On 07/11/2017 03:56 PM, Cinaed Simson wrote: Opps. > > If I look at the raw data in a frequency sink it's almost a straight > line lying on the frequency axis.
I meant time sink If I look at the raw data in a TIME sink it's almost a straight line lying on the TIME axis. > > I had to adjust the scaling to +-0.05 to see the symbols. Is this to be > expected? > > It seems odd that a device with a maximum power 116 dBm would have such > a weak signal. > > Maybe the antenna was to close? The distance of the receiving antenna > was roughly 0.1 of the carrier wavelength from transmitting antenna. > > Also, the documents indicate the channel width is from 7 kHz to 16 kHz - > the sampling rate of 8 kHz may have been to small. > > But in any case, there's a lot of good information in this thread and > it's going to take me a while to digest all of it. > > Thanks! > > > > On 07/10/2017 05:55 PM, Andy Walls wrote: >> From: HLL >> Date: Mon, 10 Jul 2017 20:44:01 +0300 >>> Hi, >>> Thank you very much!! >>> I Need to thoroughly go over your response and understand it all, but >>> thanks :) >>> >>> I also noticed the 2 different in bit timings, I thought it's >>> something electrically, since I noticed the "long" lows and highs are >>> on some specific timings and the shorts have another timing. >>> >>> Before experimenting with the graph (and the said OOT modules). I'm >>> going over it and trying to understand it, >>> what the rotator does, and what it it's role? >> >> It performs a (cyclic) frequency shift of the signal spectrum. It is >> called a rotator because the DFT of a sampled signal "lives" on the >> unit circle of the z-plane. The rotator block rotates the entire z- >> plane about its origin by a certain number of radians, thus effectively >> shifting the spectrum of the signal. >> >> I use the rotator block to shift the audio frequency bins of +350 Hz >> and +940 Hz down to -295 Hz and +295 Hz respectively. Then I filter >> off what were the negative audio frequency bins, the DC spike from the >> FM CFO, and a lot of the spectrum which is just noise. >> >>> The part with 2 pll carrier tracking is used for locking the carrier >>> of the low and high freq as I understand (I.E. The cheap digital PWM >>> or clock devider) >> >> Yes, but they both track *and* downconvert the tracked tone to DC. >> >> This is a coherent FSK receiver design, which is probably overkill for >> this application, but I used it to handle uncertainty in the actual >> audio tone bins used for the mark and space frequencies. >> >>> what is the role of the complex conjugates (mirror over the real >>> axis?), >> >> The complex conjugate is to handle a quirk of the GNURadio PLL block >> before the subtraction. When the PLL carrier tracking block does it's >> downconversion of the tracked tone to DC, it doesn't have a phase angle >> of 0 degrees (a purely real number), instead it has a phase angle of >> something a bit less than pi/4 radians. >> >> The complex conjugate is so when I do the following subtract, I will >> get constellation points on opposite sides of the circle in the I-Q >> plane. >> >> >>> subtract, >> >> This is standard for a coherent FSK demodulator and for certain non- >> coherent FSK demodulators. Google images should show a number of block >> diagrams doing this. >> >> >>> c-to-f and add part? >> >> Well, after the subtraction you have I-Q plane constellation points of >> about A*exp(j*pi/4) and A*exp(j*5*pi/4), and a fuzzy trajectory line >> going approximately straight between those points. I needed to convert >> those to real values. >> >> I could have taken the complex magnitude and the complex argument and >> somehow tried to assign the proper sign to the complex magnitude, but >> that was work. :) Since the two constellation points and the >> trajectory is restricted to quadrants I and III of the I-Q plane, it >> was easier to just add combine the real and imaginary parts to get a >> real number. >> >> >>> Are you "subtracting" the (locked) `0` square wave from the `1` >>> square wave, why? >> >> No. >> >> Let's pretend GNURadio's quirky almost pi/4 angle output from the >> downconverted tone is actually 0 radians instead of almost pi/4. >> >> When the mark PLL is locked on to the mark tone, it will output a value >> of A. When the space PLL is locked on to a space tone, it will output >> a value of A as well. >> >> To have a mark symbol represented by A and a space symbol represented >> by -A, we have to invert the output value of the space PLL, hence the >> subtraction. >> >> Also note, that one should not receive mark and space tones at the same >> time, so when the mark PLL is outputting A, the space PLL is ideally >> outputting 0, and vice-versa. >> >> >>> I think I understand most of the rest (the `missing block` from their >>> names :) ) >>> >>> Thanks, >>> HLL >>> >>> P.S. FYI, The capture I'v attached contains 4 bursts of 2 devices, 2 >>> from device A and 2 from device B. >> >> Yes, I noticed 4 bursts, two at one energy level and two at another >> energy level. >> >> Regards, >> Andy >> >>> P.S.2 It is probably some cheapo electronic components or re-using >>> the micro that is already there. >> >> _______________________________________________ >> Discuss-gnuradio mailing list >> Discuss-gnuradio@gnu.org >> https://lists.gnu.org/mailman/listinfo/discuss-gnuradio >> > _______________________________________________ Discuss-gnuradio mailing list Discuss-gnuradio@gnu.org https://lists.gnu.org/mailman/listinfo/discuss-gnuradio