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In this section we are going to cover: RF interference measurements,
EMC Precompliance Testing, Signal Strength and Site Survey measurements,
as well as recording and monitoring the RF Spectrum for Security Surveillance, Defense
Signal, Satellite Signal Monitoring,
and Intruder Watch. It is worth pointing out again that the internal
battery lasts 3 to 4 hours, but if you are driving around in a vehicle making site survey
measurements then you can run the unit indefinitely from the vehicle's cigarette lighter socket
with the appropriate accessory cable. You will see I have switched over to the 20
GHz model, the N9344C. I thought it would be good to see how well
these Analyzers perform under the microwave bands.
Be aware that all the features that we cover in this section are available on all models
in the range. You will also see I have turned on the built
in GPS receiver. Here you can see our current position expressed
as LATT and LONG and this can be saved with every measurement we make.
Depending on your field of interest you may decide to use a close field EMC Probe, such
as one of the Agilent 11940 series probes for EMC pre-compliance measurements.
Or perhaps a broadband log periodic antenna, such as this, covering
380 MHz to 18 GHz or even a cheap whip antenna, such as the one we have been using for other
demonstrations on the video. But before we start connecting antennas let
us take a quick look at the sensitivity and sweep time of the analyzer.
Spectrum analyzer sensitivity, the instrument's ability to detect weak signals is vital when
we are trying to perform these kinds of tasks. Sweep time is equally important if we are
trying to catch signals that are both weak and intermittent.
I will disconnect the antenna, and connect a 50 ohm termination to the input,
I will press INSTRUMENT PRESET, and let us select a frequency of 14 GHz, which
is a common frequency used in digital microwave links,
I will set a Span of 1 kHz, and let us press the AMPLITUDE button,
we will set the Attenuation to 0 dB, We will turn the preamplifier ON,
and let us adjust the Reference Level to bring the trace back up onto the screen.
I will press the TRACE button, and press MORE,
and we will turn AVERAGING ON, and I will turn on a MARKER.
You can see here, we have got a displayed average noise level or sensitivity, of around
-147 dBm. Let us just change the frequency to 18 GHz
and see what we get there. Once the averaging has settled, you can see
here at a frequency of 18 GHz we are still getting a sensitivity of around -145 dBm.
Quite incredible for a handheld spectrum analyzer. It is all very well having great sensitivity,
but some handheld spectrum analyzers out there in the market have gained a reputation for
generating quite a lot of RF noise and interference themselves.
Hardly ideal when trying to detect weak signals in a radio quiet secure environment or when
trying to remain undetected yourself. You will be pleased to discover that Agilent's
handheld spectrum analyzers are incredibly quiet.
The RF shielding is simply outstanding for a handheld unit.
One feature you may wish to use when using antennas or probes, is to set the Y-axis units
to uV or dBuV depending on your particular application.
Currently, you can see the marker is measuring in dBm, the scale on the Y-axis is in dBm,
but if I press the AMPLITUDE button, and select Y-axis UNITS,
you will see I have currently got dBm selected, but we can also select dBmV,
dBuV, Watts,
Volts and if I press MORE, we can even select dBuV EMF.
If your using a calibrated antenna or probe that comes with a table of antenna factors,
such as this close field probe or the log periodic antenna I have here, you can even
enter these antenna factors into a table that is held inside the analyzer and therefore
get calibrated measurements of field strength in uV/m or dBuV/m.
I simply press RETURN, press MORE,
press CORRECTION, and here you can see a range of correction
factor tables can be stored which we can turn on and then turn on the Antenna Units to display
in true field strength. Let us start by looking for some weak signals
in the 430 MHz ISM band. I will press FREQUENCY,
and enter a frequency of 437 MHz, and a Span of 10 MHz,
and to increase the sensitivity I will press the AMPLITUDE,
button reduce the attenuation to 0 dB, I will turn the Preamplifier ON,
and you can see now, we have a range of signals here being picked up by this antenna.
There seems to be some kind of spread spectrum signal here, a few modulated carriers maybe
or carriers anyway, and I noticed over here there is an intermittent signal popping up
and down every now and then over here, at various amplitude levels.
Let us go through the various steps to see how we would characterize and measure and
maybe even record these signals. First I will press the MARKER button,
and I will go SHIFT, PEAK,
and that tells me the amplitude and frequency of the highest signal on the display.
But let us press the MARKER button again and turn on some other markers,
I will turn on MARKER #2, and let us move that marker to the peak of
one of the other signals here. Let us turn on a couple more markers,
MARKER #3, set it to Normal.
You will now see we have 3 markers turned on and if I press RETURN,
and press MARKER TABLE ON, you will now see we have the 3 markers listed
at the bottom of the screen with their X-axis value, their frequency and their amplitude
in dBm. I will turn that off.
How are we going to capture this very intermittent signal over here?
There is a couple of ways we can do it. The first thing I am going to do is press
the TRACE button, you will see currently we are looking at Trace
#1, which is the yellow trace on the screen. That is set to the mode called Clear Write.
In other words it clears the screen, writes a new trace, clears the screen, and writes
a new trace. I will go to Trace #2 and that is currently
set to Blank, but if I turn on MAX HOLD,
you will see this blue colored trace is storing the maximum amplitude value seen for every
frequency point on the display. The constant signals - like these ones here
- the trace there looks pretty much the same as the yellow trace, but for this intermittent
signal over here you will see that it holds that value.
Max Hold is a very simple and quick way of identifying are there any intermittent signals
on the spectrum? Just as an aside I can turn on TRACE #3, and
set that to MIN HOLD, and that will now show us the minimum amplitude
value that the analyzer has seen for every frequency point on the trace.
I will turn that back off. MAX HOLD is a great way to identify intermittent
signals. It tells us that, since we turned on MAX HOLD
an intermittent signal has occurred. But what it does not tell us is when that
signal occurred. If we were to leave this analyzer sat here
now for a few hours and when I come back I would not have any idea as to how frequent
that intermittent signal is. That is where the Spectrogram feature on these
handheld analyzers is invaluable. If I press the MEAS button,
and press SPECTRUM MONITOR, you will see the display has been divided
into two sections. The bottom half is still showing a live spectrum
analyzer trace; the yellow Clear Write trace that we saw previously.
But the top half of the display is now showing a Spectrogram.
The X-axis is still showing frequency, but the Y-axis is now displaying time.
In fact, the amplitude of the signal is now displayed by the color of the trace.
A strong signal is displayed as yellow or red and a weak signal is shown as blue or
green. We can easily adjust the colors of this if
I just press the AMPLITUDE button, and let us set the SCALE PER DIVISION to 5
dB per division, and then I will change the Reference Level.
You will see now much more clearly we have a very strong carrier here shown in the red,
slightly weaker carriers here in yellow, even weaker ones in green,
and there is our little intermittent signal quite strong so it is in red.
You can see now, how often that intermittent signal is transmitting.
If I press the MEAS button, you will see here we can Pause and Run the
Spectrogram, we can re-start the measurement - clearing
all the traces that we have stored in the internal memory,
and we can even set the update interval currently set to a 100 ms.
But let us say I wanted only to record a new trace every 10 second, for example.
I could type in 10 seconds for that and now the instrument will pause for 10 seconds and
then add a new measurement to that stack of traces in the Spectrogram display.
I will set the Update Interval back to its fastest, 100 ms.
We can set the display mode so that it is just showing the Spectrogram, or just showing
the trace, or my preference displaying both.
Now here is probably the most useful feature of the Spectrogram measurement and that is
file logging. So if I press FILE LOGGING,
and I press START SAVE, every trace now is being stored into the internal
memory of the analyzer. We are going to be able to play that back
later and analyze what happened while we were away.
In fact, for example, if you wanted to set the analyzer up to only record during the
night, starting at 10 pm and finishing at 2 am, we can set the TIME SETTING here,
set TIMED SAVE ON, you can enter the start date and start time,
stop date and stop time, and the analyzer will automatically start logging at a pre-defined
time and stop at a pre-defined time. This is ideal for unattended logging as it
means we can leave the analyzer out onsite, return a few days later and then view what
happened during that period. I will press RETURN,
if I now press STOP SAVE, and press SHIFT,
FILE, and let us view trace data,
you will see here the TRC (the trace file) that the unit has stored for the Spectrogram
logging - here stored at 10:20 am on the 23rd of April.
If I scroll down to that and press RECALL, now I have called back onto the screen the
entire Spectrogram trace log that we have just recorded.
Now what is especially good when it comes to analyzing this Spectrogram trace is how
the markers work. I will press MARKER,
and Marker #1 is currently turned on, I will press MARKER #2 and turn that Marker
on, and you will see here we can adjust the frequency.
I will press FREQUENCY and turn the ***. You will see Marker #2 on the lower trace,
but you will also see a white cross on the Spectrogram trace.
Not only can we move that white cross across the trace and look at the amplitude values
for particular frequencies, but you will notice that the M #2 marker also has a display at
the bottom saying M #2 Time. The current trace we are looking at was the
trace stored at 10:17:57 seconds. If I press the TIME button,
we can then wind back in time. In fact here, you can see at this time at
10:17:54 seconds you will see that the intermittent signal occurred at that point in time.
The lower trace, in the turquoise color, is showing the specific trace record from the
Spectrogram. We can see the frequency,
the amplitude, and the time at which that signal occurred.
This is an amazing capability to be able to do this in a handheld spectrum analyzer logging
so much information, without any need for a PC or other storage device.
It is all being done internally within the Agilent HSA handheld spectrum analyzers.
And best of all, if we were using this in a site survey or drive test situation where
we were mobile in a vehicle monitoring for example and recording the signal strength
of various repeater sites, the GPS position information is also stored with each record
in the Spectrogram. Not only can we tell the frequency and the
amplitude of each signal, but also the signal strength at each geographic location as we
drive around. If you would like further information on these
products including; demonstration guides,
operating manuals, or application notes,
please visit: www.agilent.com/find/hsa