Watch the presentation here: https://www.youtube.com/watch?v=MefojjQ84YY
Farhan made it to FDIM 2026 (he must hold the "distance travelled" record!). We thought he might be talking about the latest version of the digital SDR sBITX, but NO! Farhan talked about the entirely analog LARCSet, a 30 dollar SSB/CW monobander. And in the process he shared a lot of good homebrew history and wisdom. I took notes on the video of his presentation:
-- Farhan recounts his discussion with Steve Hartley, President of GQRP. Farhan said he started to talk about SDR projects, but Steve steered him away from all that. Farhan said he realized that the homes of GQRP members are often small, and projects need to fit into took boxes that are pulled out as needed. There is often not even enough room to mount a screen. Analog rigs just fit better.
-- Farhan talked about the beauty of analog. He also shared some info on the recent timeline of analog rigs, going back to 1976 with the IARU gift kits made available by W1VD. Farhan very kindly mentioned the DC receiver that Dean and I are promoting. He talked about the 2003 BITX 20 rig, and the subsequent uBITX. Farhan talked about the cleanliness of all-analog rigs. "SDR's are a mess!" he said. "With SDRs it is difficult to avoid hash."
-- Farhan said he had trouble measuring the phase noise of the VFO in the LARCSet. He consulted with Wes W7ZOI. Wes told him this was NOT a measurement problem; VFOs have almost no phase noise. The level is even lower than that of crystal oscillators. Of course, crystal oscillators are more stable, but they also have more phase noise.
-- He noted that almost no recent homebrew design does not rely on an Si5351. This, he said, is "not a healthy situation." Indeed.
-- Farhan talked a bit about how Indian regulations seemingly require a deviation from the completly open source ethos. Indian regs require companies to have assets. So the PC board layouts have to remain proprietary.
-- Farhan talked about the sharpness and shape of the BP filter in the LARCSet. I remember talking to him about the shape of my BP filters in my dual banders -- I had to rebuild the filters.
-- On the crystal filters that form the heart of SSB rigs, Farhan noted that cheap low Q crystals often introduce a lot of loss in the filters (that may explain my problem with some styles of computer crystals).
-- A member of the FDIM audience asked about the Sharpie written frequency readout on the LARCset that Farhan showed to the group. Farhan told them that this was the only frequency readout used in the rig.
-- With the LARCSet, Farhan used varactors to vary the frequency. But the varactors he used were cheap but horrible. They varied the frequency as the rig hearted up. The LM386 was the source of heat. He also noted that the cheap varactors, while cheap, did not provide linear frequency readout. Farhan said the varactor scheme was still not perfect; he offered a PTO solution that could be used instead. Three cheers for the PTO!
-- Farhan said the LARCset was really an SSB rig, but when coming to FDIM he said he felt obligated to present a rig that included CW, "or they would throw me out of the room." Farhan described a scheme to generate CW based on what was done with the Atlas rigs.
-- Farhan said the LARCset might even work on 2 Meters. Hmmm.
-- On tuning, Farhan said he used a very large tuning dial (he said it was like a steering wheel) and then recommended the use of a smaller control that could serve as an SSB "clarifier."
-- Farhan pointed out that homebrew rigs are never really done; even decades later, they can still be modified.
Watch the presentation here: https://www.youtube.com/watch?v=MefojjQ84YY
BRAVO FARHAN!
ReplyDeleteFarhan's great talk on that 5W transceiver! Fully agree with you on your points about analog, and clean signals. Maybe not quite as stable as something that is "rock-bound" in some fashion, but the spectrum analysis speaks for itself. Who cares if it doesn't hold within 2 Hz over an hour....at least it won't create hash and interfere with other services.
He has a good point about the Si5351. I am quite familiar with the chip, its registers, all that. For me, there is too much abstraction going on. It is a little black box that "does all this good stuff for you", but deprives the homebrewer of understanding what is going on deep inside it, only block diagrams.
I agree - great talk by Farhan, but as ususal it sparks ideas and things to discuss. First - there is a Chinese drop-in replacement for an SI-5351, the MS5351M which I believe Hans started using for his kits during Covid. Second, while an SI5351 is a complex device it is no more difficult to understand than many of the things we build. Phase locked loop circuits, voltage dividers, voltage controlled oscillators. For any of us who do much of this stuff regularly (even like me who are no EE's or formally trained) they are not "mysterious little black boxes". Ask your favorite AI tutor to explain the internal architecture of an SI5351. I don't find it any more difficult conceptually than how a transistor works internally - and I can't build one of those either. Part of where I'm coming from is my experience in AI and frustration with people saying "nobody knows how it works." That's nonsense, we know exactly how it works and we can trace every decision if we choose to put the resources in. Its difficult and complex, but not unknowable. Anyway, kudos to Farhan for putting stuff out into the work and giving us circuits to learn from and play with.
ReplyDeleteLet me clear this up. My point is about the level of abstraction. The internal workings are given with enough detail for anyone to apply the part. It's very easy to apply, one of the easiest synthesizers to program and use. I didn't call it "mysterious"!! The manufacturers(s) give plenty of applications information, they didn't give enough information to say you know exactly, precisely how it works, because you don't need to know that.
ReplyDeleteMaybe Farhan's comment was directed to the issue of "solving the problem the same way, every time, with the same tool". From the talk, he is not just demonstrating the LARKset; He is actively trying to encourage creativity!
The freedom we have in homebrew amateur radio allows us to create our own solutions for our applications, and they don't have to all be the same.