Funk Amateur FA-VA4 User manual

Construction and User Manual
Kit for an easy to use
ector antenna analyzer
for use in the frequency range
100 kHz to 100 MHz.
Vector Antenna Analyzer
FA-VA4

BX-240 • 1© Box 73 Amateurfunkservice GmbH 2017
Radio Amateur who build their own antenna , appreciate the value of a vector antenna analyzer. The appa-
ratu pre ented here a a kit, i characteri ed by high accuracy, mall dimen ion and ea y handling.
It allow
one port mea urement in the frequency range 100 kHz to 100 MHz with a y tem impedance of 50 Ohm .
Vector Antenna Analyzer FA -VA4
Experimenting with antennas is an essen-
tial part of the hobby for many radio ama-
teurs. Measuring SWR and determining
impedance values are inseperable. The
first can be estimated with the transmitters
SWR meter, however, better and more ac-
curate data can be obtained by using an an-
tenna analyzer. ood devices are expen-
sive with less expensive models being
somewhat less accurate.
The FA -VA4 closes this gap. It was devel-
oped by Michael Knitter, D 5MK and is
presented in [1]. This is a fully fledged
vector antenna analyzer for use in the
frequency range 100 kHz to 100 MHz
(Table 1).
Vector measurement means that in con-
trast to a scalar measurement, not only is
the SWR determined and displayed but al-
so the value of the base point impedance
along with the sign based imaginary part.
The so called SOL compensation from the
professional field is used to calibrate the
device and allows precise measurements
in different configurations.
The FA-VA4 kit consists of an SMD
mounted circuit board, the graphics dis-
play with backlighting, as well as some
mechanical components such as some
connectors, push buttons, sliding switches
and battery holder along with a fully ma-
chined and printed housing. The micropro-
cessor on the board comes pre programmed.
The requirements for construction can be
easily handled by beginners if clean work-
ing practices and adherence to the instruc-
tion manual are followed.

2 • BX-240 © Box 73 Amateurfunkservice GmbH 2017
For construction, the following tools and
equipment will be required.
– Temperature regulated 60 … 80 W sol-
dering iron with a fine (pencil) tip, 0.5 …
1 mm solder with flux,
– 100 W soldering iron with flat (chisel)
tip,
– Electronics side cutters,
– Flat nose pliers,
– Slot screwdriver,
– Cross head (Phillips) screwdriver.
– Two 1.5 V batteries type AA for power
supply.
Before mounting the board the contents of
the kit should be checked against the parts
list provided.
nMounting the board
Fig. 2 shows the layout plan with the few
components still to be soldered. hese are
to be mounted exclusively on the upper
side where the six pin mounting strip for
the programmable interface is already lo-
cated.
First of all the sliding switch S4 should be
mounted on the face of the board. It should
rest with its underside on the circuit board
with the slider able to move horizontally
able 1: echnical data
Frequency range 0.1 … 100 MHz
(1 Hz resolution)
Accuracy ≤ 2 % (f≤ 50 MHz)
Measurements Complete impedance
values
Measurement range s≤ 100,
limits* Z≤ 1000 Ohms
Input 50 Ohms, BNC
Output voltage Peak to peak = 1 V
at 50 Ohms
Power supply 2 ¥1.5 V AA batteries
Current drain 49 mA** (110 mA)
Case dimensions 137 mm ¥90 mm ¥
25 mm (L ¥W ¥H)
Weight 290 g, incl. batteries
*out of limits less accurate results
** Average value without illumination at
100 MHz and 50 Ohms load resistance, peak
value shown in brackets.
Fig. 1: View of a finished FA -VA4
in a switched off state.
Building instructions

BX-240 • 3© Box 73 Amateurfunkservice GmbH 2017
(Fig. 3). The simplest way to do this is to
make a provisional solder connection us-
ing one solder tag on the switch thus al-
lowing for correct alignment whilst heat-
ing the solder. When it is in the correct
position all the connector tags for the
switch along with the two for the housing
may be soldered.
Disp ay
An LED backlit LCD screen is used to dis-
play measured values. These components
are joined together as a single unit and re-
quire partial soldering. To do this, the dis-
play must be placed on the LED backlight
so that there is no gap. All six connections
of the two 3 pin display contacts must be
soldered to the top of the LED backlight
along with the two outside pins of the 20
pin connector strip (Figs. 6 and 7). It is
advisable to use an appropriate support
under the display when soldering to the
LED backlight unit to fix both compo-
nents in the correct position.
The protective film on the display glass
screen should be removed before assem-
bly.
To finish, the three socket assemblies are
fixed to the contact points on the underside
of the display. The upper edge of each
socket must sit flush with the back of the
Fig. 3: lider switch soldered in correct posi-
tion
Fig. 4: The three plug connectors for display
connection
Fig. 2: FA -VA4 layout plan with soldered parts

4 • BX-240 © Box 73 Amateurfunkservice GmbH 2017
display after which the whole assembly,
display and sockets, must be placed onto
the board. The thin ends of the solder tags
are pushed fully into their respective holes
taking care not to press too hard and that
the tags aren't pushed too deep into their
holes. Now all three sockets can be sol-
dered on the underside of the board. The
display is to be carefully removed while
the remaining components are mounted
and is then subsequently re-attached. The
three mounted socket assemblies are
shown in Fig. 4.
After which the three pushbuttons and
both the battery holders should be installed.
All must have the underside of their hous-
ings on the circuit board (Fig. 5). When
soldering, some form of compensating
support must be used as the socket con-
nections are higher.
The battery holders must be connected to
the correct polarity, the spring connection
is the negative pole (Fig. 5). The battery
holder solder tags are made from spring
steel, please use correspondingly robust
sidecutters to shorten them.
To finish, the BNC socket must be sol-
dered to the board, set up and aligned hor-
izontally at right angles to the boards edge.
The two earth pins should be soldered to
the underside of the board using the 100 W
soldering iron. The solder must flow well
in order to avoid cold spots while at the
same time soldering iron usage must be
kept to a minimum in order to avoid dam-
aging the insulation on the interior of the
socket through overheating.
Fig. 5: Mounted pushbuttons and battery holders

BX-240 • 5© Box 73 Amateurfunkservice GmbH 2017
Function Test
Before mounting the circuit board into its
case a brief test is required. So next first of
all, the three caps should be pushed onto
the push button switch and the now
mounted display plugged into the corre-
sponding sockets. The slider switch should
be in the off position (Fig. 8). Lastly two
1.5 V batteries should be attached, making
sure of the correct polarity, and the device
may be powered up using the slider
switch.
The display will briefly show the greetings
text, then the FA-VA4 switches to measur-
ing mode. Should the display remain blank
then all the previous soldering must be
checked and reworked if necessary. When
everything is working correctly the slider
switch should be turned off and the batter-
ies removed from their holder. The fully
built board can be seen in Fig. 9.
Assemb y into the case
First of all the four rubber feet from the
underside of the case are to be fitted, it
may help to use some flat nosed pliers to
pull on the thin rubber nipple from the in-
side while slightly twisting the foot into
place, after which the excess rubber inside
the case should be trimmed with side cut-
ters to around 2 to 3 mm so that it doesn’t
interfere when the board is screwed into
the case.
The board is now inserted, with the socket
to the front, into the case sub assembly and
loosely fixed with four M3¥4 cylinder
screws in the corners. Then the BNC sock-
et should be fixed using the supplied nut
and toothed washer after which the assem-
bly screws may be tightened.
After installation, with due diligence to
correct polarity, of the batteries, the case
cover should be put on and fixed with four
countersunk M3¥4 screws. Lastly, the
supplied label should be stuck to the un-
derside of the device.
Your FA-VA4 is ready now and can be
used in an uncalibrated measuring mode.
Fig. 6: Display with backlight; shown here the
side with the six connections
Fig. 7: View of the 20 pin display contact strip
after assembly
8: lider switch in off position

Genera Notes on Use
The FA -VA4 can be used as a measuring
device immediately after assembly, it then
operates in an uncalibrated mode and the
results displayed may be more prone to er-
ror than would be the case after correct
calibration. This mode can also be selected
later from the Setup menu, for example if
doubts arise about the validity of stored
calibration data.
The FA -VA4 is a sensitive measuring de-
vice. No RF energy must be allowed to
reach the measuring socket so as not to
destroy the input components. This could
happen if for example an antenna in the im-
mediate vicinity transmits. Likewise, static
charges should be kept as far away as pos-
sible from the measuring socket. Insulated
antenna structures must therefor be earthed
before connecting to the device for example
by shorting to earth.
Rechargeable batteries should not be
used in the FA -VA4 as no deep discharge
nor charging circuitry is available. Deep
discharge can render the rechargeable bat-
teries unuseable or even destroy them. Leak-
ing batteries can likewise severely damage
the equipment.
The FA- VA4 is optimally designed to use
1.5 V AA cells. Used cells must be re-
moved from the device.
For the longest battery life it is recom-
mended to only use the backlight when the
display cannot be read. With daylight or
outside the display doesn't usually needs
backlight illumination.
The number of measurement display cy-
cles should only be as many as are needed
to ensure a sufficient repetition rate for
the measurement in question. Both param-
eters have a considerable influence on cur-
rent consumption and therefore on battery
life expectancy, they can be changed in the
Setup menu.
BNC plugs should be carefully twisted af-
ter connecting to ensure no ‘unexpected’
incorrect measurements.
6 • BX-240 © Box 73 Amateurfunkservice GmbH 2017
Fig. 9: Completed FA- VA4 board

BX-240 • 7© Box 73 Amateurfunkservice GmbH 2017
Although the FA -VA4 has a relatively
wide range of functions, its operation is
fairly intuitive therefore the following
guide has the character of a reference
book, however the general operating in-
structions from the previous section are to
be considered in each case.
The device cannot be destroyed by incor-
rect button pressing but may display in-
correct, unexpected results. It is recom-
mended therefore that the inexperienced
user starts with data from a known mea-
sured object and then explores the antenna
analyzer step by step, testing different mea-
surement and display modes, and refer to
these instructions as necessary.
For precision measurements the subject of
calibration (SOL compensation) is impor-
tant and is covered in its own separate sec-
tion.
The antenna analyzer operates according
to the following measuring principles: an
internal oscillator generates a signal with
a defined frequency, this signal is then
passed to the test object (e. g. antenna) via
the output socket of the device. Due to the
electrical properties of the object under
test, the signal will be changed in both am-
plitude and phase. This change is evaluat-
ed to determine the impedance of the test
object. All other measured values (e. g.
SWR) are mathematically derived from
the impedance by the microprocessor.
nControls and connectors
The only connection to the analyzer is the
test socket. For operation there are three
pushbuttons and an on/off switch.
All selected parameters are saved, so that
at switching on the device will have the
same settings as when it was switched off.
The three pushbuttons have different func-
tions depending on the actual measuring
or operating mode. In most cases a func-
tion or other selection is called up with the
left hand button, the middle and right but-
tons serve to increase or decrease values
through the menulists. The current function
is displayed on the display above the but-
tons.
When in measurement mode a longer press
of the left button will call up the menu.
The middle and right buttons then allow
you to select a menu item which may then
be selected or activated using the left but-
ton. Other functions of the buttons are ex-
plained in a later paragraph.
Switching on the Ana yzer
After switching on the FA -VA4 a greetings
message will appear on the display under
which also the firmware version and to the
right of that the battery voltage. The de-
fault menu language is En lish.
Directions for use

nCalibration ( OL compensation)
Every extra plug and additional piece of
cable influences the impedance measure-
ment of the test object. This unwanted in-
fluence can be completely compensated
for by the Short Open Load method (short-
ened to SOL method).
First of all, instead of the test object, three
reference elements are measured; Short
represents a short circuit, Open, an open
cable end, and Load, a resistance in the
magnitude of the system impedance (in
our case 50 Ohms.) These reference mea-
surements can be easily obtained with ac-
ceptable accuracy using three 50 Ohms
BNC co ax plugs.
In the case of the Short element the inner
connector and the plug housing are short
circuited, for the Open element the inner
pin remains unconnected, for the Load el-
ement there is a small 50 Ohm metal film
resistor between the inner connector and
the housing. If the materials aren’t to hand
further information on the reference ele-
ments (shown in Fig.10) is available at [2].
After calibration has been completed the
calculated values are automatically stored
in the analyzer so that the correct im pe -
dance is determined when the test object
is measured.
The analyzer knows two different modes
of SOL compensation.
SOL for a frequencies
It is possible to permanently save SOL ref-
erence values for the entire measuring
range. In this case, with the Short refer-
ence element connected, the analyzer runs
through the entire frequency range and
stores the determined measured values.
The same procedure is to be carried out
for connected Open and Load elements. It
is recommended to carry out this compen-
sation routine once, after commissioning,
for the built in plug, any permanently at-
tached cable or measuring device and in
between times as required. Thereafter the
measurement of a test object is possible at
any time without further compensation.
The analyzer then uses these reference
values as a standard (master compensa-
tion), in particular for multi frequency
measurements. This function can be ac-
cessed via the Operatin Mode ÆSetup
ÆSOL All Frequencies (Fig. 12).
Please note: the entire process takes sev-
eral minutes but may be cancelled, in this
case however the resulting measurements
will be inaccurate and the calibration pro-
cedure should be recommenced at the first
opportunity.
8 • BX-240 © Box 73 Amateurfunkservice GmbH 2017
Fig. 10: The optional kit for the reference
elements BX-240- OL [2] contains a 50 Ohm
termination resistor (middle) along with two
BNC co ax plugs for the Short and Open refer-
ence elements.

BX-240 • 9© Box 73 Amateurfunkservice GmbH 2017
SOL for an individua frequency
For all individual frequency measure-
ments it is possible to run through SOL
compensation for the actual frequency,
(Operatin Mode ÆSOL One Frequency,
see Fig. 11).
The procedure is the same as described
above but only applies to the currently set
frequency and therefore runs very quickly.
This makes it possible to quickly and eas-
ily compensate for temporary changes in
the measurement setup or parameters as a
result of temperature changes or other in-
terference.
For particularly high accuracy it is recom-
mended to perform such compensation be-
fore each measurement.
Important: if the measured frequency of
the analyzer is changed, the determined
SOL reference values for the current fre-
quency are indicated as invalid and the
standard values of the master compensa-
tion will be used instead for the next mea-
surement. The display shows which refer-
ence values are currently being used. For
example in Fig. 18 the master calibration is
used to measure SWR, which can be seen
as a small solM to the right of the bar on
the right hand side of the display. In case
of single frequency calibration the display
will show solf, in case of no calibration at
all it will show sol-.
Fig. 11: Menu item for OL one frequency
Fig. 12: The Master OL compensation (for
all frequencies) is started in the Setup sub -
menu.