TELE-audiovision - The World’s Largest Digital TV Trade Magazine - page 100

TELE-audiovision International — The World‘s Largest Digital TV Trade Magazine
— 1 -12/2013
power supply input (12V-
24V), two USB type B inputs
and three status LEDs. The
first LED indicates the in-
struments operational sta-
tus (OK or error), the second
LED shows the charging sta-
tus of the rechargeable bat-
tery and the third one shows
the system status.
The two USB inputs have
different functions. USB1
serves as an additional
source of power and also
provides for the data com-
munication with the PC.
USB2 is exclusively used to
provide power to the unit if
for some reason the external
power supply can‘t be used.
The Handheld Satcom Test
Source runs from an internal
rechargeable battery that
lets you use it without hav-
ing to keep it connected to
a power source. This is not
surprising considering this is
a portable signal generator.
It‘s also interesting that this
instrument can be operated
from a PC or laptop via the
USB ports and since a single
USB port cannot provide
enough power, the Hand-
held Satcom Test Source can
be connected to both USB
ports. Very clever!
On the back of the test
source is the on/off switch.
There‘s also a BNC jack that
provides a 10 MHz reference
output signal as well as an
SMA jack that provides the
signal generated by the test
The signal generator also
provides a DC voltage on this
output which is indicated by
an additional LED. Control of
the unit is taken care of by a
Windows program which also
controls a sweep function.
of High-frequency
The primary use of the
Handheld Satcom Test
Source is the measurement
of various parameters of
high-frequency (RF) con-
verters. These RF convert-
ers, also available from
WORK Microwave, convert
the signal to be transmitted
from its original frequency to
a higher output frequency.
Since these high-frequen-
cy signals could not be rout-
ed through a satellite uplink
station between all the dif-
ferent devices (modulators,
multiplexers, etc.) using co-
axial cable without incurring
some signal loss, waveguides
or very expensive cable are
needed. Instead, a different
path is used. The signal is
routed and processed in the
50 to 180 MHz range or the
950 to 2150 MHz range until
it‘s ready to be sent to the
uplink section. Only then, in
this final step, is the high-
frequency converter used
to upconvert the signal into
the satellite uplink frequency
Obviously, this high-fre-
quency converter cannot
introduce any errors that
might interfere with a neigh-
boring transponder or even
go as far as interfering with
normal satellite operation.
This kind of interference
is known as intermodula-
tion. Intermodulation occurs
when two signals are modu-
lated on two frequencies that
are very close to each other,
causing additional signal
peaks to appear on the sides
of the two main frequencies.
(see Figure 1)
To check and see how
much a high-frequency con-
verter can minimize this In-
termodulation effect, you
would need two RF test
sources so that you can
modulate two nearby signal
levels with known parame-
ters. These two signal levels
would then be routed to the
high-frequency converters.
Using a spectrum analyzer,
you could then generate an
picture of this intermodula-
It‘s exactly for this reason
1: Intermodulation occurs directly next to the wanted signal - see
the red labled signals
2: The compression point is defined to be at exactly 1 dB. From
here on the signal quality deviates from the ideal characteristic.
that WORK Microwave in-
corporated two independent
synthesizers in the Handheld
Satcom Test Source so that
now you can use just a sin-
gle RF signal source to per-
form this measurement.
Obviously this greatly re-
duces the costs involved
in acquiring these RF test
sources since now you‘d only
need one of these instru-
ments instead of two. At the
same time the test setup it-
self is simplified since only a
single cable and the upcon-
verter need to be connected.
Another parameter that is
measured when it comes to
high-frequency converters is
the so-called 1 dB compres-
sion point. This measure-
ment is used to check the
non-linear response of the
high-frequency converter.
Here the amplitude of the in-
put signal is slowly increased
until the signal distortion
due to non-linearity deviates
exactly 1 dB from the ideal
characteristic curve
Figure 2)
The red line shows the
ideal output curve. Above a
specific input level the high-
frequency converter begins
to distort the signal such
that a lower signal level is
available at the output -
hence the name “Compres-
sion“: a lower signal level is
at the output; the signal has
been compressed.
To be able to compare dif-
ferent devices, you measure
the input power level that
results in a 1 dB compres-
sion at the output. Here
the WORK Microwave Test
Source proves itself with the
ability to set the test signal
to any frequency from 50 to
180 MHz and 950 to 2150
MHz with a power level from
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