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[Articles Home]  [Add Article]  

Fan Dipole -- How Long to Make Them

jeff (N3JBH) on November 6, 2005
View comments about this article!

Okay folks I was asked about dipole measurements. Here they are print these and save them. You can add as many of these as you would like to a single coax point and make a fan dipole or what's called a multiple band dipole. Hope you all enjoy, Jeff.

FAN DIPOLE OR MULTIPLE BAND DIPOLE SPECS:
(Each leg is shown in length so you will need two legs.)

10 METERS = 8'4"
12 METERS = 9'5"
15 METERS = 11'1"
17 METERS = 12'10"
20 METERS = 16'8"
30 METERS = 23'2"
40 METERS = 32'9"
60 METERS = 43'7"
75 METERS = 60'9"
80 METERS = 65'6"
160 METERS = 123'5"
137 KHZ = 1708'1"

Now I shall tell you that a wonderful gentleman named Tom. Tom will chime in here with a bunch a links. I shall save him the effort and list them here for you:

http://www.ku4ay.net/dipole.html
http://www.qsl.net/kd7rem/antdipole.htm
http://www.hamuniverse.com/multidipole.html
http://www.angelfire.com/nb/ni4l/ni4ldipole.html
http://www.arrl.org/tis/info/pdf/9611073.pdf
http://www.geocities.com/n2uhc/2banddipole.html
http://www.qsl.net/na4it/fandipole.html

I will say any these dipoles will work either by themselves or as a fan dipole when constructed properly. Please refer to the links for proper building.

Thanks, Jeff, N3JBH

Member Comments:
This article has expired. No more comments may be added.
 
Fan Dipole -- How Long to Make Them  
by N0AH on November 6, 2005 Mail this to a friend!
Jeff,

Nice information. Now we wait for the "I AM GOD" types to correct most if not all of what you posted. This is very useful information. Thank you-
 
RE: Fan Dipole -- How Long to Make Them  
by X-WB1AUW on November 6, 2005 Mail this to a friend!
Nice comprehensive list.

Are these the starting points or ending points for dipoles you made?

Bob
 
RE: Fan Dipole -- How Long to Make Them  
by K8MHZ on November 6, 2005 Mail this to a friend!
Will these specs work if you take one leg from one band and another from a different band to make an off center fed dipole, like a Carolina Windom?

If so, that would effectively double the amount of bands that were usable.

I do have to ask this, though...

I can be found working 20 and 40 meters from time to time. I hear a plethora of antenna types being used but I never hear anyone using a fan dipole. Is the fan dipole in reality the Jack Snipe of the amateur world? Could it be that if we follow the plans and concoct an antenna with more than two legs and call it a dipole we will end up with something that shows a low SWR but radiates very little? Are we destined via the fan dipole to personally experience the reason we call a non radiating load a dummy load?

Or is it that amateurs are ashamed of the often proclaimed ubiquitous fan dipole and say they are using something different...or just leave the fan part out and say dipole?

And if we an have a fan dipole, why can't we have a fan Yagi?

And why stop at dipole? What about tripole or quadrapole? Would a 16 band fan dipole more properly be termed a hexadecimalpole?

Since no one has ever answered any of these questions to my satisfaction there is only one thing left to do....build a fan dipole and call CQ on each band until I am either answered or have a reason to post something here indicating that I suspect the entire concept of the fan dipole is a ruse.

73 to all,

Mark K8MHZ
 
RE: Fan Dipole -- How Long to Make Them  
by W6TH on November 6, 2005 Mail this to a friend!
.

Heck, there should be no undesireable comments. Just take the numbers of 468 and divide this number by the frequency in Mhz.

Like 468 divided by 7.150 will equal 65.454 feet or round it off to 65.5 feet. This is for the center of the 40 meter band for a half wave. Now divide the 65.5 feet by 2 and you will have 32.75 feet (32' 9") each side of the feed point.

3x10 to the 8th power divided by 7 times to the 6th power. Shucks this is the old engineers way of computing antenna length, but all comes out close enough for gov't work. This length minus the 5% for end effects for the 468 calculation.

Nice information om and need more of this on eHAM.
73, W6TH a non vanity call letter.

.:
 
RE: Fan Dipole -- How Long to Make Them  
by KC8VWM on November 6, 2005 Mail this to a friend!
What? no comment from N6AJR yet? ...what's wrong with you guys?

 
RE: Fan Dipole -- How Long to Make Them  
by W6TH on November 6, 2005 Mail this to a friend!
.
I suggest not to use this antenna in Mass, VT, or NH or the entire northern east coast. The snow , ice will have you out in the cold coming this winter and will spend more time on the antenna than on the air or computer.

By the way the forty meter antenna can also be used on the 15 meter band, 3rd harmonic so forget about those 15 meter dimensions.

73, W6TH the dot and dash scientist.

.:
 
RE: Fan Dipole -- How Long to Make Them  
by KZ1X on November 6, 2005 Mail this to a friend!
N0AH wrote: "Now we wait for the "I AM GOD" types to correct most if not all of what you posted."

Well, you don't need to be a deity to know that antenna wires in parallel will couple to each other, therefore detuning each other for any desired (calculated) resonance. The lengths listed are idealized for typical monoband dipole elements; don't expect that a fan dipole constructed with these specific dimensions will work exactly as you might think.

Height above ground, ground conductivity, wire type, and other variables will also affect an antenna built in this way.

Having built dozens of such antennas, I can definitely say that these figures are close. Don't be afraid to add 10%-15% or so to the spec lengths, however, and trim accordingly if need be. It's always easier to cut wire than add it back on.
 
Fan Dipole -- How Long to Make Them  
by NA4IT on November 6, 2005 Mail this to a friend!
Just remember, the fan dipole can be built one leg above the other, or "fanned" out in all directions, matching legs opposite of each other.

And I jus' proud as a peacock you include lil' ol' me in the link list!

(And yes, I still ahve one up for 40/80/160M and LOVE it!)
 
RE: Fan Dipole -- How Long to Make Them  
by THERAGE on November 6, 2005 Mail this to a friend!
Oh my gawd. Gasp! Someone is actually giving out very secret information on how to make a dipole!? What is the meaning of all this? What will ham radio do when all these NC generals get on the air? Aren't we supposed to give the newbie a little nudge and have them look it up for themselves? Will all those ARRL handbooks just sit on the shelves to collect dust? Will this be the end of the Elmers Forum on eHam?

Oh, sir I shutter to think what is going to happen to ham radio now. Those "I AM GOD" hams (as one so put it) will hunt you down for spilling the beans. You don't know how many years of sleepless nights it took to come up with 468 divided by the frequency to make a dipole. And...a Fan Dipole at that! I hope you can sleep with one eye open at night.

HI!

73
 
RE: Fan Dipole -- How Long to Make Them  
by W6TH on November 6, 2005 Mail this to a friend!
.
Hey you, THERAGE.

How about a 5/8 wavelength and using the 599 and divide by the frequency going to be used.

599 divided by 14 Mhz equals 42.785. Bet that is new to you. Heh heh.

Oh you sad SSB boys that never want to use their calls.

W6TH, this is not a vanity call.
.:
 
RE: Fan Dipole -- How Long to Make Them  
by N6AJR on November 7, 2005 Mail this to a friend!
Her I am..... and thanks for a good article. I always start them a little long and fold back and twist to tune, then trim when done, or leave a little long and bring in with a tuner.

the 40m/15 m works some of the time, but if you cut loe or high in the 40 band the 15 m band may not tune, or tune where you want, I usually put in both.

You can put them up under each other, or put one north south, the next east west, the next caddy corner one way, the next the other way.. and so on, like an umbrella.

you can put them up with a 1 to 1 balun, a 6 inch- 10 loop coil of coax ( dirty balun), or just a center hanger, or just fold the end of the coax down to keep the water out. you can put them up flat top, or as an inverted v, or even as a sloper. these all tune slightly differently so a mfj 259 is handy. tune longer wire to shorter wire.

you can build your own for about $15 or buy one from alpha-delta for a hundred bucks or so.

how it works is, lets say you have a 20, 40, 80, fan dipole up. you send a 20 meter signal up the coax, it sees aproximately 50 ohm load on the 20 wire ( closer to 36 ohms, but close) and the 40 and 80 wires are too long and have an impeadence of several hundred to several thousands of ohms, so most of the power goes down the 20 wire. simple.

try making one for 2m and 440mhz, a piece of coax, 2 wires about 20 inches and two wires about 8 1/2 inches, now hook to a meter and a 2m/440 rig, on low power check and see how close you are on both bands..

always try to take the coax away at 90 degrees from the wires for atleas a quarter wave or more..

I love the fan dipole, also known as the single feed, multiband wire dipole antenna. but fan dipole is easier to write. some folks tell me these can also be fed with ladder line window line or twin lead from the back of a mfj tuner.. go figure..

tom N6AJR
 
RE: Fan Dipole -- How Long to Make Them  
by THERAGE on November 7, 2005 Mail this to a friend!
"How about a 5/8 wavelength and using the 599 and divide by the frequency going to be used."

-- --- ... - -.. .. .--. --- .-.. . ... .-. .... .- .-.. ..-. .-- .- ...- . - --- --

"Oh you sad SSB boys that never want to use their calls."

Oh, yeah. I do pound brass. ;-)

--... ...--
 
RE: Fan Dipole -- How Long to Make Them  
by K0BG on November 7, 2005 Mail this to a friend!
All well and good. However, you forgot to mention that the lengths, at resonance, will vary depending on how high they are mounted, and how close to surrounding objects the individual wires will be. It is not uncommon for them to vary up to 5% from the lengths shown (at any given resonance). This is why I suggested the use of dangles to make tuning easier (http://www.eham.net/articles/10974).

The term "FAN" dipole that Tom Lish, N6AJR, is so proud of fostering is technically incorrect. True, the legs are fanned out, but the original "Fan" dipole as published in the pages of QST is a different animal altogether (http://www.eham.net/articles/7154).

Alan, KBG
www.k0bg.com
 
RE: Fan Dipole -- How Long to Make Them  
by W9WHE-II on November 7, 2005 Mail this to a friend!
Fan dipoles are great. I have confirmed 256 with one BUT.....

Tuning them can be frustrating. When you put 3 or more dipoles on one coax, they begin to interact, making the mesurements a good starting place, but where you will end up once it is tuned, is anyone's guess. Interaction depends, in part, on how close each of your "fan blades" are to eachother. Triming one dipole can and DOES effect the others. So tune in VERY small increments, check each band before and after each adjustment. Above all, be patient and do not be surprised if you have to make lots of adjustments to get it right.

W9WHE
 
RE: Fan Dipole -- How Long to Make Them  
by WA3IRJ on November 7, 2005 Mail this to a friend!
I have had one for a while.

It works well. 15 is a little high on the swr..but tunable. I think that is because I have 40 tuned mostly for the phone band.
Mine is 10-15-20-40-80

It seems that it favors 20 and 40 meters with efficiency. 75 meters would be good too...but mine has some high Q coils in that band that make it very narrow. But it does get a nice signal out where it is tunable on 75-80

For a small lot..not a bad choice
kb3lxy
73
 
RE: Fan Dipole -- How Long to Make Them  
by W6TH on November 7, 2005 Mail this to a friend!
.
By using open wire or the ladder line you will not have to do any pruning of the half waves, also with the open wire you can use the 80 meter length for 40 and get a gain of 1.8 dB over a dipole on 40. Use the 20 meter length for 10 meters and also get a gain on 10 meters of 1.8 dB gain over a dipole.

There is much more to be gained than the eye can meet although I am old fashioned and still go along with the center fed zepp; less expense, more efficient and can still work all of the same bands with gain as I go higher in frequency, plus no use of coax which is lossy compared to the ladder and the open wire lines.

I assume you can't teach an old dog new tricks.

73, W6TH
.:
 
RE: Fan Dipole -- How Long to Make Them  
by KG6WLS on November 7, 2005 Mail this to a friend!
Regardless of what others have posted (negative or otherwise), I think that it was good that the author gave some easy fundamentals for making a MULTI-BAND dipole. Truely it's something that most already know, but better described AND helpful than whats been posted lately here on eHam

Thanks, Jeff

Mike
 
RE: Fan Dipole -- How Long to Make Them  
by W0FM on November 7, 2005 Mail this to a friend!
For Mark, W8MHZ,

I think the reason you don't hear more hams on the air saying they are using a "fan dipole" is simply because a fan dipole is a resonant dipole on each band that it has elements for. I have been using a fan dipole in my attic for many years (Alpha-Delta DX-EE for 40 thru 10 meters...which is actually a "parallel dipole"). It works great. I have 236 countries confirmed on that antenna with 100 watts of power. However, I normally tell my contacts that I'm running "100 watts into an dipole in the attic". I don't mention the "fan" dipole, because it's irrelevant unless we are talking antenna specifics. On any given band, the radio only sees that portion of the fan dipole that is resonant on that frequency of operation. So, on 20 meters, the 20 meter element of a fan dipole is just as resonant and just as good a signal radiator as a single band 20 meter dipole.

Think of it in terms of automatic antenna switching. When I flip my FT-1000MP to 10 meters and transmit, the radio "sees" only the 10 meter elements (wires) on the fan dipole. When I switch back to 40 meters, the rig recognizes that part of the fan dipole is resonant on 40 meters and radiates just like I was using a single, 40 meter dipole.

Now, as others have said, there is some interaction between the fan dipole's wire elements because of their close proximity to one another. This makes the tuning of a fan dipole somewhat more labor intensive than a single band dipole. But once you get it set, you can just enjoy the "automatic antenna selection" feature of the fan dipole.


73,

Terry, WFM
 
RE: Fan Dipole -- How Long to Make Them  
by W0FM on November 7, 2005 Mail this to a friend!
Sorry Mark, typo: K8MHZ
 
RE: Fan Dipole -- How Long to Make Them  
by KA4KOE on November 7, 2005 Mail this to a friend!
I wanna know how in the heck you gonna make that thing rotate fast enough, re: using split rings, to create enuff of a breeze to really call it a fan dipole.

---and maybe some bright boy can figger out the doppler effects from such a radiating rotating contraption....

---Inquiring minds wanna know.

:)

Flippit
 
RE: Fan Dipole -- How Long to Make Them  
by W6TH on November 7, 2005 Mail this to a friend!
.

Reading the reviews (Reviews Summary for Alpha Delta DX-EE) it seems most are using tuners. Isn't this defeating the purpose of the antenna?

W6TH
.:
 
RE: Fan Dipole -- How Long to Make Them  
by WA3IRJ on November 7, 2005 Mail this to a friend!
As I said in the prior post..

I have a fandipole. It is marketed by Alpha Delta...as a multi-band d/p But, in all fairness , it is a "fan"
I only need a tuner for 15 meters..or if I tune out of the narrow band , that is available on 75. Otherwise it is pretty flat on the SWR. Mostly 1.2 to 1.3 on other bands. On 15m it is 1.8 or so. There I think I would use a tuner there ! But as I said, I mainly use it on 40-75 where it does a nice job. It also seems to be exceptional on 20. But I usually am on a beam up there.

I may add a single wire for 75-80...as I want more coverage. But I will leave the fan up. It works !
JohnB
kb3lxy
 
RE: Fan Dipole -- How Long to Make Them  
by W0FM on November 7, 2005 Mail this to a friend!
Vito,

I only use my rig's internal tuner to tune my DX-EE to the WARC bands. Everything else is well covered without an external tuner in my case. Maybe I just lucked out.

Terry, WFM
 
RE: Fan Dipole -- How Long to Make Them  
by W6TH on November 7, 2005 Mail this to a friend!
.
Terry, W�FM

It would be interesting to know the wire lengths of the 20, 15 and the 10 meter bands.

Do you have those values?
W6TH
.:
 
Fan Dipole -- How Long to Make Them  
by G0GQK on November 7, 2005 Mail this to a friend!
This is the first time I have ever seen recommended lengths for this type of wire antenna, I shall copy this information into my 30 year collection of antenna formula.

Earlier this year I tried to find any information on V dipoles, none anywhere. Inverted V's plenty but a V antenna, none, so I had to work it out the hard way.
Apparently an antenna of this type is not popular, but it has more gain than a flat top dipole

73, Mel G0GQK
 
RE: Fan Dipole -- How Long to Make Them  
by N6AJR on November 7, 2005 Mail this to a friend!
they are listed up there.. the length for each leg, 2 legs, 1 feedline, instant antenna.
 
RE: Fan Dipole -- How Long to Make Them  
by N6AJR on November 7, 2005 Mail this to a friend!
K8MHZ asks

And if we an have a fan dipole, why can't we have a fan Yagi?

I thopught they called the fan yagi a log periodic..

same idea, different application, but the LP uses the same operating principles, the elements clossest to the freqency radiate and the others just sit there
 
RE: Fan Dipole -- How Long to Make Them  
by N6AJR on November 7, 2005 Mail this to a friend!
another interesting application of the fan dipole is a variation called the cage dipole, which is 3 or 4 wires about the sam length in a close configuration giving broader band with, often seen on older navy ships.

also a second variation is to put up a fan with one pair cut for 3.950 and a second pair cut for 3.550 and this gives you a good cw antenna, a good ssb antenna and the pair together gives a complex mix of swr to make it pretty much under 2 all the way across the band. try it on a computer model.. 2 sets of wires, for no tune all across 75/80 m..

depending on the tx freq, it will send most ot one or the other, but near mid band say 3.700 you will be putting out pretty much half on both..

all basic applications of the dipole...
 
Fan Dipole -- How Long to Make Them  
by KE5EOT on November 7, 2005 Mail this to a friend!
Thanks for the information. I haven't been able to get on HF yet, but when I do I will probably start with a long wire through an antenna tuner and then a fan dipole later on. The more information I can collect, the better.
 
RE: Fan Dipole -- How Long to Make Them  
by KC8VWM on November 7, 2005 Mail this to a friend!

Why limit yourself to a fan dipole?

Try a spinning yo yo antenna, George Foreman grill EME reflector array. For maximized tropospheric ducting on VHF, try connecting your home furnace ducting as your next secret weapon DX antenna! For multiband operation, you can easily construct a homemade antenna tuner by connecting your longwire antenna to your pets and playing "fetch" with them when you want to extend your antenna to operate on the lower bands!

...And who says we should operate a screwdriver antenna when operating mobile? ...Try rigging up a construction shovel or a leaf rake on the back of your vehicle. If you want your first mobile DXCC award, you can install a Massey Ferguson tractor combine on the roof of your mobile!

There are no limitations when it comes to antennas. Just go out and hook up the feedline and antenna tuner to a favorite tree and your on the air!


http://www.rexresearch.com/squier/squier.htm


73 Charles - KC8VWM
 
RE: Fan Dipole -- How Long to Make Them  
by W6TH on November 7, 2005 Mail this to a friend!
.
N6AJR
they are listed up there.. the length for each leg, 2 legs, 1 feedline, instant antenna.
------------------------------------------------
I am interested in the wire length of W0FM.

W6TH
.:
 
RE: Fan Dipole -- How Long to Make Them  
by N8ZF on November 8, 2005 Mail this to a friend!
OK, some very good comments. What I've always wondered....Because of my current antenna configurations, can I use the original figures given in the first post, put up the 160M first, then a 17 because I don't have either band. More importantly, I would like the 160 as a flat top (room is no prob), but drap the 17 legs down with string in an inverted "V" fashion. In other words, from the side, it would look like a rather large bow tie. I would think this would be a great way to pick up two bands that aren't usually included in "canned" systems.

THANKS!!!!


N8ZF and yes it's vanity....but I passed the 13 wpm!!!
 
RE: Fan Dipole -- How Long to Make Them  
by N8BOA on November 8, 2005 Mail this to a friend!
How about a folded fan dipole
 
RE: Fan Dipole -- How Long to Make Them  
by KC8VWM on November 8, 2005 Mail this to a friend!
I dont know about running a folded dipole but I once ran a folded 5/8 wave mobile antenna.

It happened when I drove into a underground parking garage one day.

 
RE: Fan Dipole -- How Long to Make Them  
by WA8MEA on November 8, 2005 Mail this to a friend!
More dipole desertions:

1) Regarding fan dipoles: Once you've set the minimum SWR on the second dipole, the first dipole will need to be re-adjusted for minimum SWR. When you adjust the lowest SWR on the third dipole, the second will need re-adjusting. And then the first will need to be re-adjusted again...and then the third will need to be re-adjusted once more.....

;-)

2) I have NEVER hit minimum SWR using any measurements from any handbook, or using 468 divided by the frequency in megs. You will ALWAYS need to shorten for minimum SWR from the figures they give you.

3) Here's a fun experiment: pick a 75 meter frequency. Measure your SWR during a dry spell of weather. Now measure it after a good soaking rain. Quite a difference, eh??

4) The FATTER the elements (wire), the B R O A D E R the low SWR spectrum is. (I like using #6 ground wire available at Home Depot, Lowes, etc. for use as 20, 17, 15, 12 and 10 meter Inverted Vees.)

5) No, plastic insulation on the wire does NOT stop the signal from either leaving the wire or entering it. (Yes, I've been asked this....)

6) I've never, ever used a balun on any of my own personal dipoles in the 38 years I've been hamming. (Center insulators...yes, baluns...no.)

7) Two meter dipoles made from old TV antenna elements are fun to make and really work well cuz you can stick 'em a zillion feet in the air cuz they don't weigh nuttin'...

8) You ever try a 75 meter dipole on ten meters? Really low SWR AND very broadbanded...

9) Bungie cords make wonderful supports attached to the end insulators of dipoles.

10) Go to the nearest Pilot or TA, get yourslef two 108 inch whips and a vise grip mount. Attach the "extra" whip to the ground side of the vise grip mount and trim each antenna for minimum SWR on ten meters. Then place highly in air.

11) Just because I hit minimum SWR with the dipole at my house, doesn't mean that it will remain at minimum SWR at your house. (My dirts different from your dirt....)

Just more dipole ditties I've digested over the decades....

73, Bill - WA8MEA
http://HamRadioFun.com



 
RE: Fan Dipole -- How Long to Make Them  
by KE5EOT on November 8, 2005 Mail this to a friend!
on November 7, 2005 KC8VWM wrote:

"Why limit yourself to a fan dipole?"

Are you saying I should try for the "Fan J-pole"? Tuning it should be a real joy. Not to mention the fact that it might qualify as modern art.
 
RE: Fan Dipole -- How Long to Make Them  
by KC8VWM on November 8, 2005 Mail this to a friend!

o O hmmm, I wonder if there is such a thing as roll up multiband dipole?

...And amazingly it appears that I found one!

http://hamradiofun.com/yo-yo-vee-model4-6.htm

..Nice!

73 Charles - KC8VWM
 
RE: Fan Dipole -- How Long to Make Them  
by KC8VWM on November 8, 2005 Mail this to a friend!
Are you saying I should try for the "Fan J-pole"? Tuning it should be a real joy.

------

Ironic you mentioned this. I happen to have just installed a pitchfork on my vehicle roof that does the same exact thing as a fan Jpole!

Tuning? no problem... Just reduce your power output level to 100mw and run QRP. This new, innovative and rather amazing approach to antenna tuning instantly adjusts your SWR ratio to a minimum every time!

However, your actual milage may vary. (primarily due to gas price increases)

73 Charles - KC8VWM
 
RE: Fan Dipole -- How Long to Make Them  
by N6AJR on November 8, 2005 Mail this to a friend!
that reminds me of the fellow that had a 19 1/2 inch diameter fan that died. he took the wire and metal "finger cover" off the front of the fan and mounted a so-239 in the center, and screwed in a 2 meter antenna.

sort of a 2 meter fan monopole
 
RE: Fan Dipole -- How Long to Make Them  
by K7VO on November 8, 2005 Mail this to a friend!
First, excellent post with some nice, handy numbers and good links.

KZ1X wrote:

> Well, you don't need to be a deity to know that
> antenna wires in parallel will couple to each
> other, therefore detuning each other for any
> desired (calculated) resonance. The lengths
> listed are idealized for typical monoband
> dipole elements; don't expect that a fan dipole
> constructed with these specific dimensions will
> work exactly as you might think.

> Having built dozens of such antennas, I can
> definitely say that these figures are close. Don't
> be afraid to add 10%-15% or so to the spec
> lengths, however, and trim accordingly if need
> be. It's always easier to cut wire than add it
> back on.

I can attest to this. When I put my fanned dipole up in North Carolina I was resonant in band on 40 and 20 but I found that on 80 my antenna was simply too short. It had to be redone to make it work properly.

Also, please remember that the 40m legs will be near (but not quite at) resonance on 15m. With a tuner a the 40m legs will work well on 15. This is also true for the 80m legs on 17m.

If you were really and truly looking for criticism I must apologize. I don't have any.

73,
Caity
K7VO
 
RE: Fan Dipole -- How Long to Make Them  
by W6TH on November 8, 2005 Mail this to a friend!
.
Remember:

Just because the swr bridge indicates that the VSWR is 1;1 does not mean that the antenna is resonant. Your coax feedline has a lot to do to indicate a false reading that the antenna is properly resonant.

As an example: if the antenna reads 1.5:1 on your VSWR meter, you can play with the length of the coax and bring the VSWR down to a 1:1 reading.

.:.
 
RE: Fan Dipole -- How Long to Make Them  
by K4GLM on November 9, 2005 Mail this to a friend!
On the standiing wave ratio meter; I like the idea of a remote mounted sensor, mounted at the feed point. I is essential for remote manual tuning. I have a model that does this, made by E.F. Johnson.
The tricky part may be in the wiring from sensor to meter, as it can't pick up stray RF. I guess some shielded microphone cable or something.
I admit to obsessing about every little bit of signal, but those bits do add up. (Or they take a bite out of same...)
Shannon Boal K4GLM A vanity call
 
RE: Fan Dipole -- How Long to Make Them  
by W6TH on November 9, 2005 Mail this to a friend!
.
Yes, the best way is to check the resonant of a antenna at the feed point. Knowing this then the coax can be added to the antenna. When coax is added there may be a different reading and higher on the VSWR, so then one can prune the coax for the lowest VSWR again as the coax has lumped inductance and lumped capacitance which can act as a antenna tuner in itself.

W6TH the non vanity call.

.:
 
RE: Fan Dipole -- How Long to Make Them  
by N4ZYV on November 9, 2005 Mail this to a friend!
Nice thing about the spinning fan dipole is the circular polarization. :P
 
Fan Dipole -- How Long to Make Them  
by KC9CRM on November 9, 2005 Mail this to a friend!
Hello all

Nice article. Like N6AJR and W6TH said that a 40-meter dipole will work on 15 meters but most of the time the SWR for 15 meters is high. One way to bring the SWR down on 15 meters is to use capacitance hats. I use them on my 40-meter dipole and it works great. How to do it? Well thats easy. Take about 4 feet of 10 or 12ga solid wire and cut that in half so you have 2 two foot long pieces. Next Solder them so that they are circles then twist them so you have 2 figure 8's and solder each them about 11 feet from the center of the dipole and you are done. Check your SWR on both bands 40 meters should not have been changed and 15 should be lower and if it is not then change that shape of the hats. Now, for a buck or two you have a 2 band dipole with one feedline and have 1/2 wave dipole on 40 meters and maybe a 3/2 wave dipole on 15 meters maybe? It works great and is cheap! Good Luck!!

Jake KC9CRM
 
Fan Dipole -- How Long to Make Them  
by N9ESH on November 9, 2005 Mail this to a friend!
Isnt it a lot easier to take one dipole 135 long and feed with twin lead and a tuner?
 
RE: Fan Dipole -- How Long to Make Them  
by N8ZF on November 10, 2005 Mail this to a friend!
I noticed my capacitance hat didn't do much for blocking the sun....

73
N8ZF
 
RE: Fan Dipole -- How Long to Make Them  
by KC8VWM on November 10, 2005 Mail this to a friend!
I tried feeding my 135' dipole antenna too, but it didn't eat a single bite of lead or tuner fish for that matter...

 
RE: Fan Dipole -- How Long to Make Them  
by KG5JJ on November 10, 2005 Mail this to a friend!
Fan Dipoles...or, how to make a really, really neat harmonic radiator! ;-}

73, KG5JJ
 
Fan Dipole -- How Long to Make Them  
by WC4X on November 12, 2005 Mail this to a friend!
When pruning a fan dipole I have found it best to start by pruning the lowest frequency elements first and then progressing to the higher frequency elements, which is opposite from logic used when pruning other antennas. I have made several fan dipoles over the years and they work just fine once pruned.
 
RE: Fan Dipole -- How Long to Make Them  
by KC8VWM on November 13, 2005 Mail this to a friend!
You make it sound like yard work...

:)
 
RE: Fan Dipole -- How Long to Make Them  
by WA8MEA on November 15, 2005 Mail this to a friend!
Oh! One more thing:

If you live in the great white north, remember that depending on what type of wire you are using....the wire of your dipole will usually contract in the winter and expand in the summer.

73, Bill - WA8MEA
http://HamRadioFun.com
 
RE: Fan Dipole -- How Long to Make Them  
by WA2JJH on November 17, 2005 Mail this to a friend!
Just put in a few Pieltzer effect slabs and you have an
Airconditioner dipole.: )Just kidding!
 
Fan Dipole -- How Long to Make Them  
by AB7E on November 20, 2005 Mail this to a friend!
So ... has anyone actually used these measurements for a multi-band dipole and had them work? I'll bet not. I'll bet N3JBH hasn't either.

N3JBH's numbers are simply taken from the classic formula for a single band dipole, but adding additional dipoles in parallel with a previously resonant one will shift the resonant frequency, change the real part of the feedpoint impedance, and narrow the SWR curve. So as others have said, you'll either be doing a LOT of back and forth retuning of each dipole or you'll be using a tuner. Either way, I don't see the point of specifying lengths for each band to the nearest inch that aren't going to be accurate in real life.

I'm not saying you can't get a fan dipole to work, but you'll end up with different lengths than those quoted above.
 
RE: Fan Dipole -- How Long to Make Them  
by F6IQA on November 22, 2005 Mail this to a friend!
> Isnt it a lot easier to take one dipole 135 long and >feed with twin lead and a tuner?

Then it is no more a dipole antenna but a center-fed: at this time you should NOT consider the radiating legs ONLY but the *entire* radiator+feeder+coupler is the antenna. It is an opened line with an adaptator device. This side of the pool, some call it Levy.
 
Fan Dipole -- How Long to Make Them  
by AA9KK on December 19, 2005 Mail this to a friend!
I'm not in possession of antenna modeling software at this time, but has anyone tried modeling fan dipoles with various elements, configurations, and three-dimensional layouts? Can't expect real-world exactness but the approximate results would be interesting to see.
 
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