N1LI

N1LI
Home Page of the Long Island DX Society

MENU

Home

First Photos

N1LI from the Sky

Antennas Go Up (Sept 06)

80M 4-Square

Blog

First N1LI Operation

2006 Contests

2007 Contests

2008 Contests

2009 Contests

May 1919 QST

Photo Gallery

Guestbook


 

80M 4-Square


 

 

 

Construction of the 80M 4-Square

Here are some details of the 80M 4-square array at N1LI.

The radiators are wires, inverted-L style...about 50 feet up, 25 feet horizontal. They are out in the woods, where I spent several weekends of chainsaw-wielding prep work clearing several years of deadfall and moving a few piles of brush that neighbors put on "that vacant lot".

The lot is pretty flat, with a few outcrops of granite 2-3 feet tall scattered around. The soil is about 0 to 3 feet deep elsewhere before hitting solid ledge. The 4-square takes up pretty much the whole 0.75 acre lot. The Northeast element is about 250 feet from a 20-foot (more like 30 at low tide) cliff overlooking the Atlantic Ocean.

Each wire goes up to a pulley hanging from a rope, then off to another tree. The wire is insulated #12 Flex-weave which runs
through the pulleys nicely (it failed due to water getting inside and corroding the very thin wire strands; it has been replaced with stranded wire with larger strands...a bit stiffer but still OK in the pulley).  I figure that ought to improve the chances of survival. Eventually I will get tired of replacing wires, and will
be motivated to dig holes, lug bags of concrete out into the woods, and install the HyTowers that are in the basement. Well, 3 of them
anyway....the NE radiator is close to the street and will probably remain as an invisible wire element.

One of these wires was the original single N1LI vertical, which was pretty loud with only 9 radials under it. It now has 20 radials under
it. That reduced the feedpoint resistance from 90 ohms to about 60 - a few more radials will be added when I remove the tree that is in the way of the second 160M vertical. All radials are ground mounted, and will be covered when the leaves come down.

Each feedpoint kind of hangs near the ground, soldered directly to the RG11 1/4-wave phasing line. Radials are soldered directly to a bare
copper wire ring. The NE radiator is too close to the street for full-size radials, so it has a mix of 1/4-wave and shorter
radials....42 total. When the wind blows, the feedpoints float up in the air a foot or two, then settle back down.

NOTE: These connections kept breaking, so they have been replaced with SO239s mounted on an aluminum plate bolted to a piece of galvanized steel angle sunk in concrete in the ground, with the radials attached. I leave the wire elements a little loose so they can ride up and down as the trees sway, and they are connected to the SO239 through a wire and a heavy-duty banana jack. so if the wind blows very hard, the wire unplugs itself. I can then fix it just by plugging it back in instead of soldering.


When I got each radiator up, I carefully measured the feedpoint impedance across the band (in a couple of cases, also at a few stages
of radial installation). I also measured the impedance at the end of the 1/4-wave line. The impedance transformation was in close agreement
with theory (I always love saying that).   Two of the elements were resonant somewhat lower then the other two...as radials were added
(this past weekend), the resonant point moved up for each...now they are all resonant between 3600 and 3650 - actually 3 are right at 3650,
one is at 3600. The one that is lowest is missing a few radials that will be added when the tree guy comes to remove the brush piles that
are in the way.

I am using a Comtek feed system.

Dump power is lowest at 3650, at about 1%. Higher at the bottom of the band...about 8%. Dump power readings are pretty consistent through the different directions. The dummy load is a thing I got at a flea market for $20...I think it was once part of a power divider at a cell site. I've seen a bunch of these things at flea markets in the past few years...this one's about a foot long, 3x3 inches in cross section, and has a massive finned heat sink. I believe it is rated at 100 W. It runs warm to the touch after several minutes of continuous 1.5kW dashes. I may replace it with something capable of more power someday. UPDATE: I replaced it with on old Heathkit Cantenna filled with mineral oil.

So does the antenna work?

Limited on-the-air testing in the first couple of days suggests that it works very well. Here is a recording made by DJ5EU when I did a front-to-back test. It appears to be well above 20 dB...some European stations reported 30dB, and some were unable to hear me off the back when I was "very loud" on the front. The location, close to the ocean, helps on transmit. I do not often get beat out in pileups.

I am very happy with the performance of this antenna system.

;

  

|  © 2006 All Rights Reserved.
  |


Create a Free Website