Just an FYI, all of our USRPs define 0 dB gain as the smallest overall gain that is supported, and then it goes up. TwinRX has a wide input range of amplitudes, so much of that 90 dB is from attenuators that enable you to nicely see the +10 dBm input signals. So gain range != amplification, it's the combo of all gain-varying components.
--M On Tue, Sep 29, 2020 at 8:30 PM Mark Koenig via USRP-users < usrp-users@lists.ettus.com> wrote: > I get it, thanks for the block diagrams. I will look into doing a lab > test with a calibrated source. > ------------------------------ > *From:* Marcus D. Leech <patchvonbr...@gmail.com> > *Sent:* Tuesday, September 29, 2020 2:23 PM > *To:* Mark Koenig <mark.koe...@iubelttechnologies.com> > *Cc:* usrp-users@lists.ettus.com <usrp-users@lists.ettus.com> > *Subject:* Re: [USRP-users] TWINRX Gain > > On 09/29/2020 02:02 PM, Mark Koenig wrote: > > Yes, I understand gain varies with temperature and frequency, I just wasnt > sure if there was any receive chain analysis performed with the daughtecard > to give the developer an idea of what type of gain is provided over the > attenuation range at various frequencies. I am not too concerned about > tenths of dBs....I was just interested in what the actual gain range > provided by the card is. > > Thanks > > Mark > ------------------------------ > > If you look at the first page of this: > > https://files.ettus.com/schematics/twinrx/TwinRX%20RF%20Board%20Rev%20D.pdf > > You can see the overall block diagram. You can also see several PE43503 > attenuators, sprinkled among several different MMIC amplifiers, and > various different RF pathways through switches and filters depending on > band. It would be hard for me to unwind all of that and give you > a definitive answer. > > Even for the IF processing, there are two different IFs, depending on the > frequency band--again with various distributions of gain and > attenuation (either explicit attenuation, or attenuation via > filtering)--all of which have considerable uncertainty--due to > batch-to-batch > variability and temperature effects. I'm fairly sure that even the > designer of the board couldn't tell you, for any given board configuration > what the actual gain measured between the antenna input an the ADC input > actually was, with better than 5dB confidence. Which is where > calibration comes in. > > https://files.ettus.com/schematics/twinrx/TwinRX%20IF%20Board%20Rev%20C.pdf > > In a laboratory instrument, like a spectrum analyser, all of this is > painstakingly calibrated at the factory, usually using lookup tables (or the > analog-era equivalent), based on well-characterized calibration > sources. So when you set the gain level on the front-panel of the device > to some dB value, you'll actually get that value at the measurement > point and when you look at the measurement on the display and it > says -70dBm, it's actually -70dBm at the input terminal. SDRs aren't > that, typically. Although one could build a fairly nice lab instrument > *around* an SDR, using all the aforementioned calibration exercises, etc. > > Now, this all, I admit, sounds a tad "lecturey". I know you probably know > all of this, but many on the list don't, or perhaps haven't thought about > it much. So, I'm prompted to deliver this, or a very similar "lecture" > a few times a year due to similar queries to yours. > _______________________________________________ > USRP-users mailing list > USRP-users@lists.ettus.com > http://lists.ettus.com/mailman/listinfo/usrp-users_lists.ettus.com >
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