Hello,
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.
Regards
Stefan
[1]
https://github.com/tmair/DVB-Realtek-RTL2832U-2.2.2-10tuner-mod_kernel-3.0.…
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(a)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?