Search found 143 matches

by hotpaw2
Fri Sep 11, 2020 3:55 am
Forum: Off-Topic
Topic: short active usb cable
Replies: 4
Views: 6036

Re: short active usb cable

A short high-quality passive USB cable (I use 6 inch ones with a right-angle connector) is likely to work better than an active cable.
by hotpaw2
Thu Sep 10, 2020 9:54 pm
Forum: RTL-SDR Discussion
Topic: Direct sampling to bandwidth output, how done?
Replies: 3
Views: 876

Re: Direct sampling to bandwidth output, how done?

Anti-alias filtering can be done in hardware only for analog signal (before ADC). This is impossible in software (in digital domain after ADC output). The only way is to apply anti-alias filter to the analog signal before ADC input. If you decimate in software, and the sampled signal has a bandwidt...
by hotpaw2
Tue Sep 01, 2020 6:45 pm
Forum: Troubleshooting Help
Topic: Ceiling Fan AGC?
Replies: 7
Views: 6697

Re: Ceiling Fan AGC?

This type of noise likely has nothing to do with your RTL-SDR or your computer or software. It could be RF generated by the commutator in the fan motor, sparking or just causing fast-rise-time switching square waves, which emit lots of RF harmonics. This RF is then coupled into the room's AC wiring,...
by hotpaw2
Mon Aug 24, 2020 3:01 pm
Forum: RTL-SDR Discussion
Topic: Can any RF chip be modded to turn into an sdr or only R820T?
Replies: 6
Views: 672

Re: Can any RF chip be modded to turn into an sdr or only R820T?

Depends on what you mean by an SDR. Most WiFi, cellular, and mobile phone radios are SDRs internally. So you don't need to turn them into an SDR, as they already are SDRs. However the RF frequencies and modulations these SDR chips are capable of are often fixed to specifics bands and modes, and the ...
by hotpaw2
Tue Aug 18, 2020 2:39 pm
Forum: Troubleshooting Help
Topic: want to broadcast radio [!help]
Replies: 4
Views: 604

Re: want to broadcast radio [!help]

Some countries allow license-free broadcasting within a limited range of frequencies if one stays below mandated power levels and transmits with a given spectral purity. An amateur radio license will allow one to use even more frequency bands at much higher power levels. Check the requirements for y...
by hotpaw2
Mon Aug 17, 2020 8:43 pm
Forum: Troubleshooting Help
Topic: Librtlsdr vs SDR# sensitivity
Replies: 1
Views: 345

Re: Librtlsdr vs SDR# sensitivity

Check your rtlsdr_set_tuner_gain, rtlsdr_set_tuner_gain_mode, and rtlsdr_set_agc_mode settings.
If the AGC is off and your RF gain is way down, the RTL-SDR sensitivity will be low.
by hotpaw2
Mon Aug 03, 2020 3:44 pm
Forum: RTL-SDR Discussion
Topic: Direct sampling to bandwidth output, how done?
Replies: 3
Views: 876

Re: Direct sampling to bandwidth output, how done?

The mathematically correct solution is to use a perfect band-limiting anti-aliasing or low-pass filter before decimation or interpolation. In reality, no filter is perfect. So an anti-aliasing filter should have a stop band attenuation below the radio's desired noise floor at and above the new downs...
by hotpaw2
Wed Jun 17, 2020 2:56 pm
Forum: Signal Identification Help
Topic: Is this interference i see at 137MHz?
Replies: 22
Views: 4231

Re: Is this interference i see at 137MHz?

One additional trick that can help is to use ferrite beads or toroids. I prefer toroids, as multiple turns through the donut seem to work better than a string of multiple cores/beads on the cables. Try 1 or 2 meter passive USB cable, but loop several turns of the cable through a ferrite toroid, mayb...
by hotpaw2
Thu May 28, 2020 8:55 pm
Forum: Antennas
Topic: Airspy YouLoop
Replies: 17
Views: 3949

Re: Airspy YouLoop

A YouLoop type antenna requires a receiver with a high-gain low-noise RF front end, such as an AirSpy HF+ Discovery. IIRC, an ordinary RTL-SDR in direct sampling mode doesn't have that much RF gain, and its 8-bit sampling creates a relatively high noise floor, so you might want to try using an LNA b...
by hotpaw2
Thu May 14, 2020 2:43 pm
Forum: RTL-SDR Discussion
Topic: GQRX - unexpected plot when changing frequency range
Replies: 14
Views: 5464

Re: GQRX - unexpected plot when changing frequency range

The bigger the input signal, the more likely the spectrum is to show spurious signals (intermodulation products, etc.). That's because semiconductor devices are non-linear components. They are only approximately linear enough for a range right above the smallest signals detectable. Near the maximum ...