Not enough AGC compared to SDRSharp?

[Roger X]

Using MS Windows' SDRSharp, which has a "Hardware AGC" and "Tuner AGC" option, I can get enough AGC to have a strong signal for successful digital speech decoding.

Using Linux GQRX, GQRX only seems to have a "Hardware AGC", and using this option alone (within SDRSharp as well) does not provide a signal strong enough for digital speech decoding.  This additional "Tuning AGC" driver/software feature is likely required for a strong and clear signal, especially when decoding digital speech away from the transmitters, or typically outside urban areas.

There is a manual software Gain control slider at the bottom of GQRX, for which SDRSharp has a similar option for which can be disabled and is disabled, but this GQRX software gain only aides a small amount.  Also note, this GQRX software gain is not able to be disabled, unlike SDRSharp.

[Roger X]

I should note, I'm using a RTL2832U chip, or "NooElec NESDR Mini 2 SDR & DVB-T USB Stick (RTL2832 + R820T2)" USB device.

[Alexandru Csete]

On Sat, Feb 20, 2016 at 5:27 PM, Roger X <rog...@gmail.com> wrote:
> Using MS Windows' SDRSharp, which has a "Hardware AGC" and "Tuner AGC"
> option, I can get enough AGC to have a strong signal for successful digital
> speech decoding.
>
> Using Linux GQRX, GQRX only seems to have a "Hardware AGC", and using this
> option alone (within SDRSharp as well) does not provide a signal strong
> enough for digital speech decoding. This additional "Tuning AGC"
> driver/software feature is likely required for a strong and clear signal,
> especially when decoding digital speech away from the transmitters, or
> typically outside urban areas.

Hi Roger,

In gqrx, the "Hardware AGC" checkbox should switch both AGCs on for the rtl-sdr.

Also, there is a manual "LNA gain" control located just below the
"Hardware AGC" checkbox? While I can rule out the having tuner AGC
give more gain, the LNA control gives 50 dB og gain range, which is
quite a lot.

> There is a manual software Gain control slider at the bottom of GQRX, for
> which SDRSharp has a similar option for which can be disabled and is
> disabled, but this GQRX software gain only aides a small amount.

I believe this is the audio gain slider, which is gain after the
demodulator, so it will not help regarding sensitivity.

Alex

[Roger X]

Thanks for the clarification.  I had no idea GQRX Hardware AGC enabled both hardware & tuner AGC.

The LNA Gain was hard set by the application to ~49.5dB (ie. 50dB) immediately upon checking the "Hardware AGC" tick box.

[Alexandru Csete]

The slider is disabled when you select AGC and so it will appear
frozen at the last value that was set. But the value itself has no
significance or relation to the actual gain while AGC is active.

Alex