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Eng HF Crossed Loops Antenna Q .pdf



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°
°
°

“Theory put into practice”

Among antennas with
special characteristics of
directivity and noise
rejection undoubtedly the
loop antenna are on the
first place. Thanks to the
work of many researchers
and enthusiasts OM, we
know all the advantages
and disadvantages of
these antennas.
If on the one hand for
their size, low noise level
and the particular
directivity well differ from
the other antennas,
against the matching
difficulty and for some
aspects the uninspiring
transmission
performance, suggest an
advantage use in radio
receiving and
radiolocation application.
On the other hand
working on HF
frequencies in urban
areas is often much
easier to be heard,
sometimes increasing TX
power, that you can
receive the weak signal in
the chaos of the everpresent atmospheric and
man-made noise anyway
for 24 hours a day.
So why don’t take in use

a loop element as
alternative receiving
antenna?
Many HF transceiver
provide a separate input
for a possible second
antenna and others a
further convenient
dedicated RX input, again
high-end HF transceivers
with two identical
receivers with separate
inputs … so without
using any external coax
switch, why don’t take
advantage to improve our
listening conditions?
A typical loop antenna
properly fed with
balancing matching circuit
and vertically oriented
exhibits the highest
directivity on the

horizontal plane with a
bidirectional radiation
pattern.
The maximum gain with
respect to this plane in
the two preferential
directions (for example
North-South or if 90°
rotated East-West)
therefore occurs when
the signals of our interest,
propagated by sky waves
or by ground waves, are
polarized vertically and
their elevation angle is
not greater than about 20
degrees. Sky waves
signals returned by
reflection from the
ionosphere layers more or
less earth’s surface
distant, in a particular
time of day or night do

Fig. 1

1

Fig. 2

not have a stable
polarization because
affected by an
unpredictable
phenomenon known as
“Faraday rotation”.
The time lapse that this
phenomenon occurs is
totally random and the
signals polarization that
we want to receive may
vary by turn from vertical
to horizontal and vice
versa, for short or long
periods, often in a sudden
manner but sometimes
also with a slow variation.
When signals from sky
waves have a radiation
angle (2) larger than 30
degrees and are affected

by this phenomenon, they
can present themselves
with horizontal
polarization, in this case
the loop element will
favor all those signals
which come with an
azimuthal angle of 90
degrees to the axis that
characterizes its
maximum in the
horizontal plane.
Therefore we get best
reception by turning loop
of 90 degrees.
Paying particular attention
to the propagation on
frequencies next or below
then 7 MHz, we can
consider signals with a
high angle of radiation all

those signals that
originate from a relatively
short distance
(i.e. with a lower path to
500 ~ 600 Km) that for
reasons set out above,
when will present
themselves to an antenna
with horizontal
polarization will be better
received with the loop
element rotated in
orthogonal mode respect
to their direction of origin.
The random variation of
the frequency with which
effects due to the
Faraday rotation act on
these signals preclude,
for practical reasons, any
possibility of adopting a
mechanical system for
rotating the loop element
because is too slow and
obviously is subject to
premature wear. For
these reasons, after
having successfully
tested the Varactor Tuned
Loop Antenna, projected
by Chris Trask N7ZWY
that I recently proposed
on this magazine (3), I
wondered what could be
the most effective
method to use, to rotate
it without the aid of an
antenna rotator.
2

The answer to this
problem was suggested
me by the analysis of
typical “eight” form polar
response of such
antennas, therefore
similarly to realizations
engaged for radiogoniometric use (4), the
precise orthogonal
arrangement of a second
loop element would have
satisfied my requirements
without significantly
altering the single polar
element
response. In fact, the
Crossed Loops Antenna
that I describe has a
radiation pattern on
horizontal plane similar to
a “four-leaf clover” this
allow to receive on the
tunable frequencies with
an azimuthal aperture of
360 degrees (Fig.1). By
switching signals
individually from loop
antennas or by summing
appropriately signals to
the receiver input, you
get an almost
omnidirectional diagram
with tolerable attenuation
in the four overlapping
points of the polar curves
of the two antennas.
Therefore project uses

two identical loop
antennas with a diameter
of 82 cm, crossed at 90
degrees, mechanically
solid and individually
tuned through the same
coaxial cables feeding the
antenna (Fig. 2).
A simple tuning box, an
integral part of this
project, has the task to
tune the loop elements
and to handle with
extreme speed its
signals. So they can be
used at will, either
individually switching as
needed at the input of our
receiver, or sending them
toward two separate
receivers to be listen in
“Diversity” mode
isofrequency or dualwatching on different
frequencies.
Moreover, thanks to a
broadband magnetic
coupler integrated in the
same tuning box where
they can add up the two
signals, is obtained at a
modest attenuation price
a single “sum signal”,
thus obtaining also,
depending on their phase
angle, a omnidirectional
response of the antenna
system.

Those who are prepared
to experimentation can
change the signals
phases incoming to the
receiver, through a
suitable L/C passive and
variable network
(recommended circuit)
(5), or compare them
alternately, through the
same phase shift
network, with a third
reference signal provided
by a vertical antenna
(wideband monopole).
This allowing in certain
propagation conditions to
mitigate annoying signals
and in many cases to
cancel interference
signals coming from a
different direction from
that of the desired signal
(6).
And last but not least,
through the amplitudes
and phases signals
correlation, that arrive
with a sufficiently low
irradiation angle so to
discover with good
approximation their
direction of origin.
The tuning box that
control the Crossed
Loops Antenna also
employs two wideband,
low noise and high
3

dynamic amplifiers to
help cope to the
attenuations introduced
by matching networks
and indispensable to
those resulting from
further received signals
processing. Is almost
superfluous to say that to
match the best
performance we must
respect a perfect identity
of the loop elements and
matching networks as
well as that of the circuits
that enable it to perform
the tuning along with
those which control
signals that the antenna
will present to our
receiving system.
Selecting and checking
value with appropriate
tester the passive
components, with
particular attention for coil
windings and also active
components
characteristics, do not risk
to get different responses
in amplitude and phase of
received signals so as to
not thwarting the
achievement of our goals.

*******************
MATCHING
NETWORKS
CIRCUIT
DIAGRAM
The tuning variation
stands in continuous
coverage of two
frequency octaves, i.e.
from 3,5 MHz to 14,5
MHz. With varicap diodes
employed in the project
the voltage excursion,
capable of causing this
variation, starts from
0,20V to about 6,8V. The
graph of figure 3 is the
frequency variation curve
in function of tuning
voltage for the two
matching networks with
82 cm diameter loop
elements, while the red

dashed curve has been
obtained from a test run
with two loop elements
65 cm in diameter.
Original project (1) of the
loop element matching
network involved use of
Motorola MVAM109
varicap diodes which they
require approximately 15V
to reach minimum
capacity and therefore
maximum operating
frequency of the antenna.
Use of two varicap diodes
operating at a lower
voltage allowed me to
achieve a tuning control
that can be fed to 13,8V
DC voltage easily
available in all our
amateur stations.

*******************
*******************

Fig. 3

4

Toko KV1590NT diodes
employed in this project
are double varicap born
for the Radio-Automotive
sector and therefore with
a good temperature
stability are able to offer a
merit factor Q=200 (Fig.
4) already at few fractions
of a reverse bias voltage
with a corresponding
capacity of approximately
650pF for each diode.
As can be seen in the
diagram of Figure 5, the
circuits are electrically
separated (GND-A and
GND-B) avoid unwanted
current loop that could
affect coaxial cables
employed in antenna
feeding, and for this

Fig. 4

reason have been
assembled on two pieces
of single-side coppered
epoxy fiberglass of 30 x
65 mm (Fig. 6 and 9)
obtaining the required

few tracks with a small
Dremel cutter or similar.
With use of two short
feed lines (15 + 15 m)
with a small diameter
coaxial cable RG58 type
you make connections
without using any coaxial
connector
(i.e. by screwing them
directly on the two epoxy
fiber glass board)
after welded on the
copper layer of boards,
four standard brass
terminals for electrical
wiring with clamping
screws.
Guanella transformers
type T1 and T2 with 4:1
impedance ratio are built
on T44-6 Amidon toroidal
cores identified by yellow
color, the windings that
form them are individually
constituted by two twowire pairs of 0,22 mm
enameled wire.
Each wire pair is braided
by twisting wires for a
precise number of times,
so as to minimize
inductance differences
between the four
windings on the same
toroidal core and finally
that between
transformers.

Each transformer is made
up of 12 + 12 turns (Fig.
7) with the two doublewired pairs wrapped in
the same direction, gently
tight and evenly
distributed on the toroid
circumference.
If everything went the
right way, at the ends of
the pair windings T1-2,
T1-3 and T2-2, T2-3 we
will get an inductance of
3 H while at the extreme
ends of the windings T11, T1-4 and T2-1, T2-4 will
be four times larger or
12 H.
The 1:9 transformers T3,
T4, T5 and T6 are built
using four binocular cores
BN43-2402 with four
trifilar windings of 0,22
mm enameled copper
wire inside them (Fig. 8);
also in this case the three
enameled wires have
been previously twisted
with the same care taken
for the construction of T1
and T2 transformers.
The intermediate
inductance in each of
the four transformers
should be 33 H, while at
the extreme ends will be
about 300 H.

5

Fig. 5

Fig. 6

Fig. 8

An important note for
RPA and RPB 10kΩ
resistors in the two
matching circuits.
These are part of the
voltage divider, together
with the variable resistors
R7 and R8 (Fig.10), that
establish the right voltage
for the loop tuning
elements and therefore
must be metallic film
type.

Fig. 7

Fig. 9

*******************

6

CROSSED LOOPS
TUNING CONTROL
In figure 10 we can see
the control box electrical
wiring that provides:
loops tuning, signals
amplification and their
switching when aren’t
employed two separate
receivers as in the case
of “Diversity” mode
receiving.
Tuning are implemented
by means of two 50kΩ
multi-turn potentiometers
R7 and R8 fitted with
tachometer mechanism
RS 502-174, whose fine
numerical graduation
allows to draw a precise
tuning scale to make
repeatable and fast the
frequency excursions and
the band change.
The four wired blocks
visible in the figure are:

the “Switch Control”
constituted by an
elementary logic circuit
that controls, through the
push-button switch S3,
the sequence of
switching operations
implemented by the
respective signal relays;
the two “Loop A and
Loop B Wideband
Amplifier” containing the
broadband transformers
needed to tune through
feed lines the loop
elements together with
amplifiers and relative
relays that allow to
include them in the RF
signal path;
the “Coupler” block with
five relays that toggles
signals, at the output
connector J5, from the
Loop A and Loop B or the
result of the sum

obtained through the
broadband magnetic
coupler that employs T13
and T14 transformers.
With “Switch Control”
circuit exception the other
three blocks are
adequately shielded using
three tinplate small box
from 74 x 37 x 30 mm (w
x d x h) which houses the
flanged BNC coaxial
connectors, along with
the through-hole
capacitors needed to
connect power and
control voltages.
Although in this project
the loop elements size
and matching networks
allows you to work with a
wide margin from 80
meters to 20 meters, the
tuning box is able to
process (in accordance
with the canonical 50Ω

Fig. 10

7

impedance) all signals
with frequencies ranging
from 450 kHz up to 30
MHz offering opportunity
to experiment and
optimize antenna with
loop elements of different
diameter and / or with
modified matching
networks.

*******************
SWITCH CONTROL
To take advantage from
listening possibility that
the Crossed Loops
Antenna can offer,
without entering signals
into separate receivers, it
is necessary to facilitate
switching of the two
signals to a single output.
Discarded the solid state
switching systems with
PIN diodes for the
intermodulation limits
which by their nature
have, use of switching
relays for RF signals is
undoubtedly the best
sensible choice.
A simple logic circuit,
formed by two popular
CMOS IC from “40”
series and three NPN
transistors which act as a
relay drivers, allows use
of a practical push-button

switch (S3 in Fig.10) as a
signals switching
selector.
Figure 11 shows its
circuit diagram, IC1A and
IC1B are two of four 2input NAND Schmitt
Triggers contained in the
CD4093 used to get a
perfect de-bouncing of
the electrical impulse
provided by contact
closure of our buttonswitch. In this way when
pressed it provides a
pulse with very precise
characteristics being
defined by the time
constant determined from
R / C cell R28 / C46,
making known rising and
descent edges. This
pulse, present on pin 4 of
IC1B, is sent to the clock
input of decimal counter
IC2 CD4017 and thanks
to the Johnson counters,
in shift register function,
make advance the count
leading Q0 to low level
and Q1 to high level.
Remembering that Q0
position was already at a
high level thanks to reset
circuit formed by C47 and
R29 activated at power
on, a second pulse to pin

14 of IC2 advance the
count making Q2 high.
An additional third pulse
will lead to high level Q3
and then through the
diode D10 provides a new
reset pulse by placing
again the counter at Q0
position. Outputs Q0, Q1
and Q2 in sequence,
through the base
resistors R30, R31 and
R32 will bring into
conduction three BD517
transistors that perform
relay drivers function. On
the same practice predrilled fiber glass board,
on which is assembled
the simple circuit just
described (Fig.12), there
are also the 9 V voltage
regulator LM7809 in
TO220 case with heat
sink, the resistors R33
and R34 with 470Ω 1/2W
value, they can be limit
the maximum current
available in case of
accidental short circuit in
the tuning circuitry
formed by the two ten
turns potentiometers R7
and R8 and through the
coaxial antenna cables
also by the matching
networks.

8

Fig. 11

Fig. 12

*******************
LOOP A / LOOP B
WIDEBAND
AMPLIFIER
To perform a good RF
shielding of signals
supplied by Crossed
Loops Antenna, we must
adopting both electrical
and mechanical
adequately solutions.
We start with drilling the
two tin-plated boxes
which must
accommodate flanged
BNC connectors J1 and

J2, the eight feed through
capacitors and those for
output coaxial cables X1
and X2.
Holes for the flanged
BNC connectors will be
performed on bottom lids
of the little boxes, and
those for the feedthrough capacitors and
RG196 coaxial cables on
the side walls.
Welding of J1 and J2
BNC connectors must be
performed with an
appropriate hi-power
welder, taking care not to

clog the threads for the
four screws at flange
corners which be used to
support entire screen to
the rear panel of metal
enclosure that which
contains the entire
instrument.
After soldering the eight
feed-through capacitors
TH1~TH8, you can fix in
them all necessary
components according to
scheme in figure 13.
The two 1:1 transformers
T7 and T8 are built on
binocular cores BN43-

9

Fig. 13

202, by winding six turns
of intertwined bifilar
enameled wire from 0,45
mm.
At the end of work each
winding must have an
inductance of 117 H.
The two Quad-FET
amplifier boards are perselected by gain and
bandwidth and are built
with mixed technology
SMD/discrete
components on metalized
circuit boards with
dimensions (w x d x h)
55 x 18 x 25 mm.
Essential for a good
amplifiers reliability is the
use of selected FET J310
in the traditional TO92
case, discarding

equivalents SMD type
MMBF J310 readily
available today and
offered as replacements.
In fact, the maximum
dissipation of
MMBF J310 is 125 mW
lower than the discrete
original technology,
causing serious heat
dissipation problems that
inevitably will have a
weight on the module
MTBF value.
Characteristics of each
module FK857 are
suitable for an HF FrontEnd function and also to
the heavy task of postmixer amplifier, for typical
use in the high-end
receivers.

All modules are
individually subjected to
third order
intermodulation test: for
example two frequencies
28 MHz
and 29,5 MHz with
0 dBm input level, provide
a +12 dBm output and an
IMD value of -58 dBc,
thus obtaining a OIP3 of
+41 dBm and a IIP3 of
+29 dBm, while the
1 dB compression point
of output signal is
achieved with +19 dBm
input signal.
Noise value detected in a
sample test mode at 28
MHz was found typical at
1,3 dB and maximum at
1,4 dB and these values
were obtained by
10

powering each module at
13,8V with current
consumption of 96 mA.
By injecting alternately
the output of signal
generator in J1 Loop A
and J2 Loop B connectors
and extracting it from the
J5 output connector,
appropriately switched,
we obtain the graph of
figure 14 where is
represented in linear
mode the real gain
performance of amplifiers
(practically are coincident)
in function of frequency.
We can see that in the
stretch that goes from
650 kHz to 15 MHz, the
gain is constant at
+13 dB, while the overall
bandwidth is extended
from 470 kHz up to 30
MHz with a gain of
+12 dB ± 1 dB.

Fig. 14

11

*******************
THE COUPLER
The third tin-plate box is
the “Coupler” group, it
contain the summing
circuit at zero phase
degrees of coming
signals from the Crossed
Loops Antenna, along
with necessary five
switching relays and
three BNC connectors J3,
J4 and J5 screwed to the
rear panel of the tuning
box that supporting the
other two tin-plate boxes.
As can be seen in figure
15, the two signals
respectively coming from
Loop A and Loop B,
through coaxial cables X1
and X2, go directly to J3
and J4 connectors for
“Diversity” mode
listening. All relays are
presented in the rest
position, therefore the
power supply +13,8VN is
absent (if the power
switch S1 is in
“Diversity” mode
position) between signal
lines they will act only the
stray capacitance of the
open contacts of K4, K5,
K6 and K7 relays.
Employing designed
relays for switching small

radio signals, we have the
advantage of also predict
their behavior in sensitive
applications (such as this)
where certainly, in
function of the receiving
system sensitivity, is
required a higher signal
isolation. Figure 16 is a
photo of the seven relays
used in the project. Four
of these are completely
shielded by a perfectly
weldable and nickelplated copper cap, this
shielding allows to reach
an appropriate RF
isolation between the two
signals, which is suitable
for this purpose and is
higher than 100 dB from
450 kHz to 14 MHz,
remaining equal to or
close to this value up to
the extreme 30 MHz.
Never published coupler
circuit built by binocular
transformers BN43-202,
follows a very popular
commercial scheme
which using instead two
toroidal magnetic
elements. The adder
circuit characteristics
(or divisor, if used in
reverse mode) made with
this type of binocular
cores are better for both

higher bandwidth and
best insulation between
input ports that is
about 35 dB from 1,8
MHz to 30 MHz.
Signals attenuation
through the circuit formed
by transformers T13 and
T14 is -3 dB, but as we
will see, the
presence of signals at its
inputs with phase angles
that tend to coincide,
make this attenuation
relatively important.
To achieve this we must
pay close attention to the
built of both transformers;
T13 is made of three
turns using a bifilar
winding without twisted
wires, while T14 is made
of two trifilar turns with a
winding of previously
twisted wires, using for
windings a 0,45 mm
enameled copper wire.
In the photo Fig. 17 the
four circuit blocks, wired
on the rear aluminum
panel of the Crossed
Loops Antenna tuning
control enclosure.
The three tin boxes
without cover, showing
also the arrangement of
T7 and T8 transformers
just behind connectors J1
12

Fig. 15

Loop A and J2 Loop B
respectively close to K1
and K2 relays that insert
the two HF amplifier
modules when these are
fed by switch S2 on front
panel. Coaxial cables X1
and X2 in RG196 (Teflon)
can well withstand the
welding of external braid
in the four holes with
copper rivets that
facilitate the passage. It is
a “basic” but effective
method and economic
alternative to the possible
eight miniature SMB
coaxial connectors or
similar eventually
necessary. Also in figure
17 we can see K4, K5 and
K6, K7 relays layout,
stacked and welded on
the long side of
“Coupler” group and
centered on the opposite
side the K3 relay flanked
by T13 and T14

transformers, overlaid and
held in position by some
glue drops.
In figure 18 there is the
back panel photo where
overlook the five BNC
connectors with the fourpole power connector,
finally with finish of clear
“Dymo” stickers
thermally printed and
plasticized to distinguish
inputs from outputs. In
figure 19 we see instead,
the arrangement of S1,
S2 and S3 switches on
frontal panel, the ten
turns potentiometers R7
and R8 Bourns 3549S,
the button micro-switch
Crouzet 835420 and
above the five signaling
LEDs (5 mm).
A short tinned copper
braid, protected by an
insulating sheath, ensures
a stable electrical

Fig. 16

continuity between rear
aluminum panel and
epoxy painted metal box.
In figure 20 we can see
finished front panel of
tuning box with a simple
printed adhesive
thermoplastic label.

13

Fig. 17

Fig. 18

Fig. 19

14

Fig. 20

*******************
THE CROSSED
LOOPS ELEMENTS
The Crossed Loops
Antenna elements are 82
cm in diameter and are
build with two copper
tube pieces 2,38 meter
long with 6 mm in
diameter (Fig.21).
As well for matching
networks also the loops
elements must be
isolated each from other.
Before welding

Fig. 21

connectors, which allow
elements substitution,
were strung three

pieces of heatshrincable
tube 10 mm in diameter
on each loop.
15

One of these will be
arranged at the top of the
circumference, the other
two will be used on the
connector welds.
Latter connectors are
coaxial adapters UHF
SO239 / RCA male type,
called AD259.
Their robust outer brass
rings allow a strong
welding (Fig.22).
Further four doublePL259 male coaxial
adapters are used to
connect loop elements to
the plastic square
weatherproof box
100 x 100 mm (Fig.23)
that supports, on all four
sides, the classic flanged
SO239 connectors
screwed with sixteen
brass screws 3 x 15 mm
(Fig.24). In figure 25 it is
show its drilling plan and
we may notice the small
difference 4 mm height
between SO239
connectors on the
opposite box sides,
allowing an identical
shaping of the two loops
circumferences

before assembly.
On the box bottom we
see the drilling, to
accommodate the two

Fig. 22

Fig. 23

matching networks,
for the grommets
that accommodate
RG58 coaxial cables
and for fixing the
small watertight box
to the support
bracket, through a
solid polyethylene 9
mm thick base. The
latter (Fig.26) allows
easily adapt the 90°
support bracket 100 x

Fig. 24

100 x 70 mm, already
perforated and retrieved
from a “Brico” store, to
the watertight box,
facilitating at the same
16

time the coaxial cables
passage to feed the
antenna. Three drilling
diameters are used:
9 mm for coaxial cables;
5 mm for the stainless
steel countersunk
screws, intended for
support of the
watertight box to the
polyethylene surface
and to the 90 degrees
bracket; 3 mm for the
six holes fixing the two
matching network
boards with appropriate
threaded brass spacers,
and sixteen others to
secure all SO239
connectors.
Figure 27 shows the
polyethylene base
screwed to the 90°
bracket and ready to
accommodate the
bottom side of the
watertight box,
as is seen the two 9mm
holes were flared so as
to house the lower part
of rubber grommet,
slightly protruding from
the same fund. Figure
28 shows the internal
details with the

matching
networks in
place and inputs
connected to
respective loop
element; notice
also loop
elements
connectors
protected by
heatshrincable
of suitable
diameter.
At the end of
assembly work
of loop elements
it has been
shaped and
arranged a PVC
“egg”, this will
serve as a mold
and will be
located at the
top of the two
circles and then
at point where
they intersect.
In a second
time, through a
hole of about 10 mm in
diameter previously
practiced on the bottom
of the “egg” mold, they
were spilled about 320
grams of bi-component

Fig. 25

Fig. 26

epoxy resin adequately
mixed before.

17

This operation
allows us to confer to
the Crossed Loops
elements the necessary
mechanical rigidity so
that they can remain “in
shape” without
deforming, also under
strong winds action.
At the time of
installation at the head
of a galvanized iron pole
just over two meters
high by 50 mm in
diameter, the two
antenna feed lines
prepared in the same
manner of figure 29,
have been connected
and finally the iron pole
has been assured with
two robust wall
brackets after having
oriented “A” and “B”
loop elements,
according to the four
cardinal points
North – South /
East – West.

Fig. 27

Fig. 28

*******************

Fig. 29

18

*******************
LISTENING WITH
THE CROSSED
LOOPS ANTENNA
After installation the
first thing to do is to
annotate numerical
positions of multi turns
indicators on the two
tuning controls so we
can draw up a table
with three columns:
in the first we report
the frequency values
while the other two will
contain the numerical
positions of multi-turn
tuning knobs.
Although we can take a
quick alternative
strategy to tune “on the
fly” the two loops while
listening to the band
atmospheric noise on a
clean frequency and
emission-free, in some
circumstances this
method can be a source
of uncertainty while
positioning the multiturn potentiometers.
For this reason, a
precise reference table
is certainly useful both

to speed up tuning on
“slices” of the most
interesting HF bands or
for the band change.
The two loop elements
tuning is precise and
repeatable, and found
to be stable even with
strong thermal
excursions (day/night)
and in adverse weather
conditions (like strong
wind, humidity, rain).
Also the tuning
operations are
noncritical because in
any case, once tuned,
you get an acceptable
attenuation and
therefore good signals
to receiving up to a
distance from
frequency tuning center
of about ± 40 ~ 80 kHz
depending on HF band
tuned. As an alternative
to a signal generator
and a spectrum
analyzer, to prepare a
tuning table precise to
the decibel, you can use
as a generator, an
antenna analyzer
MFJ259 or similar,
provided with a 50Ω

load and situated at
good distance from
Crossed Loops
Antenna.
Then we will receive his
signal, attenuate it if
necessary
with HF receiver
equipped with analog
S-meter controlled, if
possible from an AGC
circuit which is also fully
analog, taking note of
top level signals from
the minimum tunable
frequency of 3,5 MHz
up to maximum of
14,5 MHz.
To understand how
great is the potential of
this small antenna we
should make many hour
of listening in the most
different propagation
conditions and also in
the most critical
conditions, comparing
from time to time with
the traditional antennas,
also sensitive to the
electric field.
Obviously, our attention
must be paid to signals
quality received in
terms of signal / noise

19

ratio, because
comparison established
only on the absolute
level of same signals,
maybe using as a
reference a well
installed full-size
antenna can be at first
listen, definitely
misleading. The
possibility to switch
single signal from the
two loop antennas and
the “sum” of these in
very quickly manner,
allow us different
degrees of freedom in
their management,

allowing finally to
improve the listen
experience significantly.
Obviously there is no
precise rule to switch at
J5 BNC output
connector, the signal
from Loop A or Loop B
or again from Coupler
as everything depends
on the propagation
conditions of the
moment on the
frequency band in use
and the time of day or
night when we listen.
With some
approximation we can
know the odds with

which certain signals
will be received with a
good or sufficient
intensity and also their
elevation angle, but
surely we will not know
their polarization.
With this antenna,
selecting the signal
from the just loop, we
are able to effectively
break down the
evanescence effect
more or less deep due
both to the Faraday
rotation and in some
cases also for the
simultaneous presence
of wave for two way,

Fig. 30

20

together from sky and
ground of the same
signal, thus allowing us
to not lose it in the
noise; and yet, when
the propagation
becomes “long”,
you can discriminate
the received signals
with a low radiation
angle (often from
remote areas) from
those with a higher
angle coming from
shorter distances.
Also, when the signals
of our interest have a
high average irradiation
angle and Faraday
rotation effect
alternates rapidly their
polarization, sum signal
provided by the
“Coupler”, attenuates
evanescence effect that
occurs normally in
single polarization
antennas and the same
time, when irradiation
angles become very
high (45°~ 90°) it is also
realized a positive
vector sum of the
signals who have
almost the same phase,

obtaining a gain which
we can read on our
S-meter of 3 ~ 12 dB
(anyway without adding
-3 dB attenuation that
two signals undergo in
the same Coupler).
This additional
opportunities that
Crossed Loops Antenna
provides are proved
advantageous in NVIS
operations.
By their nature the loop
elements are steadily
less directional to
signals received with
ever higher radiation
angles providing,
in our case, two signals
with the phase angle
difference always
smaller.
More decreases the
difference between
signals phase angles,
then higher is sum
signal to the magnetic
Coupler output.
Essentially when
realizing the Crossed
Loops Antenna we do
not only appreciate the
unique characteristics
of loop antennas in

terms of low noise and
of particularly directivity,
but we are also
extending their
operational capabilities
and making treasure of
qualities deemed less
important if not, in
some cases,
counterproductive.
I am always available
for any possible
"tips and tricks"
mailto:iz8dms@radiotra
nsverter.com
or through the editorial
staff of
Radio Kit Elettronica
Magazine.
Best 73 from Massimo,
IZ8DMS (ex I8HYF).
*******************

21

Matching Networks
Components - Fig. 6
T1, T2 = T 44-6 i 8 Amidon
12 + 12 bifilar turns 0,22 mm
T3, T4, T5, T6 = BN 43-2402
i 850 Amidon 4 trifilar turns
0,22 mm

General Wiring - Fig. 10

Switch Control - Fig. 11

L1, L2, L3 = Ferrite bead PF8
ext. Dia. 4 mm
Length 6 mm

IC1 = CD 4093N

D1 = 1N5402 200V 3A

IC2 = CD 4017N
IC3 = LM 7809 - TO220

D2, D3 = 1N4002 100V 1A

Q9, Q10, Q11 = BD 517 or
equivalent NPN IC 0,5 ~ 2A

LED1 ~ LED5 = 5 mm LED

D9, D10 = 1N4148

C1, C2 = 100 kpF 50V ceramic

LED GREEN = LED 3 mm

C1A, C1B = 100 kpF 50V
ceramic

C3 = 220 µF 25V
C4, C5 = 100 kpF 50V ceramic

C38, C42 = 68 µF 25V
tantalum

C2A, C2B = 10 kpF 50V
ceramic SMD

C6, C7, C8 = 1 µF 50V mylar

C39, C44 = 10 kpF ceramic

R1 = 680 Ω

C40, C41, C43, C45,
C46 = 100 kpF ceramic

DD1, DD2, DD3, DD4 = Dual
varicap KV1590NT Toko

RPA, RPB = 10 kΩ ¼ W
metallic film
N°2 Brass terminals for
electrical wiring with clamping
screws internal diameter 5,5
mm
N°2 Brass terminals for
electrical wiring with clamping
screws and 3,5 mm internal
diameter
N°2 Single side copper
epoxy fiberglass
65 x 30 x 1,6 mm

R2 ~ R5 = 820 Ω
R7, R8 = 10 turn Bourns
3549S RS 692-8531

C47 = 47 kpF mylar
R26 = 680 Ω

N°2 RS 502-174 Ten Turn
Counting Dial Mechanism

R27 = 1 kΩ

S1 = ON-OFF-ON switch

R29 = 12 kΩ

S2, S4 = ON-OFF switch

R30, R31, R32 = 8,2 kΩ

S3 = Micro-switch
Crouzet 835420

R33, R34 = 470 Ω ½ W

F1, F2 = 5 x 20 1,2A

N°1 pre-drilled epoxy
fiberglass board
100 x 30 mm
drilling pitch 2,5 mm

PW4 = Japan 4 pole
dia. 16 mm

R28 = 100 kΩ

X1, X2 = RG196 Teflon
ext. 2,1 mm

22

Loop A / Loop B
Wideband Amplifier
- Fig. 13
T7, T8 = BN 43-202 i 850
Amidon 6 bifilar turns
0,45 mm
T9, T10 = ANRA 42 i 650
Aros 3 + 4 turns 0,45 mm
T11, T12 = ANRA 42 i 650
Aros 8 + 4 turns 0,45 mm
L1, L2 = Ferrite bead PF8
ext. dia. 4 mm
length 6 mm
L4, L5 = 2,2 mH
Neosid SD75 110 mA
(outside SL03 box)
Q1 ~ Q4 = J310
TO92 / ID matched quartet
Q5 ~ Q8 = J310
TO92 / ID matched quartet
D1, D2 = BAV 21
C1, C2, C19, C22, C23, C24,
C25, C26 = 100 kpF 50V
ceramic
C3, C4 = 8,2 pF 50V NP0
C5, C6 = 22 pF 50V NP0

R17, R18 = 10 kΩ ¼ W
metallic film
(outside SL03 box)
R11, R15 = 10,5 Ω ½ W
metallic film
R12, R16 = 47 Ω ¼ W

Coupler - Fig. 15
T13 = BN 43-202 i 850
Amidon 3 bifilar turns
0,45 mm
T14 = BN 43-202 i 850
Amidon 2 trifilar turns
0,45 mm

K1, K2 = Relay V23105-A5403A201 Siemens

L3 = Ferrite bead PF8
ext. dia. 4 mm
length 6 mm

J1, J2 = BNC Panel mount
flanged socket

D3 ~ D8 = BAV 21

N°2 Metalized fiberglass
board AEMME 857

C33, C34, C37, C41, C42, C43,
C44 = 10 kpF 50V ceramic

N°2 Tinned box SL03
74 x 37 x 30 mm

C47, C48, C49, C50, C51, C52
= 10 kpF 50V ceramic
C35 = 68 pF NP0
C36 = 10 kpF + 100 kpF 50V
ceramic
C38, C39, C40, C45, C46 =
100 kpF 50V ceramic
TH9 ~ TH12 = feed-through
capacitors 1 kpF dia. 3 mm
R19 = 100 Ω ¼ W
carbon film only

C7 ~ C10 = 10 kpF 50V SMD

R20 = 10 kΩ ¼ W
metallic film

C11 ~ C18 = 100 kpF 50V
SMD

R21, R22,
R24, R25 = 470 Ω ¼ W

C20, C21, C27, C28 = 100 kpF
50V SMD

R23 = 33 Ω ¼ W

C29, C30 = 10 kpF 50V
ceramic
C31, C32 = 100 µF 25V
tantalum
TH1 ~ TH8 = feed-through
capacitors 1 kpF dia. 3 mm
R1 ~ R8 = 34 Ω SMD
± 10 ppm RS 614-5036

K3 = Relay V23105-A5403A201 Siemens
K4, K5, K6, K7 = Relay CUP
P001A112 Clare
J3, J4, J5 = BNC Panel mount
flanged socket
N°1 Tinned box SL03
74 x 37 x 30 mm

R9, R10, R13, R14 = 10 kΩ
¼ W metallic film

23

Bibliography
1) ARRL Antenna Book 21st
Edition, “HF Fading” cap. 23,
pp. 35 - 36
2) ARRL Antenna Book 21st
Edition, “HF Elevation Angle”
cap. 23, pp. 28 - 33
3) Ancora M. “Un’antenna
loop HF sintonizzata a
varactor”
Radio Kit Elettronica 7/8 2012
pp. 19 - 23
4) Bellini E., Tosi A.
U.S. Patent number 948086
Feb 1, 1910
Current U.S. Classification
342/367 Directive Radio Wave
Systems and Devices
5) Dallas Lankford,
“New Improved Passive
Phasers” 100 kHz~30 MHz
Aug 2, 2007, rev. May 23,
2008
6) ARRL Antenna Book 21st
Edition, “Direction Finding
Antennas” cap. 14, pp. 1 - 15

24


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