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The Fence Fan Dipole (FFD) A Quick, Easy and Inexpensive Multiband Antenna

from Howard Groveman, W6HDG on July 26, 2012
View comments about this article!

The Fence Fan Dipole (FFD) -- A Quick, Easy and Inexpensive Multiband Antenna

Background

The multiband fan dipole has always been a popular antenna choice for getting on several bands with a single feedline and without the need for an antenna tuner. The height is limited only by the nearest tall tree and the cost of the antenna is minimal. The antenna is also rather stealthy – especially if 16-18 gauge wire can be used in sub 200 watt installations. The antenna basically consists of two to five or more distinct half wave dipoles which are mounted to a common parallel feedpoint so that a singe feedline can be utilized. Some nice designs are easy to find on the internet or in antenna handbooks. Most designs now suggest (based on Stanford Research Institute data) that the feedpoint be separated by as much as 5.5 inches between dipoles and that the lower frequency (longer) dipoles can be about 4% shorter than the 468/frequency in Mhz would dictate whereas the higher frequency (shorter) dipoles need to be about 4% longer. Many designs also recommend the controversial “ugly balun” choke in the design which is nothing more than 18-21 feet of coax close wound on a 4” or greater non-conductive form at the feedpoint.

There are certain downsides of the traditional fan dipole in that the top wire must often support the entire weight of the antenna as well as the balun. The need to ideally spread out the feedpoints by up to 5.5 inches also makes the feedpoint area rather cumbersome. Complicated spreaders must also be used in order to keep each dipole taut and well separated when there are only 2 end attachment points. There also can be some interaction among the dipoles and some detuning may occur if a dipole is included which is a frequency multiple of 3 from a longer dipole in the system (3rd harmonic). For example a 30 meter, 15 meter and 6 meter ½ wave dipole may not be possible if an 80 meter, 40 meter and 17 meter dipole exists. A possible match may be obtained on 30 meters, 15 meters and 6 meters using the existing longer dipole but testing is required. Finally, it is difficult to trim and tune the antenna, since a single rope or rope-pulley system supports the entire array and it must be completely taken down for wire tuning or repair.

Objective

I am just getting back on HF after a few year hiatus and have moved to a neighborhood with some antenna restrictions. My rig is a Yaesu FT-857D and Astron 30 amp power supply. I have no tall trees on the property but do have one large feature on the property – a 45 year old tennis court with 12 foot fencing all around it. Each long side of the fencing is 120 feet total (a nice sounding number to dipole fans).

I decided to try an inexpensive antenna design as a starting point “just to get on the air”. I figured that if I lashed a 10 section of schedule 40 PVC pipe to a central fence support with hose clamps, I could get an inverted-V up at around 20 feet at the center (not an ideal height for DX, but certainly usable). I then figured that I could use the dipoles themselves as “guys” for the central support if at least two of the dipoles were attached on a short offset support on both sides of the fence. The other dipoles could be “bungeed” directly to the fence mesh to keep them taut.

The advantages of my Fence Fan Dipole (FFD) design is that just about any sturdy fence that spans the linear distance of the lowest band can be used. The center feedpoint and balun can be made from a single two foot section of 4” drainpipe with end caps for weather resistance. This could be attached and supported atop a central PVC support pipe with appropriate threaded plumbing adapter and an electrical metal threaded nut available at most hardware stores. See construction images below. Each dipole is separately lashed to the fence with a bungee-like tarp strap so individual band tuning does not require entire antenna takedown. Dipoles can be easy attached and changed at the retention/ relief posts along the drainpipe for testing, experimenting and possible future repairs. Finally, excellent spreader distances between dipoles at each endpoint can be achieved.

Construction

RG-8X coax and PL-259 connectors with adapters were the only ham radio specific parts.
The remaining parts were all obtained during a couple of trips the nearest Home Depot:

1) 18 gauge bare stranded copper “ground” wire is about $17 for 250 feet and worked extremely well. The 250 feet was just a few feet short for all dipoles so I made my 17 meter dipole from heavier bare copper stranded antenna wire I had on hand. If any of the copper is tarnished, it can be quickly rejuvenated by soaking in a few of ounces of vinegar with a half teaspoon of salt added. This allows the copper to be solder-ready in the necessary spots.

2) Two foot section of 4” ABS drain pipe with 2 end caps
3) Ten foot section of 1 inch schedule 40 PVC with threaded PVC adapter and a metal retention nut sold in the electrical section for threaded pipe. Three hose clamps to attach the PVC to a vertical member of the fence post
4) Copper clad plumbing strapping, copper electrical lugs with setscrews (Burndy KA4CBAG2R), Ten ¼ inch x 1.5 inch eye bolts, two solder lugs for coax attachment, ten ¼ inch lock washers and a total of twenty ¼ inch nuts (ten of which are included with the eye bolts)
5) Four short 18 inch pieces of PVC to be use as fence “guy” standoffs along with four U-Bolts for attachment – see close-up image.
6) Ten tarp straps (bungee cords)
7) 10 Plexiglas rectangles prepared from a single 12”x12” sheet of 1/8” Plexiglas. Each rectangle about 3 inches by 1.5 inches with holes drilled on each long end

Construction is quite straightforward if you study the images above. I separated the 80 and 40 meter dipole eyebolts by the full 5.5 inches. I compromised and separated the 40 and 20 meter dipoles by 4.5 inches, 20 and 17 meter dipoles by 3.5 inches and the 17 and 10 meter dipoles by 3 inches. Each of two copper clad straps run the length of eyebolts along the inside of the ABS pipe. The coax lugs are attached at the eyebolts closest to the “ugly balun”. Lock washers are used between the interior nut and the copper strapping. The balun itself is about 16 turns of RG-8X (21 feet) with epoxy used to seal the two inlets. The RG-8X then runs down the inside of the PVC support pipe. I used a barrel SO-239 at the bottom of the support pipe for convenience. I painted the coax, the ABS pipe and PVC all brown to keep things stealth.

A note about using two of the dipoles as “guys” to keep the flimsy PVC support pipe upright: If I had bungeed all dipoles to the fence mesh itself, I would not have had support in the “Y” plane to keep the PVC support pipe upright. I could have used two opposing rope guys for this purpose, but didn’t want to have any ground mounted supports. So I fashioned 18 inch fence top extenders by grinding a corresponding arc in an end of a piece of PVC and used a U-Bolt through the PVC to create a sturdy standoff from the fence. Good “Y” plane support can be achieved by bungeeing two of the shorter dipoles on each side of the fence with these extenders. This has kept the central PVC pipe quite vertical with resistance to winds we have seen to date.

The completed antenna is so stealth, it is quite hard to photograph. Hopefully this image with give you a good idea of the appearance of the support and at least of 3 of the 5 dipoles.

Dipole lengths, after adjusting some of the dipoles with the help of an MFJ-259 antenna analyzer were approximately:

80 meters : 61 feet each side including the loop between setscrew and eyebolt
40 meters: 32.8 feet each side including the loop between setscrew and eyebolt
20 meters: 17 feet each side including the loop between setscrew and eyebolt
17 meters: 13.6 feet each side including the loop between setscrew and eyebolt
10 meters: 8.6 feet each side including the loop between setscrew and eyebolt

Results

The FFD has obvious downsides – non-portability, height compromises and possible interaction with the fence if it is metal.

But initial testing has been quite good. During an hour of operating the IARU HF championship July 14-15, 2012, I worked 6 countries on 4 bands including Aruba, South Cook Island, Japan, Argentina, Canada and Mexico.

The antenna has acceptable SWR on 80, 40, 20, 17, 10 and 6 meters and contacts were made on all bands without an antenna tuner. 15 meters is usable.

SWR results were as follows:

3.8 Mhz 1.9 (SWR was 2.5 at 3.70, 2.5 at 3.9 and 3.8 at 4.0)
7.2 Mhz 1.3 (SWR was under 2.0 across entire band except 2.6 at 7.00)
14.13 Mhz – 1.0 (SWR was under 1.5 across entire band)
18.14 Mhz – 1.0 and same across entire band
21.3 Mhz – 2.9 and same across entire band
28.5 Mhz – 1.2 (SWR was under 2.0 across entire band except 2.2 at 29.7)
52 Mhz – 1.4 (SWR was under 1.8 across entire 4 Mhz of the band)

I may add a tuner to get a better match on 15 meters and more bandwidth on 80 meters. It is unclear if a dedicated 15 meter dipole would have worked fine or if there would have been detuning - I haven’t tried it.

I have no illusions about DX worthiness of this antenna. But dipoles and inverted-V’s can make good antennas – especially on the lower frequencies where multi-element antennas are not practical. The multiband variety of the dipole such as that described here, when well tuned, should not suffer appreciably in performance over a monoband dipole at similar height. The advantages of a single feedline cannot be overemphasized.

References

A Field Guide to Simple HF Dipoles, Cecil Barnes, et al, Standford Research Institute, Mar 1967, see
http://www.scribd.com/doc/50272493/A-FIELD-GUIDE-TO-SIMPLE-HF-DIPOLES

KJIIF, “The KJ4IIF Multiband "FAN" Dipole for 160, 80 and 40 Meters”, see
http://www.hamuniverse.com/kj4iif1608040fandipole.html

N4UJW, “BUILD THIS MULTIBAND FAN DIPOLE FOR ALL BAND HF ANTENNA EXCITEMENT”, Sept 2010, see
http://www.hamuniverse.com/multidipole.html

Paul Coats, AE5JU, Morgan City, LA "From Shortwave Listener to Extra Class" - http://www.hamuniverse.com/ae5jumultibanddipole.html

March 2013 Update to the Fence Fan Dipole

I have been very happy with the Fence Fan Dipole I first erected in July 2012, but wanted to increase the height of the central support above the original 20 feet. I had also received a few reports of some RF in my transmit audio and decided that I wanted to add a real 1:1 balun at the feedpoint.

The “Ugly Balun” choke type balun using coax windings is great for a single band antenna, but the number of turns determines its effective choke frequency – so it is impossible to cover 80 through 6 meters with one coil of coax. I had heard wonderful reports of the baluns designed by the late Jerry Sevick W2FMI. These designs were now being made by Mike Lapuzza, KM5QX who runs Clear Signal Products at website www.coaxman.com. Mike was kind enough to make a special version of his 823A balun without the eyebolts so that it would fit inside my PVC drainpipe (see original article). This fit inside the pipe at the same location where the external coax windings were removed. The balun worked like a charm and I have since received nothing but great audio reports – even after adding an Elecraft KPA500/KAT500 amp/tuner combo to my station. Mike hand makes the baluns, so he is very open to special orders like mine.

In researching lightweight support poles, I found John at http://goverticalusa.com. John sells new and used surplus military style fiberglass and aluminum 4 foot mating mast sections. The aluminum and fiberglass poles can be used in combination and fit together perfectly. To get to my goal height of 36 feet, I decided to use 6 stiffer aluminum sections for the lower mast and 3 fiberglass sections for the upper mast. My reason for using fiberglass was so that there were no metal sections at the top to interfere electrically with the dipoles. John also makes a very nice guy ring which can be inserted at any joint in the sections.

I placed the guy ring at 24 feet so that I could guy the mast at that point using some Dacron rope. I fashioned two additional ¾ inch PVC outriggers to the fence to support the ropes from this guy ring in a 360 degree fashion (see final antenna picture). Remember, my lowest 12 feet of mast was solidly supported by hose clamps along the 12 foot high tennis fence. At the top (36 feet), the antenna would be “guyed” in the same way it had always been, by attaching the dipoles to the fence top with tarp style bungee straps (using some PVC outrigger poles at the fence top to keep the antenna balanced at the vertical). With the increased height, I now needed to add some Dacron ropes to some of the dipoles to fan them out properly along the fence.

The result has been worth the effort. The only downside of the increased height is that the entire mast would need to be lowered for any work to be done on the antenna’s individual dipoles. You can’t tilt over 36 feet of military poles without damaging them, so the antenna must come down the same way it went up – by removing (adding) one section at a time from the bottom as you slide the pole down (up) through the loosened hose clamps. Not very elegant but doable with a couple of people.

Since the original article was published, several hams have written with positive experiences. One ham fashioned 8 dipoles with one feedline for multiple bands including 15 meters and said that he did not have an issue with both a 40 and 15 meter dipole coexisting (3rd harmonic could cause both dipoles to potentially radiate). So experimentation is the name of the game with this antenna design.

Howard W6HDG

Member Comments:
This article has expired. No more comments may be added.
 
The Fence Fan Dipole (FFD) A Quick, Easy and Inexpensive Mul  
by W6HDG on July 24, 2012 Mail this to a friend!
One additional item:

I used coax-seal on the copper lugs to cover the set screws.
 
RE: The Fence Fan Dipole (FFD) A Quick, Easy and Inexpensive  
by N4JTE on July 26, 2012 Mail this to a friend!
Very nicely done with realistic expectations.
Detail and photos also well presented, enjoyable informative article.
One small question is that study you mentioned about the vertical seperation of the common feed point, the copper strap would seem to be the same thing as using one eyelet but yours is much better looking!
Enjoy your antenna and tnx for sharing with us.
Bob
N4JTE
 
The Fence Fan Dipole (FFD) A Quick, Easy and Inexpensive Mul  
by K4YZ on July 26, 2012 Mail this to a friend!

Hi Howard,

Superbly written! Bravo!

When I have room to spread out (I am presently in an urban duplex) the fan dipole is one of my favorites. If I had Thomas Crown's billions, I might get the tower/monobanders to play with, but why spend $100K to talk to some place when $50 and some sweat equity will get me there too...?!?!

Last time I had one up, I had a trap dipole for 80/40 combined with a trap inverted vee for 30/17M with the antennas at 90deg legs. Minus the usual pruning that goes along with each, I was able to use this combination on all bands with my MFJ-948 manual tuner and no problems at all. I love wire antennas.


73

Steve, K4YZ
 
The Fence Fan Dipole (FFD) A Quick, Easy and Inexpensive Mul  
by WD8OQX on July 26, 2012 Mail this to a friend!
Thanks for posting! This gave me some ideas for my OWN setup.
 
RE: The Fence Fan Dipole (FFD) A Quick, Easy and Inexpensive  
by K3AN on July 26, 2012 Mail this to a friend!
Look at all those beautiful, tall trees in the photos. Why in the world would you settle for an antenna that's just 15 to 20 feet off the ground when you could press some of those trees into service?
 
The Fence Fan Dipole (FFD) A Quick, Easy and Inexpensive Mul  
by KT4EP on July 26, 2012 Mail this to a friend!
Tx Howard... this is my kind of article! I might not build one of these but I print and keep articles like this for future reference.
KT4EP
 
RE: The Fence Fan Dipole (FFD) A Quick, Easy and Inexpensive  
by W6HDG on July 26, 2012 Mail this to a friend!
Those trees are my neighbor's :)
 
The Fence Fan Dipole (FFD) A Quick, Easy and Inexpensive Mul  
by N4UJW on July 26, 2012 Mail this to a friend!
Were those dipole lengths a typo?
 
RE: The Fence Fan Dipole (FFD) A Quick, Easy and Inexpensive  
by W6HDG on July 26, 2012 Mail this to a friend!
Were the dipole lengths a typo? Yes, the lengths got "halved" twice in error. The wording is being corrected in the original article (and may be correct by the time you read this) to:

80 meters : 61 feet each side including the loop between setscrew and eyebolt
40 meters: 32.8 feet each side including the loop between setscrew and eyebolt
20 meters: 17 feet each side including the loop between setscrew and eyebolt
17 meters: 13.6 feet each side including the loop between setscrew and eyebolt
10 meters: 8.6 feet each side including the loop between setscrew and eyebolt

Also, the common name of the choke type balun is "Ugly Balun".
 
The Fence Fan Dipole (FFD) A Quick, Easy and Inexpensive Mul  
by VK3DWZ on July 26, 2012 Mail this to a friend!
Thank you for such a fascinating article, Mr Groveman. Only one problem tho', the dimensions mean nothing to us here in Australia. Australia is a "metric" country and we don't understand such terms as feet, inches, etc.
 
RE: The Fence Fan Dipole (FFD) A Quick, Easy and Inexpensive  
by WD8OQX on July 26, 2012 Mail this to a friend!
VK3DWZ

Not to be rude, but now you know how I feel when someone uses METRIC (in, & out of the USA). Especially when dealing with temperatures.
 
RE: The Fence Fan Dipole (FFD) A Quick, Easy and Inexpensive  
by KE5JPP on July 27, 2012 Mail this to a friend!
"especially if 16-18 gauge wire can be used in sub 200 watt installations"

Why 200 watts? 16-18 gauge wire will easily handle the legal limit.

Gene
 
RE: The Fence Fan Dipole (FFD) A Quick, Easy and Inexpensive  
by WX7G on July 27, 2012 Mail this to a friend!
Very nice antenna and a great way to get some distance between the wires.
 
RE: The Fence Fan Dipole (FFD) A Quick, Easy and Inexpensive  
by K7EDL on July 27, 2012 Mail this to a friend!
Use Google to translate the numbers to metric, temperatures C.to F. and money etc. its a great feature just type in something like 150 feet to meters. It works both ways.
 
RE: The Fence Fan Dipole (FFD) A Quick, Easy and Inexpensive  
by M0AFJ on July 27, 2012 Mail this to a friend!
Nice well written article from a country which doesn't know whether to use imperial or metric!

73
Tim M0AFJ
 
The Fence Fan Dipole (FFD) A Quick, Easy and Inexpensive Mul  
by KD6NRP on July 27, 2012 Mail this to a friend!
Thank you for preparing and posting this article.

One point of disagreement that I have is the description of this antenna as "stealth." I would describe it as a "reduced visual impact" or something to that effect.

To make the antenna a stealth antenna, I would:

1. Find a way to get rid of the larger diameter tube at the top of the mast. That would make the mast one long, slender tube with an uninterrupted outline.

2. I would replace the large insulators or springs at the end of the antenna elements. I would tie kevlar fishing line to the end of each wire.

3. I would use the thinnest wire that I could that did not affect the antenna's power handling ability or mechanical strength.

4. I would paint everything a dull (non-gloss) medium gray.

Of course, depending on where you live, you may not need to go the extra mile (or 1.609 kilometers) to make the antenna less visible.

73

Brian, KD6NRP
 
RE: The Fence Fan Dipole (FFD) A Quick, Easy and Inexpensive  
by WD8OQX on July 27, 2012 Mail this to a friend!
K7EDL

I think that what VK3DWZ & I were getting at (& I can only truly speak for myself) is that when one post such, that BOTH measurements should be given. One shouldn't have to resort to "looking it up".

Also, IMO, it would be nice if we were "all on the same page" & used the same method of measurements, but that won't happen. We (the USA) tried that back in the 70's (IIRC) & it bombed big time. One problem was getting people to try it & the biggest problem was agreeing on which METRIC SYSTEM to support. When it comes to THIS, the world is still a chaotic mess!
 
RE: The Fence Fan Dipole (FFD) A Quick, Easy and Inexpensive  
by WD8OQX on July 27, 2012 Mail this to a friend!
By the way, am I the only one here that thinks this design looks like the old AIR RAID SIRENS of a good while back?

I'm NOT making fun with this statement, I just was wondering, as it does to me. (& like to recall my childhood in such ways - the remember when factor, I guess - I get somewhat nostalgic at times)
 
RE: The Fence Fan Dipole (FFD) A Quick, Easy and Inexpensive  
by QRPNEW on July 27, 2012 Mail this to a friend!
VK3DWZ

Cant you get off your lazy a$$ and do a simple conversion? What do you think someone in the USA has to do when someone else writes an article in Metric?

There is a thing called google where you can search for and look for conversion tools if you cant do simple calculations!

DO you want him to come down there and bring the parts and a tape measure with dual measurements on them?

People are so demanding and critical of people who write these excellent homebrewing articles. If you cant do a metric conversion contact MFJ and order a fan dipole that comes in a packet!

Whats next? Someone going to complain that he is using the wrong font because of their bad eyes?
 
RE: The Fence Fan Dipole (FFD) A Quick, Easy and Inexpensive  
by K1AVE on July 27, 2012 Mail this to a friend!
Calculators are everywhere -
Quit the whining - this is a technical hobby afterall and most of the rest of the world uses metric.
Gene
 
RE: The Fence Fan Dipole (FFD) A Quick, Easy and Inexpensive  
by K1AVE on July 27, 2012 Mail this to a friend!
Or we can meet on the 43.47 yard band and discuss it.
 
RE: The Fence Fan Dipole (FFD) A Quick, Easy and Inexpensive  
by K8QV on July 27, 2012 Mail this to a friend!
Americans seem to be too stupid to learn the metric system. The exception would be drug dealers; they deal in metric measures all the time.

God forbid we learn a second system of measurement or even a second language like the rest of the civilized world.

Anyway, nice build on the antenna. Too bad that fence can't be used with a vertical.
 
The Fence Fan Dipole (FFD) A Quick, Easy and Inexpensive Mul  
by WA7KPK on July 27, 2012 Mail this to a friend!
Look, metric conversion is easy. All you have to remember is that the speed of light is 1.8x10^12 furlongs per fortnight and everything else follows from there.
 
The Fence Fan Dipole (FFD) A Quick, Easy and Inexpensive Mul  
by AC5WO on July 27, 2012 Mail this to a friend!
Good antenna information and pictures. One way to make this antenna more stealthy would be to use a purple martin house on a pole as the center support/place to hide a big ugly balun. This purple martin house from Home Depot even has somewhat ironic TV antennas on it.

http://www.homedepot.com/buy/s-k-american-barn-purple-martin-house-277692.html#.UBMSV6D5AdM

They even sell decoy birds to complete the camouflage.
 
RE: The Fence Fan Dipole (FFD) A Quick, Easy and Inexpensive  
by W2JD on July 27, 2012 Mail this to a friend!
My friend Ed, WY4J and I have built Fan Dipoles before, as a matter of fact, we were taking mine down today to put in an OCF 80 meter (and below), and the fan dipole will be modified to the bands that the OCF doesn't tune well. The 15 meter dipole will not tune if you have a 40 meter dipole in the fan, we played around with it, and got a 3:1 VSWR as you did. Mine had four wires, 40-20-17-10 meters, so 15 meters was tuned by the 40 meter dipole element. 6 meters will work also, but not great. I like the center feed that you have designed, and may incorporate it in my next iteration of the antenna. Good article.

Jose
W2JD
 
RE: The Fence Fan Dipole (FFD) A Quick, Easy and Inexpensive  
by KE5KDT on July 27, 2012 Mail this to a friend!
Thanks Howard, I really appreciate your article and have been using fan dipoles for a long time. Inches or metric, I thank you for submitting it, and taking the flak.

Howard the rest of my comments in the following paragraph are just for fun to take the complainer's line of thought a little further.

Could you please translate your article into all the languages that hams speak? It is short sighted for you just to print it in English. How dare you to expect the rest of the non-English speaking world to have to translate your article into their language to understand it. Ought to be a ham law or something.

All the best to you Howard.
Bob


 
RE: The Fence Fan Dipole (FFD) A Quick, Easy and Inexpensive  
by WD8OQX on July 27, 2012 Mail this to a friend!
QUOTE
RE: The Fence Fan Dipole (FFD) A Quick, Easy and Inexpensive Reply
by KE5KDT on July 27, 2012 Mail this to a friend!
Thanks Howard, I really appreciate your article and have been using fan dipoles for a long time. Inches or metric, I thank you for submitting it, and taking the flak.

Howard the rest of my comments in the following paragraph are just for fun to take the complainer's line of thought a little further.

Could you please translate your article into all the languages that hams speak? It is short sighted for you just to print it in English. How dare you to expect the rest of the non-English speaking world to have to translate your article into their language to understand it. Ought to be a ham law or something.

All the best to you Howard.
Bob
/QUOTE

Good one - made me laugh, & your point is very valid!
(just where DOES one draw the line of expectations?)
 
RE: The Fence Fan Dipole (FFD) A Quick, Easy and Inexpensive  
by W4VR on July 27, 2012 Mail this to a friend!
Interesting article. I used my neighbors trees for wire antenna supports for decades and they were always receptive to the idea. Good luck!
 
RE: The Fence Fan Dipole (FFD) A Quick, Easy and Inexpensive  
by N6AJR on July 27, 2012 Mail this to a friend!
Lots of ways to do a fan dipole, I have always been a "fan" of fan dipoles. cheep and effective.












 
RE: The Fence Fan Dipole (FFD) A Quick, Easy and Inexpensive  
by VK4NEF on July 28, 2012 Mail this to a friend!
Pity about the trees being in your neighbor's land.

VK3DWZ, I was working with imperial before metric here in VK, 1" is 25.4mm, therefor 12" or 1 foot by 25.4 is 305mm. I would suggest that you use a calculator and or a tape measure with metric / imperial markings available from your local hardware store. Also some antenna books contain the above information.

73
Eric
 
RE: The Fence Fan Dipole (FFD) A Quick, Easy and Inexpensive  
by G3LBS on July 29, 2012 Mail this to a friend!
We really must get to the promised land of disguising the Martin House with an antenna.
 
make it switchable?  
by KJ4ADN on July 29, 2012 Mail this to a friend!
Another crazy idea to add to it.

The pattern is basically a figure 8.

Would it work to add another set of wires 90 degrees, feed each set to a relay so you could switch directions (for some bands). don't know if you'd gain much on the lower HF bands (low antenna height), but it might work on the higher HF bands.

KJ4ADN - Bill
 
RE: make it switchable?  
by KB6QXM on July 29, 2012 Mail this to a friend!
Considering that 20+ years ago, I was the president of the joint Ford Aerospace/SRI amateur radio club, I have some deep respect for the SRI people. That said, I do not see the physical limitation for height. I would hang the heavy balun from one of my 200 foot redwood trees on my property. There are many tree people that are experienced tree climbers that have all of the tree climbing gear and will climb up a redwood tree, put in a steak and pulley for you for under $50.00. They will climb to the other trees and attach the other ends. All you need is the longer feedline.

If I had the actual math of length and seperation between the dipoles, I would make one for all bands from 160-6meters including all WARC and 60 meters.

How about material cost and time needed to build this antenna. Granted, fan dipoles have no gain such as a double-ended Zepp, but they are nice to have as you have one antenna, multiple bands and one feedline.
 
RE: make it switchable?  
by W6HDG on July 29, 2012 Mail this to a friend!
I think we can all agree that height is beautiful thing for most antennas. A switchable second set of dipoles would be an excellent idea if the antenna had sufficient height to achieve the typical lobes and directionality.

I found this article to interesting about dipole height: http://www.hamuniverse.com/wb4yjtdipolepatterns.html

One other item for anyone contemplating building a similar antenna. Hamuniverse has republished the article (with permission from eHam) and the pictures are a bit clearer for some reason - see http://www.hamuniverse.com/w6hdgfandipole.html
 
RE: make it switchable?  
by N4JTE on July 30, 2012 Mail this to a friend!
Thank you again Howard, great photos and detail with
real expectations from the the antenna you described.
Good work and great article, tnx again.
Bob
 
The Fence Fan Dipole (FFD) A Quick, Easy and Inexpensive Mul  
by K4KK on July 31, 2012 Mail this to a friend!
Well written and easy to understand. I, too, have been a proponent of the fan dipole and often push it toward new hams. Since they have demonstrated the ability to pass a minimal level of test, I assume that they know how to use a calculator or the internet should there be a need to change dimensions into metric (or back to SAE) terms.

One comment I would add is that for simplification, it is entirely possible to build with a single feed point and multiple wires from it rather than spaced along a longer tube. For some, that will help with minimizing visibility or maximizing portability.
 
RE: Separation Distance at the feedpoint?  
by W6HDG on July 31, 2012 Mail this to a friend!
Quote, "One comment I would add is that for simplification, it is entirely possible to build with a single feed point and multiple wires from it rather than spaced along a longer tube. For some, that will help with minimizing visibility or maximizing portability".

Thank you for that comment. If you look at the references on my article, you will see that most builders of the fan dipole adhere to the (now 40+ year old) SRI recommendation which asks for some separation at the parallel feedpoint and much larger separations at the endpoints. Yet, you see some commercial parallel dipoles which have no separation at the central tie and then only have inches between the parallel half-wave dipoles. In other words, they never fan out.

I know that my antenna had very little interaction when doing the pruning of antennas from longest to shortest dipole using a MFJ-259 antenna analyzer. But if you are only gaining easier tunability, I agree with you that it would be much more stealthy (and lighter) to have a much shorter top pipe.

Everyone is telling me to go higher (except my wife and neighbors, hi hi) so i might try another design on top of a fiberglass pole up around 30 feet. But that is for another day....
 
RE: Separation Distance at the feedpoint?  
by N6AJR on August 1, 2012 Mail this to a friend!
so.....




I have also used the single point feed and it works well. I have also tried the switched fan dipoles in an X pattern and it does give you a different set of "peak signals" but slightly less effective ae a single dipole in either direction.

I have also use a single fan dipole in the umbrella or astric * configuration.

I have also made fan dipoles out of sections of flat 5 or 3 wire ( radio shack) rotor cable.

this a fun and cheap antenna to play with and use or borrow an mfj 259b analyzer and peak it for exactly where you want it.
 
RE: The Fence Fan Dipole (FFD) A Quick, Easy and Inexpensive  
by STRAIGHTKEY on August 2, 2012 Mail this to a friend!
"God forbid we learn a second system of measurement or even a second language like the rest of the civilized world."

That would be SOCIALISM!
 
The Fence Fan Dipole (FFD) A Quick, Easy and Inexpensive Mul  
by W9GB on August 4, 2012 Mail this to a friend!
For 15 meters, lengthen the 40 meter antenna, so that, the dip (low SWR) point is 7.050 to 7.100 ..... Then the 3/2-wave for 15 meters will be 21.150 to 21.300
 
RE: The Fence Fan Dipole (FFD) A Quick, Easy and Inexpensive  
by KJ6UPZ on August 7, 2012 Mail this to a friend!
VK3DWZ

Remind me why everyone should just stop, drop, and roll to convert the measurements for you? Every time I've built something and it was metric, you want to know what I did? I CONVERTED IT MYSELF! I don't see all the SAE challenged people converting it for me...

Anyway, i'll step off my soapbox and get back to my rig, KJ6UPZ
 
RE: The Fence Fan Dipole (FFD) A Quick, Easy and Inexpensive  
by SV9ZP on August 13, 2012 Mail this to a friend!
When feeding multiply dipoles from a single feed line, dipoles need to be at right angles. This means that only 2 dipoles are accepted, so if more dipoles are placed together, RF cancellation will occur.
That is what theory says.
In practice,maybe 3 dipoles could be accepted, but with 5 dipoles setup, interaction between the elements surely takes place.
 
One note on tuning ---  
by W4DSN on August 21, 2012 Mail this to a friend!
Could someone convert the measurements to cubits for me, please?

My only serious comment is that there is some tuning required after the antenna is built because the elements will tend to interact with each other, especially with bands that are not harmonically related. This is most notable with the WARC bands, like 17m. It is less noticeable on bands like 80, 40, 20 and 10, although 15m elements will have an impact since it is not an even harmonic of 10 meters.
 
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