Inverted L - Very interesting

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Hi All,

I'm still an HOA dweller and can't put up fantastic mega beams and towers.  I've been getting by with an EF wire, 130 feet long.  It works and has worked pretty well.

I decided to put up an inverted L.  I made this decision because out behind the house I have two cottonwood trees, quite tall that would work well and conceal the antenna.

The plan is a 100 foot inverted L and just by happenstance it is ending up pretty close to 50 feet vertical, 50 horizontal.  Maybe more like 40 vertical and 60 horizontal but it is close.

So I took this week off of work and today was my first day to get it in place.  I'll put pictures on QRZ as soon as I can.  Today was just trying to get it done.

I used my tennis ball shooter to launch the fishing line to pull up the new rope and wire.  It took me 2 tries to launch the first tree.  First time I've fired this launcher and at 85 psi it put the tennis ball in orbit.  So I backed it down to 40psi and got a good launch.

The second tree took three tries and was mainly just operator error.  I got everyone wound up and ready for launch and managed to launch the damn ball straight down into the ground.  sigh...  This wouldn't be so bad if I didn't have to go close to 200 feet to recharge the launcher.

Anyway with the wire strung I set to laying out 16, 20 foot radials.  That was hard as there was a lot of crap on the ground and I kept falling over it.

I had planned to use an MFJ tuner mounted at the tree but the thing is flaky as hell and won't tune.  So I have about 150 feet of LMR 400 going from my HF Auto tuner in my shed, down across the back yard and over to the big tree.  

At initial test my Palstar HF Auto in the shed, pushing 150 feet of feedline, no balun tunes every band, even 6 meters.  Whats up with that?

A friend in town has an antenna analyzer which I plan to measure the antenna at the feed point.  For now I just used K9DUR's SWR plotter pushing through 250 feet of LMR 400.  All tuners disabled.

I'm a little shocked at the results.   No band, I repeat NO band was above 2:1.  Most were 1.5:1 or lower across the entire band. Here are images from the SWR plots:

https://www.dropbox.com/s/ufjfsai3i8mw4rn/InvL160SWR.png?dl=0
https://www.dropbox.com/s/kap71myg17vcym2/InvL80SWR.png?dl=0
https://www.dropbox.com/s/hwttxyd15y9rrc8/InvL40SWR.png?dl=0
https://www.dropbox.com/s/wr77v9w4jitryiy/InvL30SWR.png?dl=0
https://www.dropbox.com/s/ef7elyff0uyuwmn/InvL20SWR.png?dl=0
https://www.dropbox.com/s/jpvtno541yd32qt/InvL17SWR.png?dl=0
https://www.dropbox.com/s/tcbbs606vk3jbe5/InvL15SWR.png?dl=0
https://www.dropbox.com/s/seqyhslpmrpiszp/InvL12SWR.png?dl=0
https://www.dropbox.com/s/fbk3bxgu97lrbl0/InvL10SWR.png?dl=0
https://www.dropbox.com/s/16ndxhz3l7k1al8/InvL6SWR.png?dl=0

So these results are SOOO GOOD I suspect something is amiss but the antenna seems to be getting out and the results seem to repeat.  

IE if I go to a frequency and key up the SWR matches what the plots show.  Plus my HF Auto tuner SWR display matches too.

Anyway I'll keep you all posted if you are interested and will post some pictures of the build.

Mark - WS7m
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Mark WS7M

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Posted 2 years ago

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k3Tim

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Hi Mark

If it gets out and hears one can't argue with that.
Is there a 4:1 or 9:1 in the system ?
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Mark WS7M

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Hi Tim,

I have not had any time to play yet.  Yesterday was build day so I just did a few tests.

9:1 will be in in the next couple days.
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Doug Hall

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Mark,

The low SWR readings (at the transmitter end) are caused by loss in the coaxial feed line due to the mismatch at the antenna. When you measure the SWR at the antenna you'll see a very different story. That doesn't mean your antenna won't work as it is, but as you might guess you'll increase its efficiency if you match the feedline to the antenna at the antenna.

For a complete explanation see:
https://www.arrl.org/files/file/Technology/tis/info/pdf/q1106037.pdf
See the paragraph "Is That The Whole Story?" which states, "One very strange situation occurs on a long and lossy transmission line, which causes your SWR to appear good at your transmitter even if it’s terrible at the antenna." I suspect this is what you are seeing.

73,
Doug K4DSP
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Mark WS7M

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Hi Doug,

I was "generally" aware of that but did not realize until this "test" that it could make such a huge difference.

I am borrowing a friends antenna analyzer this week and will do that at the feed point.  The SWR plots were the only thing I had late in the day yesterday.

Thanks for the reference.  I will read.

Mark
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Rich McCabe

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While I 100% agree with Doug that SWR can mask the issue and feedline loss will make SWR look better than it is, I really would be surprised that 150' of LMR 400 is going to make it look that much better.

As Ken said the "proof is in the contacts". 

The SWR meter might be the worst thing that every came about for hams as it often steers us in the wrong direction. After 30 years of ham radio I have came to the conclusion that its never an indication of a "good" antenna.
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Ria - N2RJ, Elmer

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Get a TDR (rigexpert in TDR mode is fine) and run it on the system. If you see a straight ascending line that is your loss.

I also have an inverted-L for 160 and it presents high SWR on other bands.

Ria
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Rich McCabe

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How long was your inverted L?  So was final length 100'? Why not use your EF as an inverted L?
(Edited)
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Ken - NM9P

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About 135 feet is a good inverted L for 160, and will naturally tune to some other bands. Pruning helps even more. I have used my 160 inverted L on 40 to good affect.

With about 65 ft, (50 up and 15 over) you would have a nice dx antenna for 80 meters.

There are formulas that indicate certain compromise lengths that will work on multiple bands better than some other lengths. 90 ft seems to come to mind as one of those lengths. It has been a while since I read them.

But the proof is in the contacts. A compromise antenna is better than NO antenna. And a bit of strategic tuning can make a big difference.
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Mark WS7M

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Hi Rich,

I did not want to take down the EFHW.  In case this inverted L did not work well I want the EFHW to fall back on.

@Ken - I followed Cebek pretty closely.   The over all recommendation for 80-10 was 100 feet with 16, 15 foot radials.  There are some minor improvements for more or longer radials.

I did not target 160 for this antenna.  But I will see how well it works down there.

And yes, the proof is in the ocntacts.  Now I just have to make a few.
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Rich McCabe

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Mark,  I have an EFHW that I have ended up trimming to 125'. I feed it with a 55:1 UNUN.  I have a relay to the right of UNUN (the box with my callsign) that bypasses the UNUN and feeds the 125' direct. So with the flip of a switch I either have a 160 meter inverted L or a 80 to 6 meter which is an end fed 1/2 wave on 80. 

Of course your house and tree layout dictate how this can be done.

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Mark WS7M

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Hi Rich,  I like this idea so much that I ordered another EFHW from MyAntennas and and I already have switchable 12V at the feed site for the flakey tuner.  So controlling a relay is a no brainer.

Excellent idea!

How long are your radials?  I followed Cebek who seemed to show that 16, 15 foot radials were enough.  I have plenty of room to add more.

Also I'm curious about your 125' trimming...  How did you decide on that length?
(Edited)
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Rich McCabe

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Mark, I basically have hardly anything for a radial system.  I got talked into a MyAntennas.com antenna by a friend. I was not going to put it up but decided to try it.  It actually worked pretty well and when I when I bypassed the transformer and tried it on 160 meters it SMOKED my 160 meter balanced line 1/2 wave by 10db to the hams I talk to locally. 

I was not happy with the build quality of the MyAntennas.com unit (mostly the 18 ga wire) so I built one using good wire and a balun designs 55:1 UNUN.  It just drops down outside the shack and connects to my ground rod system which is three 8' rods about 5 feet apart. I added a 125' single ground radial going around the back of house in the landscaping and it made zero difference in performance however its going the wrong direction.

My vertical has 60 radials 60' long but its too far away to tie into.  I doubt I will ever add radials to this. I am in the midwest with ideal soil according to the charts so that may or may not help.
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John - K3MA

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Mark.  Reading between the lines I am making a guess that your EFHW antenna is from Myantennas.com.  If so I would have recommended that you have made your Inverted L using the same 130ft of length of wire that your current EFHW uses.  The Myantennas.com EFHW configured as a inverted L works very well, does not require a tuner, does not require ground radials and you could have ordered only one of his baluns to complete the install.  Depending upon the location of your current EFHW antenna you could have tested the inverted L by simply disconnecting the balun from it and installing it on the Inv L.  If you were happy with its performance then you could have replaced it and ordered another balun.  Another benefit you could have leveraged is to setup this Inv L to also work on 160m by adding a switch at the feed point and some radials.

I mention these not from theory but rather personal experience.

John K3MA
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Rich McCabe

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35' is awfully high for a end fed or inverted L.  Any reason you could not get the MyAntennas.com 49:1 "auto transformer" closer to the ground?  That 35' of wire is acting as another element.
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Mark WS7M

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Hi Rich,

No the inverted L feed point is at ground zero.  The current horizontal EFHW is up about 35 feet in a tree.  John was asking why I didn't just borrow the balun from that to test on the inverted L.  I was answering that I'd need to go up a tree to get to it.

I have one EFHW 130 foot antenna that is a horizontal antenna.  Feed point is up about 35 feet in the tree.  Wire goes to another tree.

Inverted L starts at the same tree the rope to the horizontal EFHW is tied to.  So feed point on ground.
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Rich McCabe

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Yea I was talking about the EFHW.

35' up in the air for the transformer seems like a long ways.  Its been my understanding that you should keep it as close to ground as possible.  But once again the proof is in the pudding/contacts.
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Mark - WS7M

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Well it is my hope that in getting the inverted L to a reasonable functionality I can take the horizontal EFHW down or move it elsewhere perhaps.
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Rich McCabe

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Let us know how it works. I would assume actual feedpoint impedance would be very high on 80 meters
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Ned K1NJ

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      Here is the word on the inverted "L"  by L.B. Cebik. (W4RNL SK)  The 100' case is
 discussed.  There is an incredible amount of information here and there are illustrations
 and tables that help clarify.
    This is worth a look even if you have little interest in that antenna.

http://vtenn.com/Blog/wp-content/uploads/2016/12/Inverted-L-Cebik.pdf


          Ned,  K1NJ
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Rich McCabe

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Thanks Ned. This has been on my list of things to read for about a month. I think I will move it up the list.
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Rich McCabe

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Just as a FYI Cebik's article says that on the bottom end of 80 meters a 100' inverted L will have a resistive component of 130 ohms and a reactive component of -490. So at the antenna the SWR is going to be around 40:1.

At the shack end of 150' of LMR400 the SWR is going to be around 15:1. Almost 60% loss in power as well.

At least that's what I am coming up with.

His antenna was 50' vertical and 50' horizontal.
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Mark - WS7M

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Hi All,

Another go around.

Today I took down the 100' and basically turned my EFHW into an inverted L as Rich has done.  I also copied his idea of a relay box and built and installed one.

So like his system I have a relay that links feedline into the EFHW transformer.  The antenna goes up about 50 vertically then goes horizontal about 80 feet.  There is a small 2 foot hang down so my trees were not quite far enough apart.

I set this up and it seems to do pretty well.  I realize I need to test at the feed point but I have to wait for my friends antenna analyzer for that.   For now on 20m the untuned SWR is 1.2:1.  This is all the coax and everything.  SWR is measured at the 130 foot point of the run. (using the tuner).

On 20m, 14002.00 with 500 watts I was able to work Spain.  I received a 55N but conditions today were not great.

Again with coax 40m SWR came in at 1.6:1.   80m is about 2:1.

Using Rich's relay switch to take the matching network out of the loop on 160 SWR is 1.7:1

So far this seems better.  Thanks all for the ideas.  I'll post results of analyzer when I can.

In a sense this takes the 130 foot HW that I've had pretty good luck on and turns it both vertical and horizontal.  I'm hopeful it will end up working as well or better.

I do have a pretty good radial system below this antenna.  I  currently have 16, 15 foot radios and plenty of space to add more.
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Rich McCabe

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Wow you are not messing around :) 

Not sure how you wired it but I had to use a DPDT relay so I could switch the ground of the UNUN out of line.  Otherwise you have the main wire connected to ground through a transformer.

My setup does not have the best SWR but not bad.  However its connected outside the shack and only have 10' of feedline so not worried.
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Mark WS7M

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Currently grounds between radial system and coax are common so I'm just switching the center lead which seems to work.

I checked continuity and it does not ground.  But today is a single step.  I can add a second relay easy enough.  Plenty of space in the box.

I will have to try 160 and see what it is like.

Yes unfortunately this has a LONG feed line.  I will probably need to play with some isolation to keep it from becoming an element.
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Rich McCabe

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I added a common mode 1:1 choke just to be safe. I was thrilled with how it worked and when I built my last patch panel I added a spot for the relay switch and one extra in case I decided to do something similar with another antenna.