On 08/30/2014 10:57 AM, [email protected] wrote: > this is an issue I have been wondering about and maybe you or someone > on the list can comment: what are the gain ranges for the various > front ends ? I have not been able to identify neither in the source > code of osmosdr & rtl-sdr nor on the datasheets what the RF and IF > gain ranges are. Are they different for the E4K, FC0013 and R820T ?
I had a look at the most popular ones: The E4K has settings for LNA (-5..+25dB), mixer (4 or 12dB) and total of 6 IF gain stages with various gains allowing for 1dB steps between 3 and 57dB. The software only deals with LNA and mixer gain and not independently. IF gain can be set through the API mentioned below. R820T also has LNA, mixer and IF gain settings - the exact steps are not known. The numbers in the library code are through measuring the gain at a fixed frequency. That gave 0..33dB for the LNA, 0..16dB for the mixer and -4.7..40.8dB for the IF gain. The current library does not expose these settings through an API, only LNA and mixer are set through some algorithm. IF gain is set to a fixed value. On 08/31/2014 10:08 PM, Tobias wrote: > On 2014-08-31 11:31, [email protected] wrote: >> This is very helpful, I had not identified these lines before. Thank >> you. >> Could you also clarify how IF gain and RF gain act ? I understand the >> hardware architecture of where the two amplifiers are located, but am >> missing >> how the settings act on each stage. Is the RF gain the RF-frontend >> gain or >> the RF-frontend + IF gain ? > > Sorry but I don't know anything about the IF gain. The API > documentation here indicates that the E4000 have six gain stages but > for other tuners, I don't know: > > https://github.com/steve-m/librtlsdr/blob/master/include/rtl-sdr.h#L226-L234 > At least for R820T a similar interface would make sense. I'm currently working on a more universal API, as the one above works only for E4K. Regards, Alexander
