I'd also like to chip in that effective TX power is /very/ dependent on frequency for devices that span several orders of magnitude in frequency -- so you can't just say "the max TX power is x dBm", you need to measure for every frequency, with every bandwidth you use, for the specific signals you transmit; often, application-specific aspects define what TX power is, and it's not always trivial to say what TX power means -- for example, the B210 being good, but not perfect, it of course has emissions a) inside f_target +-/f_sample/2 (intentional) b) outside a) but close to it c) further away how much bandwidth do you observe when saying "TX power is x dBm"? a) only? That might make sense from a specific receiver's perspective, but not do a pure RX power observation right. a+b+c) ? Impossible to measure. a+b) makes sense if you're really interested in how much power leaves the device (e.g. for legal limits), but really depends a lot on factors like how you tune, what sampling rates you're using etc.
This all contributes to the fact that when determining the signal strength, you must first careful /define /what you want to describe, and then /measure/ it. Best regards, Marcus On 02.08.2015 21:09, Marcus D. Leech wrote: > On 08/02/2015 03:01 PM, Samith Abeywickrama wrote: >> Hi, >> >> I am confused with 89dB tx gain of USRP B210 and what is the meaning >> of 89dB gain? How this value relates to maximum output of 50mW in >> B210? Because this value is too much high, as a example: If the RF >> output power of AD9361 agile transceiver is -29dBm and after we apply >> 89dB gain, transmit power should be 50dbm, But 50dBm is too much >> higher than 50mW. >> >> -- >> Best Regards! >> Samith >> > The maximum output power of the AD9361 is about +17dBm. > > Gain control is implemented as attenuators in the gain chain, so that > 89dB of gain-control range should be applied to the maximum output > power at any > given frequency, so that a setting of 0dB gain means that, > notionally, your output power is +17dBm - 89dB = -72dBm, and at 89dB > "gain", your output > power would be +17dBm. > > In RF circuits, it's very typical to use variable attenuators to > effect gain control, so that the individual gain stages operate at > fixed bias and matching > levels, and the inter-stage attenuators collectively effect some > range of gain control for the entire chain. > > > > > _______________________________________________ > Discuss-gnuradio mailing list > [email protected] > https://lists.gnu.org/mailman/listinfo/discuss-gnuradio
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