The channel scanner option transforms the Agilent HSA into a complete multi-channel
site server and drive-test system that logs receive signal strength, time and date and
GPS position directly into the internal memory or to a USB memory stick. No external PC is
required. The GPS receiver is built in and the external GPS antenna has a magnetic base.
The HSA's battery lasts up to four hours, but with the optional DC adapter cable you
can operate indefinitely from the vehicle's cigarette lighter socket. Here, we are using
list mode to measure an assortment of broadcast, air band, mobile phone and UHF telemetry channels.
We can enter up to 20 frequency channels to be scanned and these can be any combination
of frequencies within the range of your HSA, up to 20 GHz on the N9344C model we are using
here. Best of all, we can set a different channel band with an 'H' frequency. This
is vital for accurate amplitude measurements of spread-spectrum transmissions, plus we
can still select narrow bandwidths for narrowband analog or digital and mobile radio transmissions.
The HSA can be set to sweep as fast as possible, delayed by a user-defined time interval or
we can enter a user-defined distance interval as we are using here.
We have set the distance interval to 250 meters, so whenever the built-in GPS detects that
we've moved more than 250 meters, the HSA will perform a new sweep of all channels and
record the signal strength, time, date and our current position to the USB memory stick.
So first we will press the green "Preset" button to remove any strange settings that
a previous user may have set up within the instrument. And before we do anything else,
I am going to turn on the GPS. So I'll press "Shift," "System," "More GPS"
and the GPS is already on. I can have the GPS info displayed at the top of the screen,
and if you want to see how many GPS satellites the GPS receiver is currently receiving, press
the "GPS info" button and you can see here on the screen. We don't have too many
because the studio has a steel roof.
Next we press the "Meas" button and "Channel scanner." The buttons down the right-hand
side are "Scan start," "Scan mode list." The choices there are either a list mode or
the top-end five or the bottom-end five and we can here recall a previous list of frequencies
that we've been scanning, but in this instance we need to create a new list. So I am going
to press "List edit," "Insert," and the first one we will enter a frequency of
96.1 MHz and a bandwidth of 10 kHz should be wide enough to capture the carrier height.
Now here I am entering a custom frequency, but if the channels that you're scanning
are from a known frequency standard such as WCDMA or GSM then, in fact, the edit method
we can change to standard and recall one of the signal standards, as shown here.
I will go back to custom signals. I am going to put in my own set of frequencies. I'll
insert the next one. We will go for an airband frequency, the local ATIS transmission, 120.9
MHz, and I'll set the bandwidth to 1 kHz. Again, will be wide enough to capture the
carrier of that transmission, and I'll add a few more. Finally, we will add a W- CDMA
mobile phone transmission at 882, and that will have a bandwidth of 4 MHz. We then press
"Apply" and the channel list is in there, ready to scan. A couple more things, though,
regarding the setup. If I press the "Setup" button here, you'll see here we've got
measurement interval on, set to distance. This is how we used it during the drive test.
In fact here, though, we had it set to 250 meters.
What that means is that the analyzer will pause and not make a new measurement until
it has moved a distance of 250 meters from its previous measurement point. The alternative
interval type is by time. The analyzer will hold off making a new measurement for 30 seconds
from the previous measurement. But for the purposes of this demonstration here in the
studio, I am actually going to turn the measurement interval off. Obviously, we are not going
to be moving around with this analyzer here now. Now the only other thing we need to do
before we start logging is to tell the instrument where we want it to save the data: either
into the internal memory or, my preference, to a USB memory stick.
If we press "Shift" and "File" and then we want to set the default directory
to "USB." I'll press "Return" and "Escape." Now I can press "Logging start"
and we have the choice of saving the data either in KML or CSV format. I'll save as
KML for now and I'll give this file a name, if we press "Scan start" the instrument
will start scanning as fast as possible because we have no delay parameters set up. Here on
the channel scanner screen, you can see that the units were measuring on our dBm. The attenuation
is set to zero, which is correct. The preamplifier has already been turned on because that is
a default setting for the channel-scanning mode.
In the left-hand column, we have our 7 channels – our 7 frequencies – that we entered
with their ID number, 1 to 7. There's the frequency in Hz. Here you can see the 96.1
FM broadcast channel, 120.9 MHz AM airband channel, the forward telemetry, narrowband
FM channels and here is the W-CDMA channel. Here is the bandwidth setting that we set
when we created the channel list and here is the channel power. This is not the same
as putting a marker on the top of a carrier. It is actually integrating the power under
the curve, depending on what the bandwidth setting was. So on the W-CDMA mobile phone
transmission, it's integrating over a 4 MHz bandwidth and receiving a channel power
of -56 dBm.
You can see the bars here indicate the signal strength by the length of the bar, but also
color-coding: red being the strongest, blue being the weakest. Every time the screen updates,
the instrument has made another measurement of the received signal strength of each of
the 7 channels. Remember, we could put it up to 20 channels into the channel list. That
information: the received signal strength value, the time and date and the GPS position,
is all being stored directly to a KML file on my USB memory stick that we can double-click
and open in Google Earth.
Another way we can display the data is if I press "Shift display" and now select
the display mode to be time instead of bar. You will see these bars now have got time
on this axis and the color represents the signal strength. So you can see as we are
driving along the transmission may get stronger or weaker and that is represented by a change
in the color on the bars. We can also freeze this display at any time we want and refresh.
The channel scanning and logging was not stopped; all we have done was frozen the display. I
will press "Display mode" back to "Bar."
There are various ways we can sort the channels on the display. For example, I can turn the
threshold on, currently set to -100 dBm, and any signals lower than -100 dBm are now blanked
from the display. They are still being logged, but they have been hidden from view. I will
turn that back off again. Now instead of sorting by ID number, we can sort by power level.
Let's change the sort order to "Down" instead of "Up." So with sort by power
and the sort order set to "Down," the strongest signals are at the top of the screen.
But if, for example, this channel here became stronger as we drove around, the list would
be reordered and this channel here would be put nearer the top of the list. And to stop
the scanning and logging, we simply go back to the channel scanner measurement menu and
we can press "Logging stop" and "Scan stop."
All the measurements we have done so far have had the scan mode set to "List." That
is where we have a list of user-defined channels or frequencies that we are driving around
and measuring the received signal strength of. But there is another scan mode that's
especially suitable for certain applications. If I press "Scan mode" and select "Top
N 5" and "Return," and press the "Range edit" button. Now we can enter our own custom
values of frequency, but what I am going to do here is I want to know what are the 5 strongest
GSM mobile phone channels as we drive around. This is just an example.
So the edit method I've selected, instead of "Custom" I will select "Standard"
and we will select the signal standard of "GSM 900 downlink." And we will recall
that and we will tell the analyzer to being at channel one and end at channel 124. I will
press "Apply" and without knowing any of the channel frequencies for GSM 900, if
I press "Scan start," you can see that the instrument is now scanning all 124 GSM
channels very quickly and displaying the strongest of those in the left-hand column. Channel
83 is the strongest. It tells us the frequency, 951.6 MHz. It's automatically set the correct
bandwidth of 200 kHz and the integrated channel power is -58 dBm. Similarly, for the second,
third, fourth and fifth-strongest signals.
As we drive around, obviously we may get nearer to one base station than another. So the order
in which these occur – in fact, bear in mind we are sweeping 124 channels. Different
channel numbers will become the strongest and therefore appear on this chart as we get
nearer to those base stations. Of course, as with list mode we can still log all this
data to the internal memory or to a USB memory stick and each record will contain the date
and time and the GPS position. So we can open that file in Google Earth or another application.
If you have logged your results directly to a KML file, just double-click the file to
open it in Google Earth. That is the simplest method, but more flexibility is available
if you have logged the data to a CSV file. You can edit the data in a spreadsheet and
export to other mapping applications or use the supplied KML converter software to produce
color-coded maps directly in Google Earth, where the color corresponds to the received
signal strength of the selected channel at each GPS location. And, of course, don't
forget that, regardless of whether we are using the top end scan mode or the channel
list, you can save the entire instrument setup including the list of all your channel frequencies
into the internal memory or the USB memory stick. We just press "Shift," "File,"
press "Save as." We select "Instrument state" and press "Enter."
For further information on the Agilent HSA, please visit the website shown below or contact
your local Agilent representative.
Không có nhận xét nào:
Đăng nhận xét