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>
*Sent:* Monday, April 10, 2023 10:22 PM
*To:* Shenk, Trey E <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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