A priori: please read the whole (long) post because my context and experimental boundary conditions are explained.
Shortcut: the NEC input file of the experimental 40m FCP vertical is here.
One of the hard core participants in the GAMESS project worked at ‘my’ faculty.
He introduced me, as one of the few students, into supercomputing in the mid and late 80′s.
Best of all, it gave me access to -what became known as- . . . the internet!
During this time I experienced tensions between ‘practical’ and ‘theoretical’ oriented chemists.
The latter category was able to ‘synthesize’ molecules inside a (super)computer.
Although some outcomes were chemically/physically correct, it simply was impossible to synthesize these
outcomes with (at that time) current synthetic organic chemical methods.
Thus, from a practical perspective these ‘theoretical’ molecules didn’t ‘exist’.
Later … with new preparative methods some of these molecules actually have been synthesized in laboratories.
This is a complex (quantum mechanical) area and not discussed here because I forgot almost everything ; -)
For example, theoretical chemist Dr. Y believed that calculating H2 properly was only possible with 6-31+G* basis set,
Dr. X stated that STO-3G is enough (because he was pissed off on Dr. Y using too much load/time on the super computer ; -).
From that moment I decided to become an ‘end user’ of this quantum chemical knowledge and stay out of these discussions.
Just look at these orbitals as the ‘radiation pattern’ of electrons. See below.
During my PhD period I used my experience in computational chemistry in order to synthesize,
isolate and crystallize molecules in reality. The combination of practical methods and computers delivered me a few
‘firsts’ (like this one) in organometallic chemistry and peer reviewed academic publications at that time.
Therefore, antennas are molecules. They follow the same or perhaps slightly different laws of quantum physics.
You can build antennas in reality and/or model them with software. Like in chemistry, I (try to) do both.
In university I also learned an important lesson for life:
The fact that I don’t know how and why something works and/or exists, does not mean it doesn’t work and/or exists!
Folded counterpoise (FCP)
Around 10 years ago Guy Olinger K2AV published a solution for owners of small lots to become active
on 160m relatively efficient. He named his solution the folded counterpoise, or FCP.
Since then the FCP is subject to heavy debate.
At that time I also read his results and reports and categorized K2AV’s solution as ‘Tell Sell Amazing Mike‘ (SK).
One of my reasons to classify the FCP as such, was that it needs very specific conditions to ‘perform’.
Due to ‘research and development efforts’ it is firmly stated that the FCP only works in conjunction with a very special
‘isolation transformer’ (sounds to me like the ‘Flux Capacitor‘ from the movie “Back to the Future” ; -).
This ‘isolation transformer’ must be made with one specific #2 material powdered iron toroid core (Amidon T300A-2)
having 20 bifilar turns of teflon sleeved double polyimide insulated AWG14 wire.
Secondly, it is stated that the FCP only works with blank (i.e. non insulated wire).
For me it’s suspicious when requirements are mentioned so precisely.
It resembles the commercially well known slogan:
“Due to intensive R&D <insert productname> with compount XYZ, <insert productname> is very effective”.
Subsequently customers testify how excellent the product is.
This is exactly what happened with the FCP.
By chance I recently read some more/new information -and discussions!- on the FCP (google on it to find out).
Summarizing there are two categories:
1. people who firmly believe the FCP works
2. people who firmly don’t believe the FCP works
These two categories try to convince each other with orthogonally different statements and theories,
built on their perspectives on laws of physics and mathematics. Subsequently these perspectives are discussed, etc.
DM9EE (ex-DL2OBO) is an example in the 1st category and the first who reported successfull use of FCP’s in a 80m 4-square.
KN2M also constructed FCP verticals and 4-squares. Other people report using FCP verticals during 160m contests
and state that disproportionally good scores were obtained. W4KAZ is such an example.
It appeared to me that people who actually built antennas with FCP’s according to K2AV’s instructions fall in the
first category. People who didn’t construct antennas with FCP’s and model antennas fall in the second category.
Now … what is ‘true’ and/or ‘reality’?
One way to find out is ‘just do it’ and build a FCP system myself . . .
New incoming mail
(Very) recently two ingredients caught my attention.
1. K2AV published his FCP in the ‘National Contest Journal’ (NCJ) please download and read this (later)
2. HC1PF uses an inverted-L with FCP
Ad. 1 The ARRL is an esteemed organization with benchmarking magazines and publications like QST, QEX and NCJ.
If the FCP is all nonsense or a hoax editors of QST, QEX and NCJ would not have routed K2AV’s paper towards NCJ.
It may seriously damage the image of NCJ.
Ad. 2 Perhaps more interesting . . . HC1PF is Luis IV3PRK. Luis went to Ecuador in 2014.
However, due to ‘some living problems’ he wants to return to Italy soon.
IV3PRK is an avid 160m experimentator and often referred to as ‘Radio Italy’ on 160m.
Luis is a HAM who wants to get the most out of his 160m station within his specific boundary conditions.
Like me, Luis is open to new things and investigates them.
If it works and measurements confirm . . . it works. Period.
There is virtually nothing Luis didn’t measure and/or calculate in order to improve his 160m station.
If there may be a better alternative or technique, Luis is the first man to investigate, try it,
and share his findings with you and me.
Moreover, when Luis is not able to reproduce measurements/results others obtained with similar equipment
he is the first to be in your mailbox with in-depth and intrusive questions.
So . . . why on earth Luis HC1PF ended up using a FCP in conjunction with his radiating element
(inverted-L) after several decades of successfull results, experiments and experience on 160m ???
Several YouTube videos are available in which Luis HC1PF is recorded with good signals all around the world.
All this information fired up my curiosity . . .
Antennas are molecules
As already stated, I consider antennas as molecules. I prefer to calculate and build them.
The combination of theoretical and practical skills gives insight in when a converged solution of a computer model is ‘real’ or not.
I.e. being able to establish if a molecule -although perfectly in line with ‘theory’- ‘exploded’ inside the model.
The same can happen witn modeled antennas.
Similar to quantum chemical models, I am an end user and will not go into discussions concerning validity and/or correctness
of e.g. ground parametrization in NEC2 vs. NEC4 or that kind of stuff. I have the NEC2 engine and have to deal with that.
If someone is willing to sponsor me the NEC4 engine, please do ; -)
Having said this, this antenna modeling software is not written by morons, but by very capable and highly skilled scientists
working in well esteemed institutes, and perhaps know Maxwell’s Laws better than Maxwell did himself!
Last, but not least, I have no degree in RF-design or electrodynamics but have good experiences with 4NEC2.
4NEC2 prevents ‘surprises’ in practice and yields insight on e.g. degrees of freedom in antenna designs and their behaviour.
Convergence criteria yield information on (relative) sensitivity of variables and more practical knowledge concerning
performance, design and actually building antennas in practice. It’s similar with synthesizing molecules behind the fume cupboard.
While actually building antennas from modeling experiments I learned a lot from the conversion from ‘theory’ into practice.
As of today 4NEC2 never let me down and helped me getting good (and sometimes excellent) performing antennas.
First real 40m FCP experiment
A good HAM friend of mine is captured in the story of his life:
For whatever reason he always produces weak field strenghts.
Last week he invited me for a BBQ at his campsite at a HAM fest, known as ‘Bentheim‘ (Germany).
The campsite was saturated with antennas, hung between scarce trees.
He had put up a 40m inverted-V above his caravan with the feedpoint around 11m high.
However, several (40m) dipoles of other HAM friends crossed or paralleled his antenna.
The day before I worked him in the evening from my home town and his signal was, as ever … weak.
Distance was around 150 km and an inverted-V with 11m apex has to act as NVIS antenna.
I tried to explain him that his environment was an illustrative example of a ‘recipe for disaster’ as (resonant) antennas couple.
Destroying the radiation pattern and performance is the result.
The chance that all these randomly hanged out ‘resonant’ 40m dipoles form a passive array is zero.
Now the reason why people from this HAM fest were so weak became manifest to me.
My friend demonstrated that the VSWR50 of his antenna was around 1.3, which was a miracle to me anyway . . . ; -)
His conclusion was, due to the VSWR50, his antenna ‘was good’. . .
Last year we built a good performing vertically polarized 40m-deltaloop (in identical environment)
which annoyed the owner of the camping site as well as other HAMs/guests.
They almost broke their necks by tripping over the horizontal wire above the ground.
Secondly, there were more guests than last year, which meant less space. Therefore a deltaloop was a ‘no go’.
I decided to skip the beers and watching movies, and suggested him to build an antenna that was ‘different’
and also told him this antenna would be a real experiment. That is, any outcome would be new to me.
Quick & dirty googling didn’t result in 40m FCP antennas. So, would we be the first ones to try a FCP on 40m . . . ?
While others enjoyed drinks in the sun, I enjoyed modeling a 40m FCP vertical in the same sun on a laptop.
I decided to follow basic knowledge in conjunction with my own ideas, superimposed on K2AV’s counterpoise shape.
1. Starting point was a vertical part for 1.83 MHz, resonant above ideal GND -> Z = 37.2 + 0 Ω and length = 39.96m.
This results in an electrical length of (39.96/163.8) * 360 = 88°. Enough in line with theory.
2. Knowing that in this case Z equals the radiation resistance (Rrad) the vertical part was raised to K2AV’s height (2.5m or 8 ft).
3. K2AV’s FCP dimensions were entered into the model.
While W8JI used a FCP height of 10m (30 ft) and got Z = 34.5 – j196 Ω, I got Z = 31.2 – j206 Ω. Fair enough, similar trend.
It may be clear the antenna is far from resonant (j ≠ X ≠ 0). The calculated phase angle φ = -81.4°, it almost can’t get worse . . .
Similar to W8JI I noticed that varying the size of the FCP brings the contraption into resonance (j = X = 0).
Doing so resulted in Z = 33.5 + j0.1 Ω at a ‘half length’ of around 12.26m (40ft), also compliant with W8JI’s results.
However, the real part of my impedance result is significantly lower than W8JI’s result, 33.5 vs 39.6 Ω respectively.
Anyway, I was able to reproduce his trend.
The claim K2AV obtained a match with his very specific ‘isolation transformer’ attributes W8JI to ‘considerable flux leakage‘ (?)
of the toroid core material used in conjunction with the reactance of the 20 bifilar windings. It magically adds around +j200.
A ‘resonant match’ on 160m in conjunction with only K2AV’s FCP dimensions and material is the flabbergasting result.
HC1PF uses this magic ‘isolation transformer’ too. However, he had to use a trick known as overloading.
He enlarged the horizontal part of his inverted-L to obtain R = 50 Ω on 1825 kHz, as measured with his VNA.
A series capacitor was used to tune out the resulting +j reactance.
I deliberately decided NOT to use an ‘isolation transformer’ for two main reasons:
a. I don’t believe in ‘Flux Capacitors’ and don’t trust ‘flux leakage’
b. There was no ferrite toroid core available ; -)
The NCJ article states FCP ‘half length’ amounts 10m (33 ft) on 160m and 5m on 80m with 10cm (4″)
spacing between the wire. So I bluntly scaled the original FCP ‘half length’ for 40m.
4. The 40m FCP was ‘scaled’ to 7.075 MHz with an initial ‘half length’ of 2.5m and empirically placed 1.5m above
‘Average Real Ground’ (conductivity = 5 mS/m, ε = 13). FCP wire spacing was 10cm.
5. My friend said he had a spare glassfiber pole of 12.5m length. Thus, the max. vertical length amounts 12.5 – 1.5 = 11.0 m
With this data the model calculated Z = 48.2 -j 78.6 Ω , |Z| = 92.2 Ω . . . interesting.
6. Converging the vertical part of my ‘molecule’ to resonance resulted in Z = 62.4 Ω with a 13.59 m long vertical.
Considering the available (spare) pole this was too long . . . never mind. Mechanical details can be solved anyway.
This resonant impedance didn’t surprise me, as reducing radial lengths in verticals, increases R (and losses!).
Let me make this clear, the real part of Z (R) is not always Rrad!
Bluntly assuming 37.2 Ω from the original Rrad (although the vertical part is longer) the model ‘added’ 62.4 – 37.2 = 25.2 Ω.
Not considering structure losses and assuming the ‘extra resistance’ (R) is due to ‘earth losses’
the efficiency amounts 37.2 /62.4 = 60%. This is not very good, but also not very bad . . .
7. Returning to the original vertical length (11m), FCP height of 1.5m, 10cm wire spacing, converged the ‘half length’ of the
FCP to 277.5 cm with Z = 48.8 + 0.1 Ω. Even more interesting . . . from a matching perspective.
Trusting the ground model in NEC2, antenna efficiency (assuming Rrad = 37.2 Ω and no structure losses)
now increased to 37.2/48.8 = 76%.
NOT considering debates and fights concerning the ‘crappy’ ground model of NEC2, this is not too bad at all . . .
From my experiences 4NEC2 does not perform too bad in practice. Taking velocity factors of wires/conductors into
account when building antenna constructions minor/no fiddling is necessary.
‘Real Average Ground’ as ground model seems to work for me in most cases.
Also in these cases where I (mis)use the ground to ‘force’ the impedance of an antenna to a ‘desired’ value.
I succesfully use this trick for several years to ‘force’ my 40m vertical deltaloop implementation to 200 Ω,
so it can be matched with a 4:1 UNUN.
Based on my modeling experiences the 7. antenna (see above) would be a nice candidate for our experiment.
Now . . . let’s go back to K2AV’s statement on ‘cancelling currents’ in the counterpoise, giving the FCP its ‘unique features’.
Fig. 1 depicts the current distribution around the feed point in my 40m-FCP computer vertical. Click on the picture to enlarge in a new tab.
Figures 1 and 2 are zoomed to give a more precise look at the counterpoise, knowing that the current distribution in the vertical part
is well known (and predictable). By the way, it doesn’t matter whether the counterpoise is exactly 5/16λ long (cf. K2AV or NCJ article)
or its length (≠ 5/16λ) converged to resonance (j = 0).
If you don’t trust, just fill in the appropriate values for 160m into the NEC model (vide infra).
You’ll see it doesn’t matter.
What doesn’t matter? The current distribution in the FCP!
It can be clearly seen that the model didn’t null out or cancelled currents, as suggested by K2AV in figure 1D of the NCJ article.
Now let’s look at the current phase distribution inside our 40m candidate in figure 2.
Bear in mind this antenna is calculated to be resonant, so φ = 0°.
If you had calculated a non resonant antenna, the ‘starting’ phase angle (of course) differs.
It can be clearly seen in fig. 2 that the radiator and counterpoise are homogeneous 180° out of phase.
There is no current phase difference visible. Just as it should.
Note: The phase angle flips between 180° and -180° in the first segments of the FCP. This is due to the used segment size in the model
but 180° and -180° are equal. If, for your psychological convenience you want to eliminate this, fiddle with the FCP segment sizes
or bring the antenna out of resonance somewhat. At resonance there is a singular point.
If I remembered Kirchoffs Laws from school properly current cancellation within the same conductor is impossible.
In other words, if ‘current cancellation’ takes place in a FCP, a FCP is not a counterpoise.
Note: NOT considering TEM lines like coax and e.g. 1/4λ (coax) baluns.
In the latter current can flow on the inside and outside of the braid.
Presumably K2AV refers to the phenomenon that e.g. having more (elevated) in line or symmetrical radials,
the current in each radial is divided by the amount of radials. Resulting in less current per radial because there is less flux density,
i.e. the current is smeared out on a larger surface with possible reduction of earth losses as a result.
Or . . . perhaps the difference in radiation patterns between a T-antenna, having two in line top loads, and an inverted-L.
Anyway, if I remembered physics class in high school well, the fields ‘cancel’, not the current (cf. corkscrew rule)
From my perspective, ‘current cancellation’ in a FCP is busted and so is the need for an ‘isolation transformer’.
Back to my 40m FCP experiment
The results from 7. nevertheless revealed a possibility to ‘synthesize’ my modeled ‘molecule’ from scrap material
with a small foot print on my friends HAM fest lot. It unfortunately appeared that his 12.5m spare glassfiber pole was damaged.
Max. 8.5m could be saved and erected. He was located at an edge of the HAM fest terrain.
This left one option open: an inverted-L with sloping topload. By chance my friend had plastic tubes with two 4 cm separated holes.
These boundary conditions were entered into the model. Practical values were produced after optimalization,
of which lowering the FCP was one of them. It may not be the most optimal solution from a combinatorial perspective,
but from a practical perspective it was. The resulting NEC file is here.
A visualisation of the contraption showing current distributions is depected in figure 3.
The calculated radiation pattern is shown in figure 4. Feed point information is given in figure 5.
Click on each picture to enlarge in a new tab.
Figure 3. 40m inverted-L with FCP Figure 4. Hor + vert radiation pattern Figure 5. Feed point information.
The calculated radiation pattern (fig. 4) is OK. I will not go into detail concerning the claimed ‘gain’ of the calculated antenna,
otherwise I will end up in ‘basis set’ discussions.
Because the vertical part is <1/4λ 50Ω matching is required.
We needed a match for the lower SSB portion of the 40m band (7060 – 7100 kHz).
Given the available (scrap) material the good old hairpin method (matching against admittance, Y = 1/Z) was selected.
The trick is to make such a short antenna resonant (converge to j = 0) [on a somewhat higher frequency]
and then shorten (in this case) the topload until Zp reaches 50Ω at the desired frequency.
In figure 5 it can be seen that @7.075 MHz Zp = 52.2 // -j 85.5.
Only one coil of around 2 μH (+j 85.5) parallel to the feed point is required for a match.
It seemed that my friend only had PE-insulated 2.5mm² copper wire.
From my experience, using a velocity factor (vf) of 0.95 for this type of wire is a good starting point.
Oh oh, another deviation from the original FCP recipe . . . insulated wire! ; -) Also busted . . .
All dimensions were multiplied with 0.95 and I decided to multiply the ‘half length’ of the FCP with the used vf.
An alternative could have been applying the vf for the total length of the FCP wire.
After building the contraption accordingly I wanted to measure its impedance with a VNA.
Unfortunately several nearby fellow HAMs only got MFJ-259 (so not 259B) devices.
This left me with only ‘SWR’ and R values, no X . . .
The MFJ was connected through a 50cm short cable to the antenna feedpoint. The antenna ‘dipped’ around 6.85 MHz.
I decided to reduce the open end of the FCP with around 60cm.
After this, I measured a dip at 7.1 MHz with R around 32Ω, and SWR was roughly around 1.8.
I couldn’t believe my eyes . . . very suspicious! (instead of promising . . .)
The vertical part of the inverted-L was 8.5 – 1 = 7.5m. This results in a monopole length of (7.5/42.37)*360 = 64°.
The radiation resistance of a 64° thin monopole amounts ca. 30Ω (cf. 5th ed. “Low Band DXing”, ON4UN, fig. 9-8B).
Next, the topload had a sloping angle of around 65°, reducing the electrical height (l/λ) thus reducing Rrad more.
Now what? I asked for another MFJ-259 and reproduced the first MFJ measurement.
Queer . . .
Because nobody else could help me out with yet another (type of) VNA I decided to follow Luis HC1PF’s approach:
“If this is what I measure, this is what I measure.”
For my own convenience I decided to conclude that my friends caravan and other nearby 40m antennas were ‘assisting’ me.
Given the circumstances I couldn’t imagine a more plausible explanation.
A 2 μH hairpin coil was wound on a small plastic ‘smoothy’ bottle and connected to the feed point.
After this, the MFJ-259 displayed a SWR of nearly 1 with R around 50Ω. Fiddling with winding spacings on the bottle forced
the MFJ-259 to keep the SWR needle rock solid in the left corner @7.08 MHz.
An improvised ‘ugly balun’ choke was made of several feedline windings. The antenna was connected to
my friends FT-857 inside his caravan tent. There the good match was confirmed.
Below some pictures of the contraption. Click on each image to enlarge in a new tab.
First on-air experiences with the experimental 40m FCP
My friend had a coax switch (not a hoax switch ; -) and we decided to compare his inverted-V and the freshly built inv-L FCP antenna.
His immediate observation was that, compared to his inverted-V, ‘different’ stations could be heard with the FCP vertical.
Very nearby stations (< 70 km) were stronger on his inverted-V, all others had significant better SNR’s + ‘displayed’
signal strenghts. Sometimes up to four (4) ‘S-points’ on his FT-857 . . . (besides a ‘bar’ the FT-857 also displays e.g. ‘S7′).
Of course the intrinsic difference between an inverted-V and this vertical (e.g. take off angle) is obvious.
However, at first glance the results were remarkable, also at medium distances (150 – 400 km).
<Tell Sell Amazing Mike (SK)>
My friend is no DXer and it was getting dark so I decided to scan the band. I worked UN7AR after a first call through an EU-pile up
on 7094 kHz with reasonable signals (57-58 or so) with 65W PEP. Path length is around 3400 km. When switching to
the inverted-V UN7AR disappeared into the noise/QRM, so I didn’t bother to disturb his EU-pile up with antenna experiments.
</Tell Sell Amazing Mike (SK)>
After this promising but peculiar result I took my first beer and enjoyed a barbecue with fellow HAM friends and our partners.
Qualitative (not quantitative) experiment
After the BBQ, my friend was very curious if his new antenna would improve his signal in The Netherlands.
During summers there is a Dutch 40m ‘holiday round’ (‘Gooische Ronde’) with people on vacation spreaded all over Europe.
Also lots of Dutch HAMs located in The Netherlands join in.
When net control asked for subscribers I called in with the vertical, deliberately not signing /DL.
My friend eagerly wanted me to inform others that we were testing his new antenna.
I told him that this would screw up the experiment.
After a short while it was my slot.
During my slot I ‘randomly’ switched between the vertical and the inverted-V. ‘Talk punch’ was kept equal.
When finished, the immediate response of net control was that there was something wrong with my setup.
The conclusion was a loose contact somewhere because my signal fluctuated severely. I was asked to try it again.
I shortly came back on the inverted-V, asking if ‘this’ was better. Net control and others replied the signal was
weak and that I should fiddle a little. Subsequently I switched to the vertical, said I fiddled a little and asked if ‘this’ was OK.
The unanimous response was ‘that everything was OK now’ and that I shouldn’t touch anything and leave it this way.
Some (relatively nearby) people remarked they weren’t able to hear me properly on the inverted-V . . . ?
In my second slot I confessed building ‘a vertical’ and I was not in PA but in DL instead,
and that I switched between the two antennas during my initial slot.
After this confession more people called in and agreed that the signal on the vertical was significantly better.
As expected, there was a relation between signal improvement and distance.
One participant in Italy perceived +10 dB (from ‘S9′ to ‘S9 +10′) in favour of the vertical, which could be plausible.
One Dutch station, we never heard before, suddenly reported being /MM on a yacht in a harbour in
West Scotland (distance around 1100 km) in salt water.
He said he ‘had’ to comment on this ‘remarkable’ signal difference. For him it was a difference between ‘day and night’
and reported even a larger perceived difference of +20 dB in favour of the vertical . . . (?)
Stations in the Mid/West Netherlands reported around one S-point difference or, a difference between
‘mediocre’/'no’ and ‘good’/'comfortable’ copy.
Although I initially didn’t tell I was using an experimental FCP vertical, who bothers anyway ; -), the overall and
summarizing conclusion from all the participants, regardless from their distance, that evening was:
“That vertical works better than the inverted-V”. I can’t deny to confirm this was reciprocal.
I experienced the same trend in reception while switching between the inverted-V and FCP vertical.
Conclusions and remarks
This experiment was only one experiment. Therefore it has no use to draw conclusions, other than that the
experimental 40m FCP vertical in this particular situation seemed to work better than the inverted-V @11m high.
In fact, it’s ‘comparing cows and horses’.
My conclusion is that there is no such thing as ‘current cancellation’ in a FCP.
An ‘isolation transformer’ is unnecessary when making the antenna resonant.
Nevertheless, having had enough experience in building verticals (with ground nets, (tuned) elevated radials, deltaloops etc)
I have to admit that the experimental contraption performed remarkably well that evening.
Especially considering the ‘minimal’ and small earth net/counterpoise in conjunction with the small antenna foot print.
However, there have to be (significant) earth losses, reducing antenna efficiency, involved . . . but this wasn’t confirmed
with the ‘quick & dirty’ VNA measurements.
Therefore, the measured impedance of the FCP antenna is a miracle to me and I certainly want to build another one to thoroughly
investigate it with proper equipment. I also want to compare its performance with an optimized deltaloop
and/or ‘reference 40m vertical’ in the (near) future by measuring (calibrated) field/signal strenghts.
One final conclusion may be that this experiment was fun, we had a great day, nice BBQ and lots of laughs : -)