velocity factor of at least 78%. I used RG11 coax. A lot of coax is at 66% and if you cut your 1/4 wave feed lines taking this into account, you wont't have enough coax to get from the coupler to the antenna- 75 Ohm seems to work better than 50 ohm for feedlines- Some try 50 ohm but report better results using 75 ohm. I feed the system using a 400 foot piece of 9913......... Tuning and the Effects of Mutual Coupling When you make the first vertical, you need to test it as a solo antenna with it's radial system attached. You want the antenna to be around 100KHz below the desired resonant point because when the other three antennas are up, the mutual coupling will raise each single vertical's resonant point by apprx 100KHz......Thuis, the entire array will be most efficient around 100KHz abvove the original vertical's resonant point- For example, if you want the array to be most resonant at 3.775MHz, you need to tune the first vertical constructed to be resonant around 3.675MHz. Now this is a touchy subject because mutual coupling does not always produce a 100KHz jump. You might get only a 50KHz jump or have one as big as 200KHz- such as the case with mine- But 100KHz tends to be the average and the standard suggested by many 4 square operators- Of note, you must make a single vertical first, test it, tune it, then make each of the other three verticals exactly like the first one. This way, each vertical should act in a like manner as the first, and you will have a well balanced array- Just think of seeing the first vertical in a mirror with four images- and that is what you want to produce- Some four square owners report as little as 50 KHz jumps due to mutual coupling on compromised 1/4 verticals such as shortened, top loaded, antennas. Full 1/4 antennas tend to have a bigger jump- but a lot of factors will influence this jump such as the radial system, environmental factors, materials used for radiators etc...But if you go in expecting a 100KHz adjustment, it is a somewhat a safe bet that you be close- Ok, so what were some of my results- Well, first of all, my resonant point jumped almost 200KHz......so while the feedlines and spacing between the verticals are cut and measured for the phone DX window- I need to lenghten my verticals to bring them down a bit- Right now, my minimum power dump is 5% at 3.900MHz and around 8-10% in the DX ssb window- it is a whomping 20% in the CW band but I can fix this by reducing the current array resonant point- >From a perfomance standpoint, K0RF, who holds a lot of 80 meter contest records, has looked the array over and feels it has as good of F/B and side to side rejection as his 3 element yagi- Measured front to back is as great as 25dB on DX contacts and 20-25dB so far on a lot of stateside results. Front gain looks to be 6-8dBs based again, on testing the array with DX and stateside contacts and using a Butternut HF2V for comparisons- Since putting up the antenna just last week, I have worked HL5FUA, 7J4AAL, RA0CG, VK5NJ (QRP), VK2XN (dailey it seems with one QRP contact), EA8ZZ, CT4NH, and UA0FF...most of these contacts have been in heavy QRN as the season is still a bit early- The antenna does seem to hear better than the beverages in most situations- which is a good test per other 4 square owners- and even though it is a vertical array, it is really quiet compared to the Butternut HF2V As for tuning, I tested each of the individual verticals and found them all to bottom out around 3.900 MHz...so they are are acting like clones although the bandwidth of the SWR bell curves vary by as much as 40KHz............. I need to add a slight bit of inductive loading or lengthen the top hat wires to bring the antenna's most resonant point, as measured my the power dumped into the dummy load, down about 100KHz.......but over-all, I could just leave it alone and I doubt the 3-4% gain in power I'll get will make much of a difference on the phone portion of the band-- it will however bring me closer to operating in the CW window a bit more effectively- You can make the antenna operate over the entire band usaing full size 1/4 wave verticals per many reports- but you won't be as effective covering the entire band vs working inside a specific window- about a 250KHz bandwidth with a power dump of less than 10-15 percent seems most likely with my array- - but larger bandwidths are reported using more effective materials- Materials used and budget: Aluminum from Texas Towers........................... \$450 which included shipping 400 feet of RG9913.......................................... 160 220 feet of RG11............................................. 88 Army surplus parachute nylon for guys 2,400 feet 160 Wood supports and concrete............................. 50 Hybred Coupler................................................ 350 Misc supplies...solder, connectors, etc.............. 30 Dummy Load................................................... 35 Dummy load feedline 400 feet of the cheap stuff-) 100 Radial wire 15,000 surplus 16AWG insluated..... 200 total......................................................................... ....\$1,623 Not bad considering a 3 element yagi is around a gazillion \$\$\$ and the four square is almost as good- not as good, but close thus far in many tests- Ok, so if you have any questions, please let me know- This was an involved project but a great learing experience. I had over 30 hams give me feedback on putting this together- and while i didn't do everything they suggested, I never could have finished this project with out their support- too many to thank but there are a lot of them- Locally, N2IC, K0KE, K0RF, W0YG, N4VI, W0AH to mention a few- and down south, W4AG, Stan, really made my day many times as he had almost the exact design for his array as I used in mine- just a little variation in vertical height- he really provided a good model to build around- K4SQR, Jim, at Com Tek makes a great product and provided a lot of ideas- it was nice to have a product actually work out of the box ...the hybred coupler and Jim's design have worked great! IIf I get some energy, I'll be writing an artical for some magazine on it in the near future- any feedback for this would be greatly appreciated- I'm still learning about this antenna array and lack a considerable amount of smarts before I claim to be an expert on them-- and I know I may have missed a few important points- but from a ham's point of view- I hope this story helps others considering such a project- - 73 Paul N0AH Carpenter, WY -- FAQ on WWW: http://www.contesting.com/towertalkfaq.html Submissions: towertalk@contesting.com Administrative requests: towertalk-REQUEST@contesting.com Problems: owner-towertalk@contesting.com Search: http://www.contesting.com/km9p/search.htm ```
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