Hi Urban, In case there's a misunderstanding here: The X410 does real sampling at an IF, i.e., *not* direct sampling. Maybe you're thinking of the X440? If you're using the X440, then you definitely need good filters.
On the X310, there's also the option to do direct sampling with the BasicRX or LFRX boards. There, too, you need prefiltering, but you remove a lot of complexity from the analog frontends (but there's no gain available, so maybe you want to add prefiltering + some amps). --M On Tue, Jun 30, 2026 at 6:35 PM Marcus D. Leech <[email protected]> wrote: > On 2026-06-30 12:07, Urban Hakansson wrote: > > Hello usrp-users community, > I am evaluating hardware options for a project operating across the HF > band (specifically 1–30 MHz). We are deciding between adapting an X300/X310 > with a UBX daughterboard or stepping up to the USRP X410. > While we know the X410 covers this range natively, its 4 TX/RX channels > are more than our project requires. We are trying to determine if the > X410's lower frequency floor provides a massive real-world performance leap > over a filtered UBX system for a 1-channel or 2-channel deployment. > I have been reviewing the Ettus KB application note: "Experiments with the > UBX Daughterboard in the HF Band." The document shows that with careful > flow-graph design and external pre-filtering, the UBX delivers quite good > HF performance despite its nominal 10 MHz limit. > I have a few questions for anyone who has pushed the UBX into the HF band > or compared it to the X410: > > 1. Pre-Filtering Selection: The KB note mentions an FM-trap and 3-pole > LP filters but does not name specific parts. I am looking at Mini-Circuits > components to build this front-end filter chain. Has anyone successfully > deployed specific Mini-Circuits part numbers for this exact UBX setup? > Examples: Mini‑Circuits VLF‑45+, Mini‑Circuits NSBP‑108+, > Mini‑Circuits ZX75LP‑50+. > > I'm the guy who wrote that app-note, years and years ago now. I can't > remember which pre-filters I used, and they weren't mini-circuits, but I'm > sure they have > close to what you need. For the FM-trap, I used a consumer > part--typical in the CATV/SATTV market--literally available on Amazon last > time I checked. If you search > on "FM bandstop" you'll find several examples. > > > 1. > 2. Unpublished Performance Data: Does anyone have characterization > figures, noise floor comparisons, or empirical data regarding UBX > performance specifically between 1–10 MHz when bypassing/working around the > LO constraints? > > I didn't gather any detailed performance data at the time. Noise figure > won't be horrible, but I'll point out that for over-the-air operations in > most of HF, you aren't > limited by receiver noise, but rather galactic background noise, which > can, at the lower end, be equivalent to about 50,000-100,000K---MUCH larger > than you'll > find in the front-end of ANY modern receiver. > > > 1. > 2. UBX vs. X410 Direct Sampling: In practical HF deployment, how much > dynamic range or noise figure advantage does the X410’s direct-sampling > architecture buy you over a UBX using DDC workarounds and aggressive > external filtering? > > This I don't know. It certainly is the case that for HF over-the-air > operations, high dynamic range is a requirement, because you can have very > loud signals right at > the edge of your passband. I'll note that the receive-path ADC is > 14-bits on an X310, whereas on the X410, it's only 12-bits. This lowers > your dynamic range by > about 12dB, typically. I don't have access to the schematics right now, > so I don't recall whether there are any pre-amps in front of the ADCs on > the X410. If NOT, then > you'd need some gain ahead of the on the X410 to compensate for the poor > noise figure of a naked ADC. > > > > Any insights, test results, or design pitfalls you can share regarding HF > performance on these two platforms would be highly appreciated. > Best regards > > Urban Hakansson > > Principal DSP / Communications System Engineer Saltenna Inc. > M: 410-980-4577, E: [email protected] W: www.saltenna.com > [image: image.png] > > _______________________________________________ > USRP-users mailing list -- [email protected] > To unsubscribe send an email to [email protected] > > > _______________________________________________ > USRP-users mailing list -- [email protected] > To unsubscribe send an email to [email protected] >
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