On 17/04/2023 20:22, David Bengtson wrote:
You've seen the filters from Pole-Zero, right? Tunable, but very
narrow BW. I keep reading abstracts in IEEE journals but I haven't
seen anything interesting. Sub-octave band counts add up fast :-(
Dave
I've seen various interesting bits of "physics experiment" over the
years, but nothing that screams "every radio should have
some of these". The Ettus/NI approach on some of the USRP radios is
to use a filter-bank of selectable OTS filters with overlapping
ranges with relatively large fractional bandwidths. This works for a
significant fraction of the applications out there, but
not all, obviously. "Some engineering required" as they say.
On Sun, Apr 16, 2023 at 9:36 PM Marcus D. Leech
<patchvonbr...@gmail.com> wrote:
On 16/04/2023 21:13, David Bengtson wrote:
Yes, it's pretty typical that the output of an SDR needs
additional filtering and gain on the transmit side, and similarly
filters and gain on the receive side. I spent a substantial
fraction of my time at a previous job designing application
specific front ends for Ettus SDR's.
Dave
In my other job, I do radio astronomy. "Filter early, filter
often" is what gets the job done in that domain. A many-octave
tunable filter with variable bandwidth would be a nice thing,
except for the ongoing miners strike at the
unobtanium mines...
On Wed, Apr 12, 2023 at 8:39 PM Marcus D. Leech
<patchvonbr...@gmail.com> wrote:
On 12/04/2023 20:28, Ron Economos wrote:
This is what I see with a B210 at 145 MHz fundamental. I had
the analyzer on a large RBW, so the even order harmonic are
buried in the analyzer noise.
I don't think there's any remedy except for external filters.
Ron
B210 harmonics
Thanks Ron. That looks like what my TinySA produced for
250Mhz carrier. I need to learn more about it so that I can
record spectra with it. There's a Linux app for it that I
need to explore....
Anyway, the basic issue, having consulted some older Analog
Devices forum posts is that the LO produces a square-wave
signal, which means that all the odd-order harmonics will
be present in it, and naturally, mix with the baseband.
There's nothing that can be done other than, as you point
out, filter. As you move up in frequency, this becomes
very much easier of course, and at 2GHz, the 3rd harmonic
is outside the supported passband of the AD9361, and
you won't see it.
I didn't realize this about the AD9361 chip, and other Ettus
devices have automatically switchable filters that can
(often, not always) remediate this issue. The E3xx series,
the N3xx series, the TwinRX cards for the X310 and friends.
But I'll point out again that "built for purpose" radios
nearly-always have output (input) filtering to reduce or
eliminate
unintended consequences of architecture choices deeper
within the radio. Since SDRs in general don't get to be
"built for purpose" either ever, or until some specific
application is using them as their "radio bits", it's hard to
come up
with a universal RF filtering scheme that is suitable for
all applications.
I'd never noticed this issue because I don't really ever TX
in my "day job" use of these devices (radio astronomy), and on
the RX side, I always pre-filter anyway, usually rather
aggressively.
On 4/12/23 16:20, Shenk, Trey E via USRP-users wrote:
The original signal that I showed was an unmodulated carrier.
I tried a 10kHz complex exponential (plots included for
several harmonics). The carrier is clearly visible at all
frequencies. I can see copies of the 10kHz tone on odd
multiples of the carrier, but not on the even multiples.
*From:* Marcus D. Leech <patchvonbr...@gmail.com>
<mailto:patchvonbr...@gmail.com>
*Sent:* Monday, April 10, 2023 10:22 PM
*To:* Shenk, Trey E <trey.sh...@pnnl.gov>
<mailto:trey.sh...@pnnl.gov>
*Cc:* USRP-users@lists.ettus.com
*Subject:* Re: [USRP-users] Harmonic Distortion with B205mini
On 10/04/2023 14:28, Shenk, Trey E wrote:
I first tried turning the gain down. What I saw was
that the even harmonics (2*fundamental, …) did not
change power, and the odd harmonics decreased by the
same amount as the fundamental. This means that the dBc
for the odd harmonics stayed the same with decreasing gain.
Decreasing the baseband amplitude had the exact same
effect. Even harmonics stayed at the same power level,
odd harmonics decreased while maintaining dBc.
What is the nature of the modulating signal?
If you use an example app like "tx_waveforms" with, let's
say, 10kHz SIN signal, what are the harmonic results?
*From:* Marcus D Leech <patchvonbr...@gmail.com>
<mailto:patchvonbr...@gmail.com>
*Sent:* Monday, April 10, 2023 8:39 AM
*To:* Shenk, Trey E <trey.sh...@pnnl.gov>
<mailto:trey.sh...@pnnl.gov>
*Cc:* USRP-users@lists.ettus.com
*Subject:* Re: [USRP-users] Harmonic Distortion with
B205mini
Check twice before you click! This email originated
from outside PNNL.
Turn down the RF gain a bit as well as the baseband
amplitude. Does this make any difference?
Sent from my iPhone
On Apr 10, 2023, at 9:41 AM, Shenk, Trey E via
USRP-users <usrp-users@lists.ettus.com> wrote:
I'm using a B205mini to transmit signals. When
transmitting, I can see copies of the SOI at
harmonics of the center frequency. I ran some
measurements of total harmonic distortion, and
found it to range from 39% with a 100MHz to 23%
with a 1GHz carrier. The second harmonic is
<-50dBc, but the third harmonic is usually around
-10dBc.
My main concern is for the lower frequency
carriers, like 100MHz, because multiple harmonics
will show up on a spectrum analyzer set to a
wideband. I've looked at putting an RF filter at
the output, but I need the system to be able to
switch transmit center frequencies in a range from
100MHz to 5GHz.
Is it possible to reduce the harmonics by some
hardware setting (driving with gnruadio)?
Thanks,
Trey
<carrier_freqsweep_fc0200M_gain55.png>
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