# Is a unipolar signal bad as an input for a USRP receiver?

**URL:** <https://www.ruby-forum.com/t/is-a-unipolar-signal-bad-as-an-input-for-a-usrp-receiver/242563>\
**Category:** GNU Radio\
**Created:** [July 2, 2015, 5:04pm UTC](https://www.ruby-forum.com/t/is-a-unipolar-signal-bad-as-an-input-for-a-usrp-receiver/242563 "2015-07-02T17:04:53Z")\
**Posts on this page:** 3\
**Page:** 1

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**Author:** ![musicdenotation](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/m/ea666f/32.png) [@musicdenotation](https://www.ruby-forum.com/u/musicdenotation)\
**Post date:** [July 2, 2015, 5:04pm UTC](https://www.ruby-forum.com/t/is-a-unipolar-signal-bad-as-an-input-for-a-usrp-receiver/242563/1 "2015-07-02T17:04:53Z")

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I am using LFTX and LFRX to transmit and receive data between two nodes.

I am modulating a bit stream with on-off keying (OOK) in which bit 1 is  
modulated into HIGH voltage and bit 0 is modulated into LOW voltage  
close  
to zero.

What I concern is, USRP can process bipolar signal, has a low noise  
amplifier (LNA) and an ADC at the receiving end. I’ve heard that LNA and  
ADC take a heavy stress if they process a unipolar, a DC biased signal.I  
want the statement to be clear. I have a particular condition that I  
can’t  
make a transmitted signal a bipolar NRZ signal instead of OOK…

PS. I make a thread in discuss-gnuradio since I’ve got no reply on  
USRP-users several days or weeks ago (I don’t remember exactly…).

Regards,  
Jeon.

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**Author:** ![Jeon](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/j/e8c25b/32.png) [@Jeon](https://www.ruby-forum.com/u/Jeon)\
**Post date:** [July 2, 2015, 5:28pm UTC](https://www.ruby-forum.com/t/is-a-unipolar-signal-bad-as-an-input-for-a-usrp-receiver/242563/2 "2015-07-02T17:28:16Z")

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Hi Jeon,

> What I concern is, USRP can process bipolar signal, has a low noise  
> amplifier (LNA) and an ADC at the receiving end.  
> That’s not true. The USRP motherboard itself doesn’t have an amplifier;  
> amplifiers are, if they exist, on the daughterboards.  
> The LFRX doesn’t have an LNA – it just has an OpAmp configured as a  
> voltage follower.  
> I’ve heard that LNA and ADC take a heavy stress if they process a  
> unipolar, a DC biased signal  
> The ADC doesn’t mind static signals (in fact, signals are always  
> presented to the ADC as differential), and the OpAmp is speced to  
> withstand any signal within its input range. So you don’t have to worry  
> 🙂

NRZ might be a good idea for other reasons, but these depend solely on  
your application.

Best regards,  
Marcus

PS: I’ll try to locate your thread on usrp-users. Normally we strive to  
not miss anything on that mailing list.

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**Author:** ![Jeon](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/j/e8c25b/32.png) [@Jeon](https://www.ruby-forum.com/u/Jeon)\
**Post date:** [July 2, 2015, 6:32pm UTC](https://www.ruby-forum.com/t/is-a-unipolar-signal-bad-as-an-input-for-a-usrp-receiver/242563/3 "2015-07-02T18:32:32Z")

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Dear Marcus.

Thank you for your answer.

Yes, I mean daughterboards, not USRP. I made an expression too short 🙂

And I am happy to hear that I don’t need to worry about what I’ve been  
concerning.

Regards,  
Jeon.

2015-07-03 0:27 GMT+09:00 Marcus Müller [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid):