First time working with a Horizontal Loop

[Chris Icide]

We moved up to the pacific northwest on 21 acres from a post stamp lot in the SF Bay area a little over a year ago.  We have a good number of 100+ foot coniferous trees and I had been eyeing putting up some kind of wire antenna.

I recently got a 125 foot tower put up and have a three element tri-band yagi (Mosely) as well as a 40m rotatable dipole on the tower.

Two weeks ago I finally got a loop up that I had been planning for quite a while.

The loop is anchored at four points, three trees and the 125 tower.  It's in the shape of a deformed square with:

• a short side (~ 80 ft.) from point 1 on the  NNE (~ 20 degrees broadside) side of the square to point 2, 
• a long side ( ~ 380 ft. ) from point 2 on the WSW ( ~285 degrees broadside) side to point 3, 
• another shorter side ( ~ 180 ft. ) from point 3 on the South ( ~ 185 degrees broadside ) side to point 4
• and another long run ( ~320 ft. ) from point 4 on the East ( ~ 105 degrees broadside ) side back to the first point.

 I've attached an image to better explain the loop.

Point 1 is the tower and the loop achieves a height of approximately 110 feet at this point (the insulator is about 10 feet away from the tower when the loop is fully elevated and tensioned).  The insulator is run through a marine grade pulley and has two 10 lb. weights tensioning the connection point.  One weight is about 8 feet above ground level and the second rests on the ground, but free to move in the case of changes in the loop due to wind and tree motion.

Point 2 is a tree at the edge of a cliff which drops about 150 feet down to the Juan de Fuca strait.  The loop only achieves a height of about 80 feet at this point.  The loop support rope also runs through a marine pulley but is secured to a fixed mount with no freedom of movement.  The insulator for the loop is about 20 feet away from the tree under tension.

Point 3 is a tree and the loop achieves a height of about 115 feet at this point.  The insulator also runs through a marine grade pulley with a 15 lb. suspended weight (~ 4 feet above the ground) with full freedom of movement.  The insulator is approximately 15 feet away from the trunk and about 10 feet clear of any branches.

Point 4 is a tree and the loop achieves a height of about 70 feet at this point.  The loop support rope also runs through a marine grade pulley, but is secured to a fixed mount with no freedom of movement.  The insulator is about 20 ft clear of any branches.

The loop is fed on the segment between point 4 and point 1 at almost the exact middle of that run (point 4 in the attached image).  The feedline is 600 Ohm open wire 87 ft. long running to a 4:1 dual core balun.  From the balun there is ~ 12 feet of coax cable to a Balanced L manual tuner.

I used #14 THHN wire with a tensile strength of 44 lbs and a velocity factor of 0.91.

Both long runs have some decent sag.  the 380 foot run probably sags down to about 50 feet in the middle of the run and the 320 foot run does about the same where the feed point is.  There is no support at the feed point, just tension between point 1 and point 4.

I used a single length of wire for the entire loop.  The only points of electrical connection are at the feedline, no other breaks in the line.

I have some concerns on the construction.  

1. I'm not sure having just two points with freedom of movement to account for wind/tree movement is good enough.
2. I currently have no real grounding solution besides the shield is connected to an RF ground where the coax from the balun to the tuner enters the building
3. I used ceramic insulators for the four connection points and I had to buff out some mold seams and that left the area where the wire passes slightly rough and I suspect I'll have a break there eventually

Operationally, the loop has been extraordinary. 

• 80m:  
• I find that it significantly outperforms a 80m wire dipole I had up between point 1 and 3 at about 60 ft.   I've made SSB QSO's on this to nearly every state, EU, SA, AF, and Oceana.  I've had no problems tuning it with the tuner, however there are several phase reversals over the 80m band and there are some spots where tuning is very touchy and I have to be careful with any frequency changes.  One of those is right near the 80m ft8 frequency.  I have noticed some noise that I didn't see before with the 80m dipole and I've reverted to using my active phased array for recieve which gives me some good directionality if I need to operate where the noise is.  I have a timewave ANC-4 noise phase canceller I'm going to hook up and try seeing if I can use that to cancel out the noise.  EZNEC model shows max gain of 8.02 dBi at 37.5 degrees take-off angle.  This drops off to -1.61 dBi at 90 degrees.  
• 160m
• I don't have anything to compare this to for 160m.  I didn't have any options (I thought about shunt loading the tower, but I don't have any radials set up) other than the loop.  I've been able to make SSB QSO's in the states, and have been able to snag a couple in Asia and Oceana.  I made one ft8 QSO to EU and one to Africa.  This band can also be quite noisy, and I've found using the receive phased array for directionality tends to perform better overall than using the loop for receive. EZNEC model shows a max gain of 6.56 dBI at 52.5 degrees take-off.  This drops off to -0.95 dBi at 90 degrees.  The antenna is a breeze to tune and seems very stable across the entire band
• 60m
• Also a band I have no comparison for.  I've not tried much on this band, just a little ft8 and it seems to be about the same performance as it has on 80m.  There are no issues tuning in the 5 channels on 60m.  EZNEC max gain of 8.73 dBi at 30 degrees, dropping to -11.85 dBi at 90 degrees
• 40m
• The antenna doesn't need a tuner, < 1.5:1 across the entire band with the 4:1 balun.  I have a rotatable dipole on the tower at 120 ft. as comparison.  There is no comparison.  The loop outperforms the dipole by a huge amount.  The only downside is the inability to control directivity.  I've made over 80 DXCC SSB contacts on 40m in the two weeks of operating on the loop.  EZNEC shows a max gain of 12.18 dBi at 22.5 degrees dropping to -9.24 dBi at 90 degrees.   Lobes in the horizontal plane are starting to get a little crazy, with two main lobes two lesser lobes, and a number of nulls down about 10 dBi from the peak main lobes.
• 30m
• Easy to tune.  I was able to load up 30m on my old 80m dipole, but it was coax fed, so I suspect I lost quite a bit in the feedline when loading it up, so I don't really consider it comparable.  The loop easily outperforms that configuration on this band.  I've only run ft8 here and I've made contacts on every continent with very good reports.  EZNEC shows max gain of 13.83 dBi at 15 degrees dropping to 2.45 dBi at 90 degrees.  There is a noticeable purely vertical lobe.  Horizontal pattern is surprisingly reasonable, as the difference between the nulls and lobes averages about 3dB.
• 20m and up:  
• I have yet to test these bands out.  I was able to tune 20m and 17m just fine and load the antenna up all the way to 1500w, but I haven't yet attempted to work on these bands with this loop.  EZNEC info for the rest of the bands posted below.
• 20m: 11.87 dBi @ 15 degrees,  -1.34 dBi @ 90 degrees.  15 dB difference between peak and nulls in horizontal plane
• 17m: 13.64 dBi @ 7.5 degrees, -8.52 dBi @ 90 degrees.  20 dB difference between peak and nulls in horizontal plane
• 15m: 14.19 dBi @ 7.5 degrees, 1.72 dBi @ 90 degrees.  25 dB difference between peak and nulls in horizontal plane
• 12m: 14.42 dBi @ 7.5 degrees, -3.83 dBi @ 90 degrees.  20 dB difference between peak and nulls in horizontal plane
• 10m: 14.01 dBi @ 7.5 degrees, -7.93 dBi @ 90 degrees.  25 dB difference between peak and nulls in horizontal plane

All in all, I've been extremely happy so far.

Chris, WY7W

[Donald Bowders]

Well done OM. You have a winner. Excellent antenna. I wish you much DX with it. Mine is similar to yours and can tune through 6 meters. Only band it doesn't like is 30 meters.
Let us know how it is working for you and tell us where it tunes. If you are like me, you will do more testing than calling CQ. It is an amazing antenna.
Best 73,
Don K5HF

[John Dennison]

I’m constructing a 1000’ loop in Pinehurst NC. I have used pulleys on all support point. I had to use additional support points to help eliminate sag on the long runs this has made the loop into a multi dimensional polygon. Hoping for the best. Using a big ugly to get true latter line to 50ohm coax then to ICE arrestors then 15’ to an AT100 then to 7300.
Asking about the need for a 4:1 balun? Maybe connect it as a transformer only? Will try all combinations, but asking for advice
John Dennison, KW4OI, 73

[George Riedel]

Hey John 

FWWIW

I have a 1,500 ft loop here in Akron OH up 70 foot tied around oak trees.

I have used an ARRAY SOLUTIONS AT-200 Tuner Balun (AS-200-T )

for almost six years with great success 

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[Donald Bowders]

George,
What do you tune it with?