EDIT: Inverted L antenna... read on

[Robot Matrix]

So, after figuring out that my mobius loop antenna needs a preamp, I decided to build an end fed antenna in an inverted L configuration.

I had some random toroid and wound around it 10 times with spare CAT5 wire and hooked it up with the diagrams I found online. Some schematics showed to put a 100pf capacitor between the feed point and ground, and also have ground radials below the feed point, which I just used my backyard fence for that.

It WORKED!

Here's some of the diagrams I used...

and

[RobRich]

You might also checkout a end-fed half-wave if you want to target a specific band (and its harmonics). 49:1 and 64:1 are popular unun ratios to try.

Awhile back I deployed a temporary ~7MHz EFHW horizontal mounted a few feet off the ground more or less for NVIS reception. It works decently for the usual 43m pirate band with just a Tecsun PL-330 or ATS-20+ receiver for some background radio on the back porch.

BTW, while currently out of stock, eddieson (KG6ZBN) on eBay often has EFHW end-fed transformers for ~$15 shipped. The designs are subject to change, but the link is usually:

https://www.ebay.com/itm/303563418877

I have had good results with his various EFHW transformers, and the price is quite decent compared to DIY unless you buy the various parts in bulk.

[Robot Matrix]

You might also checkout a end-fed half-wave if you want to target a specific band (and its harmonics). 49:1 and 64:1 are popular unun ratios to try.

Awhile back I deployed a temporary ~7MHz EFHW horizontal mounted a few feet off the ground more or less for NVIS reception. It works decently for the usual 43m pirate band with just a Tecsun PL-330 or ATS-20+ receiver for some background radio on the back porch.

BTW, while currently out of stock, eddieson (KG6ZBN) on eBay often has EFHW end-fed transformers for ~$15 shipped. The designs are subject to change, but the link is usually:

https://www.ebay.com/itm/303563418877

I have had good results with his various EFHW transformers, and the price is quite decent compared to DIY unless you buy the various parts in bulk.

I neglected to mention the antenna was an inverted L. The horizontal part (about 30' long) acts as a capacitance hat of sorts. And since the horizontal part of the antenna is about 20 feet up, I DO benefit from NVIS on the 160m-40m bands. I've logged numerous hams talking within 400 miles of my location with ease in the morning and after dark, as well as pirate broadcasts if their signal is propagating my direction and with enough wattage.

I initially made a few mistakes with it, like not having the feed point low enough to the ground, below 3 feet (which I still need to move it lower).... and also to put my 1:1 choke (current balun) outside just below the feedpoint rather than inside by the radio. Made a HUGE difference. I just keep reading and reading about it and make adjustments. The only thing I can't really do is to change from the unun to an antenna match... because that would make the antenna tune to a very specific range, which defeats the purpose of having an antenna that receives fairly well from 1.8-29MHz. In fact, I'm really surprised how well this works on 160-40m. I can hear the OG's talking in the morning to each other as well as after sunset. Does GREAT on 20 and 10m during the day, which its very quiet on. Also picks up the AM BC band really well day and night as well as the MF WSPR freq.

Unfortunately, I don't have a pure DC supply, so at LF there are lots of harmonics and makes it difficult to receive NDB's and whatnot. I plan on fixing that in the coming weeks with a homebrew DC supply schematic that I found, which would work perfectly.

Tune in sometime and check it out: http://75.134.33.242:8073/

You'll see all the noise from the switched mode power supply on the low bands, but its not bad further up except on occasion with some harmonics. Eventually, I'll hook it up to my Lifepo4 battery, with the voltage regulator, and it should last for at least 30 days straight before draining the battery, and all those spurs should disappear.

I will do some research on the 49:1 and 64:1 ununs. I might have to get bigger toroids to wind that since I wind them all myself and build and cut my own antennas.

[Robot Matrix]

I made a HUGE mistake. Up until the day before, I've been having big problems with noise at different times of day in different bands. After quite a bit of DD, I realized that I cannot use a 9:1 unun with an inverted L. Unlike the feedpoint of an end fed horizontal antenna, which is WELL above the ground and has an impedance of at least a couple thousand ohms, the inverted L's feedpoint is at or near the ground... making the feedpoint impedance MUCH lower... so you don't need that unun! I don't know how I overlooked this all this time!

Solution? I removed the 9:1 unun, left the current choke in place at the feedpoint, and hooked the antenna up directly to the coax... with the fence and radials connected to the shield. WHAT A DIFFERENCE!

Last night,  I picked up lots of pirates with an S3 level of noise instead of S5 or more. BIG difference! So picking up an S5 signal with an S3 noise floor gives me 2 S units of headroom at a minimum. Made all the difference in readability without question.

So... being that the vertical part of the antenna only goes up 20', and the horizontal part maybe another 40', that's only 60' total. Which is fine for somewhere between 3.9-11.7MHz as a rough 1/4 wave. But a big problem if I want to tune lower.

Now that all the snow and ice is melting here, I'm gonna climb the trees and elevate the antenna height another 20' and add wire for horizontal length, but that still puts me somewhere around 2.6MHz at the very bottom of a 1/4 wave above ground (electrically). So, I've opted to include a tapped, base loaded coil, wired in series with the antenna, where I can tune the antenna, on a whim, for the band I want to hone in on.

If I want to tune to LF or below,  I'm gonna need A LOT of wire. But so far, I can still tune in to the 400-500kHz WSPR and navtex signals. WWVB and the Navy signals are still really good,  and a few NDB's.

Gonna order an Amazon special LC meter soon and eventually a Nano VNA of some kind. I DO NOT like buying antennas if I can make them myself.

Anyway,  stay tuned!

[RobRich]

Impedance increases as an antenna becomes a very tiny fraction of a frequency's wavelength.

Depending upon the core material, transformers for HF can act differently at low frequencies, thus the ratios can be a YMMV situation at longwave and similar. I often opt for mix 73 for low frequencies, though it tends to suffice for most basic receiving applications to 30MHz and sometimes higher.

I use a LDG 4:1 unun (mix 43 perhaps?) on my 31' vertical, and it works fine from longwave to upper-HF for receiving. I have tried various homebuilt and commercial transformer over the years on it. It more or less finding a decent compromise if going for a wideband 0-30MHz antenna.


Alternatively you could opt for a preamp at the feedpoint to deal with the impedance mismatches.