My compliments to Paul on a very nicely written and informative article.
Great job Paul!
Two years ago I put an 80 mtr 4 square here using the K8UR configuration
("Lazy H", or "bent dipole") shown in ON4UN's book with the wires hung off
the 120' guy ring on my rotating tower. I did find that the mutual coupling
of the antennas in this configuration did NOT raise the resonant frequency
of the array (as compared to a single element)
as the classic vertical configuration does. I discussed this at some length
with Jim at Comtek (who was very helpful). He commented that he had heard
of similar observations from other "K8UR" configuration builders. So. . .
just a word of caution. . . don't always plan on the resonant frequency
rising by 100
Khz or so. It may or may not happen.
73 and good DX to all in the coming lowband season. . . Dave
W0FLS
-----Original Message-----
From: Dinsterdog@aol.com <Dinsterdog@aol.com>
To: towertalk@contesting.com <towertalk@contesting.com>; Dinsterdog@aol.com
<Dinsterdog@aol.com>
To: <towertalk@contesting.com>
Date: Monday, August 30, 1999 5:32 PM
Subject: [TowerTalk] RE: 80 meter 4 square array notes from N0AH
>
>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 raise
d
>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
>
>
--
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
|