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[Discuss-gnuradio] Re: Need help on questions about two switches and two

From: zhifeng chen
Subject: [Discuss-gnuradio] Re: Need help on questions about two switches and two Rx in RFX series daughter boards
Date: Thu, 5 Jul 2007 01:38:40 -0400

Is there anyone who may help to answer my questions below? I will give more detail descriptions if they are unclear. Thanks a lot!

2007/7/3, zhifeng chen <address@hidden>:
I am wondering why there are two switches in the RFX series daughter from schematics. It seems their purposes is different: one for switch between Tx and Rx, another switch between Rx and Rx2. So, my questions as:
1. we may use one tx and rx enough, why need to use two Rx?
2.I follow the python code into usrp.pick_rx_subdevice(u) and the return value is side and subdev. Since there are two rx there, how may I know subdev refer to rx or rx2?
3. if we call set_auto_tr(), it refer to which switch?

I also test usrp_fft.py and find both Tx/Rx and Rx2 have signal input (by using the same usrp_siggen.py), while input from Tx/Rx is stronger than Rx2. Since Tx/Rx is followed by a filter, it should be less than Rx2, so, what happens here?

I use two sets of USRP with RFX900 to test a FDD( frequency devision duplex) by cable connection. According to my experience, the cable loss should be less than 0.5-1 db, right? (which come with RFX900) So, If I set the same gain for two RFX900 tx, say -a 100, the received signal is much smaller than the coupled signal from itself, whatever the different frenquency is. So, why there are both input signal? it is coupled signal or intentionally designed? I think it is intentional designed, and since the tx signal is routed to Rx2 directly, so it is much stronger than come from its peer end, is it right?

Thanks for your reply!


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