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Re: [Discuss-gnuradio] Transmitting bursts with GRC by inserting SOB and

From: Frederik Wing
Subject: Re: [Discuss-gnuradio] Transmitting bursts with GRC by inserting SOB and EOB
Date: Tue, 21 Oct 2014 14:56:17 +0200
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:31.0) Gecko/20100101 Thunderbird/31.2.0

- You're using an ancient UHD version. Is there a reason you can't
>>>>use a
>>>>newer one?
>>>I am using Ubuntu 14.04 LTS and just pulled GNU Radio and UHD from the
>>>packet sources. There is no newer version available. And I don't
>>>like to
>>>compile myself unless it is absolutely necessary.
>>Consider it outdated. Ubuntu's packet sources are most of the time
>>horribly out of pace compared to GNU Radio's development process.
>>For UHD it's the same. Note that Ettus ships its own Ubuntu packages
>>for UHD*and*  GNU Radio, so you can get a non-ancient version of both
>>without even compiling it.
>>By the way: GNU Radio is a software radio developer's framework. You
>>can do great things with it without touching a compiler, but at many
>>points it becomes helpful when one can write his own C++ block, so
>>you definitely need to lose your fear of compilers if you want to use
>>GNU Radio to its fullest potential:)
>After some hours of compiling time I could finally update GNU Radio to
>version 3.7.6 and UHD to 003.008.
>>>I don't think it's because of an outdated version of UHD as the
>>>"tags_demo" application is working perfectly with my current version.
>>... Well, my old tube radio also still works;)
>Unfortunately, even with the newest version the USRP is still
>transmitting its carrier over the air. I tried both with the Message
>Burst Source as well as with the Stream to Tagged Stream Block
>combined with setting a Length Tag name in the USRP Sink. With the Tag
>Debug Block I see tx_sob+tx_eob and the Length Tag, respectively. They
>all seem to be at the right place and have the right value.
:(  ok, so we see something that looks like significant LO leakage.

You can use offset tuning, by specifying a tune request instead of
simply a target frequency f_t. By doing so, you instruct the USRP to
tune the oscillator of the daughterboard to some frequency f_LO, and let
the FPGA shift the resulting signal to baseband by a second frequency
f_FPGA, so that f_LO+f_FPGA = f_t.

You thereby would move the LO leakage out of your desired signal. Would
that help you?

Thanks for this suggestion. It would be a workaround to the actual problem. And if there is no other way I have to do so.

I cannot believe that there is no solution to it since the "tags_demo" application shows that it is indeed possible. :-/


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