On 10/23/2020 03:29 PM, Jon Beniston wrote:
Hi Marcus,
It seems to make a difference if set_tx_bandwidth is called before or
after get_tx_stream.
In the example programs, they all seem to do it before, however, it
appears to work better afterwards. Please see the attached two
programmes, which are basically just your tx_samples_c program, except
I've added in calls to set_tx_bandwidth and set samples to 0.
I run with the args: -f 868300000 -g 89 -r 6000000
For lo_leakage_pre.c where bandwidth is set before get_tx_stream,
carrier is at -1dBm. For lo_leakage_post.c, where bandwidth is set to
56M before get_tx_stream, then 6M afterwards, carrier is at -30dBm.
Yup, so the default behavior in UHD for B2xx is to set the analog bandwidth
to be commensurate with sample-rate, and that is done inside the
parts of UHD that set sample rate--sample-rate setting is done before
you create a stream.
So a set-bandwidth call will only have an effect *after* the sample-rates
are
established.
Sorry, but I don't follow. The order in the example programs is:
set_tx_rate
set_tx_freq
set_tx_bandwidth
get_tx_stream
So bandwidth is set after tx_rate, but before getting the tx_stream.
However, this seems to result in large LO leakage on my B210.
What seems to work better, is:
set_tx_rate
set_tx_freq
set_tx_bandwidth(56e6)
get_tx_stream
set_tx_bandwidth(desired)
Does that make sense to you?
The software I'm working on should ideally work with any USRP device, so how
can it be written to support all devices?
Thanks,
Jon
There is likely some "setup" stuff done to the AD9361 chip during stream
creation, because the chip needs to know about the stream parameters
it would not surprise me to find that there's some filter-setting
done during stream creation.
Calls like set_bandwidth, set_gain, set_frequency can all be done after
the stream is created, so your ordering should work on any USRP device--
although I'll point out that there are significant swaths of the USRP
universe where set_bandwidth does nothing.
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