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The Fan Dipole Fence (FFD) - A multiband antenna Quick, Easy and Cheap



With W6HDG 
(Article courtesy of W6HDG and eham.net originally posted here , July 26, 2012.


Background
Multiband fan dipole is always a popular choice to get the antenna on multiple bands with a single feedline and antenna tuner without. Altitude is limited only by tall trees nearby and the cost minimal antenna. Antenna also somewhat hidden - especially if the 16-18 gauge wire can be used in sub 200 watt installation. antenna basically consists of two to five or more different half-wave dipole mounted parallel to a common feedpoint so feedline singe can be utilized. Several good design is easy to find on the internet or in the handbook antenna. Designs at present proposed (by the Stanford Research Institute data) feedpoint separated as much as 5.5 inches between the dipole and the low frequency (again) dipole can be about 4% shorter than 468/frequency in Mhz will dictate while higher frequencies (shorter) dipoles have about 4% more. Many designs also recommend "ugly balun" controversial choke in the design that is no more than 18-21 feet of coax close wound on a form 4 "or more non-conductive at the feedpoint.

There are certain drawbacks of traditional fan dipole in the wire often have to support the entire weight of the antenna and the balun. need to ideally spread out feedpoints to 5.5 inches feedpoint also make the area a bit tricky. Spreader complex should also be used to maintain each point end of the dipole taut and well separated when there are only 2 attachments. There can also be some interaction between the dipole and the detuning some may occur if the dipole including three frequencies that are multiples of the length of the dipole in the system (3rd harmonic). example 30 meters, 15 meters and 6 meter 1/2 wave dipole may not be possible if the 80 meter, 40 meter and 17 meter dipole there. A match may be obtained at 30 meter, 15 meter and 6 meter dipole using existing anymore but testing is needed. Finally, it is difficult to cut and tune the antenna, because the single strap or rope-pulley system supports the entire array, and it must be really down to the wire tuning or repair.

Destination
I'm just getting back on HF after a hiatus a few years and had moved to the neighborhood with some restrictions antenna. Rig my Yaesu FT-857D is and Astron 30 amp power supply. I do not have tall trees on the property but has a big feature on the property - tennis court 45 years with a 12 foot fence around it. every side of the fence is 120 feet long total (number sounds good for a fan dipole).

I decided to try a cheap antenna design as a starting point "just to get in the air." I think that if I am condemned section 10 of schedule 40 PVC pipe to the fence support center with hose clamps, I can get inverted-V arrive at about 20 feet in the center (not the ideal height for the DX, but it certainly can be used). I then knew that I could use the dipoles themselves as "the people" to support the center if at least two of the dipoles are attached to a short offset support on both sides of the fence. other dipoles could "bungeed" directly to the mesh fence to keep them tight.

Advantages of the Fence design my Fan Dipole (FFD) is that almost all solid fence that extends linear distance from the lowest band can be used. The central feedpoint balun can be made ​​from the two single-leg 4 "exhaust pipes with end caps for weather resistance. It can be attached and supported on the PVC pipe threaded adapter support center with proper plumbing and electrical metal threaded nuts are available in most hardware stores. Look under construction drawings. dipole separately each tied to a fence with a tarp bungee cord-like band tuning so each one does not need takedown overall dipole antenna can be easily attached and turned on retention / support writing throughout. drainpipe for testing, experimenting and improvements in the future. Finally, the distance between the dipole propagator at each endpoint can be achieved.

Construction
RG-8X coax and PL-259 connector with adapters are certain parts only ham radio. 
remaining parts are all acquired during several trips Home Depot nearest you:

1) 18 gauge stranded bare copper "ground" wire is around $ 17 for 250 yards and it works very well. The 250 feet was just a few feet short for all the dipoles so I made ​​my 17 meter dipole antenna weight of bare copper wire stranded me in hand. If there are copper-stained, can be quickly rejuvenated by soaking in a few ounces of vinegar with half a teaspoon of salt added. This allows the copper to solder-ready at the required locations.



2) Two leg 4 "ABS drain pipe with two end caps 
3) Ten feet 1 inch piece of PVC with schedule 40 PVC threaded adapter and metal retention nuts sold on the electricity for threaded pipe. three hose clamps to attach the PVC to the vertical members of the fence posts 
4) Copper clad pipe strapping, electrical copper lugs with setscrews (Burndy KA4CBAG2R), Ten 1/4 inch x 1.5 inch eye bolt, two solder lugs to induce attachment, ten 1/4 inches and a total of two lock washers twenty 1/4 inch nut (ten that came with eye bolts) 
5) Four short 18 inch pieces of PVC to be used as fencing "man" standoffs with four U bolts for attachment - see close-up shots. 
6) Ten tarp straps (bungee cords) 
7) 10 rectangular glass is made ​​from a single sheet of 12 "x12" of 1/8 "glass. Each rectangle about 3 inches by 1.5 inches with a hole drilled at each end of the long




Note: I use a coax-seal the copper lugs for screw cover set. 










Construction is fairly easy if you study the picture above. eyebolts I separate the 80-meter and 40 dipoles by a full 5.5 inches. I was irritated and separating 40 and 20 meter dipole with a 4.5-inch, 20 and 17 meters with a 3.5-inch dipole and 17 and 10 meter dipole with 3 inches. Each of the two copper-clad rope eyebolts long run along the inside of the pipe ABS. Coax lugs attached to the eyebolts closest to the "ugly balun". lock washer is used between the nut and the interior copper strapping. The balun itself is about 16 rounds of RG-8X (21 feet) with epoxy is used to seal the two holes. The RG-8X and then walked to the inside of the PVC pipe support. I use SO-239 barrel at the bottom of the pipe support for comfort. coax I paint, ABS and PVC pipe all the chocolate to keep things stealth.



Notes on using the two dipoles as "the people" to keep the support of thin PVC pipe straight: If I have bungeed all dipoles to mesh fence itself, I would not have the support in the "Y" to keep the PVC support standpipe. I can using two opposite rope for this purpose, but do not want to have any base mount support. So I made ​​18-inch extenders top rail grinding corresponding arc in the final piece of PVC and use U-Bolt through the PVC to create a solid impasse of the fence. Both "Y" can be achieved with the support plane bungeeing two short dipoles on each side of the fence with extenders. It has made ​​quite a vertical PVC pipe center with resistance to the wind we have seen to date.



Antenna is complete so stealth, quite difficult to photograph as shown below. Hopefully these images to give you a good idea of the appearance of support and at least 3 of 5 dipoles.



Dipole length, after adjusting for multiple dipoles with the help of an MFJ-259 antenna analyzer is about:

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

Result
FFD has obvious drawbacks - the non-portability, compromise and less likely if the interaction with the metal fence.

However, initial testing has been pretty good. During the IARU HF Championship hour surgery July 14 to 15, 2012, I worked 6 countries in 4 bands including Aruba, Cook South Island, Japan, Argentina, Canada and Mexico.

The antenna has a SWR received at 80, 40, 20, 17, 10 and 6 meters, and contact is made ​​on all bands without a tuner antenna. 15 meters can be used.

SWR results are as follows:
3.8 Mhz 1.9 (SWR was 2.5 to 3.70, 2.5 and 3.8 in 3.9 in 4.0) 
7.2 Mhz 1.3 (under 2.0 SWR across the band except 2.6 at 7.00) 
14:13 Mhz 1.0 (SWR is below 1.5 in all bands) 
18:14 1.0 Mhz and the same in all bands 
2.9 and 21.3 Mhz band together around 
28.5 Mhz 1.2 ( SWR is below 2.0 on all bands except 2.2 to 29.7) 
52 Mhz 1.4 (SWR is under 1.8 in all 4 Mhz band)

I can add a tuner to get a better match bandwidth at 15 meters and over 80 meters. 's not clear whether a dedicated 15 meter dipole will work well or if there would have been detuning - I have not tried it.

I have no illusions about the feasibility of DX antenna. But dipoles and inverted-V antenna can make a good - especially at lower frequencies where the multi-element antennas impractical. variety of multiband dipole as described here, when tuned well, do not have to suffer passable in performance during monoband dipole at the same height. Advantages of single feedline can not be overemphasized.

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

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

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

N4UJW, "multiband dipole FAN IS BUILD FOR ALL BAND ANTENNA HF excitement", September 2010, see 
http://www.hamuniverse.com/multidipole.htmlDescription: The Fan Dipole Fence (FFD) - A multiband antenna Quick, Easy and Cheap Rating: 3.5 Reviewer: Unknown ItemReviewed: The Fan Dipole Fence (FFD) - A multiband antenna Quick, Easy and Cheap
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