My favorite one-pass laser is the nitrogen-gas laser described as a home project in Scientific American's "The Amateur Scientist" monthly column....

My favorite one-pass laser is the nitrogen-gas laser described as a home project in Scientific American's "The Amateur Scientist" monthly column. The version described produced "a piece of light the size and shape of a broomstick." Actually, two pieces, one out of each end. My modified design reduced the back radiation to insignificance. Jerry

Here's a basic question that I'm looking for a clear answer to (I think I know what it is). Let's say I have a one Watt BPSK transmitter and the...

Here's a basic question that I'm looking for a clear answer to (I think I know what it is). Let's say I have a one Watt BPSK transmitter and the received bit error rate is 0.1% (no FEC). Now let's say I change the modulation to QPSK but leave the power alone. Will the received bit error rate still be 0.1% ? Why? Thanks, John

OK, sorry about the lack on information. What i'm trying to do is get access to the data being sent from a transmission from a 868...

OK, sorry about the lack on information. What i'm trying to do is get access to the data being sent from a transmission from a 868 burglar alarm for some testing on the security of the system wrt jamming, interference etc. Obviously the first step is to gain access to the actual data. The transmissions are short pulses, persumably containing a short data sequence, maybe a few bytes. M...

Hi, I am implementing a RF modulator for video signals. I am caught in dilemma of choosing between two different implementations...

Hi, I am implementing a RF modulator for video signals. I am caught in dilemma of choosing between two different implementations strategies, One that involves taking hilbert transform of the video and then modulating it while the other modulates video to IF and then bandpass it to get the VSB using an appropriate BPfilter. For last few days, I have been trying to collect information reg...

Hi all, I have to demodulate an O-QPSK signal. As usual in this kind of modulation, symbols (chips) have an half-sine shape, and the Q...

Hi all, I have to demodulate an O-QPSK signal. As usual in this kind of modulation, symbols (chips) have an half-sine shape, and the Q channel has a 90 degree (half simbol) offset with respect to the I channel. The first thing I have to do (and perhaps the most difficult) is removing the frequency offset from the received I and Q signals. I cannot use a simple Costas loop since it doesn't wo...

Hi, I have a simple matlab question: I have a baseband signal with a 2MHz bandwidth (wideband), sampled at 100MHz. I would like to use this...

Hi, I have a simple matlab question: I have a baseband signal with a 2MHz bandwidth (wideband), sampled at 100MHz. I would like to use this signal to modulate a 5Ghz carrier. What is the simplest way to proceed? I was thinking using the ammod function, but in that case I would need to resample my signal to a higher sampling rate (which may add some distortion). Is there a more elegant way to g...

Hi Folks, I have a telecom application coming up and would appreciate advice on the best choice of DSP for the job. The DSP would be...

Hi Folks, I have a telecom application coming up and would appreciate advice on the best choice of DSP for the job. The DSP would be required to perform bandpass filtering and demodulation of an FM carrier containing voice modulation. The BPF must have good adjacent channel rejection at +/- 20 kHz from wanted channel center frequency, and good in-band group delay. It also must detect...

Hi! Using Matlab, I need to send a message through a simulated AWGN channel. I have defined the signal pulse to be a square pulse with...

Hi! Using Matlab, I need to send a message through a simulated AWGN channel. I have defined the signal pulse to be a square pulse with different amplitudes depending on the bit, a0 for a 0 and a1 for a 1. I modulate the signal by tx = tx .* cos(2*pi*fmod) where tx is kron(bits,signalpulse). If I do not add any noise, I am able to retreive the message using first a filter to remove the mo...

Hi all, I would like to know how I could model the effect of beamforming in a monte carlo simulation (running Matlab). A simple simulator...

Hi all, I would like to know how I could model the effect of beamforming in a monte carlo simulation (running Matlab). A simple simulator structure for the beginning could be something like: 1.random bit input 2.modulation (M-PSK or M-QAM) 3.beamformer 4.channel 5.demodulation 6.error counter, calculate BER as a function of SNR So, how to implement the beamforming part? Can I do the si...

There is a communication link using simple PSK or FSK in a channel and receiving that by a microcontroller with analog comparator. Changing a...

There is a communication link using simple PSK or FSK in a channel and receiving that by a microcontroller with analog comparator. Changing a protocol or a hardware is not an option. Now I am trying to make this system work through the bandlimited and phase distorted channel. The problem is the receiver input is behind the comparator. The signal gets heavily damaged due to the linear ...

I am looking for an example of using a software pll for demod of FM. I tried the other fm demod routines (arctan, differentiator) and...

I am looking for an example of using a software pll for demod of FM. I tried the other fm demod routines (arctan, differentiator) and think there could be an improvement using a software pll. I found some matlab code posted by Tom ? that works on his data (generated by matlab) but fails on mine. I think it has something to do with the hz/volt or modulation index. I am also not exactly su...

Hi All, I new to DSP and and trying to get all my fundamentals correct. I am currently studying Differential Quadrature Phase shift keying. I...

Hi All, I new to DSP and and trying to get all my fundamentals correct. I am currently studying Differential Quadrature Phase shift keying. I have gone through theory of the modulation techniques (XIONG) and quadrature processing (lyons). But the theory doesnt sink in for me unitil i see a practical example. Are there any online project on FPGA or DSP that I can use to understand the co...

I am trying to caracterize a system consisting of a 1) pseudo random generator (binary pulses, "on-off modulation") --> 2)laser diode --> ...

I am trying to caracterize a system consisting of a 1) pseudo random generator (binary pulses, "on-off modulation") --> 2)laser diode --> light beam --> reflection from surface --> 3)photodiode detector --> 4)amplifier I would like to formulate at a model from measurements that mathematically describe how the binary pulses are "shaped" thru the chain 2) to 4). I need to do this because I w

I have implemented a Viterbi soft decision (1/2 k=7) for a BFSK modulation. I need to know the minimum level deeper into the trellis to get...

I have implemented a Viterbi soft decision (1/2 k=7) for a BFSK modulation. I need to know the minimum level deeper into the trellis to get symbol. In a book, i read something about a good value is 4 or 5 times the constraint lenght. Now, for example, after 32 levels (or states) i get the first symbol, but then o have a delay of 32 bits. Can i get a good measure of metric after 8 o...

Hi, I understand that simplified equalization is one of the good reasons for going with OFDM. But, how do they manage it ? That is, The OFDM...

Hi, I understand that simplified equalization is one of the good reasons for going with OFDM. But, how do they manage it ? That is, The OFDM may be viewed as using many slowly-modulated narrowband signals rather than one rapidly-modulated wideband signal. So, The Differential modulation such as DPSK / DQPSK if applied to each sub-carrier, equalization can be completely omitted. ( Reason - ...

Hello, I'm playing around with single side-banding using amplitude modulation for thge phase shift and a filter using the Hartley...

Hello, I'm playing around with single side-banding using amplitude modulation for thge phase shift and a filter using the Hartley Transform. I've read on the web a brief text saying I could easily use the FHT to also do the Hilbert Transform - basically I need the spectrum to reflect about the SRate./4 point. Can anybody point me in the right direction please? Thanks, Dave ...

Hello, I've been trying to apply a hilbert transform from DC to around 10kHz @ a 57600Hz sample rate however the 90 degree phase shift doesn't...

Hello, I've been trying to apply a hilbert transform from DC to around 10kHz @ a 57600Hz sample rate however the 90 degree phase shift doesn't work well close to DC (which is expected). Btw, this is for an implementation of the phasing method for SSB-SC modulation. Is there some way to get around this problem? or a better way to perform the phase shift? I've been experimenting with up...

Hi all, I would like to know how to regenerate the clock bit from the symbol clock for multiple level PSK modulations ? For QPSK modulation...

Hi all, I would like to know how to regenerate the clock bit from the symbol clock for multiple level PSK modulations ? For QPSK modulation we need to recover a clock bit twice the symbol clock. I don't found any help on google... Thanks. Best regards.

Hi dsp/wireless gurus, please answer my previous questions, i am really stuck at those points..will be thankfull to you dsp gurus for...

Hi dsp/wireless gurus, please answer my previous questions, i am really stuck at those points..will be thankfull to you dsp gurus for doing helping me out. meanwhile i got one more fresh doubt after reading pasupathy paper of [ MINIMUM SHIFT KEYING:A SPECTRALL\r EFFICIENT MODULATION ] by subbarayan pasupathy 1979. in that paper he explains about few diagrams and it means the follow...

I would like to design filter which has frequency frmo 0 hz to 1mHz with passband equal to all filters. I have dsp which is top notch and will...

I would like to design filter which has frequency frmo 0 hz to 1mHz with passband equal to all filters. I have dsp which is top notch and will do out of band processing. I would like to make sure all pass band is free from phase modulation so that no problems acure with my delicate process. Can some one help me with this problems. I hope every who contributes to this group has a great hol...