HFU HF Underground
Technical Topics => Equipment => Topic started by: Matt285 on February 12, 2019, 1258 UTC
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I don't have the space for a beverage antenna and have been thinking of building a full wave dipole cut for 49m. Does anyone have experience with this type of antenna? Any feedback would be helpful. Thanks
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Is this for a receive application? Or is it transceive?
I have played with longer dipoles, full wave and longer than that. In general, I see little reason to go with a full wave dipole over other types of antennas. Particularly so if you are going to feed it with coax.
A half wave dipole exhibits a slight null off each end, but a broad beam perpendicular to the element. The classic broad toroid (doughnut shaped) radiation pattern. Pretty predictable and easy to visualize while setting the antenna up. The full wave dipole, or two half waves, has a couple dB gain over the half wave dipole, but at a cost.
There ain’t no such thing as a free lunch, so that slight gain has to come from a changed pattern shape. What I have found is that the full wave dipoles I have built exhibit a bit of a null perpendicular to the element, and a bit more gain at an angle. Think of it as a roughly butterfly shaped pattern, a null at each end and a slight null on the broadside.
I have found it harder, compared to other wire antennas, to place full wave dipoles in orientations that take advantage of the pattern shape. For example, a terminated long wire (a beverage) of the same length works, roughly, in a cone towards the terminated end, and I have found it easier to place them, for example allowing one lobe to point towards the polar path, while the other is towards Africa, or something like that.
And then there is the operational bandwidth. In my experience dipoles fed with coax (and with or without a balun) tend to be narrower banded than the same lengths end fed with coax and a balun. But, a full wave dipole fed with ladder is more forgiving.
I guess the question comes down to what do you hope to gain with the full wave dipole, vs a half wave dipole, that cannot be done with an end fed full wave?
If you are looking for a little gain, what direction / directions are you looking for gain? If you are looking for gain in specific directions, have you considered a V-beam or something like that?
T!
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Forget a full wave it wont work, well it isn't low Z at the centre so you cant feed it with coax (could feed off centre like a Windom).
ANY odd multiple of halfwave will however altho' no idea why you should bother?
3/2 will give a clover leaf pattern and work on 3 x f too so a 7MHz 3/2 dipole will work on 21MHz too.
Just stick to a regular dipole.
If you want gain use parasitic elements with a Yagi or Quad design.
If you want a decent (omni) vertical use a Delta loop fed 1/4 wave from apex.
Str
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Thank you for your detailed responses. Yes it would be receive only. Just trying to think of some options. I'm about to install a new 135' OCF dipole for for general HF use. That should work a bit better than my current 40m dipole at low height. I was planning on leaving the coax run in place for a receive antenna in the future. The new antenna will be a shorter and closer run. Thanks again!
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Obsessive Compulsive Fed Dipoles often display a low swr every other MHz or so. I always say just determine the site for the antenna and fill that space with whatever length of wire will fit, then use a transmatch to extract the most signals from it if you feel. Also consider a linearly loaded dipole, aka the cobra;
https://www.kb6nu.com/yet-another-new-antenna-the-cobra/
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Hi Matt.
Full wave length Dipol not work easy.
If you got the space for a Dipol for 48m Band, think about a G5RV Antenna, two times 15,5m element and arround 10m of open ladder feedline.
At the end of the open ladder feetline you conect maybe your koax an go into you shack.
No tuner needed if you Receive only and this antenne will work from 80m Band up ...
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Believe me, the Double Extended Zepp works for both listening and transmitting. They're a pure pain in the ass to maintain, but they do work. The ladder and TV line you feed them with that feels like nothing in your hand? It catch a lot of wind and like to dance around.
MFJ sells them for under 80 bucks, built. They look fairly rugged. This may be one of the few times I've ever advised someone to buy an antenna instead of building one. I'm so ashamed!
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I actually had a G5RV in a sloping configuration back in 08/09. Worked a fair amount of DX on it. Even on 30m it seemed to perform fine. Antennas are always an interesting topic of debate. People tend to have very strong opinions about them. Thanks for your reply!
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https://www.w8ji.com/folded_dipole.htm
cough