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Author Topic: 160 Meter Inverted L Question: Is 117' Enough?  (Read 2260 times)
K5TEN
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« on: October 12, 2017, 08:12:12 PM »

I have an Inverted L rated for full USA legal limit I plan to put up in a couple of weeks.

It's 117' long for the "L" part (vertical for 55' then horizontal for the rest).  No problem with a 160 meter counterpoise and radials for 60, 40, 30, and 20.   I plan to use a 3kw tuner and full legal limit amp.

Is less than a quarter wavelength OK for the 'L" part.  I can add more wire, but not much on my 100' x 130' lot.   I can fudge on counterpoise and radials as I have plenty of nearby property approval to put up multiple counterpoise/radials with neighbor approval, each at 10' high.

For the vertical/Horizontal "L" part, is 117' long enough?

Thank you in advance for your input.

Bruce
K5TEN
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KC4ZGP
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« Reply #1 on: October 13, 2017, 05:36:47 AM »


Extend the horizontal part three other directions for a top hat. You'll get out after that.

I'm hot for some 160 meters action tonight. Three other folks were talking over each
other Wednesday evening.

Yow!

Kraus
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W1VT
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Posts: 2488




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« Reply #2 on: October 13, 2017, 07:46:25 AM »

The maple tree I use for my 160M antenna isn't far enough from the property line, so I bend the wire down to resonate it around 1840 kHz.  I also use a matching transformer to get to 50 ohms.  Works well enough to work DXCC on 160M CW  Grin.

What really makes a difference on 160 is the ability to hear.  There are stations that here amazingly well, as well as those that are totally deaf.

Zack W1VT
« Last Edit: October 13, 2017, 07:50:49 AM by W1VT » Logged
KC4ZGP
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« Reply #3 on: October 13, 2017, 01:07:46 PM »


So Zack, I'll see you at about 2300UTC on 1.815MHz, Morse?

Alrighty.

Kraus
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KD0ZV
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Posts: 40




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« Reply #4 on: October 21, 2017, 08:37:00 AM »

At my QTH I have played with inverted L antennas from 117' up to 130'.  117' would be too short at this location and 125' is ideal and I run the top end of the band.

73
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K6AER
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« Reply #5 on: October 21, 2017, 09:14:57 AM »

The length of the antenna will be determined by several factors:

Your counter poise system.

Height above ground.

Wither any metal is near the antenna.

Shape of the run (zig zag to fit a space).

Capacity hat at the end.

If the antenna run is not at resonance you can always add series capacitance at the feed point to raise the resonance frequency or add inductance to lower the resonance frequency. In addition, the feed impedance of the antenna will vary depending on the height above ground. Your balun requirements will vary depending on your space application but basically a 1:1 balun will work if you have room for the antenna and counterpoise to be ΒΌ wavelength. The feed impedance of the antenna is about 50 ohms. My inverted L is about 80 feet on the vertical and runs to the next tree.

L(Ft) = 234/F(MHz)

Frequency............Radiator Length.........Counterpoise Length
1.85 MHz..............126.5'....................133.0'
1.95 MHz..............120.0'....................126.2'

You will have to make a decision on which part of the band you want to operate in.
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K6JH
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« Reply #6 on: October 23, 2017, 01:53:45 PM »


Frequency............Radiator Length.........Counterpoise Length
1.85 MHz..............126.5'....................133.0'
1.95 MHz..............120.0'....................126.2'

You will have to make a decision on which part of the band you want to operate in.


How bad does the match get at the other end of the band? How usable is the other end for those occasions when you want to operate there (with a good in-shack tuner)? Or do you need to build a custom tuning network at the antenna base?
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73
Jim K6JH
K0UA
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Posts: 1362




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« Reply #7 on: October 23, 2017, 02:02:55 PM »


Frequency............Radiator Length.........Counterpoise Length
1.85 MHz..............126.5'....................133.0'
1.95 MHz..............120.0'....................126.2'

You will have to make a decision on which part of the band you want to operate in.


How bad does the match get at the other end of the band? How usable is the other end for those occasions when you want to operate there (with a good in-shack tuner)? Or do you need to build a custom tuning network at the antenna base?

Mine is tuned to the lower end, and if I remember right it it is well over 4 to 1 at the upper end. Maybe higher.  I wanted mine at 1840khz for FT8.
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KM1H
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« Reply #8 on: October 23, 2017, 05:15:07 PM »

Insulated wire will lengthen the antenna electrically about 3-5%.  You can also cheat and use some of the coax as part of the antenna and put the common mode choke after that.

Carl
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N3HEE
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« Reply #9 on: October 24, 2017, 05:32:03 AM »

You will most likely need more wire for the aerial (radiating) wire.  Closer to 130 feet.  It can be bent down towards the ground if need be.  If running the wire through trees make sure to use HIGH quality insulated antenna wire such as Wireman 531.  Stay away from THNN house wire.  It will not survive long in trees.  Making the antenna resonant on the lower end (1825 KHZ) of the band will be better for working DX and contesting.  If you are looking for SSB ragchewing then shot for something around 1900 KHZ or above.  See K2AV.COM for details on inverted L construction, placement and counterpoise details. 
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Joe
N3HEE
CW Academy Advisor (Level II)
NO9E
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« Reply #10 on: October 24, 2017, 07:08:22 AM »

There is no magic length of wires and counterpoises unless you want exact matching without external components..The longer they go (up to half wave), the higher the bandwidth and efficiency.   

With nonresonant length, a coil will be needed for matching and feed needs to be insulated  to avoid common currents (via a transformer or excellent balun).  This will make multiband matching difficult. But on 30/40m, my dipole beats my 160m inv L by a large margin.

I use THHN wires. With flexible tensioning they seem  to last forever.   

Ignacy, NO9E 
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W1VT
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« Reply #11 on: October 24, 2017, 08:24:55 AM »

How bad does the match get at the other end of the band? How usable is the other end for those occasions when you want to operate there (with a good in-shack tuner)? Or do you need to build a custom tuning network at the antenna base?

I've recall SWRs on the order of 2 to 4 with my compromise Inverted "U" antenna. No matching at the feedpoint.  I found it quite acceptable to use an in shack tuner with a 70' run of LMR-400 coax.  Around 0.2 dB of tuner + feedline loss. You can calculate the actual loss for your setup with either TLW (comes with the ARRL Antenna Book) or TLDetails by AC6LA (free download).  But, I recently put in a transformer and tuned it so I can instantly pounce on whatever DX that shows up on 160.  

But, I'd want to measure the loss of any cable that uses a plated steel center conductor, like RG-6.  It is possible for the copper to be so thin that the loss of the cable becomes excessive at 160 meters. I'd rather use RG-8X with copper conductors on the low bands.

Zack W1VT
« Last Edit: October 24, 2017, 08:32:19 AM by W1VT » Logged
KM1H
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Posts: 2486




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« Reply #12 on: October 24, 2017, 08:45:01 AM »

Quote
But, I'd want to measure the loss of any cable that uses a plated steel center conductor, like RG-6.  It is possible for the copper to be so thin that the loss of the cable becomes excessive at 160 meters.

That depends upon the application. A little loss in a TX feedline will broaden the VSWR bandwidth and may eliminate spending $$ on a tuner.

I use CATV hardline where loss is very low and just modify the amp pi network a bit to load into whatever there is, that way I can cover all of 160 and 80 without regard to the VSWR and those added losses are not even worth worrying about. After all the pi net is basically a tuner to start with.

No arcing in the tank circuit has ever occurred either at 1500W. I also modify 10M a bit for the same reason and results.

It is just another reason to stay away from the serious restrictions and extra cost options needed for SS.

Carl
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KL7CW
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Posts: 256




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« Reply #13 on: October 24, 2017, 11:18:06 AM »

Bruce,
    117 feet is long enough (with a 55 ft vertical portion) to be "reasonably" efficient IF you match it properly and have a very good counterpoise or radial system. However I always try and make the total system resonant at or slightly below the operating frequency.  So if reasonably possible I would try to lower the resonant frequency (K6AER has some good suggestions).  A capacity hat at the far end of the horizontal wire is one good option.  Possibly even just something like a 10 or 20 ft wire dropped down vertically may work if it is not right in a tree and if the end is still not too close to the ground...say something like at least 20 feet above the ground is best.  Get a copy of Low Band DX'ing and the ARRL antenna book (available from ARRL, etc.), many good ideas.  Another method often used by 160 meter folks is to use a folded back elements for the horizontal wire (and sometimes even the counterpoise wires if absolutely necessary).  For example if you need 15 feet more wire and have no more horizontal room, you might add something like 20 or 25 feet of wire to the end of your wire and fold it back toward your vertical.  If possible space the folded back portion away from the horizontal wire at least several feet, but it will also work if you need to space it closer...some folks even use open wire line for the folded back portion.  This is just a possible solution, a loading coil somewhere along the horizontal wire may be as good or better than the linear loading (folded back scheme).  Linear loading is not always a good or the best scheme.  One more idea often used by 160 and 80 meter DX folks is to put a 80 meter trap around 1/4 wavelength from the start of the antenna.  The trap will then isolate the 80 meter antenna from most of the horizontal wire.  The trap will have some net inductive reactance on 160 meters, so will act like a small loading coil on 160 meters.  You will get two bands with perhaps some decrease of bandwidth on 80 meters, and only a slight loss on 160 meters, and your horizontal wire acts likea longer wire.  These are just ideas for you to think about, since I do not know what will work for your situation.  One caution...the 80 meter trap must be built towithstand rather high voltages on 80 meters, especially if you run high power.  DXpeditions often use this scheme successfully....do some research...many good designs.

                        Rick  KL7CW   Palmer,  Alaska

         
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KL7CW
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« Reply #14 on: October 25, 2017, 11:43:26 AM »

Bruce,
   I will throw out another crazy idea to consider but is not really my suggestion.  I was considering using one of my 3/16 inch galvanized steel guy wires on my tower for the top (horizontal wire) of my inverted L.  I constructed a test 160 meter copper wire dipole and made field strength measurements.  I next replaced end portion of both dipole elements with guy wire.  The end half of each dipole element was guy wire.  The resonant frequency of the dipole decreased, and I needed to shorten the guy wire cables by ROUGHLY 10 percent to restore resonance at 1.85 mHz.  So the guy wire dipole ends, lets say they were 66 feet, acted roughly like 73 ft wires.  The copper + steel dipole was ROUGHLY 0.5to 1.0 db down from the all copper dipole.  These were all near field measurements, so bring on the flames.  Sorry I did not do better documentation, but the purpose of the experiment for me was just to see if the guy wire scheme was what I wanted to use.  I decided to use another scheme.  My recollection was that the 2:1 bandwidth was ROUGHLY the same.  It is a known fact that the magnetic properties of steel wire, such as copperweld, may begin to have some effect on the lower HF bands like 160 meters which are often not a problem on higher frequencies.  I do not know if smaller galvanized steel wire has similar properties.  I do not know if a loading coil, an 80 meter trap, linear loading, or an end wire dropped down toward the ground would result in more or less loss than the galvanized wire.  For sure I would not use the galvanized wire for much more than the end half of an antenna, since it will carry more current and the losses probably would increase significantly.  If this idea works, you would have a simple strong antenna top wire without loading coils, etc with possibly less than a dB of loss over the full size version.  It is possible the antenna will have somewhat more SWR bandwidth (since there is some loss), however I never wrote down the BW of the two versions....although when I did the SWR scan, I never noted anything drastically different.
    Once again, this is just something to think about, not suggesting it as the best solution for anyone.  I used a good spectrum analyzer and took care to be careful and cross check readings, however I never did far field measurements or used the care I would use if this was a professional paper or even something to publish in a ham magazine. 
               Rick  KL7CW    yes I do operate 160 meters !!
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