Deepace KC908 Manual de usuario
1. Introduction
KC908 is a wide-band sweep receiver, it is capable of measuring radio
frequency spectrum and field strength as well as demodulating and
monitoring common signals. As for uncommon signals, KC908 can record the
raw IQ signal and save for later analysis.
KC908 is based on SDR theory. Different from other SDR receivers, KC908
integrates complete digital signal processing unit and user interface, so there
is no need to depend on a computer. KC908 supports SDR software like
HDSDR and is able to connect with GNURadio.
As a reconnaissance equipment, KC908 is capable of sweeping swiftly and
discovering signals. Being different from traditional sweeping spectrum
analyzer, KC908 obtains spectrums of certian width using FFT and then splice
them together to acquire a panorama. In this manner, KC908 reaches a speed
of 3GHz bandwidth per-second with a 10kHz precision, which is equivalent to
120,000 25kHz channels. As for specific radio stations within 300-500MHz, it
takes less than 0.1 second to finish. We're proud of such a decent
performance on a micro-size hand-held equipment.
KC908(10.8/18.6GHz model) comes with 2 receiving channels. It can
measure the amplitude difference and phase difference between two channels.
Also, it it equipped with signal generating function to output the CW and
simple modulated signals. With GNURadio connected, KC908 is even capable
of outputing relatively complicated digital modulating signals.
1.1 Theory
KC908 contains a zero IF receiver, covering a range of 0.75-6ghz.(The left
port's range is 0.5-6Ghz). By mixing, the frequency outside this mentioned
range is moved to the range of 0.75-6ghz. The zero IF receiver samples the
baseband directly to get the digital IQ signal. The bandwidth of digital IQ
signal is 40MHz, spectrum result can be obtained by FFT. Because baseband is
generated by analog mixer, local oscillation leakage can not meet the high
requirement of spectrum analysis. In order to solve this problem, the
instrument discards a sideband and poor performance part of the FFT result
and only takes 15MHz width to display, which is the origin of effective real-
time bandwidth (15MHz). If the sweep span is wider than the effective real-
time bandwidth, the LO scans the whole sweep width with 15MHz intervals
and splices the results.
Since the spectrum is generated by splicing FFT results, the display effect,
as well as certain concepts, would definitely differ greatly from conventional
sweeping spectrometers. RBW, resolution bandwidth, for example, no longer
means the bandwidth of resolution filter. Instead, it means the equivalent
resolution bandwidth of the windowed FFT result. Limited by the computing
power, RBW can only be set within a certain range under a certain sweeping
bandwidth. As for time-varying signals that are larger than the real-time
bandwidth, the amplitude on the splicing point could possibly leap due to the
fact that those two sides of the splicing point are sampled at different
moments. What's more, the shape of the signals could be quite different from
those in the conventional sweeping spectrometer. Take the spectrums of
modulated signals as an instance, what KC908 displays is the peak value (or
average value, according to the setting), without the "illusion", which is caused
by the concept of sweeping from left to right, that at any moment only one
frequency can be swept. For this reason, the experience of analysing signals
on a traditional spectrometer, which is mostly abstracted from those
"illusions", may not work anymore.
From another persepective, real-time spectrometer does not necessarily
represent the "truth". The fact is there is a limit for the time resolution. In
other words, even there is some sort of machine that are capable of achieving
10k FFT/s, no monitor can match this speed, let alone human eyes to catch up
with that monitor. It's believed that no matter what amount of data is to be
dealt with, there will always be some kind of method to abstract the essence in
it and present those essence within a budget of several dozens of data frames.
This process is known as "detection". The detection mode setting is to set the
rule to which the abstracting process is made according. Options are like
extracting the peak value of each frequency point frame by frame, or
averaging the results of all the frames. In this manner, the result shown on the
display no longer represents the instantaneous situation of the signal, thus it's
no longer the "truth". As a matter of fact, the "truth" of a varying signal can
only be described with a time domain waveform or a mathematical formula.
Why? Because a decent frequency resolution requires a large amount of FFT
sampling points (like, 2048) to achieve, and during the sampling and
processing time, the original signal has probably changed. Yet, compared to
the sweeping spectrometer, normally the real-time spectrometer is much
closer to the "truth".
What's more, there is a limit for frequency resolution of displaying, as well.
Each frame of FFT produces more than a thousand data points, and with
splicing, these data points can even reach a magnitude of hundreds of
thousands. Due to the fact that the maximum displaying capability of KC908's
horizontal axis is 800 pixels, each pixel has to represent multiple frequencies.
How to define "represent" is another major concern of detection. In KC908,
the solution is displaying the peak value of all those frequencies a single pixel
represents, to ensure no signal is missed, which is the basic principle a
reconnaissance equipment should live up to. However, this method of
presentation may make certain frequency/phase modulated signals look like
stable signals. Thus, while analysing a single signal, it's advised to reduce
frequency span and change the dectection method to "Sample" to mitigate
this confusion.
Due to the wide frequency coverage, in order to avoid the receiver's
overload caused by the total energy of external signals and improve the anti-
interference performance, there are several pre-selectors in the front end of
KC908. The pre-selector segmentation methods of the two ports are different,
and the anti-interference performance of the two ports in different frequency
bands will vary. The specific technique will be described later. Although a large
part of RF circuits' proportion are preselectors, they can only perform rather
preliminary filtering due to the size of the instrument. Therefore, if it is used in
complex interference environment, some external filters should be used.
Digital signal processing is implemented by FPGA and MCU. While
demodulating the signal, FPGA converts the digital IQ signal again for strict
filtering. The demodulation bandwidth of KC908 is from 150Hz to 300kHz,
which is suitable for most private network signal analysis. If wider
demodulation bandwidth is needed, USB3.0 can be used to transmit the
original digital IQ signal to the computer, and the third-party software (such
as GNUradio) can be used for processing. The bandwidth of IQ signal can up
to 40MHz.
1.2 Basic Function
1. Spectrum analysis
2. Field strength measurement
3. Simple signal generator (10.8/18.6GHz model only)
1.3 Useful Functions
1.Better than 15KHz frequency measurement accuracy with any sweep span, a
single measurement can get the accurate frequency.
2.Comfortable monitoring with multiple squelch mode
3.Automatically log strong signals for reconnaissance
4.Storing up to 999 channels
5.Waterfall figure display
6.Record IQ and audio to TF card
7.Level tone function for tracing on foot
8.Analogical demodulation with high volume audio for noisy environment
1.4 Application
KC908 can be used as a traditional spectrum analyzer. It's also the ideal
choice for digital, pulse or unstable signals(like magnetron output) .
1.Professional communication engineering
2.IoT project
3.Interference searching
4.Concealed signal source searching
5.Electromagnetic radiation measurement
6.Radar and satellite station
7.Radio reconnaissance and monitoring
8.Spectrum resource occupancy analysis
9.Industrial microwave engineering
10.Electromagnetic environment evaluation
1.5 Main Parameters (note 1,2)
The main design goal of KC908 is not absolute high performace, but
sufficient performance with convenience, affordability and mobility at the
sweet spot.
Item
Min value
Typical
value
Max value
Note
Frequency range
9kHz
10.8/18.6
GHz
Real time bandwidth
1kHz
15MHz
Analysis bandwidth
1Hz
2MHz
can be set to
8MHz
Demodulation
bandwidth
150Hz
300KHz
100% POI(note 3)
210us
Where
SPAN=15MHz
Level measurement
range
+20dBm
Level measurement
uncertainty
1.5dB
Receiver only
Noise floor
-120dBm
@12kHz BW, avg
Instrument noise
coefficient
13dB
With max gain
Third input Intercept
Point
-42dBm
46dBm
REF=-70dBm
REF= 20dBm
First image
suppression
50dB
60dB
IQ image suppression
50dB
Residual
response(note 4)
-110dBm
-90dBm
Port N.C
With whip
antenna
Spurious response
-50dBc
Battery life
4h
Weight
900g
Note:1. This table just shows the parameters that user are concerned about,
for detail please see the technical parameter table in the user manual.
2. Performance is measured with the right port. The receiving performace
on the left port maybe inferior to the right port.
3. We define the intercept in POI as accurate measurement.
4. KC908 will transmit EMI during the measurement. If the antenna is
close to KC908 it will receive the EMI. This parameter is measured by a 0.2m
whip antenna, 1m from the KC908 in the microwave anechoic chamber.
2.Description of instrument
This picture shows each part of KC908. The RF port is at the top of KC908.
On the left part is mainly the data port and the knob. Speaker and microphone
are at the bottom of front panel. There is no other functional port on other
sides of the equipment.
2.1 Top panel
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