160 Inverted L Antenna – by N4JTE.
Between watching unending Law and Order repeats and the XYL’s Lifetime movie sagas, compounded by a dead 40 meter band here at night, I became so totally bereft of late night activities that I got the bug to get back on 160 meters again with something that would fit in my backyard. I have had, in previous QTH’s, the luxury of a full size 160 dipole, those were the days.
Well, 240 plus feet at any reasonable height is beyond my backyard limitations as I am sure it is, along with many of you. The 160 band is to me, a throwback to my AM and SWL days as a youngster when I would lay in bed at night with my crystal radio and listen to all the AM broadcast stations I could discern and check them off on my Knight’s Radio Log. Those days, are to me, the genesis of my love for the magic of radio, some of those AM stations are still legendary! Enough nostalgia.
I wanted to get back on the band with a respectable signal and try out the much discussed and prevalent 160 inverted L antenna. Previous to the inverted L, I tried a few ideas, some of which I am sure others have attempted also.
1; 80 meter dipole, coax fed. Whew, lucky I did not burn something up, I know why it stunk but there are still some out there that figure if their good old trusty tuner loads up and somehow a length antenna seems too work on 160 they are good to go, NOT! Besides the neighbors getting tvi, your tuner and feedline were probably contributing to global warming.
2; 165 ft. 40 edz at 60 ft. ladderline fed. I really thought this antenna would work as its only 60ft. short. The fact was that my 3kw tuner told me that with anything over 100 watts, I was dreaming, as Christmas came early with all the flashing lights inside the tuner.
3; The good old G5RV with the shorted feedline and ground plane approach. I’m sure I remember a contact or two on a quiet night but pretty lame imho.
160M Inverted L .
There are a lot of 160 designs out there on the internet with quite a few adding coils etc to match shorten verticals, or top loading with various configurations. My feeling is that the coil losses and tricky matching problems with top loaded wire antennas make the inverted L the way to go for simplicity of construction and relative ease in matching 50ohms.
The inverted L is what it is; picture your Hamstick or any vertical and bending it 90 degrees halfway up and expecting some improvement over a nice simple straight vertical. Let’s be aware of the physics involved and keep our expectations within reality.
But: That’s the mystery and fun unique to the 160 band, anything that approaches a well thought out antenna, even in a restricted place will compete well. The really big guns with the phased 120 ft towers and 4000 buried radials only show up for the contests. The rest of us peons have a pretty level playing field when we are content to work a new state or keep in contact with friends around the country, with the occasional DX station popping in to say hello.
The best I could do here was to get the old trusty 2oz weighted fishing line over my now bare 65ft. maple tree. Hobby money is tight here so I scabbed together 120 ft of insulated # 14 wire form previous endeavors and pulled back some masonry line. Taking care to keep the ends from tangling, the string was attached to the 60 ft. midpoint of the insulated wire and hoisted up to the top of an outside branch on the tree with the feed point end about 6 ft. off the ground.
Because I had nothing better on first thought and it was getting dark I ended up having to slope the remaining 60 ft. to a tie off point in the backyard which resulted in the end at about 10 ft. off ground. I hooked up two raised insulated radials at 120 ft. long each and hung them up at 6ft. high along the wood fence. Definitely not as symmetrical as I would have preferred with some zigs and zags thru the available branches etc. but ran them at 180 degrees from each other. Be advised there will be a lot of voltage on the radial ends and make a supreme effort to isolate the ends from any human contact.
Not bad, first of all the amp, AL80B, was finally showing some life and providing 400 watts indicated. Reports were good from local to 1500 miles out but the S/N, noise was horrendous, so I figured it was time for some improvements.
Well, I was happy to be heard and the amp and 3kw tuner were silently applauding my work so I figured lets work on the noise situation. I figured out a way to get the horizontal portion over a nearby tree at about 45 ft. high, and try to get closer to a flat top configuration, but unfortunately it is only about 40 ft. away. End result was that the last 20 ft ended up coming down in a vertical direction to the tie off point, sorta ended up with a skewed inverted U configuration.
Voila! Ended up with a relatively flat 1.5 to 1 on 1865. I know that can be misleading, especially when using a bizarre shaped vertical, but it works. See note #5 in final comments.
1; If you are in tight restricted environment, the inverted L will get you on the air with a respectable signal and good match to 50 ohm coax.
2: Yes it will be noisy in an urban near field environment; I use my 40 meter antenna as a listening antenna when my local noise competes too much.
3; I placed a 1 to 1 current balun at the feedline junction; I did not see any significant noise reduction.
4; From talking to other Hams more advanced and experienced with the 160 inverted L, I found a few that liked the 3/8 wl configuration as it moves the current point further up the antenna and improves efficiency beyond the 28% we can expect from the inverted L. However I believe the 3/8 configuration is adding more horizontal polarization as a trade off for better efficiency which is fine if your interests are more in line for closer in contacts. I don’t see any major signal loss on close in stations but the inv L definitely shows it’s worth beyond 800 or so miles, (whose counting ?) as compared to a 165 ft. flattop at 60 ft.
5: If you build it, I offer the following insights from my experiment. Going the raised radial route is the only way I could consider this or any vertical design with my rocky conditions, your mileage may vary, but read up on them. If you do use raised radials make every effort to run the feed line away at a right angle if possible, mine isn’t. As mentioned, a 1 to 1 current balun is a big MUST; it will reduce any stray induced current on the coax shield.
My MFJ analyzer indicated 40 ohms resistance and about 1.2 to 1 swr. Anything way above or below that number should tell you that your ground plane is inadequate or you have common mode current problems. To achieve your best match, prune the horizontal section length.
Lastly, the hard part, try to make the vertical section as tall as possible and if you are concerned with a DC path to ground while using elevated radials, throw a choke between the coax shield and the ground rod or equivalent. Do not just hookup the coax shield directly, unless you like talking to worms.
FINAL FINAL COMMENTS:
The setup as laid out in this article is working than better than expected and has reawakened my appreciation for the challenge and fun to be found on the 160 meter band. It is noisy at times here in upstate NY with my backyard surrounded by commercial businesses and transformers for the extended care facility 100 ft away, (there, but for the grace of God go I) so I use my flattop 40 as a backup receive antenna when it gets too annoying.
Try it out, the inverted L is as cheap as it gets and will give you a horizontal and vertical sky wave easily matched to coax. Definitely more entertaining than the Lifetime Channel!
Don’t forget; 160 meters separates the men from the boys, see you there!
Tnx for reading,