# About gr\_buffer\_add\_reader

**URL:** <https://www.ruby-forum.com/t/about-gr-buffer-add-reader/207332>\
**Category:** GNU Radio\
**Created:** [May 24, 2011, 7:27am UTC](https://www.ruby-forum.com/t/about-gr-buffer-add-reader/207332 "2011-05-24T07:27:40Z")\
**Posts on this page:** 2\
**Page:** 1

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**Author:** ![luislavena](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/l/0ea827/32.png) [@luislavena](https://www.ruby-forum.com/u/luislavena)\
**Post date:** [May 24, 2011, 7:27am UTC](https://www.ruby-forum.com/t/about-gr-buffer-add-reader/207332/1 "2011-05-24T07:27:40Z")

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Hi list,

I have a USRP N210, running on Ubuntu-10.04, when I try to use the  
Gnuradio-Companion to make a fm\_receiver,

I success generate the python code, but when i try to run it,

## it shows

## terminate called after throwing an instance of ‘std::invalid\_argument’ what(): gr\_buffer\_add\_reader: nzero\_preload must be \>= 0

what is that mean?

I know that I might have some problem in the flow graph or parameter  
because  
I use the old version example(USRP1) which I search on the internet as  
the  
reference, can any one help me?

PS I would like to ask an additional question: If I only have DBSRX  
RFX1200  
RFX1800 these three daughterboards, is that means I can’t receive the  
100MHz  
FM Radio Signal by my fm\_receiver through the USRP N210 (bandwidth not  
right)? or there is some other ways ?

thanks,

Eddie

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**Author:** ![Eddie\_Sun](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/e/ecc23a/32.png) [@Eddie\_Sun](https://www.ruby-forum.com/u/Eddie_Sun)\
**Post date:** [May 24, 2011, 1:58pm UTC](https://www.ruby-forum.com/t/about-gr-buffer-add-reader/207332/2 "2011-05-24T13:58:58Z")

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On 05/24/2011 01:26 AM, Eddie Sun wrote:

> what(): gr\_buffer\_add\_reader: nzero\_preload must be \>= 0

* * *

> what is that mean?  
> Not sure, would have to see your GRC flow-graph.

> PS I would like to ask an additional question: If I only have DBSRX  
> RFX1200 RFX1800 these three daughterboards, is that means I can’t  
> receive the 100MHz FM Radio Signal by my fm\_receiver through the USRP  
> N210 (bandwidth not right)? or there is some other ways ?
> 
> thanks,

The DBSRX covers about 800MHz to 2.3GHz, the RFX1200 covers 1.15GHz to  
1.45GHz, the RFX1800  
covers from 1.5GHz to 2.05GHz. I don’t see 100MHz anywhere in there.

If you want good coverage of the FM radio band (88MHz to 108MHz in North  
America), you would  
need a TV\_RX2 card or WBX card.