TELE-audiovision - The World’s Leading Digital TV Industry Publication

32 / 164

32 TELE-audiovision International — The World‘s Leading Digital TV Industry Publication — 01-02/2015 —
terrestrial receiver antenna
terminal without adding any
additional coax cable.
Next ist the SLTE 60: it of-
fers very steep edge ampli-
tude response right above
790 MHz. However, it is not
a low pass filter but a band
stop filter. So, above about
850 MHz its attenuation be-
comes small again. It has
IEC connectors and due to
that it is well prepared to be
added to the TV receivers
equipped with this type of
antenna connector. Some-
times some of signal dis-
tribution components are
equipped with this type of
connector and then SLTE 60
is a very convenient choice.
Finally, the SLTE 90 is
a low pass filter with ex-
tremely steep character-
istics. According to SPAUN
specification, SLTE 90 per-
formance is really the best
among these three models.
It has female F connectors
on both ends, so in most
applications you will have
to add an additional short
coax cable with male F con-
nectors to hook it up.
In order to test the filters,
we created a setup consist-
ing of a wideband noise
generator and a terrestrial
TV spectrum analyzer. We
took a number of screen
shots. We maintained the
same frequency span set-
ting so that you could see
the difference in the steep-
ness of filter characteristics
among the filter models.
As expected, both SLTE 60
and SLTE 90 had very sharp
roll-off while the SLTE 30
filter had a moderate one
(Figure 1 through 7).
Then, we measured all
the filters at the frequen-
cies for which their attenu-
ation had been specified by
SPAUN. We got results very
close to the manufacturer’s
data. We must note here
that in some measurement
points filter attenuation was
so deep that our TV analyz-
er was not able to measure
it accurately. For example,
our analyzer measured at-
tenuation “> 41.2 dB” at the
point where SPAUN specifi-
cation read 45 dB. Simply
our general purpose TV sig-
nal analyzer was not able to
measure characteristics of
high quality filter at points
of high attenuation. In this
case, we left 41.2 dB as a
measurement result but we
had a good reason to be-
lieve that indeed those 45
dB were achieved for SLTE
90 at 823 MHz.
In the graph, we present
the measurement results of
all three filters at the fre-
quencies at which we com-
pared their performance
with the specification. Also
here you can easily see the
difference among the filter
models. Please note though
that straight line interpola-
tion between the measured
values does not reflect actu-
al filter characteristics. The
purpose of those straight
line segments is just to
make it easier to identify
which measurement point
belongs to which filter mod-
el. The actual character-
istics are presented in the
analyzer screenshots.
Finally, we took the ana-
lyzer screen shots showing
all three filters response
in the full analyzer band-
width: up to 1 GHz. In these
pictures, it is clearly vis-
ible that the SLTE 60 is a
band rejecting filter while
the other two are low pass
filters. If you take a clos-
er look, you will also no-
tice that the SLTE 30 has
smoother transition from
pass band to stop band