# Tag Info

6

This is how the mathematics of complex signals work. The proof begins with Euler's formula: $$e^{i\varphi} = \cos \varphi + i \sin \varphi \tag 1$$ For signal processing, instead of $\varphi$, we are usually thinking about some sinusoidal oscillation at angular frequency $\omega$ that varies with time $t$, which we can write as: $$e^{i\omega t} \tag 2$$ ...

5

The sawbird H+ looks like a nice LNA, do you have the H+ H1 version? The plan version seems to be for 1542 MHz, "center frequency of the module is 1.542GHz with approximately 80MHz of bandwidth (-6dB rolloff). As such, it should be used for reception of frequencies between 1.50GHz-1.58GHz" but the H+ H1 has "65MHz bandpass region, centered ...

4

This isn’t a solution to your problem, but I had similar challenges with UHF RFID at 865 MHz. In UHF RFID the tags are electrically short dipoles modulated by the chip impedance. I thought it would be impossible to measure the two way traffic due to the huge difference in the TX and RX signal amplitudes. I solved this by making a tiny hole through the tag ...

4

The RTL-SDR interfaces to your computer via USB. The USB interface and driver will buffer the data and send it to your software at the requested sample rate on average (baring underflow due to software glitches), but with varying timing due to interface jitter. The RTL2832U USB is likely sending larger chunks of data over USB in blocks of far more than 512 ...

4

512 samples should take 256 microseconds, so your times look about right. The exact time it takes to execute those lines of code will depend on the rest of what your computer is busy with. And it's unlikely that the elapsed time counter will be accurate to better than 10 us anyway (but I may be wrong, try it yourself by timing a delay loop). Whats slightly ...

4

If you use SDRSharp with an Airspy Mini, instead of an RTL-SDR, the supported sample rates allow up to 6 MHz bandwidth, due to the use of an ADC with a higher sample rate than the RTL2832 is capable of. For a wider bandwidth display than 6 MHz, you either need to use different software that can scan or stitch across a frequency range, instead of directly ...

3

Unfortunately you cannot increase the bandwidth much: the sampling rate in RTL2832U is at maximum 3.2 megasamples / second. In theory (Nyquist theorem) you could get ±1.6 MHz banwidth, but that is already pushing the limits of your hardware. The ± in the bandwidth comes from the fact that you are sampling the I and Q, or signals with a 90° phase shift ...

3

A lot of the RTL-SDR code is open source on GitHub. This code runs just fine on a Raspberry Pi 3B or 4. The C code inside rtl_tcp to set the frequency is only a few lines long. From a remote system, after starting the TCP connection, send 5 bytes, 1st command byte 0x01, then 4 bytes containing the desired frequency in little-endian 32-bit integer format. ...

3

Probably not. Looking at the chips: NXP TDA18271HDC2 is the RF frontend / "tuner" chip. Afatech AF9033B is the DVB-T demodulator. Conexant CX23102 is the analog TV demodulator. NEC (now Renesas) uPD720114 is a USB hub, which shares the USB port between the AF9033B and the CX23102. Neither the AF9033B nor the CX23102 seems to have a feature to ...

2

Check my project at https://github.com/josevcm/nfc-laboratory Regards Jv

2

More than one block can be read into the psd if you want a result that is averaged (thus usually smoother) over several blocks. A sample rate in Hz can be divided by 1e6 if you want a spectral plot labeled in MHz, instead Hz.

2

The real number of samples from an RTL-SDR is not available via the USB interface. The RTL2832U chip samples at 28.8 Msps, but then mixes and downsamples the internal samples to lower rate IQ samples at from 240k to about 3 Msps, to allow transport over its slower USB 2.0 bus. The front-end R820T tuner can first downconvert VHF and UHF signal to a low HF ...

1

HackRF One will give you 20MHz bandwidth. Edit for more detail: If you buy the HackRF One instead of the Noelec SDR dongle, you will have 20MHz instead of 2MHz. Note that the HackRF One costs about \$300 which is still 10 times cheaper than a spectrum analyzer but 15 times more expensive than the SDR dongle you currently have.

1

An RTL-SDR outputs 8-bit integer IQ values via its USB connection data packet. That creates a fixed limit to the range of possible values (0 to 255 unsigned, or -128 to 127 signed, not -1.0 to 1.0, unless scaled somewhere). Your IQ signal will usually be a result of a mix of RF sources. A significant portion of RF noise is additive (a smaller portion might ...

1

The number of samples to read. Probably because whoever wrote it wants the graph to read in MHz rather than Hz.

1

This would indicate that the decoder software (Dump1090) is responsible for setting the SDR to the appropriate frequency Yes, this is exactly what happens. You can see the relevant code here: https://github.com/antirez/dump1090/blob/master/dump1090.c#L381 The function that dump1090 calls, rtlsdr_set_center_freq() and all other functions that start with ...

1

I repeat my comment now as answer. With a small addition. Depending on the settings in the RTL control program there is a first conversion to zero-IF or near-zero, or low IF, offset from zero. The front-end mixer for the range 24 MHz and higher is a mixer with a variable LO that converts the FM broadcast frequency to that lower IF frequency. The LO contains ...

1

In 3.7.13.5, thanks to Duck Dodgers (I think) who mentioned block paths coming up twice, such as: Block paths: C:\Program Files\GNURadio-3.7\share\gnuradio\grc\blocks C:\Program Files\GNURadio-3.7\share\gnuradio\grc\blocks I too (after fresh install of 3.7.13.5) got the very long and slow-building text list of 'already exist' warnings, before finally ...

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