[USRP-users] TDD mode with USRPs in GNU Radio

Andy Walls andy at silverblocksystems.net
Tue Feb 26 12:10:45 EST 2019


Hi Marcus:

On Tue, 2019-02-26 at 12:00 -0500, usrp-users-request at lists.ettus.com
wrote:
> Message: 2
> Date: Tue, 26 Feb 2019 09:40:17 -0500
> From: "Marcus D. Leech"
> To: usrp-users at lists.ettus.com
> Subject: Re: [USRP-users] TDD mode with USRPs in GNU Radio
> 
> On 02/26/2019 08:41 AM, Andy Walls via USRP-users wrote:
> > 
> > In my opinion, yes.
> > 
> > It seems kind of funny that Ettus would make a board that can blast out
> > 20 dBm on Tx, can only tolerate -15 dBm max on Rx, and then have only a
> > single device that provides only 17-20 dB isolation between the Tx and
> > Rx.
> > 
> > If all the specifications from the UBX-160 page are to be believed,
> > you always have to have the UBX Tx gain turned down by at least 15 dB
> > to not damage your UBX board.
> > 
> > 
> 
> RX is protected by TWO layers of RF switch, not just one.  That gives 
> you about 30-40dB of isolation.
> 
> 
[snip]

> > Ah, yes.  As long as the USRP switches this one over to RX2, (and that
> > sounds like your configuration,) it looks like you get an additional
> > 13-15 dB of isolation.  Still not enough to cover the whole 35 dB, but
> > you're up to a worst case minimum 30 dB isolation.
> > 
> > If all of the specifications are to be believed, and you know you'll
> > receive negligible energy on the RX2 port antenna, you only need set Tx
> > output gain to 5 dB of attenuation, and make sure you are using RX2 for
> > Rx.

If one configures a USRP Sink to use the "TX/RX" port for Tx and a USRP
Source to use "TX/RX" port for Rx, does one still get both switches'
worth of isolation during Tx, or is it only the single switch's worth
of isolation in that case?

(I'm too lazy to run that down in the source code at the moment. :] )


Thanks,
Andy




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