FCP or Folded CounterPoise (idea by K2AV)
There is a new method published by K2AV and W0UCE called FCP-Radials or „Folded CounterPoise“ Radial.
please read also the NEW (Mai 2012) article in NCJ by K2AV about FCPs folded counterpoise:
It is: an elevated, non-radiating, space saving, folded radial (counterpoise) which serves to get 50 Ohm to your vertical antenna feedpoint . If you can not use ground radials and if you CAN NOT ensure that your (paired) elevated radials are NOT-radiating,
give the FCP a try.
My short summary:
If you can lay out many ( 60-120) ground radials: do so. This is the best way you can do (no compromises).
If you can install (per vertical) 4 elevated ( >3m / 8ft) radials of 1/8 wavelength with a common loading coil (per vertical): do this
fullsize elevated radials are causing problems if you are not experienced or not careful…beleive me!
next best choice (for me) is FCP or OE3REB radial style.
I have chosen the FCP style – after reading all the details from K2AV, I found this the best solution for my 4 square !
If you have enough land and time : use ground radials: please do not even think about elevated radials!
After all, you will install ground radials after a few seasons.
FCP and elevated radials are not replaceing a dense ground screen. They are just the best solution for SOME hams with
not haveing a big lot or restrictions with buildings etc… 🙂
The FCP radial (about 25m long) is folded back and forth so there is NO radiation from it and it fits in nearly every garden. Not only it is a space saving installation, I am sure it is SAFER to install a FCP radial that will NOT interact with ANY OTHER radials around THAN to install a 2 or 4 elevated radial system which is maybe even fullsize…… there will be crossing radials and so on and if any of the radials will have a different resonance frequency than the wanted design frequency, it will mess up the cancellation of the 2 or 4 radials structure. Remember: if you install a single elevated radial for your (elevated) vertical, the radial will radiate ! horizontally! means high angle radiation! means it’s not realy, what you really want. This antenna is more like a bent dipole with 50% verical radiation and 50% horizontal radiation. Is this what you want ? If you install PAIRS of radials ( 2, 4, ..) they will (hopefully) not radiate. A good way to tune them is: Install your vertical part. Install ONE radial. Cut it to your desired operating frequency. Do not change the vertical length now. Disconnect the first radial. Connect the second radial. Cut it to the desired operating frequency too. Connect first radial. So BOTH radials are now connected to the coax outer shield. Check where your lowest SWR dip is. It should be on your desired frequency. The Dip might not be as LOW as with only one radial connected but at least the Dip is where it should be. You can use now a Hairpin across Coax inner and outer or you may install a variable C in the vertical part to lower the SWR. I haven’t really had the time to test my new FCP Radial system on my 4 square yet. I have a feeling but I haven’t done precise comparisons yet, so pse QRX…….
Info on FCP-Radials
Please visit W0UCE and K2AV at their website www.w0uce.net for more info on FCP radials…. they have invented the FCP. More info there!
btw. I am lazy, I bought my FCP-transformer at www.balundesigns.com
FCP hints: Do not use insulated wire! Raindrops on the Radial might detune the FCP because of the isolation. Guy recommends bare wire. I have used enameled Wire (Kupferlackdraht 2mm) for my FCP. I can tell you later how they work and if there is a change in wet weather. I would never use wire with a thick insulation because K2AV warns you NOT to use it. But I had the enameled wire here and I hope that the layer is so thin that there will be no capacity from the raindrops. K2AY also wrote in an email to me, that water/rain does not from drops on bare copper wire. Thats why he recommends BARE wire….I think if you live in the dessert, normal insulated wire won’t cause any trouble. But ask him, it is just my idea….
This is how the feedpoint of my southeastern vertical looks like……
I think the spreaders are important so the wires are parallel.
Haveing enough space, it is not a big deal to build a 4 square nowadays…..you may order everything plug&play from www.dxengineering.com (Comtekboxes) if you are satisfied with -90-0+90 angles and „standard“ gain…
.if you want a killer 4 square like PA0GMW and others, you will have to build your own phase network with 8 directions and: you eed excellent ground and terrain and no neighbours.
Finally I decided to build my radials as mentioned in the article of OE3REB (see link below). He recommends 1 elevated radial which is folded back so the radiation cancels out and there is no radiation from the Radials so only vertical radiation (low take off angle) from the vertical part and NO (horizontal, high angle) radiation from the radial. It is easy to tune and is roughly 8m into two directions = 16m wingspan. Because of the smaller footprint it might not interact so much with other radials and antennas around. I found this to be the best solution for me. I would use the same solution being on a beach front.
I use a relay and a 1000pf doorknob capacitor to switch from CW to SSB. So I tuned the radials to 3420khz. Each vertical must be tuned while the other three verticals are „left floating“. (pull the coax off). Otherwise the will couple into each other while tunig……they will couple into each other later and they have to do so! Otherwise the 4 square will not work.
so tune each single antenna to 3420. When connected to the hybrid they will interact and the resonance frequency will shift up about 100khz, so then you have your array working in the CW DX window.
to shorten the antenna for SSB part, try a 1000pf doorknob capacitor. It is current maximum, you do not need vacuum capacitors but take good care of the conections and wires (high currents!)
Again: elevated radials will work, but you can run into trouble when they interact with other antennas or other radials of the array. If you can, you better try ground radials. You might save time when you have to put up 4radials only but then the trouble starts and you can be sure that 60+ ground radials will work good to excellent.
A post of Tom W8JI at the topbandreflector:
Some food for thought on this that might make limited space counterpoise systems work a little better and be easier, faster, and cheaper to install.
This is just intended to get people to think about the system a little more in a different way.
Folding a wire to simulate a longer wire or element generally has no electrical advantages. It does not make a wire act like it is longer, so far as radiation goes, for the same net common mode current distributed in the conductor system.
I thought I would model this and verify if it applies to folded radials…
I just modeled several antennas, and found the folded counterpoise (with #16 wire spaced one foot) needed to be about 80 feet long to be resonant on 160 meters. This makes perfect sense.
The models of 132 foot length verticals of #16 wire show the following impedance, gain, and + – frequency 2:1 SWR BW. (this is „one-side bandwidth“, or how far up or down you can go from resonance with a perfect
broadband matching system) Counterpoises are all 8 feet high, and I just
parallel connected the existing wires when loading coils were added to keep the playing field level (same effective wire bundle diameters) :
132 ft vertical over perfect ground 37.7 ohms 4.93 dBi 55kHz
with one folded counterpoise 40.4 ohms 4.64 dBi 25 kHz
Real ground set at .005 s/m
one folded CP 53.3 ohms 0dBi 35 kHz
four folded CP 43 ohms .44 dBi 44 kHz
one Q=200 coil loaded 80 foot radial 51 ohms .21 dBi 40 kHz
four coil-loaded 80 ft radials 42.4 ohms .47 dBi 50 kHz
The widest bandwidth and lowest loss counterpoise, with radius limited to 80 feet is coil loaded, even with modest coil Q in each radial. This is typical even for folded antennas, where a lumped inductor is generally just as good or better in every way than folding a wire.
By the way, a check of voltages shows the voltage from radial center point to ground is 226 volts RMS at 1500 watts when four radials are used. This is for infinite isolation. While this clearly shows we need a common mode choke, as most elevated radial or sparse radial systems do, why does a voltage this low demand an isolation style transformer?
It seems to me a few thousand ohms common mode impedance, or less if we use a buried cable or ground rod on the cable below the antenna, would be more than enough. I would think a conventional common mode choke at the radials, along with a few ground rods on the cable shield on the shack side of the choke, would be more reliable and easier to implement.
No matter what we do, differences will be very small unless we do something wrong. There just isn’t any magic. 🙂
73 Tom W8JI
important Links with 4 square topics
This is a Flash-Gallery. To see more pictures, please click on the thumbnails, the PLUS+ sign , or press „play“. Enjoy.
REMEMBER !!! this is my OLD 4-square ! with the FCP it worked better than with 1 or two elevated radials systems. Now I bought my neighbours house and garden and have installed a ground mounted 4 square. I do beleive in single element elevated verticals. I will not try again with an elevated radial system in a 4 square, exept with an FCP system.