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.
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