It's all about the Software

Hello All,

I been searching for an answer, however, I can't seem to find the answer. I use SDR Console 3.20 with NooElec SDR RTL USB Dongle. When setting up the SDR using RTL-USB in the definition, there is an option for GAIN. -30 to 30, default is 0. Then there is RF Gain when Monitoring. What is the difference between the two and what would be the best usage for them? I heard something like adjust RF Gain to the highest number prior to the Noise Floor Level moves? What does that mean?

Thanks in Advance for any help,
Jeff

Hello Jeff

I think with the RTL-SDR (at least with mine) you will see two gain controls, RF Gain and Visual Gain. I think the GAIN that you are referring to (marked -30 to +30) is actually marked "Visual Gain"? This is effectively a method of calibrating the level of the displayed signals in the spectrum display. So, for example (not saying this is perfect method) you might disconnect the antenna, and use the visual gain to set the noise floor on the signal-meter or the spectrum display to somewhere around S0/-126 dBm/-20dBuV (depending on which scale you have set). When you plug the antenna back in and receive a signal, you probably want to generally then set the RF Gain to the lowest figure that makes your signal pleasantly audible without causing overload. This is going to be largely dependent on the quality and gain of the antenna you have attached. You will just need to experiment with this one. For starters, try and receive some VHF FM broadcast signals. That's something that almost guaranteed to be receivable. Then maybe some known airband signals.

To reiterate, the Visual Gain control in SDRC is not actually changing any gain in the receiver. It is just an arbitrary setting to help calibrate the display to a "normal" setting (in simplistic terms). But the RF Gain is actually changing the gain applied inside the hardware (the amplifier inside the RTL-SDR).

Hope it helps.

Max

And the rtlsdr gain numbers are entirely estimates. I'd not be surprised at errors up to 5 dB in some cases.

{o.o}

On the same subject, SDRC running a Pluto has RX options of Manual/Slow attack/Hybrid/Fast attack. What are these?

Hi David

Take a look here. I believe it explains all:

https://www.sdr-radio.com/implementation

and the full index of info:

https://www.sdr-radio.com/pluto

73

Max

Thanks for the information, that makes sense completely.