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Ham Radio - The 75/80 meter fan dipole experiment. The final word.
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- čas přidán 24. 10. 2019
- As promised, I put the experimental antenna up one last time, to answer a question many posed.
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Thanks for the experiment Kevin, theory and practice is different so good to see this in action. This is what our hobby is all about.
I invented an antenna I call the Pyramid Antenna: It's two inverted vees at 90 degrees to one another and fed by the same feedline at the top, and that sort of looks like a pyramid. One wire pair is designed to resonate at about 3600 kHz and the other pair, at right angles to the first, resonates at around 3900 kHz. It does exactly what you want: below 2:1 SWR across the entire band; and, as long as you get it up 45 feet or more, it's nice and efficient. It also has the advantage of being much nearer to omnidirectional than a conventional dipole or inverted vee, because all the elements radiate to some extent, even the ones with less current cut for "other end" of the band, thus filling in the nulls.
A J-Pole is 3/4 wave, a half wave radiator with a quarter wave matching stub at the bottom, fed at the bottom of the matching stub, looking for the best match.. BTW I built a folded dipole for 6 meters out of ladder line and it works great. 73, de N4QM
As always, thanks for bringing us along on your experiments. I always learn something, and it's easier and cheaper than doing the experiments myself!
Kevin, I used to go to a field day where a guy used to build HF j-poles out of 450 ohm ladder line. We used to hoist them with a baloon so they would act as a vertical dipole. I seem to remember that they picked up a lot more noise than inverted v antennas though. I look forward to seeing what you find out.
The height of the center feed and the ends is making the antenna a NVIS array. Works great for 300 ish miles or so.
Great video Kevin. Glad you made it back to the desert safe and sound. Hope I get over there for Quartzfest this year. Take care...be safe. JJK
Yo Kevin!:
GREAT video. I'd like to see a 20 mtrs j-pole! Keep up the experimentation. Hope you got my update in e-mail. Motor on guy! 73's
de seeker/Jeff
You should try separating the 2 antennas about a foot at the end.
Have you thought of using a Bow Tie antenna for a wide band antenna.
Long wire EF balloon antenna or kite antenna next ?
one thing that would have helped .
Drop the ladder line and use thin gauge wire like 18ga , use zip tie material as for spreaders this will lighten the overall weight, or better yet just drop the spreaders altogether . I understand that your wanting to to make it portable and quick to deploy , but really, how hard is it to simply unroll four 60+ feet of wire on four small separate rolls really ? 60' of 18ga will roll up on a tiny reel.. this also gives you the opportunity to angle the bottom antenna offset from the other .BTW I've learned from experience that you tend to get better results when you have the longest antenna on top . 73, and Happy Rag chewing
I too would like to see a 20m J-Pole or Slim Jim if you have the time, Kevin. I built a 10m Slim Jim back in the Spring, the base is up around 10m high. Really great antenna for DX. Keep posting!
I think, the J-Pole Antenna is completely about a 3/4 Wavelength (Lambda) long. But the Part of the Antenna, that actually radiates ( at least, it should be the only Part that does that.. :D) ) is about 1/2 Wavelength (Lambda) long. The "Matching" Section of a J-Pole is about 1/4 Wavelength (Lambda) long. And at least to me, that Part that Feeds the Antenna looks "symmetrical" to me. Because it is something like symmetrical "Feed-Line". But People seem to feed that Antenna Type mostly unsymmetrical.. :D (directly with Coax Cable). That could change something.. And done this Way, maybe Parts of the J-Pole Antenna radiate as well, that should normally _not_ radiate at all.. :D
I would love to see a 20 meter J pole. Thanks for your videos.
A j-pole is essentially a half wave antenna with a quarter wave matching stub. 3/4 wave of window line should about do it.
I have seen a cage dipole used to try to get 80 and 75 on the same antenna. I think that is in one of the old ARRL Antenna Books.
the wires are probably too close together (too tightly coupled). looser coupling should smooth out the pair of resonances. how practiced are you with antenna modelling (4nec2, for instance)? have spare wire and spacers (monofilament or paracord bits) to make a wider spaced 'fan'?
I wonder if it would work if you cut it 80 & 40 or 40 & 20.
My fan dipole works very well across 80 (incl 75), 40, 20, 15, 10m without any tuning required, also all the other HF bands and 6m with some help from a tuner. See my comment on an earlier part of this series for details.
Good to know. Where did you find the design?
@@mrtechie6810 I just made it up after thinking about it for a bit and looking at other designs. It took a bit of trimming to get it to resonate on all planned bands, but with 48 wires and a bit of time that wasn't to hard.
The surprise was that it worked so well on other bands, although 6m was a bit of a struggle
Hi Kevin, Great job with the experimenting. What about using 600 ohm ladder line with a 3.5" spacing? 73 WB3BJU
Looking forward to your next video
Thanks Kevin for giving that a try. I figured it would make a difference but didn’t know what to expect. I haven’t studied Fan dipoles yet but wonder if they need to not be parallel.
They are referred to as a fan because they are in parallel. The typical design is based on the separation of resonant frequencies. Mine has 40/15, 20, and 10.
Correction, fan because of construction, the legs fan out. But the multi band part is as described. Just like feeding multiple resonant ham sticks from a single coax.
Enjoyed the video but I'm looking forward to see you set-up the Chameleon mag loop with and without the "snake oil" out in the desert. By the way the temperature in Rockport dropped like 20 degrees immediately after you left.
Thank you so much, I have problems with anything bellow 30 meters. I will try it out and see if this dipole will give me at least one contact other then my friend down the street, 73s
You muffed it, your short leg is under 3.7 MHz, it should be at least at 3.9 MHz.
The two ends of dipoles are capacitively coupled together as was that short floating section, the wire is the inductor for a tank circuit. You could have just removed the wire and left the plastic.
Fan dipoles do not work well with under four inches if separation at the ends. (more is better)
Ron W4BIN
NVIS
I have learned a lot from watching your videos. Sorry the fan dipole experiment did not work; logic doesn't always apply to electronics I've noticed. I thought it was a good plan. I have a Chameleon EMCOMM III and I assume it has a similar toroid to the ones you used for your outside box as it is resonant on lots of different bands. Oddly, it does better on 75/80 than it does on 40 meters, which makes no sense to me. But I love the EFHW type antenna. I live in an HOA environment, and the wire disappears against the trees. Please keep showing us your work. I'm NOT a tech guy, but I have learned enough from you to at least attempt an antenna build. I'd do a video of that, but there's probably enough comedy on CZcams already.
This is 720p. Nice detail in the picture
No go back to the UNUN driving a long wire antenna as anything else won't work.
Add a third wire splitting between the lengths and see what happens. Just a piece of magnet wire will do...
Kevin, may I ask what camera you are using for this video????
A Nikon p900 and my cell phone for the outdoor stills.
Instead of having the two wires for 75/80m so close and parallel to each other, have you thought about putting up two dipoles (one for 75m, one for 80m) with some more significant angle between them? AB2RA has an article about her experiments with this arrangement; separating them in a fashion similar to a bowtie antenna, with something like a 45-60 degree angle between the 75 and 80m elements, will decrease the SWR across the band (in her case, less than 2:1 pretty much everywhere). wireless-girl.com/Projects/Antennas/Broadband80mDipole.html
Try using 4 separate lines not closely connected. Take the 2 dipoles and make an x out of them, basically one dipole east/west and one north/south connected at the same center point. Would be an interesting experiment.
Thanks for following up the experiment Kevin. 20m J-pole would be interesting. I have used window line to make J-poles for 70cm, 2m and 6m. All work just fine. I have thought about a J-pole for 20 - the attraction being that, although a quarter wave longer than a regular dipole, it is essentially end fed (without having to use any matching components). Though a 1:1 balun or current choke may help if co-ax is being used as feeder. Shame the 80m dipole didn't quite work as planned but it was interesting to give it a try - thank you.
Good...mr.......?