High-resolution time axis spectrograms provide new opportunities for clarifying wireless signals
Pfullingen, July 1, 2015 – Narda Safety Test Solutions has expanded the features of its
Interference and Direction Analyzer: Spectrograms
with a time resolution of as fine as 1 μs now allow insights into signal structures that were otherwise only possible
with large scale lab equipment. This means that interference and hidden transmitters with rapidly changing frequencies
can also be analyzed and then localized with subsequent operating steps.
Because the available frequency spectrum is limited, many modern communications methods increasingly make use
of frequency hopping (frequency hopping spread spectrum, FHSS): By changing frequency
continuously, several devices can always find frequencies or channels that are unoccupied. Typical applications
in the ISM frequency band include WLAN and Bluetooth, along with remote control for drones. Some GSM operating modes
also use frequency hopping. Illegal transmitters make use of this method, too, hopping about to make themselves
almost impossible to pinpoint. This type of interference can also occur unintentionally with transmitters operating
legally. For example, if several mobile phone transmitters share the same transmitter location, the rectifying effect
of just a couple of rusty rivets on the mast can generate in-band interference that is very difficult to distinguish
from the wanted signals.
In the IDA 2's new High Resolution Spectrogram
display mode, the type of signal, i.e. its "fingerprint", can be identified. The instrument writes the spectrums
line by line, with levels indicated by different colors. In this way the time and spectral relationships can be
seen immediately. With time resolution as fine as 1 μs, for example, LTE frame structures can be displayed, with
any underlying dissimilar signals being immediately apparent because of their different frequency and time characteristics.
The frequency and time signatures 2/4 allow conclusions about the type of source to be drawn and mutual interference
detected in multi use frequency ranges such as the ISM bands. The Magnitude display mode shows the level characteristic
versus time and is useful for identifying signals using their time structures, for setting triggers, and lastly
for locating their source.
Technical Background
The High Resolution Spectrogram and Magnitude display modes are based on the I/Q Analyzer operating mode. The
IDA 2 operates with "zero span", i.e. it is tuned to a fixed frequency or a particular channel, which it captures
selectively and records the digitized data. A special feature of the instrument is the ability to set channel bandwidths
(CBW) of up to 32 MHz. For the High Resolution Spectrogram, the IDA 2 analyzes the data with a FFT using user definable
parameters that can also be changed subsequently. For example: The FFT produces a usable bandwidth of 22 MHz for
a channel bandwidth (CBW) of 32 MHz. With 256 FFT nodes, the IDA 2 computes a spectrum with a resolution bandwidth
(RBW) of about 240 kHz. If a window overlap of 87.5 % is selected, the spectrums obtained will have a time resolution
of 1 μs. In other words: one million spectrums per second. For this reason, conventional analyzers compress the
data for resolutions finer than about 20 ms. IDA 2 is the first hand held device that retains the uncompressed data
in the background and can display it with its original resolution as a Zoom: Every row of pixels corresponds exactly
to one spectrum. The color corresponds to the particular level. The marker can be used to display each separate
spectrum in the conventional way as level versus frequency.
IDA 2 Basics
The Interference and Direction Analyzer IDA 2 was designed to identify and localize the sources of electromagnetic
signals. Its uses cover the fields of communications and security. For communications, it is important to locate
and eliminate intrinsic or extrinsic interference. For security, the device can be used to trace unknown transmitters
and identify potential dangers. Here, the IDA 2 can automatically determine 3/4 the direction of the transmitter
based on a horizontal scan, and display the bearing angle on a polar diagram. The IDA 2 then automatically computes
the position of the interferer from several bearing results and displays it. This result can be superimposed on
readily available electronic maps or on your own map material, allowing the source to be localized down to street
level with pinpoint accuracy – just like a navigation system.
The basis for finding the position of an interference source is formed by a GPS receiver in the measuring instrument
and the electronic compass in the antenna handle for determining direction, elevation and polarization. Various
antennas optimized for specific frequency ranges are available, which can be fitted to the ergonomically designed
handle in horizontal or vertical alignment. IDA 2 automatically recognizes the antenna being used and applies the
correction data stored in the instrument. An optional antenna adapter allows hassle free use of antennas from other
manufacturers.
The hand held device for on-site use weighs less than three kilos, including the battery. The handle and antenna
together weigh less than one kilo, thanks to the power supply from the basic unit. An internal buffer battery allows
hot swapping of the battery without interrupting operation.
Caption, press image 1 High Resolution Spectrogram of the ISM band at 2.4 GHz. The radiation from a microwave
oven impinges on the signal from a Bluetooth-enabled keyboard.
Caption, press image 2 Scenario: The radiation from a microwave oven impinges on a Bluetooth signal. At the top
is a conventional spectrogram, in center is a High Resolution Spectrogram from IDA 2, at the bottom is a zoom of
the area of interest, i.e. a full resolution display of the data in the device.
About Narda Safety Test Solutions
Narda is a leading supplier of measuring equipment in the RF safety, EMC and RF testing sectors. The RF safety
product spectrum includes wideband and frequency-selective measuring devices, and monitors for wide area coverage
or which can be worn on the body for personal safety. Under the PMM brand, Narda offers instruments for determining
the electromagnetic compatibility (EMC) of devices. The RF testing sector covers analyzers and instruments for measuring
and identifying radio sources. The range of services includes servicing, calibration, and training programs. The
company operates a management system complying with ISO 9001/2008 and ISO/IEC 17025.
Narda has development and production facilities at three locations: Hauppauge, Long Island / USA, Pfullingen
/ Germany and Cisano / Italy and has its own representative in Beijing / China. A worldwide network of representatives
guarantees closeness to customers.
Narda is part of L-3 Communications, New York.
For more information contact
Narda Safety Test Solutions, GmbH
Sandwiesenstr. 7
D-72793 Pfullingen
Tel.: +49 - (0) 7121/97 32
- 0
Fax :+49 - (0) 7121/97 32 - 790
e-mail:
info.narda-de@L-3com
com http://www.narda-sts.com
The Name and Logo are registered trademarks of Narda Safety Test Solutions GmbH and L-3 Communications Holdings,
Inc. – Trade names are the trademarks of their respective owners.
Posted July 7, 2015
