Linrad with rtlsdr with and the e4000 tuner.

Stefan Sydow st at
Thu Jul 5 14:42:40 UTC 2012


I've played around with your code and also had a look into the linux
kernel driver which contains some elonics code [1].

There the LNA gains have an offset of 3dB compared with rtl-sdr.
In the rtl-sdr header is also a constant defined but not used, to switch
to 5dB gain steps. I'm wondering how this fit's with your observations.
I've read your blog entry and would like to evaluate the gain values of
my device, but it is not clear to me what equipment is needed - I assume
at least a 144 MHz oscillator with defined level.
Regarding your changes to the gain setting function, fear they contain
lots of bugs, but I agree it would be nice to have a function which make
IF-gain setting easier.

The elonics code also contains a more stuff to configure the auto gain.
Maybe this is interesting for rtl-sdr too.




Am 05.07.2012 13:27, schrieb Leif Asbrink:
> 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 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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