* When you say a max gain of 89 dB, that is the gain you set in GNU Radio on the USRP block right? Yes (USRP Sink, not Source).
* With a 30dB attenuator, regardless of what I set the gain to on either the rx/tx blocks in GNU Radio, and regardless of how far apart I position the antennas I won't be able to damage the rx side will I? Those are back-of-the-envelope calculations which assume max output power of 30 dB, far-field positioning, and USRP B2xx as the receiver with 0 dBm max input power (most daughterboards of N and X series have lower max input power). It sounds like you're mostly experimenting and don't really care about dynamic range and received power. In that case, why don't you put 60 dB attenuation? It's way more than enough. Oh, you should also take into account the antenna gain, if they are both simple omnidirectional, add the tx and rx antenna gain to the calculated output power to get a more accurate measurement (60 dB should cover you here if you use normal antennas). * One thing I'm wondering also is how you calculated the dBm value for 49 dB tx gain? I assumed 89 dB tx gain outputs ~ 15 dBm. Reduced 40 dB from the tx gain and got 49 dB tx gain, thus reduced 40 dB from the output power and got ~ -25 dBm (15 - 40). The best thing for you to do is to take the parameters requested in the FSPL calculator, fill them in, and understand better the RF conditions of your experiment. On Sun, Mar 4, 2018 at 2:29 PM Christopher Richardson < chrisrichardso...@gmail.com> wrote: > Thanks a lot for your reply, lots of very useful information! > > A few questions: > > * When you say a max gain of 89 dB, that is the gain you set in GNU Radio > on the USRP block right? > > * With a 30dB attenuator, regardless of what I set the gain to on either > the rx/tx blocks in GNU Radio, and regardless of how far apart I position > the antennas I won't be able to damage the rx side will I? > > * One thing I'm wondering also is how you calculated the dBm value for 49 > dB tx gain? > > Cheers > Chris > > > On Sun, Mar 4, 2018 at 6:00 AM, Gilad Beeri (ApolloShield) < > gi...@apolloshield.com> wrote: > >> B200 has a max output power of ~ 15 dBm (give or take) in max gain (89 >> dB), depending on the frequency, and a max input power of 0 dBm. To be on >> the safe side, you can and should take a 10 dB backoff, so for the sake of >> discussion, assume the max input power is -10 dBm. >> >> You can use the Free Space Path Loss formula (calculator: >> https://www.pasternack.com/t-calculator-fspl.aspx) to get a sense (the >> formula is for the free space) of how much power you "lose" by using a >> wireless channel, the results depend on your choice of frequency and >> distance between antennas. You need to make sure the antennas are "far" >> enough to be on the far field of each other. >> >> You can also take into account the attenuation the SMA cables add on both >> sides, or, to save you all of the trouble, >> you can just transmit with a gain low enough such that the transmitted >> signal is weaker than the max input power (i.e., if 89 dB tx gain is ~ 15 >> dBm, then 49 dB tx gain is ~ -25 dBm, so you're good), and/or you can put a >> 30 dB attenuator either in the tx or rx port, that way you'll know that >> even if you make a software mistake, you're on the safe side. >> >> On Sun, Mar 4, 2018 at 3:38 AM Christopher Richardson via USRP-users < >> usrp-users@lists.ettus.com> wrote: >> >>> Hi, >>> >>> I'm just wondering if anyone could give me some advice, I'm using the >>> USRP >>> B200 with GNU Radio with a simple FM example to transmit and receive on >>> the same frequency. >>> >>> I made use of telescopic whip antennas on the Tx port and another on the >>> Rx port, I had the antennas tilted away from each other, but I've been >>> informed this could still be a bad idea and could overload the receiver? (I >>> had also played with different Rx/Tx gain values while testing this). >>> >>> I'm just hoping I haven't damaged anything. >>> >>> I'm planning on now getting 2x 3 metre SMA cables to separate the >>> antennas by around 6 metres, does this seem sensible? >>> >>> Cheers >>> >>> Chris >>> _______________________________________________ >>> USRP-users mailing list >>> USRP-users@lists.ettus.com >>> http://lists.ettus.com/mailman/listinfo/usrp-users_lists.ettus.com >>> >> >
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