KA4KOE Inverted L

[ka4koe]

My inverted L is 145' total length. The vertical section is about 60'. The horizontal section is 85'. I'm working against 6 - 60' radials. I ran MMANA-GAL and came up with some interesting plots.

I can't seem to talk much past the Mississippi on 160m. 80m is not too bad, although the plot looks awful.

Opinions?

PHILIP
KA4KOE

[K5UJ]

you have nowhere near enough radials in your ground system.  You need at a minimum 60.  they don't have to be a full 90 degrees long.  40 to 60 feet is FB.  Of course if you want to make them longer that's fine too.

don't waste your time and money on cheap wire.  Steel, barb wire, aluminum....any such junk will be gone and non-functioning in months or a year or two, unless your earth is dry sand or rock in the southwest.  You need to (unfortunately) spend some coin on copper wire.  No. 14 solid is a good compromise between strength for burial and walking on and ruggedness and economy.  You can and I encourage you, put down more than 60 radials.  Congratulations on a start on a real antenna for 160 but the job is only half way done.   The ground system is the other half of the antenna.   You should see a vswr at the feedpoint of 4 or 5 to 1 with an adequate ground system on an inverted L of your dimensions.   You should notice a difference in performance.  If you have no obstructions--buildings, trees etc. in your ground field and you have the room for a full lay of radials in all directions you are lucky and should take advantage of it.  

nay sayers will say this is all overkill--they are only trying to justify their own lazyness and thrift.   I have yet to hear a strapper with an inverted V or a chain link fence "ground system" on 160.   I've heard a lot of piss weakers with antennas like that though.

what kind of feedline are you using?  tell us about your matching network.  You'll need a separate receive antenna once the inverted L is working well.

rob

[kb3ouk]

I'll look for it tonight, but there's a chart in one of the lowband DXing books that shows the optimum number of radials depending on their length (meaning that having more radials of that length over the number given does not improve the performance any). If you don't want to add more radials but have the room to elevate them, move the feedpoint up about 10 feet and lengthen out the horizontal part so that now the vertical section is 50 feet and the horizontal part is 95 feet, and keep the radials about 10 feet above ground.

[ka4koe]

Matching at the base with a remote tuner. The tuner is fed with RG-8 double shield "bury flex" from the Wireman. I started rebuilding the radial field since the xyl K4SMN destroyed the last one with her John Deere.

It will be difficult to get that many since we have a lawn/backyard that the xyl is proud of.

I used No. 12 AWG stranded for the radials, insulated. I live fairly near a swamp by the coast so I'm assuming the conductivity is decent (Richmond Hill, GA).

Lightning ground is provided by 3 - 10', 3/4" copper coated steel ground rods driven around the tree the L is strung from. They are interconnected with No. 4 AWG solid CU, and then to the system ground.

The vertical portion of the wire does NOT run against the tree. It actually slopes up at about a 10 degree angle away from the base and is suspended about 10' away by a pulley/halyard line and dacron cord.

[kb3ouk]

Just curious, you say you can't talk any farther than the Mississippi, how much power are you running?

[ka4koe]

100w carrier.

Correction. I can talk further. I had a qso with Washington state on AM awhile back. This was after I fixed my antenna.

Ran some more sims using dielectric soil constant of 13 and conductivity of 8 ms/M (AM BCB map, FCC) 6 radials gives 2.57 dBi. 60 radials gives 3.4 dBi. 120 radials gives 3.6 dBi. These are all vertical dominating polarization.

Once you get the hang of MMANA-GAL, its actually cool. Don't know if its accurate.

PAN

[kb3ouk]

Looking at how close you are to the coast, you're probably putting out a good signal towards Africa. I've done propagation modelling for my station using VOACAP, and even as far inland as I am, on 75 meters there is a large lobe out over the ocean, and that's with a dipole.

[kb3ouk]

Ok, here's that chart I was talking about earlier. The book says for a given number of radials, there is a corresponding length where radials beyond that length do not give a noticeable improvement.

# of Radials          Optimum Length
4                         0.10 wavelength
12                        0.15 wavelength
24                        0.25 wavelength
48                        0.35 wavelength
96                        0.45 wavelength
120                       0.50 wavelength

So according to the chart, if you figure for numbers in between, your six 60' radials are just about right. At 160 meters, the .10 wavelength radials would be 49 feet, and the .15 wavelength radials would be 73 feet. And looking at your modeling, 60 radials only gives you less than 1 dB over 6 radials, which is not noticeable on the other end. You would get the same effect just by bumping your power from 100 watts to 125 watts.

[ka4koe]

Miss Sheri K4SMN will be glad to hear that I won't be tearing up her backyard anymore.