On 19/09/2023 03:24, ouzan...@hotmail.com wrote:
50-54 dB TX/RX isolation is very low as a dynamic range of many
applications. For our application, this is our main problem. That is
why we want to try to bypass and see if the isolation of the card
increases. There is no data about the TX/RX isolation of AD9364 in its
datasheet. There is some information in the forums indicating that the
TX1/RX1 isolation is measured as 65 dB.
Let's assume 65dB on the AD9361. If you're transmitting at, let's say
+10dBm, that means -55dBm is "seen" by the RX path,
in addition to your signal of interest and other "stuff" that is
presented to the RX path. If that's too much, you can consider
lowering the TX power over the USRP, and using external RF
gain/isolation/duplexing to achieve the final system requirements.
SDRs should be considered *components* in an overall RF *system
design*. That means that often, you'll need to engineer
other bits of "plumbing" around them.
Now, in the past when customers have wanted to do something like this,
they simply depopulated C809, which is the capacitor
that links the TX-side switch to U807. There's no impedance-bump
implications for this since the desired antenna configuration
doesn't use that pathway at all--it just improves the isolation a bit
on the cross-talk pathway. But as I said, the TX/RX
isolation on the AD9361 isn't spectacular--not the 80-90dB you'd get
with separate TX/RX subsystems and a duplexer.
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