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Leif Asbrink leif at sm5bsz.comHello 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? > > > >