Hello Brian, I'll see if I can reproduce with my TwinRX. Please provide some more information to help me reproduce...
1. Center Frequency of fixed channel 0 2. Tuning range on channel 1 3. What tuning rate have you tried and what's the threshold between a clean spectrum and a bad one? 4. Please share screenshots of what you are seeing 5. Please share uhd_usrp_probe output so I know your serial, revision, uhd version, etc 6. Can you reproduce this problem when it's two channels on different daughterboards? In other words, ch 0 and ch 1 on the same TwinRX, and ch 0 and ch 1 across each DB slot. There's several switchable routes before and after each stage LO going across channels, so it's possible there are some isolation problems between channels. My first thought is also to remove LO sharing cables, but as you said, it doesn't improve. Maybe switching the switches that are not used might help give better isolation. From schematic, if channel 1 uses its own LO, then only switch 16 is needed, and switch 14 which routes LO 1 to the sister channel 2 isn't used. So I'm wondering if the state of switch 14 makes a difference in terms of isolation. I'd have to check the software to see if you can independently flip these switches, and if it's recommended, to test this hypothesis. I will also check internally if similar issue is reported and get back to you. Regards, Wan Liu On Tue, Oct 25, 2022 at 6:16 PM Brian Padalino <[email protected]> wrote: > I have an application where I am using both channels of the TwinRX without > using LO sharing. I am using channel 0 as a single frequency channel, and > I am using channel 1 to tune to different frequencies. > > I am noticing that some transients happen on channel 0 - the fixed > frequency channel - as I am changing channel 1. This happens with even > terminated inputs on both channels. I also notice that if I change the > rate at which I am changing channel 1, the spectrum, on average, is much > cleaner but the transients stay there from a "max hold" perspective. So > once the LO has settled, things don't seem to be as noisy. > > My setup does not install the LO sharing cables, so those MMCX connectors > are left floating/open. > > My question is if Ettus has seen this or knows about this? As I stated > previously, I don't need the LO sharing feature of the TwinRX and I am > worried that constantly retuning the PLLs might be causing the noise and > distributing it to the fixed frequency channel? If that is the case, are > there some resistors or modifications I might be able to make to the TwinRX > that could remove this as a source of noise knowing I never want to perform > the LO sharing? If I didn't connect the MMCX LO sharing ports, am I > already removing this as a possible noise source? > > Lastly, a thought is that the noise might be coming from digital switching > noise to reprogram the LOs. How feasible is this? > > Thanks, > Brian > _______________________________________________ > USRP-users mailing list -- [email protected] > To unsubscribe send an email to [email protected] >
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