What are reasonable SWR readings for full wave 160M H-Loop?

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Nella Ludlow

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Apr 27, 2020, 8:54:05 PM4/27/20
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Hello Skywires Group--

I may be asking a novice question.

What are reasonable or expected SWR readings for a Skywire Horizontal Loop?

My goal was to put up a 160m Horizontal Loop and be able to operate on 160, but also on 80-40-20-15 with one antenna.  I heard loops were quieter and were resonant and matching impedance
on even multiples unlike a dipole on only odd half-wavelengths.

I am testing a 500' Horizontal Loop.  I placed it at 25-30' feet up at 6 attachment points which is a rough circular area around a big backyard along the edge of 
trees/shrubs.  I was given a 500' Home Depot 10-AWG THHN Stranded Insulated roll of wire, so I used that to start. I plan to add length but wanted to test where resonance 
points were and make adjustments before doing the work to get it to 50-60'.  I connected each end of the wire to an Alpha Delta "Delta C" center insulator which connects to a
CX213 100' of coax.

I used 1005/Freq Mhz = feet formula, and adjust for insulation at 96%, this comes out cut to be resonant around 1.930 Mhz.  I used a MFJ-269 Antenna Analyzer and found 
the dip in SWR to be at:

1.934 (fundamental)
3.868 (2 wavelengths)
7.739 (4 wavelengths)
15.513 (8 wavelengths)
23.330 (12 wavelengths)

Clearly resonance as advertised.  I'll add length later to get to more desired frequencies.  I also noticed the noise floor dropped about 1dB.  Using a tuner on the loop for 80m, signal strength to a friend at same power, was down to S8-S9, when on simple 80m dipole at same height was S9+10, so somewhat worse signal report on the loop.  I also could receive better on the 80m dipole about one S unit - this was just one person, so I don't want to read too much into that.

My main concern was that SWR 2.0 on fundamental frequency, and all multiple wavelengths the SWR's were in 3.x range, some even at 4+.  

Then I realized a mistake as I was testing this in the shack, on the other side of 100' of RG213 Coax.  I am a novice to Big Loop antennas, and I was used to dipoles and even
yagi's where I could pretty much just use coax without much concern.  I pulled out an antenna tuner and adding a 6' coax from tuner to rig and tested again and received a different SWR.
I concluded I have a big impedance mismatch, and 100' of coax might be a very poor choice, and I can change to 450-ohm window ladder line.

Before I make that change, I decided to test at height the feedpoint and with the shortest coax I have which was 3' feet, I measured the antenna again (as I wanted to see how the antenna was performing without feedline or as close I as could).

These were the results:

Wavelength   Freq   SWR    R      X
============================
1                   1.933    1.6     87      0
2                   3.857    4.2    165    98
4                   7.810    4.1     98     10760
8                 15.533    5.4     36      72
12               23.304    6.3     14      48

So the fundamental frequency SWR came down from 2.0 to 1.6, but my other SWR's are even worse.  They dipped at the ame/correct locations, and with a tuner I can get SWR to something under 2, so it is usable, but I am wondering what others get for SWR on wavelength multiples without a tuner for their Skywire Loops.  I noticed the ARRL antenna handbook and several online articles say things like "reasonable" SWR but don't cite their actual numbers.

Is this normal?  Do I need worry about the feedline and get it the right length to reduce SWR?  What are your recommendations?

I do plan to add some length to cut loop for 1.775 - 3.55 - 7.1 - 14.2 - 21.3.  I haven't done that yet as I was hoping to see broad low SWR across 160m and could conclude cutting it for 1.775 was good enough to still work in 1.800's while hitting 80-40-20-15 ham bands.

Options I can think of:  
1) raise it higher - as it is just at height or slightly above height of brush and smaller trees.  I plan to do this for permanent install, but wanted to experiment with it at this lower height.  Some articles say 40' but will perform even at 20 or even 10'.  Shouldn't I have better results with this at 25-30 feet?

2) Change to 450-ohm ladder line.  I am thinking this will help get better SWR into the shack, but was expecting the antenna on its own to perform better.  Or is the feedline part of the magic of making this work?

3) Assume this is how all loops work and people don't care about the antenna SWR and fix it with feedline and/or tuners?  I'm not seeing the seeing the upside of having a loop at its current performance.  I think I may be doing something wrong.

4) I miscalculated something?  I am hoping you can give me some good advice of things to try.

Thank you and 73,

W7LUD / Nella Ludlow


Nella Ludlow

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Apr 27, 2020, 8:59:28 PM4/27/20
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Mistype of reactance
Wavelength   Freq   SWR    R      X
============================

4                   7.810    4.1     98     107    not 10760  :-)

Donald Bowders

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Apr 27, 2020, 10:58:59 PM4/27/20
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Good evening W7LUD,
My loop is 520 ft long at 30 ft high 4 corners and supported by the trees on each side. i feed it with 450 ohm ladder line from a 4:1 DX engineering antenna balun.
Here are the current figures from my Rig Expert AA54. Taken in the shack at point of entry.
1.825   2.6:1   R=19.4   X=5.9
1.900   3.2:1   R=50      X=40.9

3.800   2.9:1   R= 139.8  X=28.7

7.250   1.12:1 R=49.5   X=-5.5

14.250  2.5:1  R=49.5   X=48.0

21.350  2.6:1  R=28.0   X=-30.2

24.950  2.8:1  R=17.6    X=2.7

28.100  2.1:1  R=29.7    X=21.6
28.500  3.5:1  R=19.6    X=28.8

50.125  1.1:1  R=52       X=-5.6

I recommend 450 ohm ladder line feed for no loss to antenna. also recommend 575 to 520 foot antenna length. I chose 520 after calculating 936/1.800 freq.= 520. could be longer but have not tried it. Too much trouble getting it up. I may change it if it ever needs repaired. I have been using this antenna for 7 months.
Hope it helps. Good Luck,
Don K5HFG


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Louis de Kort

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Apr 28, 2020, 1:34:38 AM4/28/20
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Hi Nella,

I made a delta lop with a total length of 83 meters, feed in one corner with coax rg213 trouhg a balun 1:2 ( the impedance is 100 Ohm in the corner so I transform this with the balun to 50). It working fine and the common bands, 80, 40,20,10 without a tuner. On the other bands I need a tuner. The loop is tied up between trees at three points at a height of 15 meters. Worked Japan, Australia and many other countries with it on ssb.
Hope this information will help?
Best 73's.
Louis
PA3FTP
The Netherlands.

Groeten, Louis

Op di 28 apr. 2020 02:54 schreef Nella Ludlow <nella....@gmail.com>:

Chris Icide

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Apr 28, 2020, 4:35:01 AM4/28/20
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Options I can think of:
1) raise it higher - as it is just at height or slightly above height
of brush and smaller trees. I plan to do this for permanent install,
but wanted to experiment with it at this lower height. Some articles
say 40' but will perform even at 20 or even 10'. Shouldn't I have
better results with this at 25-30 feet?

As you probably know already, height is everything. Sure it works at
a lower height, but it works better higher. You'll have less
interactions with the ground and other metal objects the farther away
from them you are, and this will affect your SWR readings.

2) Change to 450-ohm ladder line. I am thinking this will help get
better SWR into the shack, but was expecting the antenna on its own to
perform better. Or is the feedline part of the magic of making this
work?

The nice thing about a long loop is it's an efficient radiator for any
frequency that is equal to or below it's total length. The SWR could
be horrible but if you can get power into the antenna, it will
radiate. By using a good tuner, you can show a clean 50 ohm load to
your txvr. If you are running balanced line to the antenna, even if
you have an swr of 1:10, you aren't losing the power. That is unless
you are running unbalanced line over a segment with high SWR, if so
you increase the cable loss significantly. If I had any choice at
all, I'd run ladder line for any multi-band wire antenna.

3) Assume this is how all loops work and people don't care about the
antenna SWR and fix it with feedline and/or tuners? I'm not seeing
the seeing the upside of having a loop at its current performance. I
think I may be doing something wrong.

I can't speak to others, but I don't care all that much, I can account
for the antenna with a tuner, and I have confirmed in comparisons to
my yagis, that my modelling in nec seems quite accurate with respect
to gain. Anecdotally, I heard a UAE station on the air, and tried for
over an hour to work him with my 40m two element yagi, to no avail. I
figured I'd give the loop a shot as he might be in one of my high gain
lobes (my loop is ~1000 ft, so it's 8 waves on 40m) and I got him
immediately. So loop wins for that contact vs. two element 40m yagi
at 90 feet.

4) I miscalculated something? I am hoping you can give me some good
advice of things to try.

I may have missed it in your description, but you should at least put
a 1:1 current balun either at the antenna feedpoint if you insist on
feeding it with coax or at the end point of your ladder line. (Some
tuners will have a balun in them, so if you run the ladder line all
the way back to the tuner's balanced line output you may not need
one).


It looks like you aren't too far down the road from here (by olympic
peninsula distance standards).

-Chris, WY7W

Ronald Johnson

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Apr 28, 2020, 11:42:44 AM4/28/20
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I run a 80 metter loop 270 ft...23 feet off the ground...40 ft of 450 feedline thru a MFJ-462D tunner...my swr's are under 1.6 on all bands 80 thru 6 meters at 100 watts with no balun in line. t been the best ant I have  ever used.

scottsa...@gmail.com

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Aug 17, 2020, 12:19:47 AM8/17/20
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Hello Nella and others.   I have a triangular shaped loop fed at 40 degree angle up about 25ft using 22AWG insulated wire, three supports, and totally in the clear. 

(see Steve Cerwin's article titled The Long Wire Loop: an Omnidirectional, Multiband, Low Angle Radiator)

The small wire with the  proper tension and counterweights at the two far end supports gives the approximately 200ft runs virtually no droop.  This loop has been up for two years through high winds, rain, snow, and intense sun without any issues.  It definitely needs to go higher but at it's current height it performs rather well.  I cut it to be resonant in the 40m band which I believe is the magic trick when selecting resonance for a 160M loop.  I am feeding the loop with RG8X coax to a good quality 4:1 Balun located right at the feed point.  At it's current height and length it requires a tuner on 160 and on the phone portion of 80M.  However WITHOUT  the tuner, it is resonant on:
the 80m CW portion of General band
all of 60m
most of 40m
all of 20m
all of 15m
all of 12m
10m up to 29.5
most of 6m
many non ham frequencies in between, and possibly even higher ham bands like perhaps 2m.

I'm sure this will change a bit once the height is raised, but I will just raise it and then tune it right back where it is now.  The article I referenced above was my horizontal loop inspiration and it was written by a Ham who is also a physicist and scientist.  Just last week I discovered that the author of the loop article recently wrote a book on antennas with a chapter on loop antennas.  I just received the book Friday and I'm extremely impressed with how it's written and how much I'm learning.
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