# Tag Info

8

You'll need an experimental radio license (Versuchsfunk) from Bundesnetzagentur link for research operation. For demonstration/teaching purposes, a demonstration radio license (Demonstrationsfunk für Bildungseinrichtungen) would be in order. I'm not a lawyer nor have I ever applied for either of these; I'd recommend contacting BNetzA on these aspects. ...

7

As for other legal alternatives, one might be transmitting inside a suitably shielded Faraday cage. I’ve seen such facilities at labs where various prototype and pre-production (and competitors?) electronics systems were being tested to measure how far out-of legal compliance they were.

7

As you might suspect, the data rate impacts the required RF bandwidth. Besides the data rate, the modulation method, encoding, packet overhead, duplexing, and other factors ultimately determine the required RF bandwidth. As an example, the 4G network has a data speed of ~20 Mbps and consumes a bandwidth from to 5 to 20 MHz. In the United States, the 70 cm ...

5

Just to answer the second part of the question, you do not want an amplifier that has too wide a bandwidth, mainly to lower the complexity (and hence also the cost) of the amplifier. All users of radio spectrum (including radio amateurs) must not cause any interference to other users of the radio spectrum, and that means that out-of-band transmissions must ...

5

The RF architecture of the HackRF One is diagrammed here: This is a bit elliptical so I'll explain what I read from it (describing the receive-mode operation; transmit is just the reverse). There are two integrated LO/mixer units: One is in the RFFC5072 chip. This is the one that provides the HackRF One's wide tuning range. It mixes the incoming signal ...

4

The Nyquist limit is half the sampling rate because otherwise you can't distinguish a signal at a frequency $x$ from a signal at $f_s - x$ which starts 180° out of phase from the first one — they give exactly the same sequence of real samples. But quadrature sampling gives exactly the phase information needed to resolve this ambiguity. Knowing $\sin \omega t$...

4

That is DC offset, either in the analog to digital converters, or their driving circuitry. The average voltage at the ADC's input is ideally exactly in the middle of the ADC's range, since this maximizes the maximum voltage swing up or down before clipping. The DC offset is the difference between the ADC's "middle" voltage and the average voltage ...

4

Outside of the -w receive options, hackrf_transfer always deals in 8-bit signed IQ samples, raw with no file headers. You must also make sure that the sample rate of the data matches the sample rate specified on the command line and is a rate supported by the HackRF hardware. WAV files contain the sample rate information in a header, but raw files have no ...

3

Another way to look at it is that an IQ ADC is really taking 2 independent (not added together) samples per IQ sample. Thus the rate of information gathered is double from a just scalar sampling at 22 MHz. The 90 degree offset between the 2 IQ sample components allows capturing phase information that can help a complex FFT (et.al.) differentiate between ...

3

If you're using four independent GPS receivers as your time synchronisation source, you may be able to feed some version of the GPS 1PPS signal into the receiver, and recover it later in the data. It's possible to synchronise two A/Ds, usually by time tagging the samples and resetting the counter in the FPGA using an external sync signal like GPS, but this ...

3

The device usually doesn't have anything to do with legality, it's what you do. So, rule of thumb: Without a license, you can't transmit – full stop. I'm not quite sure about federal Swiss law, but chances are you can only receive broadcast transmissions (meant for everyone to receive) and transmissions especially meant for you, and everything else is ...

2

Picking up NOAA imagery is mostly a feat of constructing a good antenna than having a high bandwidth, or great clock. Thus, for reception only, build a nice helical antenna, and any cheap RTL Dongle, as long as it works at 1.698 GHz – if you don't want to waste the signal quality you've earned through the antenna, a cheap LNA (Lna4all seems to be nice) will ...

2

Do you mean removing the antennas from each device, and connecting them directly with a piece of coax? Yes, that does provide complete shielding. Though you'd want an attenuator to avoid overloading or possibly damaging the receiver. Unfortunately this will also render the phone incapable of receiving other signals. No way around that with a passive device, ...

2

As this is SDR, the HackRF hardware presents the received signal as I/Q to the computer. The actual demodulation is done in software.

2

Are the two channels added together? Yes and no. The whole point of collecting I and Q is so they can be treated as real and imaginary parts of a single complex sample. This is one of the key methods of SDR. This answer explains it well: https://electronics.stackexchange.com/questions/39796/can-somebody-explain-what-iq-quadrature-means-in-terms-of-sdr

2

First synchronize all 4 clock generators in frequency using an external source (say, GPS or atomic clock derived into the 10MHz ref input). Start receiving continuously on all 4, and use the received sample counts as your Raspberry Pi timer time bases. Second, place a reference source (such as a cheap FM transmitter, FMRS, HT, et.al.) in the center of the ...

2

Do you mean you want to put your phone and a small SDR in a faraday cage together such that the SDR only receives the phone’s emissions? If so, a metal lunch box should work for everything except the power and data cables. Heavy RF choking of the cables just outside the box entry would take care of common mode current but you may face other RFI issues from ...

1

There are three receive gain stages in the HackRF one. Two of them are on the MAX2837 chip (the ones controlled by "LNA gain" and "VGA gain"), and the third is the MGA81563 preamp, which is either on (+14dB) or off (+0dB), and controlled by the "amp" toggle. You have indeed blown the MGA81563. I did the same thing to one of mine ...

1

Check the sample rate configuration in the software you are using. Older Apple products used a hardware sample rate of 44.1 ksps, whereas newer Apple products all seem to use a hardware audio sample rate of 48k (or a multiple thereof).

1

Synchronizing clocks without wires usually involves radio. But since you're building a radio, "just use a radio" is probably not a useful solution. Unfortunately, it's unlikely NTP (the most common protocol for synchronizing time over IP) is able to provide sufficient precision to keep the receiver's phase coherent enough to be useful. The jitter in network ...

1

I know there's actually people working on a system for that band. It'll be SDR-based. There's no technical restriction that says you can't have a couple hundred kilobits per second in a couple hundred kilohertz. It might just be the case that for commercial bands, the available bandwidth isn't attractive and regulatory restrictions make it unfeasible to ...

1

Your problem seems to involve USB permissions under Ubuntu, so perhaps your question would have been better-suited for askubuntu.com. But you probably didn't know that when you asked, so we shouldn't really hold that one against you ;) Anyway, your question seems to be the first one in the HackRF FAQ. If the advice there were short I would repeat it here, ...

Only top voted, non community-wiki answers of a minimum length are eligible