Fan dipole 40m/15m questions

If a fan dipole has a 40m element and a 15m element which one radiates when operating on 15m?

If they both radiate, do they both radiate equal amounts of RF or does one perform more grunt than the other?

I ask these questions because I have been looking for the answers for a long time and have had no luck. I have had one person who appears to be knowledgeable tell me that they will both radiate, but no further explanation to why or how or how they may effect each other etc.

From my own experiments I have found that having both elements attached improves the receive on 15m over having just the 15m or 40m attached. Actually radiating a signal though, I have no idea on the effect. Does anyone know the answers, not personal theoretical ones (I have lots of those of my own ), something definitive in writing somewhere that I haven't managed to find through my own searching?

Thanks

I think that normally only the resonant element radiates, mainly because it presents the best impedance match to the feeder. 

That situation becomes a bit fuzzy in your case as 21 is the 3rd harmonic of 7. You could probably dispense with the 21 element but may require an atu?

Best guess is they radiate in proportion to the impedance each element presents. I have no proof of this however

Yep, could definitely dispense with the 15m element. The 40m one with a little adjustment would cover operation on 15m. I have read notes from years past that have given instruction not to inc a 15m element in a multiband dipole antenna which has a 40m one a part of it. But nowhere says why, other than the obvious which is that 15m is covered already.

In my setup I had elements for all bands from 10m to 20m inc 11m, and 15m was working very well. I knew the theoretical RF pattern that was being projected from it. I was a little worried about adding a 40m element because I was unsure how it was going to work with the 15m one. That and the 40m legs would be zigzagged around my small loft making the efficiency far from optimal on 40m, and if that element would be doing the radiating for 15m, it probably would not be optimal for that band either. I have finally added a zigzagged 40m one, and luckily the whole setup is working as I am making contacts on 40m and 15m. Great! But, I would just love to know for sure which bit of the antenna is doing what now. I just don't feel comfortable with it working and not knowing why

Hi Neal,

My own fan dipole array in the loft came about after remembering an old Ham friend from my childhood, (many years ago!!), who had such a setup much to the apparent bemusement of his radio colleagues. This idea does resurface every now and then and can be seen in the following article :-

http://www.qsl.net/g0kya/multibanddipole.pdf

Seemed ideal as I have a large loft and wire is cheap. (Unless you pay a company to cut the lengths for you!  )

I set this up years ago luckily before I became disabled for SWL activities and due to the use of discarded/surplus domestic mains wire I was able to press it into transmission use too. (With a homebrew Pi-Network ATU and RG11 feed.)


I had similar issues and questions until I came across 'Wireless Girl' AB2RA Janis and several of her articles. Her work with fan dipoles can be found here :-

https://wireless-girl.com/Projects/Multiband-Dipole/

But the main crux and as you have stumbled across already is the 40m/15m question which she explains eloquently here :-

https://www.wirelessgirl.net/Projects/Antennas/4015mDipole.html


Often as with many things we question 'conventional wisdom' now and then to find less than ideal if any suitable answers. Sometimes it's just a case of 'accepted wisdom' more than anything due to history or how many times it's printed.

Is it ideal? 
Well, I'm still testing the transmission abilities but it has already proved itself exceptional as a SWL antenna and on my lowly 10 Watts I've had no issues. It's high up, fires through the tiles, (even when raining  ), and best of all totally hidden so gets no disconcerting gazes from neighbours nor suffers weather damage. Flipping inexpensive too!

I had over the years started to pick up more noise thanks to modern electronics but the addition of a common mode choke eradicated that. So successfully that even my wife's hairdryer doesn't disturb a SWL session anymore!

Luckily I'm not firing hundreds of Watts through it or chasing 'rare' DX nor 'software modelling' it or even have the time to argue, ahem, discuss it ad infinitum. Antennas can be the proverbial 'quest for the holy grail' and I haven't enough years left for such adventures. It works admirably for my needs and I can fire up everything from 160m to 10m including WARC bands.


As always I wish you the best with everything you do Neal, but I've always enjoyed reading about your antenna adventures.

All the best
Victor

And there is the answer Victor, I think anyway. Links I have visited previously, but clearly have not read properly.

I have read the bottom section of the "40 and 15 Meter Dipole - a Myth Exposed" writeup a few times now. Although not explicitly spelled out in the wording I was searching for, I am understanding the 15m resonant element is doing the work on tx for 15m, and 40 for 40. Thank you.

I would disagree with her about the statement "the reactive effect of the 15 meter dipole ruins the performance of the 20 and 10 meter dipoles". My 15m element has been in place for a quite a while now. 10m works just as it should, especially for this time of year as per the weekend contacts posted in the HF Contacts 10m thread, and 20m seems just fine too whenever I do go on there. Maybe it's down to the way I have the elements spread out. Pinching the diagram from the multibanddipole pdf, my 40m wires are like the red and blue ones not as per the original diagram..



plus there's more wires for 15 and 12.

Thank you (thanked) again though Victor  I am glad I reread these. Satisfies me for now  and if anyone else is thinking to make such a stealth setup I can heartily recommend for the receive side of 15m. tx aside, the 40m element is definitely helping the 15m one pull in more signals.

I think Janis was stating her experiences with an 'inline' fan array where each dipole sits under each other and have heard other people face similar issues. It does seem that when you crisscross them in a loft space the effect is greatly diminished and you've experienced the same as I in that respect.

Glad my mumblings/experiences are of some use and still compos mentis enough to recollect memories or look through my bookmarks.

Really well done with your work Neal and loving that inquisitive mind. Many have been put off with stories of how radio waves couldn't possibly escape roof tiles or too close to house wiring, etc. but the reality remains that it can be a great antenna setup.

Oh, and yes I did add a dipole for 15m to mine with much improved characteristics as well as performance.