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Re: [Discuss-gnuradio] UHD disable receive

From: Josh Blum
Subject: Re: [Discuss-gnuradio] UHD disable receive
Date: Wed, 20 Apr 2011 16:01:57 -0700
User-agent: Mozilla/5.0 (X11; U; Linux x86_64; en-US; rv: Gecko/20110223 Lightning/1.0b2 Thunderbird/3.1.8

On 04/20/2011 03:24 PM, Feng Andrew Ge wrote:
> Josh,
> Thanks for the clarification.
> Does it mean that, by this hacked code, turning off RX mixer at
> transmitting time happens on FPGA?  Or does it happen at UHD on the host
> side?

In this case the mixer is controlled by FPGA GPIOs that automatically
change state when the streaming mode in the FPGA changes state (RX only,
TX only, full duplex). The effect is instantaneous with some small lag
time for the mixer.


> Andrew
> On 04/20/2011 06:15 PM, Josh Blum wrote:
>> On 04/20/2011 03:03 PM, Feng Andrew Ge wrote:
>>> Josh,
>>> When you say " In any case, you can shutoff the rx mixer in full duplex
>>> mode with this little change:", is it true that this radio, once started
>>> with the changed code, cannot receive anymore at it runtime?
>> No: When, and only when, the device is simultaneously transmitting _and_
>> receiving (full duplex mode); the change will cause the rx mixer to be
>> turned off. This effectively feeds noise into the ADC.
>> So if you are always receiving, the mixer will only turn off when you
>> pass samples into the usrp sink block (which causes a transmission to
>> occur). Once all samples have been transmitted, the mixer will come
>> back on.
>> The change is a "quick hack" and is not the recommended way to do things.
>> -Josh

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