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Re: [Discuss-gnuradio] Simple WBFM Transmitter - How to configure the US

From: Tom Rondeau
Subject: Re: [Discuss-gnuradio] Simple WBFM Transmitter - How to configure the USRP1 block to transmit ?
Date: Thu, 1 Aug 2013 10:34:21 -0400

On Tue, Jul 30, 2013 at 10:35 PM, Bruno Cardoso <address@hidden> wrote:
> Hi Tom,
> I tried to follow your tips but the FM transmitter is not working yet. Here
> is the file:  WBFM_transmitter_Bruno2.grc
> <http://gnuradio.4.n7.nabble.com/file/n42845/WBFM_transmitter_Bruno2.grc>
> I'm matching the sample rates all the way through my flowgraph.
> I'm also using the USRP1 through the ¨UHD: USRP Sink¨ block with a 250k
> sample rate, which is a rate that's supported both by N2XX family and
> USRP1/B100 family.
> There is something missing yet.
> Thanks for your help.
> Bruno


1. You don't need a throttle block. A throttle is only necessary when
running without any hardware. You have both an audio sink (running at
44.1 kHz) and a USRP sink (running at 250 kHz). These are your
rate-limiting blocks and the throttle is just getting in the way.

2. You are massively overloading the signal into the USRP sink. That
signal level should be +/- 1 at the very most. But you'll want to back
off from that for linearity reasons. Instead of setting the gain of
the LPF to 40, create a slider for that that goes from 0 - 1 with 100
steps. Default it to 0.5. The signal looked very clean that way.

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