# Tag Info

7

That's an expected phenomenon: Real-world physical systems tend to be frequency-selective (i.e. not constant over frequency), and "at large scale" low-pass systems. This applies to amplifiers, mixers, oscillators, and even transmission lines and connectors. So that's normal. Ettus even publishes exactly such measurements at https://files.ettus.com/...

5

The frequency allocation chart is really more artistic than informative. You can not and should not use that as a guide for selecting a frequency. There is too much information to fit on the chart, and as much as is there anyway, it's not surprising you feel lost looking at it. (That may be part of the intention of the chart.) There are multiple bands ...

5

Well, the need for one ADC that's twice as fast is definitely a very important factor! The same "it gets harder with rising frequency" argument applies to the anti-aliasing filter: Building a low-pass filter of pass band edge frequency $f_{cutoff}$ and stopband start frequency $f_{stop}$ depends in complexity on how narrow the transition between pass- and ...

5

General principle: In GNU Radio you cannot ever have a flow graph with a loop in it. If you wish to have feedback of some kind, it must be implemented in a single block. (There are many existing blocks that do this, such as AGC blocks and IIR filter blocks, and classes to help create them, though they still require writing C++ code.) However, you do not ...

4

For a complex-valued sampled stream, the sample rate must be greater than twice the signal represented. The sample rate in your graph is set to 384k, so it's not possible to represent a 98400 kHz signal. GNU Radio won't stop you, though. Mathematically, when you try to generate a sampled signal that's too high, you get aliasing. As an experiment, try ...

4

UHD requires a USRP to be owned by one process only, so no, you can't share the same USRP across two flow graphs, but you could use for example the ZeroMQ PUB/SUB sink/source pair to stream data in from a second application to your first flow graph. But then again, there's nothing wrong with putting a whole flow graph into a hier block¹ and using that in ...

3

I have connected the TX/RX port of one radio to the RX2 port of the other with an RF cable as a simulated radio link. DO NOT DO THAT. Always, always, always, in any case, under all circumstances, use an attenuator when directly connecting the output of one radio to the input of the other. Have I been setting my gain too high / frying my radios? Ettus ...

3

I would like to add a bit of my intelligence to this topic as I did some extra reading. This answer isn't a stand alone answer but merely a minute extension to the answer posted by Marcus Muller. I feel like one strong reason to generate/extract I,Q waveforms at an earlier stage in architecture-1 is to stop the interference by negative frequencies. More ...

3

Imagine your data is not white. That means that at certain periods, it contains more variance, and hence information, than on others. That's bad, because now certain frequencies become more sensitive to noise than others. Other than that: Many things that a receiver needs to do (AGC, equalization, synchronization) depend on the temporal stochastic ...

2

I don't see anything wrong with your basic GNU Radio flow graph, so it is likely a hardware configuration issue. I'm not familiar with the USRP N210 in particular, so this is a bit generic: In my experience, the most common software reason for getting no visible signal is incorrect gain settings. Is 15 dB an appropriate middle-of-the-road setting or is it ...

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

The B210 / NI-USRP 2901 has no problems with an open end condition or a short: You can't damage the transmitter with its own power. There's no significant PA on that board. So, it can handle any mismatch. Also, shutting down (whatever that means) isn't a reaction anyone included in the hard- or software in reaction to an impedance mismatch.

2

According to the Ettus Research Knowledge Base: The maximum input power for the B200/B210/B200mini/B205mini is 0 dBm. and Power Output >10dBm 10 dBm to 0 dBm is a difference of 10 dB, so an attenuator of at least 10 dB would be advisable. More would probably be a good idea, since the specifications specify a minimum performance: transmitter output ...

2

However, depending on which options I choose on the Spectrum Analyzer, my measurements are different by up to 6-10 dB(!). Using a spectrum analyzer needs a bit of understanding what it does: it sweeps a filter across the spectrum and measures the power passing through that filter. I didn't know how to properly use a spectrum analyzer when I first did, and ...

2

You've got a few very concerning conceptual and technical problems there, many of which will be adressed by the console output, which you should probably read! You can only sweep within your nyquist bandwidth. That is at most 25 MS/s (at 16 bit sample depth) or 50 MS/s (at 8 bit sample depth) for the N210 You want a single-tone sweep from negative baseband ...

2

Not at all. The file sink, as any sample-processing block in GNU Radio, is not aware of RF properties – all it sees are the baseband samples. So, the representation of things being centered around 0 Hz is correct; that's all the information there is in the signal. You will need some other mechanism to save such information. SigMF is one option, filenames ...

1

Does GPS port of USRP B210 only used for GPSDO? Yes. You can actually follow the RF trace on the board if you have it in front of you. Also, Ettus has their schematics online and you can see the connection there: The antenna port is connected to the antenna connector of the GPSDO alone.

1

In SDR receivers which use a mixer in front of the ADC to receive radio spectrum above the ADC sample rate(s), the sample rates and down-conversion frequency are usually independent settable (except possibly for the very bottom end of the range in some SDRs which don’t work (well?) for center frequencies below the sample rate.)

1

500 kHz = 0.5 MHz = 0.0005 GHz. You're providing a signal at +500 kHz, and then upconverting it to produce a signal at 2.5005 GHz. Are you sure that your measurement of the output frequency (and the USRP's oscillator) is precise enough to distinguish between 2.5000 GHz and 2.5005 GHz, absolute? A way to tell if your signal generation is having any effect is ...

1

The difference was caused by the splitter I was using to send the signal to both channels.

1

The safest way to run a transmit / receive application is using a loopback cable. Just remember to include an attenuator in your path so that the receiver doesn't get damaged.

1

The TX channels are separate from the RX channels. Hence, there will be a singkle, dual-stream RX streamer, and a single, dual-stream TX streamer. The subdev strings in your pseudocode aren't doing what you want; docs. You also don't need them – if you request a dual-stream streamer, the default behaviour is to count them ascendingly. So, if you just get ...

1

There is nothing which fundamentally prevents any radio, software defined or otherwise, from changing bands dynamically. Next to me I have a Yaesu FT-897 which is quite old and not an SDR, but it can change bands in the time it takes to switch a relay, commanded to do so either by a button press or a command from the serial port on the back. In fact ...

1

Your uhd_usrp_probe output shows: | | | | RX Frontend: 0 | | | | Name: Unknown (0xffff) - 0 and | | | | TX Frontend: 0 | | | | Name: Unknown (0xffff) - 0 this is typically the symptom of a not properly connected daughterboard, or one with broken power rails; less often, sign of a corrupted daughterboard eeprom. ...

1

Other common sources of problems: This happens more often than one would think: Are you sure your antenna is suited for the band? I've talked to way too many people that complained about bad reception, then to proceed to show they were using a 2.4 GHz antenna for 433 MHz. Many broadcast antennas you can buy have a 75Ω impedance, whereas all USRP ...

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