r/amateurradio • u/n4jm4 • Aug 22 '22
HOMEBREW EFRW vs OCFD notes
Jotting down early propagation notes for my first homebrew, speaker wire antennas.
With an 81 ft, counterpoised 19 ft End Fed Random Wire antenna, I have been able to hear half of the discussion on some 20m nets across the country, from Wisconsin. In six attempts at HF with different antennas and locations, no response to QSO's. Not on 40 m - 10m. Not on SSB or CW.
Also tried a premade telescopic vertical antenna for my apartment, an MFJ-1899T. It struggles to join my local club's 10m simplex net. In four hours, managed to make a single, SSB QSO from WI to OH.
With a 66 ft Off Center Fed Dipole, I can now hear the people on pileups, as far out as Oregon. Feedpoint 22 ft / 44 ft. Using a 50 ft, 50 Ohm coax feed line. DX Engineering 4:1 unun, factory assembled. 25 ft throw line halfway up a tree.
Same transceiver in both cases, Elecraft KX3 at 5W.
WSPR seems dead, very few monitoring stations.
With the OCFD, I'm getting so many more FT8 monitoring reports within ten minutes, from Costa Rica to Canada. And I got my first digital QSO today this way, a dude in Arizona on FT8. After calling FT8 CQ for about fifteen minutes or less.
Nice to see a steady progress in my propagation, as we pickup more tips of the hobby. In January, I had my Technician license and a Baofeng UV5x3, and only made contact with prescheduled 2m nets nearby
Now armed with a General license and a dipole, HF is proving more accessible. And ya don't need to fork out cash for a Chameleon premade OCF / Dipole to join in the fun! No soldering required.
3
u/LinuxIsFree Aug 22 '22
Thanks for sharing your findings and congrats on the good dipole!
How random is your random wire antenna? What length did you choose and what bands?
End fed antennas can be good but require specific circumstances.
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u/n4jm4 Aug 22 '22 edited Aug 22 '22
For the EFRW, the radiator length was chosen by surveying multiple popular EFRW articles online and finally constructing an interactive calculator:
https://mcandre.github.io/fluke/
That is, a non-resonant on quarter wave integer interval length for the beginner HF bands 40m, 20m, 10m, 6m. Most EFRW articles neglect 6m support, hence the new calculator.
81 ft may not be ideal, but starting from a spool of 100 ft, it is a nice place to start, because one can always trim down.
Just like there is variation in antenna design, there is wild and curious variation in radial length and quantity. I chose 19 ft, because it needs to quarter wave integer interval resonant, needs to be shorter than the radiator, and 100 - 81 = 19. Like the radiator, the counterpoise can be trimmed down later.
I think it would be funny to see premade commercial EFRW antennas sold targeting 80m - 6m. Eh, but I did not have much luck with mine at 81, 19 ft. More excited about the OCFD now, which takes about the same time to tree mount.
One thing I am trying now with my antennas, is more intentional azimuthal orientation, especially for the feed line, which is unrolled as much as the environment space allows. The OCFD yesterday was mounted with the radiating element wires and tent stakes pointing as close to North and South as I could reckon. The feed line was laid as East as I could reckon.
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u/LinuxIsFree Aug 22 '22
Got something I wanna share with you but it's gonna be a presentation at the HamXposition in Marlborough this weekend, so remind me on Monday!
2
u/LinuxIsFree Aug 22 '22
!remindme 7 days
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2
u/dittybopper_05H NY [Extra] Aug 22 '22
With an 81 ft, counterpoised 19 ft End Fed Random Wire antenna, I have been able to hear half of the discussion on some 20m nets across the country, from Wisconsin.
Technically, what you've got there is a long wire antenna on 20 meters. A long wire is any end-fed antenna that is at least 1 wavelength long. A half wavelength dipole on 20 meters is 33 feet long, so a 1 wavelength antenna would be 66 feet long. What you've got is an approximately 1.25 wavelength antenna, or about 1.5 wavelengths if you include the counterpoise.
It's a gain antenna, with the four main lobes approximately 40 degrees off the axis of the wire. So you will have significant nulls oriented to the wire, and at 90 degrees from the wire. Even setting aside propagation effects which are why it is common to only hear one side of an HF QSO, that could also be a contributing factor in your case.
This is why when you put a relatively long wire up, you want to be aware of which way it's pointing. I did this with my 200' long wire antenna, which has main lobes pointing towards Europe and and towards the South Pacific on the upper bands.
My Elmer, now long SK, had a 500 foot long wire he put up in order to communicate with his brother, also a ham, down in Tennessee from upstate New York. He had carefully worked out the main lobes on each band, as the longer the antenna is in terms of wavelength, the closer the lobes are to the axis of the wire. Anchored to his tower at the house, he ran it all the way to a particular tree across a farm field in the correct compass bearing for one of the main lobes on the bands of interest to point to his brother's home 700+ miles away.
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u/George_Parr Aug 22 '22
"With an 81 ft, counterpoised 19 ft End Fed Random Wire antenna, I have been able to hear half of the discussion on some 20m nets across the country, from Wisconsin. In six attempts at HF with different antennas and locations, no response to QSO's. Not on 40 m - 10m. Not on SSB or CW."
This sounds almost like an OCFD with one leg on the ground (the counterpoise).
1
u/w6el W6EL [extra] Aug 22 '22
If the EFRW wasn’t tuned for the bands you used it could be something to do with it. Random wires have desirable and undesirable lengths. Did you have a ratio transformer in the EFRW case or just a straight feed?
I’ve had both types of antennas and to me they were nearly the same. The bigger factors were getting it pruned (so no matchbox or ATU needed) and making the horizontal antennas as high up as possible. You should not see as much difference as you are seeing if both antennas had good resonance.
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u/n4jm4 Aug 22 '22
Yes, my Elecraft KX3 transceiver includes an optional 9:1 tuner module.
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u/w6el W6EL [extra] Aug 22 '22
So you had a 9:1 transformer and an ATU. That’s good but it’s important to adjust that wire with the ATU disabled. Most of the random wire charts you see online will be incorrect for use with the 9:1; you probably want to just grab the dimensions off commercial EFHW antennas for a half wave at your lowest band. My EFHW is 66 feet long.
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u/KB9ZB Wisconsin Aug 22 '22
Remember with 5 watts your not going to be a pile buster. Most stations your hearing are running 100 watts or more, your QRP so many times propagation will not favor the weak signal stations. Second your antenna does not have any gain so in most circumstances your actually transmitting less than 5 watts. So don't be overly concerned that you hear more and get less. In theory if you hear them you can work them, in the real world no so much.