The spur spacing and amplitude aren't affected by the sample rate nor by
the baseband frequency.
I did discover that offsetting the LO from the desired carrier leads to
many spurs well away from the carrier. For example, a carrier at 175
MHz and an offset of +20 MHz gives spurs at 155 MHz, 195 MHz, 370 MHz.
The close-in spurs are present (same offset, same amplitude) when the LO
is not offset.
I suspect that the spurs are in fact artefacts from my spectrum
analyser. I'll find a way of looking at the signal some other way.
Thanks for your trouble.
Dave Abel
------ Original Message ------
From: "Marcus D. Leech" <[email protected]>
To: "DAVID ABEL" <[email protected]>
Sent: Wednesday, 1 Feb, 2023 At 5:33 AM
Subject: Re: [USRP-users] Re: B200mini spurs
On 31/01/2023 06:17, DAVID ABEL wrote:
Neither the spur amplitude (in dBc) nor the offset are affected by the
baseband amplitude nor by the carrier amplitude..
The AD9364 specs do include carrier leakage of -50 dBc. The offset
(through uhd.tune_request(freq, 15000000)) places this leakage well
away from the carrier. This trick is effective as removing the offset
shows up the leakage close to the carrier. I can't see anything in the
specs suggesting the spurs I am seeing.
Thanks
Dave Abel
The other thing to check is whether the sample rate affects the spurs
presence and spacing...
------ Original Message ------
From: "Marcus D. Leech" <[email protected]>
To: [email protected]
Sent: Monday, 30 Jan, 2023 At 2:38 PM
Subject: [USRP-users] Re: B200mini spurs
On 29/01/2023 22:26, DAVID ABEL wrote:
I have a B200mini. As a test of spectral purity, I generated a CW
signal at 175.0025 MHz using Gnuradio, I see spurs at +/- 132.5 kHz,
at -50 dBc; with offsets of 265 kHz at -60 dBc; and another at 702.5
Khzat -60 dBc.
Is this expected behavior for the B200 mini, please?
Some further detail: the Gnuradio flowgraph is a signal source
generating a sine waveform at 2500 Hz, followed by a lowpass filter.
The USRP sink has a frequency of 175 MHz with an LO offset of 15
MHz. Sample rate is 384 kHz. The spurs are present on other carrier
frequencies with the same offsets.
Thanks
Dave Abel VK1DJA
That's almost certainly "in spec" for the AD9363 chip that does all
the "heavy lifting" on the RF side of things.
Does the baseband amplitude affect your observed spur performance?
That is, if your signal source has an
amplitude that is somewhat-less than 1.0 (like 0.85) do the spurs
reduce correspondingly?
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