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14 votes

Why is 20m band waterfall showing signals every 50 kHz?

Those equally spaced lines in the waterfall are very likely from EMI/RFI noise generated by modern electronics, often harmonics and/or intermodulation coming from DC-to-DC power converters. Could be ...
hotpaw2's user avatar
  • 13.5k
9 votes
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How to choose the right sampling rate and bandwidth for RTL-SDR dongle?

What the FFT sink shows as frequency axis actually has no basis in "real world signal" – it just takes the sample rate you set (here, you set 1 MHz), and scales the full nyquist bandwidth to that. If ...
Marcus Müller's user avatar
8 votes
Accepted

Cell Tower distance measurement

One approach would be to capture the GSM Cell ID. This uniquely identifies a particular GSM site. You can then lookup this ID in a database such as one offered by Cobain to determine the tower ...
Glenn W9IQ's user avatar
  • 18.6k
8 votes
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VHF 50 Ω Antenna Over 75 Ω TV Coax

I will need a UHF/VHF diplexer on either end to suitably merge/split the signals from each antenna Yes, this is correct. A tangent: If you wanted to save some money by using mass-market parts, ...
Kevin Reid AG6YO's user avatar
  • 24.7k
7 votes
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RX antenna and RTL SDR with upconverter ..How to hear something?

Fun setup! I have many of the same components and need to try them out myself, but here's a general outline. (Plenty of this may be review for you, but I'm including it for others who may not be as ...
natevw - AF7TB's user avatar
7 votes
Accepted

Broadcast signal deviating with time

Since you said you're using an RTLSDR, it's very likely that you aren't receiving a station on 22,695 kHz, but rather one on 6,105 kHz. NHK World Radio does broadcast on that frequency (according to ...
hobbs - KC2G's user avatar
  • 12.5k
6 votes

How to distinguish SDR 820T and 820T2 dongles on Linux?

The R820T and the R820T2 differ. The R820T can set a narrow IF filter (300 kHz) - but not if the gain is set at maximum. The R820T2 can not set a narrow filter - minimum bandwidth is about 800 kHz. ...
sm5bsz's user avatar
  • 1,009
6 votes

RTL-SDR dongle - what antenna should I use for APRS receive only?

Here are the fundamentals of improving VHF antennas from what you've got: "Rubber ducky" (loading coil shortened) antennas are less efficient and more frequency-selective than un-shortened antennas. ...
Kevin Reid AG6YO's user avatar
  • 24.7k
6 votes

Why is 20m band waterfall showing signals every 50 kHz?

I notice you said 50 KILOhertz, not 50 hertz. Big difference, folks! You're picking up interference from some sort of electronic device that has a component producing a 50 kilohertz wave. Since this ...
Erik's user avatar
  • 61
6 votes
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Chaining multiple coaxial adapters

The reason you are having difficulty finding an adapter is because the N connector is heavy and the extra weight will stress out the MCX connector and probably break it eventually. Instead, you want ...
user10489's user avatar
  • 6,485
6 votes

Why can a monopole antenna receive wavelengths significantly longer than its physical length?

As Marcus Müller says, a small antenna is still an antenna, just a less efficient one. Adding to that: an inefficient transmitting antenna is something we try really hard to avoid if we can. An ...
hobbs - KC2G's user avatar
  • 12.5k
5 votes
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How to determine the PPM value of a NESDR SMArt?

Given that I don't have a frequency standard or other known transmitter available, what is the easiest way to calibrate the NooElec NESDR SMArt which is using a TCXO rated at 0.5 PPM.? I.e. to ...
Kevin Reid AG6YO's user avatar
  • 24.7k
5 votes
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How important is the impedance and resonance of a receive antenna?

The answers given so far provide good food for thought. I would like to add a slightly different perspective. Today's home is loaded with sources of RFI (radio frequency interference). Routers, ...
Glenn W9IQ's user avatar
  • 18.6k
5 votes
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Advantages of IQ generation at Mixer Stage or within FPGA for SDRs

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-...
Marcus Müller's user avatar
5 votes
Accepted

HackRF + Amplifier = HF/VHF QRP Radio?

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 ...
Scott Earle's user avatar
  • 4,619
5 votes

How to attach a magnetic loop antenna to the 50Ω coax of an RTL SDR?

You may be overthinking this. To make a long story short, just connect it and tune the capacitor to resonance and don't worry about the impedance of your pickup loop. When tuning the radio to ...
user10489's user avatar
  • 6,485
5 votes
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RTL SDR "dark region"

700-900MHz is "blocked" by law in the US and a number of other countries due to a (now antiquated) law that was designed to prevent wideband communications receivers from eaves dropping on old analog ...
Hamsterdave's user avatar
  • 1,844
5 votes

Digital transmission sounds

See SigiWiki: This wiki is intended to help identify radio signals through example sounds and waterfall images. Most signals are received and recorded using a software defined radio such as the ...
Aleksander Alekseev - R2AUK's user avatar
5 votes
Accepted

How much power does an RTL-SDR draw?

To extend what hotpaw2 said: So, it seems the front panel USB sockets are maybe not providing enough power for the Dongle to work? I googled how much power the Dongle draws? and apparently it ...
Marcus Müller's user avatar
5 votes
Accepted

How is gqrx producing audio?

GQRX contains signal processing code, mostly executed in the shape of GNU Radio flow graphs, that convert the complex baseband representation of the RF signal that you get from your SDR device, to ...
Marcus Müller's user avatar
5 votes
Accepted

How to track down and neutralize this apparent mixer creating noisy emissions around my signal?

This is caused by the RTL-SDR I was using to view my signal. Here's a quote from the guide at https://www.rtl-sdr.com/rtl-sdr-blog-v-3-dongles-user-guide/: Note that this feature makes use of direct ...
Rosa's user avatar
  • 191
5 votes
Accepted

Heterodyning complex values in gnuradio

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 ...
Phil Frost - W8II's user avatar
5 votes

Failing to detect Hydrogen line with 105cm dish

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 (-...
tomnexus's user avatar
  • 11.4k
4 votes

Transposing gqrx setup to rtl_fm?

This will be an incomplete answer to begin with, hoping that collectively we can come up with a workable solution: Freq 156.425 Mhz -f 156.425e6 Filter: ...
Edwin van Mierlo's user avatar
4 votes
Accepted

Improving VHF airband reception

Controllers and ATIS are transmitting from the ground, so they're always harder to receive because terrain, trees, and buildings are in the way. The best thing you can do to improve your reception is ...
Kevin Reid AG6YO's user avatar
  • 24.7k
4 votes
Accepted

Video transmission between ATV and SSTV

So, a teaser first: With GNU Radio, you can transmit various DVB standards. Here's Alexandru Csete demoing his DVB-S2 transmission: As you can see from the FFT Plot generated by the flow graph in ...
Marcus Müller's user avatar
4 votes
Accepted

SDR with the Raspberry Pi

Yes, with some important qualifications, you can "directly" generate SSB on the Raspberry Pi. The rpitx software you mention does that, and in combination with an RTL-SDR type dongle you would indeed ...
natevw - AF7TB's user avatar
4 votes

How to determine the PPM value of a NESDR SMArt?

I want to add some solutions to Kevins answer. Apparently I'm lucky to own the SMArt device as it is really stable with a PPM between 0.5 - 1.0 at all bands I've ...
not2qubit's user avatar
  • 378
4 votes

How to attach a magnetic loop antenna to the 50Ω coax of an RTL SDR?

You don't necessarily need a coupling loop. Nor do you need to worry too much about matching the antenna to 50 ohms. Firstly, because SWR is not very important for receive performance, and secondly ...
Phil Frost - W8II's user avatar
4 votes

RTL-SDR dongle - what antenna should I use for APRS receive only?

Rubber ducky antennas are not very efficient indeed. Also for best performance they may require a ground plane or radials, which I guess you could omit. Personally I used RTL-SDR Blog Multipurpose ...
Aleksander Alekseev - R2AUK's user avatar

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