|From:||Anderson, Douglas J.|
|Subject:||Re: [Discuss-gnuradio] gr-uhd: rx_freq tag and lo_locked|
|Date:||Tue, 31 Mar 2015 21:25:30 +0000|
That makes sense, I hadn't thought of the DSP tuning issue, though I think it would be infinitely more useful to make the stream tagging logic aware of LO/DSP tuning and tag the first usable block in either case. Slightly more involved than I assumed though.
I was actually going to ask this on the Ettus list later but since you brought up DC offset: is there a technical reason that there is no uhd_rx_dc_offset cal script? Is is because the LO can be offset so it's considered unnecessary or would a cal script not work as well for the RX side as it does the TX side for some reason? I read through the tx_dc_offset cal script last week and was curious...
From: discuss-gnuradio-bounces+address@hidden [discuss-gnuradio-bounces+address@hidden on behalf of Marcus Müller address@hidden
Sent: Tuesday, March 31, 2015 2:15 PM
Subject: Re: [Discuss-gnuradio] gr-uhd: rx_freq tag and lo_locked
the rationale behind that is that these tags correspond to the stream metadata coming from the USRP, which tell the host when the tuning *operation* has taken place. Now, you're right, it's a problem to think you're tuned although your LO still hasn't settled, but since tunes could also be digital-path only, using the "earliest" time seems correct.
By the way, you might also want to try a different approach, based on timed commands: you can set a time for things like tune requests, thus making sure that the tuning happens at the exact point in time you want it to (and not influenced by the latency and load of your general purpose PC). You can then simply "take" the right samples without caring about tags at all, because you know when these should occur (i.e. which numbers these should have).
PS: try turning off the DC offset correction, if you're on the N210, for fast-tuning applications. You'll have a bigger DC offset, but less "swinging" after each tune.
PS2: I don't know whether your overall frequency range allows this, but as long as you tune within your USRP/daughterboards physical bandwidth, you might just tune digitally and avoid LO retuning:
On 03/31/2015 09:54 PM, Anderson, Douglas J. wrote:
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