BTV MLA-M User manual

MLA-MMLA-M
Magnetic Loop Antenna - Multiband
Instruction Manual
Thank you for purchasing this new product small Magnetic Loop
Antenna Multiband. Manual contains important information.
Please read all instructions carefully before operating the antenna.
B P L U S T V a . s .

Description
Technical parameters
Design details
B P L U S T V a . s .
B PLUS TV a. s., Požárnická 140, 742 83 Klimkovice, Czech Republic
phone: [phone], fax: [phone]
e-mail: [e-mail], http://www.btv.cz
MLA-M
Frequency range
Input impedance
Max. power
SWR after tuning
Input connector
Dimmensions
Weight of antenna
Diameter of the loop
630 x 750 x 180 mm
PL
3,5 - 28 MHz
10 W
1:1; max. 1:1,2
2,6 kg
600 mm (<2ft)
50 Ohm
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MLA-M
Magnetic Loop Antenna MLA-M supplied by the BTV corporation (http://www.btv.cz ) is „plug and play“
type product. Antenna is given up to the QRP service on all HF radioamateur bands except for the 160 m. In
spite of the fact, that the diameter of the MLA is only 60 cm (less than 2 ft), it is possible to use this antenna
with minimalistic design for communication on 8 HF bands 3,5, 7, 10, 14, 18, 21, 24 and 28 MHz.
In the case of small magnetic loop antenna you can not suppose the same efficiency in transformation of HF
current into HF (electro)magnetic field as for let`s say half-wave dipole. Power loss is min. abt. 10 dB. But
antenna MLA-M is supposed to be acceptable compromise which enables to carry on the radioamateur hobby,
not only for portable QTH, but for example in condominium with restricted possibilities of building classic
antennas, in conservation urban areas etc.
MLA-M is ideal for the communication through digital modes with sofisticated protocoles convinient for very
low signals. The loss of abt. 10 dB due to using indoor antenna is in comparison with another influences of
ionosphere atc. negligible.
Perfect impedance adaptation of the antenna in all HF radioamateur bands from 3,5 to 28 MHz is achieved
by the industrial protected solution developed by the corporation BTV. Point of such wide range of tuning of
magnetic antenna is based on two-turns construction of the main antenna circuit inductivity with the
possibility of partly short-circuiting see fig. 1-3.
Possible switching of the antenna
1. Mode 3,5 MHz
Loop consists of two turns, jumper J1 is switched off and the
jumper J2 connecting parallel capacity is switched on, see fig. 1.
2. Mode 7-10 MHz
Loop consists of two turns, jumper J1 is switched off and the
jumper J2 connecting parallel capacity is switched off, see fig. 2.
fig. 1
fig. 2
J2
J2
J1
J1

fig. 4
3,5 MHz 7 a 10 MHz
fig. 5
fig. 6
B P L U S T V a . s .
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3. Mode 10-28 MHz
Loop consists of one turn, the jumper J1 is switched on and the
jumper J2 is switched off, see fig. 3.
Unusual method of tuning of the MLA-M by means of two
variable condensers does not represent any complication in
case of desk-top design. Circuit works by analogous way as a
classic matching circuit. This type of circuit favourably enables
exact tuning of the antenna in whole range of HF frequencies
and input impedance is very near to 50±j0 Ohm. For another
types of feeding circuits for magnetic antenna it is in principle
unpossible. Switching among low and high bands by means of
mechanical switching of jumper inside the box of antenna
14 - 28 MHz
fig. 3
J2
J1
represents in case of desktop design of MLA-M also no problem, see figs. 4-6. It is necessary to emphasize
that without using SWR-meter is exact tuning not simple, at least during the start of this procedure.
B PLUS TV a. s., Požárnická 140, 742 83 Klimkovice, Czech Republic
phone: [phone], fax: [phone]
e-mail: [e-mail], http://www.btv.cz

B P L U S T V a . s .
Setting the antenna for the 10 MHz band is possible either in one turn or in two turns mode. We reccomend
testing of both these alternatives.
Due to short circuit of one turn and different values of L/C ratio at each band the quality Q of the antenna
circuit is not identical through all HF range. Testing of antenna demonstrated that it is acceptable penalty for
the possibility of simple tuning in whole range of HF frequencies with SWR near to 1:1. After correct tuning the
SWR ratio does not exceed value 1:1,1 see measured impedance characteristics and SWR on next figures.
Typical diagrams of the parameters of MLA-M antenna measured by means of antenna analyser AA-230PRO
are provided on pages 6-12.
Employment of MLA-M is very simple. For concrete band we switch proper mode by means of the jumpers
see figs. 4-6. After connecting the 50 Ohm coaxial cable from transceiver we try to set strongest received
signal or noise by setting both variable condensers. Then in TX regime with input max. 10 W we must find by
changing the ratio of capacitance of both condensers the very small value of SWR. Due to very high quality Q
of the antenna circuit, especially in mode with two turns (figs. 2 and 3) is the selectivity of the antenna so high
that correct tuning changes even under the influence of closeness of operators hand a few attempts and
some training will solve this possible problem.
Horizontal radiation diagramm of MLA oriented perpendicurarly towards earth see fig. 7. It shows two
rounded maxima and two sharp minima (¥ - shaped). The depth of minimum depends very strongly on
neighbour objects (instalation in wall), on the type of propagation, ionosphere etc. Diagram in horizontal
plane with loop paralel to earth is ilustrated on figs. 8, 8a. Possible inclination of the loop (figs. 9, 9a) enables
alternatively to obtain a few dB increase.
MLA-M
MLA-M
Operation
fig. 8
magnetic
field lines
15°
all signals attenuated >10 dB
fig. 7 fig. 7a fig. 8a
fig. 9a
fig. 9
page 3
B PLUS TV a. s., Požárnická 140, 742 83 Klimkovice, Czech Republic
phone: [phone], fax: [phone]
e-mail: [e-mail], http://www.btv.cz

B P L U S T V a . s .
MLA-M
MLA-M
Antenna is predetermined for QRP operation only (power max. 10 W) and enabled indoor using. During
transmission avoid any direct touch contact with „hot“ parts the copper coil which may cause painfull
burning smell!
The health impact of long term influence of HF magnetic field is not fully recognized, so set the proper
distance from antenna. Do not try to use power higher than 10 W danger and possibility of the breakdown of
some parts!
Antenna MLA-M is not constructed for outdoor usage and is not waterproof. Take it into consideration if you
place it for example on the balcony etc.
Important safety warning
Photo
page 4
B PLUS TV a. s., Požárnická 140, 742 83 Klimkovice, Czech Republic
phone: [phone], fax: [phone]
e-mail: [e-mail], http://www.btv.cz
detail

MLA-M
MLA-M
Measurement protocols
fig. 10
fig. 11
B P L U S T V a . s .
page 5
B PLUS TV a. s., Požárnická 140, 742 83 Klimkovice, Czech Republic
phone: [phone], fax: [phone]
e-mail: [e-mail], http://www.btv.cz

MLA-M
MLA-M
fig. 12
fig. 13
B P L U S T V a . s .
page 6
B PLUS TV a. s., Požárnická 140, 742 83 Klimkovice, Czech Republic
phone: [phone], fax: [phone]
e-mail: [e-mail], http://www.btv.cz
Measurement protocols

MLA-M
MLA-M
fig. 14
fig. 15
B P L U S T V a . s .
page 7
B PLUS TV a. s., Požárnická 140, 742 83 Klimkovice, Czech Republic
phone: [phone], fax: [phone]
e-mail: [e-mail], http://www.btv.cz
Measurement protocols

MLA-M
MLA-M
fig. 16
fig. 17
B P L U S T V a . s .
page 8
B PLUS TV a. s., Požárnická 140, 742 83 Klimkovice, Czech Republic
phone: [phone], fax: [phone]
e-mail: [e-mail], http://www.btv.cz
Measurement protocols

MLA-M
MLA-M
fig. 18
fig. 19
B P L U S T V a . s .
page 9
B PLUS TV a. s., Požárnická 140, 742 83 Klimkovice, Czech Republic
phone: [phone], fax: [phone]
e-mail: [e-mail], http://www.btv.cz
Measurement protocols

MLA-M
MLA-M
fig. 20
fig. 21
B P L U S T V a . s .
page 10
B PLUS TV a. s., Požárnická 140, 742 83 Klimkovice, Czech Republic
phone: [phone], fax: [phone]
e-mail: [e-mail], http://www.btv.cz
Measurement protocols

MLA-M
MLA-M
fig. 22
fig. 23
B P L U S T V a . s .
page 11
B PLUS TV a. s., Požárnická 140, 742 83 Klimkovice, Czech Republic
phone: [phone], fax: [phone]
e-mail: [e-mail], http://www.btv.cz
Measurement protocols