#demodulation

Network science provides powerful tools for analyzing and optimizing complex systems, including advanced technologies such as robust fiber-optic microphones. In particular, a modified dual-wavelength demodulation algorithm for low-frequency sound detection can greatly benefit from network science principles, enabling precise, high-quality signal capture in challenging environments.

Network Science in Signal Transmission By applying network science concepts, the fiber-optic microphone achieves optimal signal flow and coordination across various nodes in a sensor network. Each microphone operates as an individual node, collecting data and relaying it within a larger network structure, thus enhancing signal reliability and reducing the risk of data loss.

Enhanced Signal Clarity through Dual-Wavelength Demodulation The modified dual-wavelength demodulation algorithm uses two distinct wavelengths to differentiate low-frequency sounds from background noise. This dual-wavelength approach improves clarity, especially critical in low-frequency detection, where interference and signal degradation are common challenges.

High Sensitivity and Noise Reduction By leveraging the network structure, the microphone can dynamically adjust its sensitivity to surrounding acoustic environments. Neighboring nodes share contextual information, allowing the microphone to filter out irrelevant noise and focus on the target low-frequency signals.

Resilience in Challenging Environments The networked system of fiber-optic microphones can adapt to variations in environmental factors, such as temperature and pressure changes, without compromising signal quality. This resilience is made possible by network algorithms that distribute signal load and prevent node failure from impacting overall system performance.

Robust fiber-optic microphone with modified dual-wavelength demodulation algorithm for low-frequency sound detection

International Conference on Network Science and Graph Analytics

Question 3: Why use a germanium diode in a crystal radio set?

Diodes by very function are able to take an AM waveform and recover the audio signal by removing the unwanted half of the AM signal.  It passes one half of the incoming radio signal and blocks the other half.  See this post for more info:

http://tymkrs.tumblr.com/post/4690901056/20-envelope-detector-ham-lesson-o-de-day

The germanium diode is known as a point contact diode (think wire pressing against germanium crystal).  The PN junction in this is very small and this also means that the junction capacitance will be very small.  That means that the point contact diode can operate appropriately at higher frequencies than an ordinary silicon junction diode.

Because the radio AM demodulator must work at high (radio) frequencies, the germanium diode, with its very small junction capacitance is ideal for the purpose.

Another interesting reason for germanium diodes is that they will conduct at a forward voltage of only about 0.15V, but a silicon diode will not start to conduct until a forward voltage (positive on the anode) of 0.6V is reached.  Germanium diodes are therefore useful for radio frequency circuits involving small amplitude signals.  And if you remember, our radio doesn't even have a battery - we rely on tiny amounts of power from the bombardment of the antenna - so it's good that germanium doesn't require as much oomph.

Question 4: Where do you put the germanium diode in a crystal radio set?

Well let's start with the foxhole radio which the crystal set is an evolution of:

http://tymkrs.tumblr.com/post/5578218921/this-is-the-schematic-i-made-for-my-foxhole-radio

It would seem that the detector portion of the schematic would be where we'd put the germanium diode.  Below is someone who used the germanium diode and made both a schematic and the real-world implementation:

Interestingly - another schematic that I found has the diode pointing the other direction:

Seems like the diode has been flipped.  But this'll be easy enough for me to flip and see which works the best!  Some sites I've read say a LED can be used too, so I might see what happens when I substitute the germanium diode with a LED :).

And according to @brainwagon, the direction of the diode doesn't matter.  But that it's a puzzle :)  So I shall have to check this out as well!

@atdiy/@tymkrs

So I touched mostly on different types of modulators and the circuits that could be part of the actual modulation.  I've decided I'd be cheating myself if I didn't at least attempt to cover demodulators.  As briefly, briefly, mentioned before, demodulators separate out the data/voice signal from the carrier signal.

AM Demodulation/Detection

For AM signals, the simplest kind is an envelope detector that produces an output voltage that reproduces the modulated signal’s envelope.

So if we think back to AM modulation, the modulating signal (data or voice) is like a sandwich smusher that changes the amplitude of the carrier wave.  That sandwich smusher is known as the signal's "envelope" (Red line below).

An envelope detector detects the envelope of the incoming signal by using a rectifier and capacitors.  (I know, I used the name in its own definition - bad form!)

Background reminder: Rectifiers are diodes capable of handling large currents.  Diodes in turn only allow current in one direction.  Because of this, an AC signal that comes through will show up as a DC signal made up of pulses.The simplest way to demodulate AM is a diode detector. 

AM waves are the same above and below the y axis, so with a detector, it doesn't matter whether you use the positive side of the envelope or the negative side. 

So in come AM radio frequencies, into this circuit where it encounters a rectifying diode which is placed in parallel with a capacitor and resistor. 

While the amplitude of the the input signal is positive, the diode is forward-biased meaning that charge is flowing in the proper direction.  The capacitor (C1) charges up to the max value of the input signal. 

Then when the amplitude of the input signal is negative, the diode becomes reversed biased meaning that due to the properties of the diode, no current is able to run through.  The capacitor then starts discharging through the resistor (R1) it's coupled with.

If I'm not mistaken, that smooths out the voltage, because before the capacitor's able to completely drain, the input signal's amplitude is positive again.  This leaves you with a relatively smooth data signal!

The main limitation with envelope detectors is that it can only be effectively used with DSB (no distortion) and VSB (very low distortion) signals.  For a more indepth look at the reasons:

http://www.radio-electronics.com/info/receivers/am_demod/diode_am_demod.php

http://sound.westhost.com/articles/am-radio.htm

Next - SSB/CW demodulation via product detectors which I will cover in my next post! 

A foreword

In the Off-The-Shelf industrial monitor system, commonly used information transmission mode is as follows, digital microwave, digital transmission radio station, wired optic fibre, have wire cables etc., digital microwave and digital transmission radio station will be the transmission distance and restriction that the frequency will be permitted, and wired optic fibre and the intersection of network and the intersection of cost and great to have wire cable, fit for controll point, disperse and transmit under the far situation using very much.

To control target disperse and every control among the node lacking organic connectioning, controlling information volume to be relatively less, the real-time nature requires that relatively low grade characteristic, CDMA 1X has offered a very good information transmission mode. CDMA 1X like to refer to the first stage (speed is higher than IS-95, lower than 2MB/s) of CDMA 2000 ,Can support the data transmission of 308kb/s, the part of the network introduces packet switch, can support to move IP business, it is a kind of new bearer service coming out in development in existing CDMA IS-95 system, the purpose is the formal data traffic of offering to CDMA user dividing into groups. Because CDMA 1X has adopted reverse coherent demodulation, new technologies such as power-controlling of fast forward direction, transmission diversity, Turbo code,etc., its capacity ratio IS-95 is greatly improved, according to analysis result of the theory, are used for conveying the speech business, the total capacity of CDMA 1X system is 2 times that of IS-95 system, used for conveying the data traffic, the total capacity of CDMA 1X system is 3.2 times that of IS-95 system, the bandwidth reachable 300kb/s of CDMA 1X theory, take spaciously to make an appointment about 100kb/s (transmit two-wayly and symmetrically) in present real application ,Offer TCP/IP to connect on this signal channel, can be used in application such as Internet connecting, data transmission. 2 wireless Communication based on CDMA 1X

2.1 Scheme of network connection

The wireless data transmission system is generally made up of data traffic centre, Communication network and data terminal, consider factors such as the data bulk of the business, safety, reliability, network state and cost,etc. synthetically, adopt the following network connection ways: The Communication server fixes IP or stationary domain name and inserts Internet, CDMA data terminal unit (DTU) with the public network Behind the power up, set up connection with Communication server voluntarily, if Communication server there is no fixed IP, can get the stationary domain name, it is stable that this scheme has low cost, Communication quality, the safety is moderate, characteristic of running reliably etc. through installing the shell software of peanut. 2.2 Wireless data transmission principle

According to the above-mentioned network connection scheme, the machine format up run transmits the principle as follows:

( 1) The lower-position unit passes the data to DTU through RS232 serial port;

( 2) DTU types the data into TCP/IP to wrap up, sends to The wireless network;

( 3) TCP/IP data packet passes the systematic packet data service node, transmit at Internet and go a designated data service centre that look for at Internet ' Communication server) ;

( 4) The Communication server passes the data to the upper computer and stores to the historical database.

Machine format to fall and transmit it contrary to above-mentioned course, no longer go into details, the structure chart of system Communication is shown as in Fig. 1.

3 system design

3.1 The upper computer designs

The upper computer includes two parts of real-time monitor system and historical database. The real-time monitor system chooses InTouch systems of Wonderware Company, mainly realize the following functions: Systems management function; Data processing function: Including reporting the function regularly in data inquiry function, storage function of the data, data; Alarm function: Set feature service including handling the function, reporting an emergency and asking for help or increased vigilance in real time response function, linkage of reporting an emergency and asking for help or increased vigilance, reports an emergency and asks for help or increased vigilance and confirms the function, storage function of reporting an emergency and asking for help or increased vigilancing, operate control function, the historical database chooses Industrial SQL Server of Wonderware Company, mainly realize the following functions: Data statistics, report form function, historical data inquiry function, historical data curve chart, printing the function. 3.2 The lower-position unit designs

The lower-position unit chooses ABB AC31 series PLC, including CPU module and I/O module, CPU receives one or more appointed operation control commands of the Apparatus of control center, carry out corresponding operation control actions through the relevant apparatuses of I/O pair of module, and return and operate the result to the control center, the lower-position unit mainly realizes the following functions:

Data acquisition function, data inquiry function, report the function regularly, operate control function. 3.3 CDMA data transmission break

CDMA the intersection of data and transmission break choose the intersection of Shenzhen and great the intersection of electricity and technological the intersection of CDMA H7710 DTU and terminal to have the following characteristic this of Development Co., Ltd.:

( 1) H7710 DTU offers RS232/422/485 interface directly, offers transparent, full duplex, even data transmission channel for users' der Datenaufbereiter. ( 2) Ordinary GPRS/CDMA Modem usually needs affixing to PC and dialing up on the telephone fictitiously, carries on data receiving and dispatching and protocol conversion with the resources of the PC, H7710 DTU built-in automatic network connected sum agreement puocessing module, do not need backstage supporter's computer to support. ( 3) H7710 DTU can realize some - one, some - multi-point, the centre - data transmission of multi-point peer, transmission delay is generally smaller than 1s. ( 4) H7710 DTU can be affixed to GPRS or CDMA network automatically when beginning, and the data centre with you sets up the Communication link, receive and dispatch the data of user's der Datenaufbereiter at any time. ( 5) H7000 mobile data Communication needn't depend on the data interface unit of the operator switching center, cover the fictitious mobile data Communication private network of the whole of China through the construction whenever and wherever possible of Internet network. CDMA H7710 DTU must presume the parameter of meeting accident before inuse: CDMA 1X network lands user name and password, fixed IP address and domain name of the port or Communication server, online working way of DTU of Communication interface parameter, Communication server,etc.. 3.4 Design and realizing of the Communication server

The Communication server is a pivot of the overall system, mainly realize the data transmission between different agreements, the design of the Communication server is because of OPC standard, OPC can be interpreted as the connected sum embedding of the target of proceeding control (OLC for Process Control is a kind of technology used for application program interface that is developed under Microsoft's operating system, because of Client/Server mode, in order to realize the Communication of the overall system, needs to hold 3 pieces of software on the Communication server; OPClink of Wonderware Company, IOServer of IOServer Company, CDMA Server. The management between working phase and every software of the Communication server is shown as in Fig. 2.

Tell the functions and application of 3 pieces of Communication software on the Communication server separately as follows.

3.4.1 OPClink

OPClink application software of work under the intersection of Windows and platform, main function to come, realize the intersection of OPC and server and the intersection of InTouch and the intersection of will and data transmission of sword Wu through protocol conversion. OPCLink all rightly and now or long run OPC server end software (IOServer, RSLinx) Connect, he converts the order of InTouch to OPC agreement then sends to OPC server end software, and read data fetch from OPC server end software, return to InTouch. Likewise, OPCLink can be connected to long run InTouch now too.

3.4.2 IOServer

The function of IOServer is the data transmission that is realized among different agreements, IOServer supports the following 14 agreements: Modbus agreement, AB agreement, ASCII agreement, Courier agreement, DNP agreement, GE agreement, HR6000 agreement, IEC103 agreement, KingFisher agreement, LoopBack agreement, Melsec agreement, Omron agreement, TI505 agreement, UCA2 agreement. In this system, what ABB PLC adopted is Modbus agreement, IOServer reads the data of ABB PLC from CDMA Server, and convert to TCP/IP agreement, convey to OPCLink.

The disposition of IOServer mainly includes 3 following parts:

( 1) Board (interface is disposed) : IOServer supports many kinds of interface, among them the most frequently used one is TCP/IP and serial port, while disposing the interface, need to define the agreement of the interface unit;

( 2) OPC Explorer: Offer the platform of built-in testing, can also observe and monitor the data.

( 3) OPC Gateway: Allow the data transmission between every OPC server based on different agreements, and the data transmission between IOServer and a certain control unit. 3.4.3 CDMA Server

In this system, uses VisualC ++6.0 to write CDMA Server software, CDMA Server is regarded as the Communication pivot of the overall system, include two parts of functions: Carry on the Communication with IOServer, carry on the Communication with DTU.

The Communication of CDMA Server and IOServer is based on SOCKET programming, adopts TCP/IP agreement to transmit, needs to set up port and IP address, IOServer sets up Communication through this port and IP address and CDMA Server.

The Communication between CDMA Server and DTU uses and develops the dynamic storehouse wcomm_dll.dll in the bag, this file includes and all required API functions of DTU communication, start, data transmission, die Datenannahme including being served, closing to serve etc..

It is user's routine interfaces based on development tool kit that the Communication of OPC Server and DTU is designed, namely the dynamic linking storehouse cdmagprs.dll, this storehouse includes all required API functions of communicating with DTU, for example:

start_gprs_server: This function is used for starting the bottom layer to serve, after serve and start and DTU communication, after starting this service, there should be a function of the response message at the main window, so that and the bottom layer serves the communication.

stop_gprs_server: Stop serving;

do_read_proc: Read the data. Bottom layer serve, receive behind the data that DTU send, will to start, serve window file of DSC that appoint in the function, the intersection of news and response function in the window this should call read the intersection of data and function send DBU data read-out that come over immediately;

do_send_user_data: To DTU transmission data;

da_close_one_user: Close a DTU terminal station, make it roll off the production line;

do_close_all_user: Close all online DTU terminal stations, carry out this API before the general stop service.

Because Windows drives on the basis of news, after the bottom layer serves the data which receives distal DTU, will send one news to window to start function, so we can define one the intersection of news and response function come processing center and data transmission of DTU in procedure, in the response function of news, transmit data come through transferring die Datenannahme function and data transmission function in the dynamic linking storehouse, after data transmission finishes, the call closes and serves the function to finish the communication.

4 experiments and result analysis

The experimental procedure is as follows:

( 1) Set up DTU specification:

DTU identity heading code: 139 ********

Online report interval: 40s

Local Communication port: 5001

Maximum transmits Bao Chang: 1000B

Main DSC IP address: 219.229.3.24

( 2) Add users on CDMA Server, as shown in Fig. 3, among them set up unanimity on the terminal mouth and DTU, it is 5001. The gateway exports ports, namely CDMA Server and IOServer connecting port is set up as 5002.

( 3) Add port and Apparatus on IOServer, as shown in Fig. 4, in this system, because IOServer and CDMA Server are mounted on the same machine, so the IP address is set as 127.0.0.1, the port number corresponds to port that CDMA Server offers, namely 5002.

Through the above-mentioned step, have already set up Communication between IOServer and DTU, has continued only needing to dispose concrete Group and Item on IOServer and OPCLink, no longer go into details here.

This system has already been applied to the actual project, compared with wired data collecting system, this system has the following advantages:

( 1) Have reduced construction cost and maintenance cost of the Communication line;

( 2) Having improved the systematic flexibility, controling range is not limited by the region, the nodal control goal can be expanded arbitrarily.

( 3) The Communication line is more steady, not incident Communication trouble, even if go wrong, also can find and get rid of rapidly.

5 conclusions

Core scientific and technological Co., Ltd. (NationalChip) of Hangzhou country Introduce its high-performance national standard ground demodulation chip GX1501 of bimodulus. GX1501 to support the intersection of digital television and the intersection of broadcast transmission and standard channel demodulation of GB20600-2006, ground of China, decode the chip totally. Support the single carrier to involve all 330 kinds of modes of the multi-carrier. Adopt multiple innovative technology, optimization technique, parameter adaptive techniques, make it have unparalleled fixing to receive and move receptivity.

GX1501 still supports DVB-C (ITU-T J.83 A/C) at the same time 16, 32, 64, 128, 256 QAM all modes that transmission standard can be that the acceptance criteria stipulates. Integrate pairs of 10bit high-accuracy ADC inside the GX1501, support direct intermediate frequency to sample or the base band is sampled, support all Can Tuner of the market mainstream at present, the compatible Silicon Tuner development trend in the future too, bring the right to choose of the maximum scheme to customer. Meanwhile, the chip adopted the treatment technology of Full Digitalization, reduced the quantity that China and foreign countries of complete machine solution enclose the device to the maximum extent, having reduced system cost and scheme complexity, thus reduce BOM cost effectively.

GX1501 has remarkable digital signals that obtains ability. In case of unknown modulation mode, automatic detection can be and which run all DTMB modes, also have very strong inverted identification ability of automatic frequency spectrum. Inside adopts the unique synchronization mechanism, and it is blind to make it have outstanding high speed and sweep the characteristic. Its frequency swing of carrier resumes the range and is greater than & plusmn; 500kHz, even can reach & plusmn; 1MHz. As timing deflection of sampling over situation of 200 ppm, still but hold-in.

In order to cooperate with the conceptual design of the complete machine, GX1501 has offered the flexible humanized peripheral interface. AGC interface substantially as offering the two-way PWM wave to export, RF_AGC and IF_AGC; Includes Line two I2C's transponder, has reduced the interference on tuner of the digital signal to the greatest extent; TS data flow can carry on bunch / run side by side two kinds of format conversion, and output the base pin order and can be disposed arbitrarily, have helped the routing of the complete machine hardware scheme designed greatly; Signal quality is real-time monitored, the instant reflects the real signal state.

GX1501 has used multiple innovative technology, optimization technique and parameter adaptive techniques, make it have outstanding co-frequency to imitate television interference and interference rejection capoability of the monofrequency. Especially have very strong inhibitory potencies on impulse rate, are especially suitable for the severe movement of impulse rate and receive the environment, can expand coverage received effectively.