Linrad with rtlsdr with and the e4000 tuner.

Leif Asbrink leif at sm5bsz.com
Thu Jul 5 19:05:28 UTC 2012


Hello Jay,

The e4k chip has many registers. For example the function
e4k_manual_dc_offset() changes the way the if gain settings 
work.

There could also be something that affects the lna gain.

The purpose of the changed code that I made available
is to allow rtlsdr users to have the full performance
of the RTL2832/E4000 dongles NOW. Today.

I do not have access to any data for the chips. Performance
is reasonably close to the theoretical limit and all AGC
functions are disabled so it is now a good radio with Linrad.

The function e4k_manual_dc_offset() is named in a way that
suggests one can change the DC offset on the output from
I and Q. Pointless, at least with the dongle I have because
the E4000 is AC-coupled to the RTL2832. (I checked with
an oscilloscope.)

Regards

Leif / SM5BSZ



On Thu, 5 Jul 2012 08:06:11 -0500
"Jay Salsburg" <jsalsburg at bellsouth.net> wrote:

> I assume everyone involved in constructing the Control Code for the Tuner
> Dongles started out by recording the I2C stream on the Dongle coming from
> the Original Dongle Software that comes with the Dongle for watching TV and
> FM Radio.
> 
> -----Original Message-----
> From: osmocom-sdr-bounces at lists.osmocom.org
> [mailto:osmocom-sdr-bounces at lists.osmocom.org] On Behalf Of Leif Asbrink
> Sent: Thursday, July 05, 2012 6:27 AM
> To: osmocom-sdr at lists.osmocom.org
> Subject: Re: Linrad with rtlsdr with and the e4000 tuner.
> 
> I changed the numbers to get a reasonable agreement with the gain values I
> observed on the dongles I have.
> 
> I did not care to match the gain setting to the real gain better than within
> 3 dB (the gain step size in Linrad.) The reason is that I assume that the
> routines from osmocom will be changed and that other softwares that support
> rtl dongles will allow gain setting in a reasonable way and that the
> performance will become similar to the current Linrad performance. When that
> happens I will rewrite Linrad to use the library as intended. 
> 
> I see two alternatives, there could be lna gain as well as IF gain as
> separate controls. 
> 
> The other alternative would be a single gain control, but in that case both
> lna and if gain have to be controlled. 
> The first few gain reduction steps have to be on the IF because the most
> common problem is close range interference and the improved dynamic range is
> useful. (In case the lna gets blocked one should install a filter.)
> 
> Regards
> 
> Leif / SM5BSZ
> 
> On Thu, 05 Jul 2012 02:06:31 +0200
> la at tfc-server.de wrote:
> 
> > > The gain setting is clumsy
> > If it only was your gain setting function, but no, even your gain 
> > values for the lna are just plain wrong.
> > I just have to ask: Why? What made you "improve" them?
> > 
> 
> 




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