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ANTENNAS ( AERIALS ) 3
SCERRI VK4FUQ DISCUSSES
HIS ANTENNA EXPERIENCES
Renewed Love Affair With The Quad Loop Antenna.
A recent chain of events has led me back to the beginning in a
sense! Going back to the 'early' days (the mid to late
was a huge fan of one wavelength loop antennas like the Delta Loop and
the like, however over the years the simple half wave inverted V has
become my favourite antenna for HF use for various reasons.
Recently however a number of unusual events has seen me re- erect my
old fixed wire Quad loop for 20 m. It is currently working
well. It is an antenna with some endearing features and
I suppose that many Amateurs would know of the story of the Quad's
beginnings at the broadcast station HCJB in Ecuador where owing to high
transmitter power and high altitude, the yagi antenna in use was slowly
destroying itself due to destructive coronal discharge and
arcing. One of the stations engineers, Clarence Moore W9LZX
conceived the idea of a 'pulled open' folded dipole with no 'ends' as a
possible solution. It worked! A little later on
realised that this 'Quad' antenna was also a pretty good antenna and
thus the Quad mystique was born!
The original version of the Quad as used at HCJB was a two element
design, reflector and driven element, and subsequent HF designs also
included directors. Each element contains approximately one
wavelength of wire in a closed loop except for the driven
element. The parasitic elements are tuned in a similar
yagi antenna parasitic elements. At this QTH I use one single
loop resonant midband on 20 m as a bidirectional radiator (in and out
of the loop). I use the formula, length in feet = 1005/
which appears to be sufficiently accurate. A check with a
coupled GDO at the feedpoint can be used to check the resonant
frequency. Even on its own it is an excellent
is it such a good antenna?
Over the years despite the true excellence of the Quad design, many
'myths' regarding the operation of the Quad have abound. One
these involves the inherent gain of the Quad element. I have
written in many older but well regarded antenna texts a quoted a figure
of 2 db 'inherent' gain over a dipole for the Quad element.
is incorrect. Whilst a single Quad element has some slight
over a dipole it is probably closer to 1 db, not 2 db.
of the real truth it is a very efficient radiating system.
general radiation pattern is similar to a horizontal dipole but with
deeper nulls off the ends*.
In my own installation, my loop
erected as a diamond shaped loop hung off a 33 ft pipe mast.
'looks' to the North and South and is fed at the bottom, horizontally
polarized with high quality 300 ohm feeder as a tuned line, and of
course a good quality 4:1 balun and ATU is necessary. One
the Quad Loop's operation that I find particularly valuable is its low
noise 'receive' profile. As a person who has been plagued at
by RF noise of many kinds, but mainly power line sizzle over many
years, the low noise profile of the loop is much appreciated and the
apparent cancellation of power line sizzle has to be heard to be
believed!. It is much 'quieter' than dipole type
operating well out of its resonant frequency range, it is also an
excellent low noise receive antenna for general short wave listening
applications, where the low noise pickup is also evident and
Practical considerations: As one wavelength of
wire is used in any given loop design, available space is a limiting
factor and indeed 20 m is the only band where available space allows
its construction at this QTH. It does require a fair bit of
People who successfully build large rotatable Quad arrays have my
complete respect! Thankfully though the diamond shape is
supported off a simple pipe mast and installation is quite
straightforward assuming sufficient space is available. I
used 2.5 mm
plastic covered 'earth' wire to make up my 20 m Quad Loop and it works
fine. According to various references the actual loop 'gain'
somewhat dependent on loop shape, with a circle giving the highest gain
and the 'delta' triangle shape the lowest. The square or
diamond shape is not too far off the circle in terms of inherent
maximized gain. That's nice to know!
The Quad Loop in operation:
guess this part gets a little subjective but there is something a
little unique about even a single Quad Loop, in my opinion.
mentioned earlier the low noise receive pick up profile is a major
plus, in my opinion. Interestingly enough this aspect hasn't
mentioned too much in the antenna books based on my
experience that has 'led me back' to the loop was the realisation of
matters pertaining to directivity. Although a simple dipole,
V or Quad Loop is 'broadish' in its radiation pattern there are nulls
off the ends which are actually somewhat more pronounced with a Quad
Loop. Thanks to some compass checks I finally realised why my
V was not performing as well as expected. It was not actually
in the correct intended direction. It was in fact almost in
of the antenna. Earlier evaluations with my Quad Loop
the same positional flaw, and owing to the deeper nulls of the Quad
Loop 'off the ends', this actually showed the Quad Loop up worse than
the inverted V! This basic error took many years to
realise! D'oh, as
a certain TV cartoon character might exclaim!
operation the Quad Loop is one of those highly dependable and
consistent performing antennas 'putting out' a signal much better than
it should, based on the minimal complexity of the design! S
readings are always well up on the meter and I feel this is a HF
antenna ideal for QRP HF duties. A highly recommended HF
Err Is Human' or 'When One Can't See the Forest for the Trees!'
Yes there is an aspect of 'humble pie' to this story but I have decided
to tell it anyway, a simple story of not being able to 'see the forest
for the trees' or the inability to realize a very basic long term
error! For some years I have had weekly skeds with an Amateur
friend of mine in vk3 on 20 m. Over the years we have had
excellent skeds with good signals in both directions despite both of us
using basic single element antennas. However in recent times
'path' has become poor and many of our weekly contacts have been
essentially non- existent!
As a consequence I have been giving much thought to improving my 20 m
antenna set-up. One recent Saturday after lunch whilst having
doze and staring at the Amateur Radio Map of the World in front of me,
it occurred to me that perhaps my inverted V dipole was not really
'looking' at the vk3 area at all, as I had previously thought that it
was. Well, it wasn't! It was firing essentially to
and NW from this location in Northern vk4 and was skirting the edge of
the vk3 area, a long way away from the intended target area in vk3,
confirmed by a couple of basic compass bearing checks! I
ventured down to the backyard and reorientated the direction of the
inverted V to 'look' due south and due north. Before I did so
noted the signal strength of Radio Australia on 15.240 MHz from the
Shepparton transmitter with the 20 db attenuator in circuit as a
'reference' signal . It was 5 db over S9. When I
to the shack a few minutes later after repositioning my inverted V, the
Radio Australia signal was now at 15 db over S9, a definite
I sat there for a few minutes as the significance of this sank
in. In a flash of inspiration I decided to put my wire 20 m
loop back up again as now in this 'new' position it was completely
clear of obstructions unlike its previous position in the same location
as the inverted V in its original position when it was used for
comparison testing with my inverted V, where it had a frequent
unfortunate tendency to get caught up in our family's clothes
hoist! The Quad loop was hauled up the mast in a few minutes
('Murphy' was obviously away for the day), and I did more receive
tests. Radio Australia was still at around 15 over S9 on the
loop. I made a quick phone call to my friend in vk3 and
a contact on 20 m.
The result: Despite poor and disturbed propagation (a 'K' index of 5),
a good solid contact at the 100 watt SSB power level with no problems
resulted with the S meter indication at both ends 'well up' on the
meter throughout the lengthy contact. I was quite happy, as
might expect! The whole incident has been a real eye opener
had not properly appreciated the importance of correct aiming, even of
a basic single element antenna. One does not ordinarily think
a single element antenna as a 'directive array'. An 'array',
perhaps not, but 'directive', yes! I had always assumed that
single element antenna's radiation pattern was broad enough to be
relatively non critical! Well, yes it is but there is a
limit! The Quad loop actually does have a slightly sharper
pattern with deeper nulls 'off the ends' than a dipole making optimised
positioning even more important.
In the time since that fateful day I have rethought many aspects of
this general situation and why I had not properly appreciated it
before. My other antennas for HF are separate inverted V
for 40 m and 80 m. As they are physically quite long, in this
they fit in the backyard pretty well as dictated by the available
space. For this reason they run essentially in the N to NE
to SW directions, firing broadside to the wires, yet they give
excellent coverage to the desired vk coverage area as evidenced by my
weekly 40 m Sunday morning WIA news broadcasts. This, despite
being positioned poorly and firing mostly E (out to sea) and W, in
theory anyway. Why? Well, it is worth remembering
inverted V antennas tend to have a somewhat more omnidirectional
pattern than true horizontal dipoles, and combined with the fact that
dipoles on low HF frequencies and close to real 'Earth' tend to
exacerbate this tendency! A big blob of radio frequency
going just about everywhere and up is the main result. 20 m
band where perhaps these 'omnidirectionalising' effects are
substantially absent, making more precise positioning more important
and practically mandatory. Well, it certainly works out that
in practice at this QTH!
Well my 20 m Quad loop is still up and whilst I'm still not totally
convinced that it is noticeably better than my half wave inverted V for
various reasons, such as 'effective height' considerations, it is
working very well in practice and I have to concede that it does have
some other unique virtues such as excellent noise cancellation on 20 m
and also when used as a general coverage 'receive' antenna which as a
keen SWL, I find a most desirable quality! Especially on the
lower short wave frequencies and the AM medium wave broadcast band this
noise cancellation and the resultant improvement in 'listening' S/N
ratio has to be heard to be believed! For this reason as well
its good performance on 20 m, I think I might leave it up! I
admit to having a considerable aversion to noise of all kinds!
Although in some ways I'm a little annoyed at how silly this error was,
thankfully the antenna still worked quite well despite its non- optimum
positioning into the vk3 area. Sometimes I think that it
preferable if things simply didn't work at all when things aren't right
rather than 'sort of working, after a fashion'. But perhaps I
shouldn't be too annoyed as this sort of thing happens in life all the
time, or so I'm told. Hi.
* * * * *
of The Cubical Quad
As reported by W6SAI and W2LX in "All About
Cubical Quad Antennas", Radio Publications Inc. 1972
In the year 1939 a group of radio engineers from the United States
travelled to the South American republic of Ecuador to install and
maintain the Missionary Radio Station HCJB, at Quito, high in the Andes
mountains. Designed to operate in the 25 metre short-wave broadcast
band with a carrier power of 10,000 modulated watts, the mission of
HCJB was to transmit the Gospel to the Northern Hemisphere, and to tell
of the missionary work in the wilds of Ecuador. To insure the best
possible reception of HCJB in the United States a gigantic four element
parasitic beam was designed, built and
erected with great effort and centered upon the heartland of North
The enthusiasm of the engineers that greeted the first transmission of
Radio HCJB was dampened after a few days of operation of the station
when it became apparent that the four element beam was slowly being
destroyed by an unusual combination of circumstances that were not
under the control of the worried staff of the station. It was true that
the big beam imparted a real "punch" to the signal of HCJB and that
listener reports in the path of the beam were high in praise of the
signal from Quito. This result had been expected. Totally unexpected,
however, was the effect of operating the high-Q beam antenna in the
thin evening air of Quito. Situated at 10,000 feet altitude in the
Andes, the beam antenna reacted in a strange way to the mountain
atmosphere. Gigantic corona discharges sprang full-blown from the tips
of the driven element and directors, standing out in mid-air and
burning with a wicked hiss and crackle. The heavy industrial aluminum
tubing used for the elements of the doomed beam glowed with the heat of
the arc and turned incandescent at the tips. Large molten chunks of
aluminum dropped to the ground as the inexorable fire slowly consumed
The corona discharges were so loud and so intense that they could be
seen and heard singing and burning a quarter-mile away from the
station. The music and programs of HCJB could be clearly heard through
the quiet night air of the city as the r-f energy gave fuel to the
crowns of fire clinging to the tips of the antenna elements. The joyful
tones of studio music were transformed into a dirge of doom for the
station unless an immediate solution to the problem could be found.
It fell to the lot of Clarence C. Moore, W9LZX, one of the engineers of
HCJB to tackle this problem. It was obvious to him that the easily
ionized air at the two mile elevation of Quito could not withstand the
high voltage potentials developed at the tips of the beam elements. The
awe-inspiring (to the natives) corona discharges would probably
disappear if it were possible to operate HCJB at a sea level location.
This, however, was impossible. The die was cast, and HCJB was
permanently settled in Quito.
What to do? Moore attacked the problem with his usual energy. He
achieved a partial solution by placing six-inch diameter copper balls
obtained from sewage flush tanks on the tips of each element. An
immediate reduction in corona trouble was noted, but the copper orbs
detuned the beam, and still permitted a nasty corona to spring forth on
the element tips in damp weather. Clearly the solution to the problem
lay in some new, different approach to the antenna installation. The
whole future of HCJB and the Evangelistic effort seemed to hinge upon
the solution of the antenna
problem. The station could not be moved, and the use of a high-gain
beam antenna to battle the interference in the crowded 25 metre
international short-wave broadcast band was mandatory. It was
distressingly apparent to Moore that the crux of the matter was at hand.
Birth of the Quad
In the words of W9LZX, the idea of the Quad antenna slowly unfolded to
him, almost as a Divine inspiration. "We took about one hundred pounds
of engineering reference books with us on our short vacation to
Posoraja, Ecuador during the summer of 1942, detrmined that with the
help of God we could solve our problem. There on the floor of our
bamboo cottage we spread open all the reference books we had brought
with us and worked for hours on basic antenna design. Our prayers must
have been answered, for gradually as we worked the vision of a
quad-shaped antenna gradually grew with the new concept of a loop
antenna having no ends to the elements, and combining relatively high
transmitting impedance and high gain."
A Quad antenna with reflector was hastily built and erected at HCJB in
the place of the charred four element beam. Warily, the crew of tired
builders watched the new antenna through the long operating hours of
the station. The vigil continued during the evening hours as the jungle
exhaled its moisture collected during the hot daylight hours. The
tension of the onlookers grew as a film of dew collected on the antenna
wires and structure, but not once did the new Quad antenna flash over
or break into a deadly corona flame, even with the full modulated power
of the Missionary station applied to the wires. The problem of corona
discharge seemed to be solved for all time.
The new Quad antenna distinguished itself in a short time with the
listeners of HCJB. Reports flooded the station, attesting to the
efficiency of the simple antenna and the strength of the signal. In his
spare time, Moore built a second Quad antenna, this one to be used in
the 20 metre band at his ham station, HC1JB, in Quito.
At a later date, after Moore had returned to the United States, he
applied for a patent covering the new antenna. the fact that the
Quad-type antenna radiated perpendicular to the plane of the loop was
deemed by the Patent Office to be of sufficient importance to permit
the issuance of a patent to Clarence C. Moore covering the so-called
Cubical Quad antenna.
To understand the characteristics of the antenna, it is convenient to
borrow the description of the Quad element given by W9LZX - "a
pulled-open folded dipole."
This interesting account is taken from William I. Orr's book, "All
about Cubical Quad Antennas". In it, technical details are addressed at
length. However, there are only two pages devoted to the four element,
full sized quad. Orr calls it the "Monster Quad". We know why.
Wavelength Quad Loop Optimisation.
Initial Investigations: In previous articles I've written on the
single Quad loop antenna I mentioned possible concerns about the
'effective height' of loop antennas compared to dipole or inverted V
types of antennas. This is an unfortunate fact! Sadly this
has been confirmed by many on air contact signal strength observations
between my Diamond Quad loop antenna and a test half wave inverted V
dipole cut for 20 m at the same top mast height over recent
On 'transmit' anyway, the simple inverted V dipole was the superior
antenna by several 'S' points! Not wishing to give up on my
beloved Quad loop I've been embarking on a long series of trials, tests
and evaluations all aimed at improving the general 'transmit'
capabilities of the loop antenna at 'lowish' mast heights.
observations are ongoing, but some improvement has indeed been
achieved. The modifications involve shifting the feedpoint from
the bottom to the top of the loop in an attempt to optimise the loop
'effective height', along with the inclusion of a home brew 1:1 choke
(or current mode) balun at the feedpoint, whilst feeding the antenna
with 300 ohm balanced feedline as a 'tuned' line.
In the past I have been somewhat impressed with the quasi- magical
properties of these choke baluns in 'forcing' equal currents into a
load and this, combined with 'top' feeding seems to have improved the
general 'transmit' performance of the loop possibly through improved
'decoupling' of the feedline from the actual 'radiating system' (the
The use of a choke balun may seem unnecessary when
balanced feedline is being used, however the choke balun is useful in
compensating for 'incidental' unbalance and asymmetry in the antenna
system and I suspect this is also the reason for the improved noise
cancellation noted. Although in this new feedpoint position the
loop polarisation remains horizontal, I have noted an unmistakeable
reduction in noise pick up over an already low noise receive pickup as
mentioned a moment ago.
These so called 'choke' or 'current mode' baluns have many interesting
applications in unconventional duties. Apart from this
application in conjunction with 'balanced' feedline I have also used
them in the past to feed a 'groundplane' antenna being fed with coax,
another application where it might be thought that the use of a balun
(or 'unun') was unnecessary, however its use was necessary in order to
stop the braid of the coax interacting with the resonant radial system
Further Investigations: This investigation just keeps getting
more interesting! It has often been my personal observation that
one discovery then makes other things possible, and as such has been
the case with this investigation. One slightly disturbing thing
noted with 'top' feeding through a 1:1 choke balun was that under
'some' conditions power line noise pick up was actually quite bad
depending on local weather conditions, indicating that a particular
local power pole mast probably had faulty or electrically 'leaky' pole
'hardware'. This noise pick up made reception difficult, yet at
other times the noise pick up was very low as was expected with loops
Further thinking inspired me to try one other
experiment, that of feeding the loop at one side resulting in nominally
'vertical' loop polarisation. I had tried this in the past with
slightly disappointing and generally inconclusive results.
Overall there was no real improvement compared to feeding at the bottom
as originally arranged (horizontal polarisation), along with other
strange observations such as a significant narrowing of the SWR
bandwidth and detectable mast 'interaction' despite using the same
length of feedline and all else being the same, when fed in one side
and vertically polarised!
Quad loop for 20m and side feed
position with choke balun
However this time there was a difference, feeding through the 1:1 choke
balun. So I tried it, and the difference was massive!
Despite the loop now being 'vertically' polarised, the general power
line noise pick up was much reduced under all conditions, making
reception of even weak signals easy and a pleasure! DX
performance seems improved, indicating a lower radiation angle in this
feed position and most interesting of all, the 'narrowed' SWR
bandwidth and the mast 'interaction' noted on previous occasions did
All of these changes seem entirely due to the
inclusion of the 1:1 choke balun, thus showing the great value of its
inclusion. These devices have quasi - magical properties!
Overall I am very happy with these improvements. Actually, I am
Quad loop for 20m and side feed
position with choke balun
The choke balun itself couldn't be easier to make! I made mine
simply by winding about ten turns of 1.25 mm enamelled winding wire as
a 'tight bifiliar' winding on a small piece of ferrite rod leaving a
small space between each adjacent bifiliar turn ('super glue' type
adhesives help keep things in place!) This type of balun is not
'polarity conscious' as such, simply connect the feedline to one end
and the antenna feedpoint to the other.
I simply covered the
balun in self amalgamating tape to provide some protection for the
winding, but as is obvious in the photos that is how it is mounted in
the air along with a little silicon sealant applied to all
73. Felix Scerri vk4fuq.
For the sake of 'completeness' it occurred to
me that perhaps I should
do one more experiment with my Quad loop, shifting to feedpoint
position back to the original bottom (horizontally polarised) position,
this time feeding through a 1:1 choke balun. I am currently
evaluating this configuration although a number of different things are
The operational SWR is definitely widest in this feedpoint position
although the SWR bandwidth widened in all feedpoint positions tried,
due to the use of the 1:1 choke balun. Noise pick up (again due
to the effect of the 1:1 choke balun) is again impressively low, but
ongoing evaluations over a longer time frame will indicate the best
feedpoint position for optimal noise cancellation. It is worth
remembering that every QTH (location) may give differing results in
this respect as every QTH is highly individual along with their
respective noise sources!
The one very obvious result of this series of experiments is the great
value of the feedpoint 1:1 choke balun regardless of whether coax or
(tuned line) balanced feeder is being used. There is little or no
doubt that it's addition has been highly beneficial regardless of the
feedpoint position used, in terms of reduced noise pick up and generally
improved antenna efficiency both on transmit and receive within the 20
m band. Allied with this, I've noticed that the resonance of this
antenna has become more 'apparent' after the inclusion of the 1:1 choke
Tuning on either side of the 20 m band it is now more readily noted
that the general noise pick up has become (just noticeably) greater,
something that I had not noticed previously, although the loop remains
'low noise' on receive. From a speculative viewpoint this appears
to be additional confirmatory evidence that the choke balun is very
effective in 'decoupling' the feedline from the antenna, allowing the
loop to function as intended as a truly resonant and independent
As an aside, it is interesting to observe that baluns do not appear to
have been regularly used with Quad antennas. From memory I can
only recall seeing one Quad article in the past that recommended the
use of a feedpoint balun. I have often seen the recommended use
with 50 ohm coax, of a quarter wave matching section of 75 ohm coax as
a means of providing an impedance 'step up' to the nominal 120 ohm
resonant impedance of a Quad loop, but no balun. Given the
improvement I've personally witnessed through the use of a feedpoint
choke 1:1 balun, perhaps it's time we did so more routinely!
Conclusion: This has been a fascinating exercise! Clearly
the performance of a Quad loop antenna is affected (to a greater or
lesser extent) by its feedpoint position. The main alteration
here is polarisation and this has implications on several things,
namely noise pickup and signal radiation angle. As touched on
earlier, every QTH (location) is a little different and therefore so
will be the results. If one is in the mood to investigate the
possibilities then a wire Quad loop with insulators at each corner is
probably the 'way to go', as then the loop's polarisation can be
shifted easily by the simple exercise of physically rotating the
loop. The other important conclusion to come out of this research
as mentioned earlier, has been the great value of a feedpoint 1:1 choke
balun. I have praised these devices numerous times. The
reduction in general noise pick up with the balun in use is
unmistakeable and most welcome, and in addition the loop just seems to
'work better' regardless of the feedpoint position with a feedpoint 1:1
choke balun in use.
29/04/09 - 2/5/09
* * * * * * *
Since the last update to
this discussion, although I had wanted to go no further with my
research, indeed this has happened 'helped along' by the discovery of
an interesting article on the so called 'hybrid' balun. Before I
discuss this interesting balun, a couple of words on my Quad
Loop. I have settled on 'side feed' that is, vertical
polarisation. In this QTH vertical polarisation gives me at least
two and a half S points less power line noise pickup than horizontal
polarisation, and sometimes the difference is even more dramatic!
Yes I know that seems to go against 'conventional thinking' on the
subject of noise pick up but at least at this QTH, it is a fact!
Other QTH's, of course may be the opposite!
Back to the 'hybrid'
balun. Information on this unique type of balun can be found
at http://www.arrl.org/qex/2005/qx9roos.pdf It is simply a
series connected 1:1 choke (current mode) balun with a voltage mode 4:1
voltage balun. The combination is said to represent 'the best of
both worlds', as it were. My extensive testing with this type of
balun appears to confirm the claims for this type of balun when used
with a station ATU. So much so that I no longer recommend the use
of a separate feedpoint 1:1 choke balun, at least when the loop is
being fed with balanced line as a 'tuned feeder'. I now advocate
the use of this 'hybrid' balun in conjunction with a good station ATU
with direct feed to the loop feedpoint with balanced line as a 'tuned
Extensive on air testing
with this type of balun being fed from my T match tuner has been
excellent in practical use with very low apparent loss and excellent
current balance at the antenna load. The really good (and easy)
thing about this type of balun is that it can be easily 'retrofited' to
existing voltage mode only 4:1 balun arrangements that are normally
incorporated into commercially made ATU's.
On other little changes,
another interesting thing I'm evaluating at the moment is the placement
of a half wave 'counterpoise' beneath my Quad loop at around 1.5 metres
above the ground, as a means of reducing potential 'earth loss'.
This experiment follows on from another interesting article I've also
recently read in an old copy of the Australian 'Amateur Radio' magazine
(November 1996). The original article used this half wave
counterpoise below a dipole for 160 m however I see no reason why it
cannot be used on other (higher) frequencies as well. Certainly
the counterpoise does have an effect of the loop as noted by a
detectable 'tightening' in the SWR bandwidth with the counterpoise in
place as explained in the original article. Evaluation of this
counterpoise is ongoing. It is my thought that with
vertical polarisation of the loop, earth loss may become more of an
issue so this counterpoise may have real value in reducing earth losses
and improving overall antenna efficiency.
Digressing on to the
performance of loops in general terms, also in recent times it has
become apparent that on some ionospheric paths the loop may be 'too
good' given the inherent lower angle tendencies of loops compared to
dipoles, inverted V's and the like especially at lower heights, where a
higher overall radiation angle may indeed be advantageous over a more
'local' path eg across vk (Australia). The various graphs
supplied by the IPS in Australia are somewhat enlightening as
ionospheric propagation is indeed a complex thing.....interesting
though, a bit like life itself!
Unwanted Mast / Antenna Interaction
This is an issue that I consider very much underestimated in its
possible negative impact on antenna performance. In previous
installations of this article I have commented on interaction between
the mast (about 33 ft in length) and my Quad loop antenna, especially
when the loop has been vertically polarised. As 33 ft is
essentially a 'worse case situation' (a resonant half wave length), I
have frequently wondered if the loop performance has been compromised
by a metal pipe mast of this length and if so, what are possible ways
around it? I did not set out the make a pipe mast of this
particular length, but sadly things just turned out that way!
Earth stake at base of 33 foot pipe
mast holding up Quad Loop 002
Very recently I've been giving the whole matter a great deal of thought
and a solution was found through a rather unrelated matter, that of
lightning protection! In the end I drove a five foot length of a
copper plated steel electrician's earth stake into the ground near to
the base of the metal pipe mast and electrically bonded the two
together with a short length of braid material.
After driving the
earth stake into the ground it was determined that although 'in the
ground' through a piece of water pipe cemented in the ground, no
measurable electrical connection to earth was found at the mast,
possibly exacerbating the coupling between the loop and mast as a
'floating' half wave element.
In the time since installation of the earth stake, 20 m contacts have
indicated clear improvement in strength, sometimes dramatically.
To be perfectly honest, an exact analysis of the mechanism involved is
difficult to come up with, but purely on the basis of signal reports
there is no doubt that things have definitely improved. A bit of
a revelation actually.
ARRL Guy Wire Interaction Chart
Interestingly enough in my
very old copy of the ARRL Antenna Book,
there is a very interesting table on 'guy wire' lengths to avoid in the
various Amateur Radio bands and the length of my (electrically
floating) metal pipe mast was right in the middle of the range to avoid
in the 20 m Amateur Radio band. No, I'm not surprised that there
was undesirable interaction between the mast and loop antenna!
Vertical polarisation would be the worst possible case, but horizontal
polarisation is still not ideal all things considered. Even more
interesting in this table is the statement that 'grounded' wires will
exhibit resonance at odd multiples of a quarter wavelength',
effectively, in my case anyway, shifting the resonance out of the 20 m
band, as I understand it anyway. This is certainly consistent
with my own observations of improved performance.
Possibly a loop antenna is more badly affected by mast interaction as
wire exists in all geographical directions despite 'defined'
polarisation unlike say, a dipole or similar antenna. Be that as
it may be, I love my 20 m Quad loop antenna to bits....and now it's
even better. The possibility of antenna/ mast interaction is
definitely a point to watch on your own antenna installation, and as an
aside I now (hopefully) have better lightning protection!
* * * * * * * *
In a brand new discovery allied with the general subject of unwanted
interaction, a series of interesting observations and 'chance'
discoveries in this shack and QTH have made me aware of yet more
examples of unwanted interaction, this time between different
antennas! Specifically between my 20 m Quad loop and 'one' leg of
my 80 m dipole which 'runs past' my quad loop although not at a
particularly close distance, but close enough it would seem judging by
It would appear that (powerline) noise is being picked up and
're-radiated' by one leg of my 80 m dipole (fed with balanced line
directly as a 'tuned line') onto my quad loop causing a large increase
in 'apparent' noise pickup on the loop. This was proven whilst
listening on 20 m with the loop and simply grounding one particular leg
of the 80 m feedline here in my radio shack. It is quite bizarre
but simply amazing to observe an at least 2 S point drop in noise pick
up on the loop when one leg of the 80 m dipole is grounded with no
negative effects on received general signal strength! It makes
general listening a lot easier as one might expect, and as an added
bonus the noise blanker then works more effectively at reducing the
Why this is happening is difficult to explain but the effect is quite
real yet and despite the obvious 'coupling' between the two separate
antennas there is no apparent shift in the transmit SWR or other
deleterious effects on the loop's general performance when one
leg of the 80 m dipole is grounded to reduce the noise pickup.
Strange but very welcome! Antennas....don't you love them?
With antennas, the general possibilities are seemingly endless.
Radiation Angle - The
forgotten factor in antenna performance
Over the last few months as a consequence of various evaluations with
different one wavelength single loop antennas, I've come to realize
that there is one very important, yet seemingly forgotten or at least
underestimated factor in overall antenna performance, that of the
antenna radiation angle. Everybody seems to be 'chasing' antenna
'gain' as a matter of some priority whilst my most recent research
suggests that optimised radiation angle for the path desired is at
least as important as 'gain' if not more so.
The analogy I use to
define antenna gain is that of bright spotlight with higher gain being
represented by a brighter spotlight. In a way I see this as
somewhat of a 'brute force' solution. Obviously a brighter
spotlight will be seen at a greater distance however my observations
indicate that optimised antenna radiation angle is a more elegant
approach and if combined with appreciable antenna gain, the results can
be most impressive indeed!
One of the really nice things about one wavelength loop antennas is
that polarisation, and as a direct consequence radiation angle can be
changed at will by a simple change of feedpoint position even with the
loop at low physical height. This does not seem to have been much
realised in the past as the 'traditional' way to feed a Quad element
was always at the bottom and as a consequence, horizontally polarised
and a reasonably high radiation angle. In contrast, a simple
horizontal dipole type of antenna needs to be placed high above the
ground in order to reduce the radiation angle when horizontally
polarised (the usual situation). For very low angle performance
from a yagi on 20 m, I have seen written that the optimum height is
roughly 1.5 wavelengths (105 ft or thereabouts). Considerable
mast and tower engineering is needed as a result!
one wavelength loop at low height can easily produce low angle
vertically polarised radiation at around 20 degrees, a much easier
engineering achievement! The type of actual polarisation of sky
wave propagation through ionospheric refraction is essentially
unimportant given the polarisation scattering that inevitably takes
place, however what is important is low angle take off.
My long time interest in general short wave listening has shown me the
value of low angle radiation at least 'on receive' as when listening on
the loop up on the 19 metre broadcast band, some greater distance
stations are much better copy on the loop when comparing a 20 m
inverted V dipole and a Delta Loop vertically polarised for low angle
radiation both 'looking' in the same directions, (time signal station
WWVH in Hawaii and the BBC World Service relayed from somewhere in
Asia, on 15.310 MHz) as shown in the audio
file. 'Reciprocity' applies on transmit applications as
well. Allied with this is the realization that for much inter VK
working, at least for the higher HF frequencies, low radiation angles
are actually a distinct disadvantage, resulting in poorer apparent
This neatly explains why Quad loops used at this
QTH in the past have been frequently 'less than ideal' for more local
working. The are also other relevant factors of course, but too
low a radiation angle is the predominant one in my opinion.
Indeed I have found that for local working on the higher HF bands,
traditional (bottom feed) horizontal loop polarisation resulting in
higher radiation angles is preferred. I am presently working
relay switching of alternative feedpoints in order to optimise working
conditions. The possibilities are amazing.
I've recently embarked on
a whole new series of loop experiments, this time with a Delta Loop (3
sided equilateral triangle) one wavelength loop. In actual fact
Delta Loops were my first loop antennas many years ago and a number of
interesting articles recently found on the 'net have been most
inspiring. Indeed my experiments with my Delta Loop have made me
realize how very little I knew! My Delta Loop is of the 'apex up'
variety and my experiments have centred around the possibilities
afforded by altered feed position.
Although the SM5JAB
article is based on a loop designed for 30 m, my loop scaled for 20 m
as shown in reference 2 confirms the practical observations in the
SM5JAB article. Switching feedpoint is essentially like using a
completely different antenna! The low angle/ DX performance with
vertical polarisation at this '1/4 wavelength feedpoint position' is
extremely impressive to the detriment of more 'local' working where
higher radiation angles are more suited (around the general VK area,
for example). Effective height appears not to be overly important
in this configuration, making the Delta Loop an excellent performer at
lowish mast heights.
Interestingly enough, for
reasons that I cannot quite understand my vertically polarised Delta
Loop outperforms my Quad Loop when also vertically polarised in low
angle/ DX coverage! Why, I don't know although I suspect that the
'quarter wavelength' feedpoint position possibly results in a more
defined low angle vertically polarised lobe. Whatever the true
reason, it works superbly! Specifically for DX working, this
simple antenna is very highly recommended!
Essentially a Delta Loop
follows the same length formula as all one wavelength loops in general
of 1005/ f = length in feet, but a loosely coupled GDO or antenna
analyser can be used to check for the resonant frequency. I am
using balanced feder all the way to the feedpoint as a tuned line using
a 'hybrid balun' and ATU for matching down to 50 ohms
'unbalanced'. This feedline system works very well.
I have to admit that the last month or so of intensive loop research
has been rather exciting, almost like those early days in 1985 when I
first gained my 'full call' Amateur Radio licence, and discovering the
magic of one wavelength loops for the first time!
This latest research dealing with altered feedpoint position and the
implications on radiation angle has been incredibly enlightening!
I've since placed my diamond Quad loop back up vertically polarised
(side feed), and I'm quite gratified to say that the low angle/ DX
results I've obtained have been identical to my vertically polarised
Delta Loop and if anything the diamond Quad loop should have 'slightly'
more gain by virtue of slightly increased internal enclosed area.
Another interesting change has been the re-inclusion of a feedpoint 1:1
choke balun. In the past after discovering the so called 'hybrid
balun', I no longer recommended a feedpoint balun however I now think
that its inclusion is a good idea, even with balanced feedline feed as
a 'tuned' line.
Certainly the use of a feedpoint 1:1 choke balun is recommended in the
excellent SM5JAB Delta Loop article, and after placing it once again in
both my earlier Delta Loop and present diamond Quad Loop, a very
significant widening (without any additional loss) in SWR bandwidth was
noted indicating much improved decoupling between the feedline and the
loop antenna itself. I am using a simple ferrite rod cored 4:1
'voltage' balun in my shack following my T match ATU in conjunction
with the 1:1 choke balun at the feedpoint of the loop and fed with high
quality balanced 300 ohm as a 'tuned line'. This overall feedline
system works very well with very little loss. If using all coax
feed with a 'quarter wavelength' matching section of 75 ohm coax then
the 1:1 choke balun is mandatory!
I think I've finalised things now, more or less (maybe). In
general terms vertically polarising my 20 m loop has been a bit of a
revelation to be perfectly honest, now that I've finally worked out and
realised the implications on radiation angle! I am hearing just
so much more compared to previous horizontal polarisation (and high
angle) radiation, especially during the night time hours where
previously the band would appear quite 'dead'. Although 'closer
in' working may be less than optimum with vertical polarisation, it
probably isn't quite as bad as I first thought, at least here in
vk! I don't feel that I'm losing out much at all with vertical
73 Felix v
23/10 & 27/11 2009.
a (very) Stupid Mistake!
Although I consider myself
quite ok with HF antennas, very recently I realised a basic (very
stupid) long term error I'd made that prevented optimum operation from
my favoured HF antenna type, one wavelength wire loops. In recent years
they just never seemed to perform as well as they should have and
despite many, many investigations the mystery was never actually solved
and I guess the expression D'oh, might apply now!
Very recently as a general
test, a simple half wave 'sloping' dipole was erected for 20 m and this
simple antenna performed much better than any of my various loop
antennas. I simply had to work out why and slowly but surely, and
with a little guesswork, the true reason was finally revealed! My 34 ft
metal pipe mast! All of my loops were symmetrically 'hung off'
this mast and although over the years I had often wondered if this
arrangement might not be a good idea especially given that the length
of the metal mast was very close to the resonant half wave on 20 m and
ran right through the active radiating area of the loop, I had
considered the possibility of undesirable interaction, but then
In any case, the loops
seemed to work well enough, but my 'gut feeling' was that they should
have been better. My original Delta Loop constructed back in the
1980's was mounted 'between' two metal masts! The experience with
my sloping dipole now made me sure that that something very basic was
seriously amiss. On a hunch, and using the 'Sherlock Holmes'
approach to fault finding, the metal mast was considered the most
likely suspect, so after my 40 m WIA Amateur Radio news broadcast one
Sunday morning recently, I was inspired to shift things around to take
the metal pipe mast out of the radiating area of the loop as much as I
could and see if that improved things.
Space was restricted, but
I managed to put up my pre- existing one wavelength Delta Loop mounted
'on its side' as it were, strung up between my 34 ft metal pipe mast
and a shorter 15 ft metal pipe mast and fed at the junction of the side
mounted two sloping sides, giving I think, vertical polarisation.
A general immediate improvement was noted and signals reports, both
transmitted and on receive, were much better than previously (and
better than the sloping dipole).
Several other distinct
changes were noted and it seemed to me that the mast was interacting
very adversely with the loop in several ways. Firstly, by direct
absorption of transmitted RF. Secondly, pattern distortion, and
thirdly increased noise pick up. In the time following since the
repositioning of my Delta Loop, power line noise pick up (always a long
term problem on any of my loops at this QTH, in whatever 'shape' they
were), is now markedly reduced and my HF transceiver's 'noise blanker'
actually works when it did nothing before!
The pattern distortion
aspect is interesting as in the past I had noted that vertical loop
polarisation was best for DX and horizontal loop polarisation was best
'locally'. Now the Delta Loop performs equally well on both DX
and local signals, despite being nominally vertically polarised. I have
to think about that one! In the past, a friend had presented me
with some IPS data that suggested that low angle radiation was best for
'all' paths. As the loop is now working so well vertically
polarised, perhaps this is another indication that the Delta Loop is
now working as it should, as vertically polarised loops inherently
produce excellent low angle radiation!
Needless to say, I am
quite delighted at this turn of events! Perhaps I should have
realised my error years ago, however a recent internet search found
only one article (out of many found), expressly suggesting that metal
within the radiating area of a loop antenna was a bad idea! Well,
I've certainly learned my lesson! I suspect that the self
resonant length of my mast was also a big factor, however the lesson
is, whenever erecting a one wavelength loop antenna, keep any or
appreciable lengths of metal out of the area of the loop, completely if
possible. Then you'll see how good a one wavelength loop antenna
really is! I cannot emphasise this point strongly enough!
Delta Loop offset from metal mast -
Felix Scerri VK4FUQ
The photograph above is of the reconfigured
Delta Loop. I wish it was a little 'neater' and a bit more
'separation' but it's much better regardless, and an article from one
of my antenna books that I've read a thousand times, but somehow I
never noticed the note about a 'non metallic pole'!
Delta Loop -
Practical Wire Antennas
UPDATE - February 2011
Sometimes the most unexpected things happen and 'great discoveries'
happen by accident. This is one of them (more or less)! In
the previous installment [see
of the ongoing loop adventure I mentioned the
improvement arising from removing the metal mast from the internal
radiating area of my full wavelength Delta Loop. Well a few weeks
ago our general location was badly damaged by a very large tropical
cyclone (Severe Tropical Cyclone Yasi). http://en.wikipedia.org/wiki/Tropical_Cyclone_Yasi
Apart from all the other damage, most of my Ham Radio masts and
antennas were either badly damaged or destroyed in the 250 plus kph
wind gusts. I've since rebuilt most of my antennas and masts (one
to go!), but the really interesting thing is that at least for my 20 m
Delta Loop, I've had to shorten the mast quite a bit due to available
undamaged mast material, from around 34 feet to about 25 to 27 feet,
and believe it or not my Delta Loop is now working much better as a
result! The improvement on 'all' signals (local and DX) is
In the past I have often read the anecdotal comment that HF Delta Loops
seem to work better at lower heights. I can't really explain this
phenomenon as observed at this QTH (location), but it is real.
When I look out my window and observe how low the antenna looks now
with the lowest corner only a couple of feet above the ground, it seems
ridiculously low, but it does work very well indeed! Perhaps that
previous longer (resonant length) metal mast, although now 'outside' of
the loop, was still sufficiently close to and adversely interacting
with the loop, I don't really know!
It is my feeling that this observed result may not necessarily happen
in others' QTH, but it does give hope to those with only limited height
available. I've been very pleasantly surprised! As things
stand now, I might even be able to put up a fixed parasitic element for
a bit more 'gain', but even as a single element antenna it couldn't be
any better in terms of general performance!
73 Felix vk4fuq 19-24 Feb 2011.
it's even better!
I guess I really should put an end to these ongoing loop experiments,
however I've just made another change which is most interesting.
Yes, another change in feedpoint position, now to the bottom corner,
giving I think a mixture of low angle vertically polarised radiation
but also an appreciable high(er) angle horizontally polarised component
as well. At least at this QTH this 'corner' feed position appears
to give the best overall result between 'local and DX' coverage, in
fact DX coverage seems essentially unchanged, however 'local' coverage
within the general VK / ZL area is markedly improved. This is not
without some penalty though. Corner feeding does introduce a
strange asymmetry in the 'sides' of the polar pattern of the Delta Loop
but this appears to be of little real disadvantage in practice.
One other little change relates to feeding the antenna. I use the
'hybrid' voltage/ choke balun design as mentioned previously, however
after some recent reading and online discussion on this type of balun
it was suggested the two individual baluns are better interchanged in
their positions. This does make sense to me as the 1:1 choke
balun is then kept to lower impedances which is preferred.
Anyway, I have tried this and I think it is better. One more
thing to try anyway.
73 Felix vk4fuq 15 03 2011.
Further to the interesting 'possibilities' afforded by differing
feedpoint position, my friend Mick SM5JAB has run several antenna
modelling simulations for me on the 'on its side' 20 m Delta Loop I use
at this QTH showing that with differing feedpoint position, the same
physical antenna becomes very different!
I use the lower corner feed position giving horizontal polarisation
with high angle radiation for 'local' working around Australia (vk)
with excellent results, and my other feed position giving vertical
polarisation with low angle radiation for purely DX working.
The same results are achieved with the more traditional apex up or
down Delta Loop by feeding in the appropriate position, either 1/4 wave
along one of the sloping sides for low angle vertically polarised
radiation, or the middle of the horizontal side or (equivalent
position), for horizontally polarised high angle radiation.
vk4fuq. 17 05 2011
Use Of A Non Conductive PVC Mast:
Further 20 m Delta Loop experiments involving a new mast!
it's been quite a while since my last installment and this latest round
of experiments was prompted by a desire to install a new non metallic
mast to hold up my 20 m Delta loop in order to finally conclusively
determine if a metallic mast was as detrimental to the loop's
performance as I had suspected. So, just this last Monday morning
after my usual early morning 50 minute walk (oh, the things one needs
to do to manage type 2 diabetes!), my walking partner (a fellow local
Radio Ham), and I decided to erect a mast entirely built of sturdy PVC
absolutely no experience with this material, however my friend comes
from a engineering/ tradesman background and he assured me that such a
structure was entirely feasible. So off we went to a local
hardware store bought two lengths of PVC pipe, PVC glue and luckily,
transport was provided free for me to this residence only a relatively
short distance away! The two lengths were quickly glued together
making an overall height of about forty feet. We knew that some
guying would be required, however we had seriously underestimated this
aspect and our first attempt to raise with new PVC pipe mast was a
needed to cut the mast back to about thirty one feet (a more manageable
length), and still slightly higher than the old metallic mast and we
decided to enlist the assistance of another adult helper and obtain
more guy rope. The 'erection' was then set for the following
morning. The following morning arrived and our improved
preparedness proved effective, and the mast was indeed successfully
raised and once the guying was completed, it looked a substantial and
solid enough assembly, but that guying is critical! The Delta
Loop was successfully installed and experiments and observations
began. I was secretly hoping for a large improvement in general
VK4FUQ Felix Scerri's New PVC Mast
the results so far have been interesting and experiments are ongoing,
however it is quite apparent that the metal mast was indeed affecting
the electrical performance of the loop! The first thing I noticed
was the SWR bandwidth had broadened very considerably, being only about
1.35:1 at both band edges (through the station ATU and direct balanced
feed), instead of rising steeply at the band edges with the loop
vertically polarised at the 1/4 wavelength feed position on the loop
with the metal mast, (as previously discussed elsewhere in this
page). However testing over a few days indicated that the general
level of performance was similar to previous!
that got me thinking and further experiments today involving past ideas
has yielded positive results. Readers may recall my past
experiments involving the use of a feedpoint current mode or 'choke'
balun as a means of providing effective feedline/ antenna
decoupling. So early this morning I made up a simple 1:1 choke
balun with ten bifilar turns on a short length of ordinary 'loopstick'
ferrite material wound with 1.25 mm copper winding wire and I installed
it at the feedpoint.
tended to change my mind frequently on the value of this feedpoint
balun however after installing it, I noticed something quite
interesting that suggests that it is indeed acting to effectively
'decouple' the feedline from the antenna. The measured SWR with
the balun in circuit do not noticeably change, however it was apparent
that the ATU 'tuning' had become much less critical and 'touchy',
suggesting a generally lower Q situation inferring that the 'effect' of
the feedline was greatly reduced! Further evidence of greatly
reduced feedline 'effect' was observed when a 'birdie' evident on my
main HF transceiver, produced by another receiver in in this shack was
much lower in strength than usual. It is thought that feedline
'unbalance' was mostly picking up this annoying 'birdie'. This
also suggests improved feedline 'balance' as well as effective
'decoupling'. As of now, things look promising!
More to follow!
14th October 2011.
BALUNS: A Rethink, Observations and Unexpected Results!
This update might also be entitled 'Was I wrong? Maybe', as recent
experiments and observations have yielded very unexpected results! As
I mentioned in the last instalment, I've never been quite sure about
the use of a feedpoint 1:1 choke balun with balanced feedlines. As of
now, I say don't use one! As an experiment I installed feedpoint 1:1
choke baluns on all my HF dipoles as well, and general testing
indicated poorer signal reports and in conversation with a friend
knowledgeable in transmission line matters, he also suggested that the
use of a feedpoint 1:1 choke balun with balanced line was ill advised
I still cannot see why this might be the case, but the observations
seem to confirm this. So don't use one, (at least with balanced
line)! Interestingly enough, further investigations with an ATU
'hybrid balun' as originally designed and mentioned in earlier
instalments, with the 1:1 choke balun on the 'output side', appears to
work extremely well and signal reports are good.
More interesting were the observations and comparisons made between a
simple 4:1 voltage balun and this 4:1 'hybrid balun' showing a full 3
'S' point reduction in received (power line) noise in favour of the 4:1
hybrid balun, suggesting massively improved feedline balance and common
mode noise rejection. This result was totally unexpected! This
'hybrid balun' gets my define tick of approval.
vk4fuq. 2nd November 2011.
The End Of The Whole Loop Saga?
Hopefully this is the end of the whole
Loop saga, but I really love my 20 m Quad loop again! This week I had a
real breakthrough. In a previous instalment I mentioned incorrect
positioning of my loop, well even after 'repositioning' it, it still
wasn't right! Another unexpectedly poor signal report very
recently forced me to check this again, thankfully.
I have a shocking sense of direction,
even with a compass in hand! I even enlisted the help of an older
'bushie' friend who is very familiar with correctly using a compass, and
he confirmed that I now have my loop firing North and South (broadside
directions to the 'line' of the loop)!
And what a difference it makes.
Now when I call a station, I now get answered....every time, unlike
previously. Analysis of compass bearings indicate that I was
firing in 'null' directions and this leads me to another interesting
observation. In tech school years ago we were taught that a 'three
decibel level difference was about the minimum discernable' level
change. Don't you believe it! It all depends on prevailing
A three decibel level difference can
(and does) make a potentially massive difference. Nulls in the
'ends' of a full wave loop when horizontally polarised can be up to 12
decibels. Aiming that loop correctly 'is' very important. So
now I have my 20m Quad loop up (in a slightly different position in my
backyard),and 'looking' truly North and South fed with balanced line as a
'tuned line' direct into my shack and into a 4:1 hybrid balun and T
match ATU, and I couldn't be happier. No, it's not a beam and it's
not rotatable, but for what I want I couldn't be happier!
Fascinating observations with two 20 m antennas or the value of comparing two antennas side by side
G'day all, I had a fascinating
afternoon recently comparing two separate 20 m antennas. Readers
will know of my constant experiments with simple 20 m antennas, so on
this afternoon I put up two separate antennas. My beloved 20 m
Quad loop (horizontally polarised), looking North and South at a top
height of 28 feet (quite low in absolute terms), and a separate 20 m
vertical ground plane with the base at about 15 feet above ground with
two elevated quarter wave resonant radials with a 1:1 choke balun at the
feedpoint. Two elevated radials are all you need,
not three or four, as long as they are some distance off the earth, or
ground loss will be a problem. There is almost no eccentricity in
radiation pattern despite the use of only two in-line radials. Both
antennas were fed with balanced line as tuned lines and are sufficiently
distant from each other to avoid interaction.
Both antennas were fed into two
separate receivers which were reasonably well matched on receive with
closely matched receiver sensitivity and S meter calibrations. I
listened to various signals, both local and DX, during the IARU contest
on 20 m between 0400 and 0600 hours UTC. The results on receive
were absolutely fascinating and it is great when theory agrees with the
Across VK (I am in Northern VK4) the
Quad loop, in the broadside directions, was the clear winner with very
low noise on receive and about 2 to 3 S points better than the
vertical. However on all DX signals (America and Europe), the
vertical was very superior by on average 3 to 5 S points! With the
vertical the noise level was slightly higher (S2), but not
obtrusive. These results were absolutely amazing to observe.
The S meters don't lie! There seems to be an interesting
transition zone around the ZL region, as the Quad loop and the vertical
were approximately equal.
Conclusions: The Quad loop was/is
clearly the best antenna for working across VK in the broadside
directions. Into VK6 (nulls on the loop), the vertical was about 1
S point better (varying somewhat). The books say that a low Quad
loop horizontally polarised radiates at very high angles and I agree.
Although the higher radiation angles are clearly better for local
working across VK. The radiation angle of the vertical ground
plane is low and DX performance is superb, the expected result.
All tests were receive tests, but I would expect similar results for
I myself have been comparing my antennas on RX over the last couple of
days. I have been comparing my Inverted L, a small fan dipole that I
have in the loft for 10m and 6m and a Delta Loop that I have recently
hung up. The loop's wire is about 16 metres in length, but I also have another
wire handy that is 12 metres in length to form a smaller loop for the 24 MHz band that I can
easily hoist in to position.
The Inverted L has the addition of an extra sloping wire element tuned for 17 metres.
I have mainly done RX comparisons on 20m, 17m and the local 11 metre CB
band. It's quite amazing how switching between antennas can produce
entirely different results. For example while monitoring the local CB
band (which isn't in itself very edifying!! ) I could hear strong
signals on the horizontal 10m dipole in the loft, but switching to the
Delta Loop produced an entirely different transmission on the same
channel and almost equally strong signal. This is a product of the delta
loop being fed at the bottom corner which should give polarisation
somewhere between horizontal and vertical (mixed) and its position fires roughly
north east / south west, whereas the dipole is horizontally polarised and fires
east / west.
Similar, but less spectacular, differences have been observed on
20m and 17m. I'd say that overall the loops antennas are better
compared to the Inverted L for their particular bands, but differences in directionality will
sometimes favour the Inverted L in both cases.
I installed the loop to try to improve access to the higher frequency
bands. The horizontal fan dipole in the loft for 10m and 6m while being
extremely efficient does suffer with quite high noise pick up and I fear
that using 100 watts may cause EMC issues for neighbours - anyway it's a
useful and cheap aerial!
As for my loop experiments then I am quite encouraged so far.
While the 80/40 Inverted L tunes up easily on 20m, 15m and 10m, with 20m
being fine, results are not especially amazing on 15 and 10 -
acceptable when conditions are above average, but not as good as
dedicated antennas. This prompted me to try some loop
antennas. While loops are supposed to be single band antennas, I
have read that a number of people have used them as multi-banders with
some success, so I thought I'd try one out for 17metres and upwards and the other for 12 metres.
Initial results are good and I am certainly tempted to leave the loop as
a permanent fixture, but while I don't find either the 12m or the 16m
loop to be noticeably quieter than the Inverted L, they are, however,
quieter than the loft dipole for obvious reasons!
All very interesting!
73, Mike. M0MTJ
The other morning after feeling a bit
negative about aspects of balun performance, I started this thread on
the QRZ.COM technical forum. http://forums.qrz.com/showthread.php?357490-Are-we-all-being-fooled-about-baluns
whole thread is definitely worth reading! I started out
questioning whether the 'current mode' baluns were really any good, and
by the end of the thread I had more or less changed my mind after
running a couple of impromptu tests.
The so called 'hybrid' balun that I
have mentioned before is actually quite remarkable in the way it reduces
noise pick up over a standard 4:1 voltage balun. That 1:1 choke
(current mode) balun in the hybrid assembly does the magic! It
makes one realise that in the 'real world' things are never even
remotely close to the perfect, but the hybrid balun has a quasi magical
way of bringing things closer to the ideal through enforcing equal
currents and choking off 'common mode noise'. As I mentioned in
one of the posts my dipoles/inverted V dipoles are now as 'quiet' as my
beloved loops, thanks to the hybrid balun! Others have also noted
large reductions in 'apparent' noise pick up when using a current mode
In many cases the transmission line
is picking up more noise than the antenna and this is greatly reduced
through proper 'balancing'. It is all quite involved when one
thinks about it. Here are two another quite interesting and though
provoking articles. http://audiosystemsgroup.com/RFI-Ham.pdf
More thoughts, and W8JI
In recent times, things have been ‘coming together’ as it were, when it
comes to antennas and the jigsaw puzzle is starting to come together
nicely. It appears to me that a lot of quite important yet
slightly ‘intangible’ things are now being seen for their real
Things like feedline unbalance and the
generally unrecognised results of this like increased noise pickup which
are often ‘blamed’ on the antenna itself (incorrectly) when noise
picked up on the feedline is actually (mostly) responsible!
Current mode (i.e. choke) baluns are close to magical in what they can
do in improving feedline (current) balance. In recent times I have
proven this conclusively to myself.
In the past I have always regarded
loops are having this ‘magical’ reduced noise pickup advantage, however
simple dipole type antennas if feed through a well-constructed
choke balun/feedline system, whether it be coax or balanced feedline,
with a choke balun positioned as appropriate (at the antenna feedpoint
when using coax and at the shack/ATU end if using balanced feedline),
are equally good in this respect and do have the advantage of inherently
greater ‘effective height’ which is always helpful!
Proper attention to the ‘little’ things
often does make a very large difference, even when one may not think
so! This website has an enormous amount of very useful and
Click on the ‘antenna’ tab and you might be reading for weeks! http://www.w8ji.com
Metal Poles and The Quad Loop
After more work and experiments I have concluded that the reason for the
apparent degraded ‘transmit’ loop performance that I have frequently
reported in these pages is the way that I used a metal mast as the
I had actually identified this earlier, however a recent opportunity to
re-mount my single Quad loop in ‘between’ two metal masts (at not very
great height), transformed the performance of my loop. The loop is
still ‘looking’ in the same directions, by the way! Given that I
am somewhat physically disabled, it was a challenge to successfully do
this by myself but I persevered and succeeded! Thankfully
aluminium makes for a light and manageable mast, but it is expensive
I now have negligible noise pick up, compared to a solid and constant S7
as previously mounted ‘around’ my main metal mast, and the loop is now
both radiating and receiving very well. Mounting a loop in ‘diamond’
fashion off a metal mast is very convenient, but it seems to mess up
An interesting thing is that modelling done by others for me using EZNEC
showed very little negative effect of a metal mast running through the
middle of a full wave loop. However, practical results appeared to
show that the modelling was wrong or perhaps incorrectly applied.
I am still using balanced ‘tuned’ feedline with a hybrid balun at the
shack end which I think all helps, but the ultimate lesson is to use two
masts and keep any metal out of the loop! Yes, it complicates assembly
but that is a small price to pay for excellent antenna performance.
73 Felix Scerri
Mostly for convenience reasons more than anything else I now have a 20 m
Delta Loop mounted ‘on its side’ and fed for vertical polarisation (at
the ‘side’ positioned apex).
Although the Delta Loop has slightly less ‘gain’ than a Quad Loop, I’ve
found the Delta Loop every bit as good as the Quad loop in practice, and
is much easier to mount, requiring only one ‘high’ mast at one end and
an approximately ‘half size’ mast at the other ‘apex’ end.
I am actually surprised that this usual arrangement is not known of
and/or used more as its ease of mounting is a very significant
advantage, and of course feeding at the ‘apex’ end will yield vertical
polarisation. For ‘local working’ with horizontal polarisation,
fed at the lower corner, works very well and of course all metal
masts are kept outside of the boundary of the loop.