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posted by Fnord666 on Monday July 08 2019, @03:11PM   Printer-friendly
from the does-it-take-10-minutes-to-warm-up? dept.

Antique radio receivers retain a significant charm, and though they do not carry huge value today they were often extremely high quality items that would have represented a significant investment for their original owners. This guy acquired just such a radio, a Philco 37-11 made in 1937, and since it was it[sic] a bit of a state he set about giving it some updated electronics. Stripping away the original electronics, he gave it a modern amplifier with Bluetooth capabilities, and a Raspberry Pi.

One of the coolest applications for a Pi I've seen.


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  • (Score: 2) by Knowledge Troll on Tuesday July 09 2019, @04:57PM (3 children)

    by Knowledge Troll (5948) on Tuesday July 09 2019, @04:57PM (#865051) Homepage Journal

    the noise blanker processes the signal chain after the spectrum/waterfall, so turning it on in a high noise environment (of which I am the not-very-happy subject of) does absolutely nothing to clear up the display.

    Hrm I'm sure they put the noise blanker on the demodulated audio so I'm not surprised it is after the waterfall on the 7610. The 7610 is a weird radio for being SDR - it's SDR architecture used to implement the traditional ham radio with out really treating it as SDR. I'm curious though what kind of noise blanking you use for the wideband signal. How does your blanker work?

    I don't have a lot of noise issues but i did need to spend some time tweaking the waterfall configuration to get it to generate graphs I could read well on all bands with the varying noise floor. I don't usually have to do something like run a noise blanker and the noise remover doesn't help either. Being able to noise remove the waterfall though is a great feature!

    Icom did miss the memo about SDR in a lot of ways. I'm sure if I could have waited longer to get an SDR rig I'd have something a lot more SDR like available to me in a few years. There is a new HF and VHF SDR ham radio that just became available which is just a windows computer in a box with knobs and a display and a full screen touch interface for the radio UI, which you can then minimize and open up the start menu and launch fldigi or what ever. I don't want something integrated like that but for the average ham I bet they got the right idea. These are neat times for radios!

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  • (Score: 2) by fyngyrz on Tuesday July 09 2019, @06:25PM (2 children)

    by fyngyrz (6567) on Tuesday July 09 2019, @06:25PM (#865091) Journal

    Hrm I'm sure they put the noise blanker on the demodulated audio

    No, it's definitely an RF blanker; you can tell because in a noisy environment, with the blanker on, the AGC turns the RF gain up. If they were only reducing audio noise, they couldn't control the RF levels with it effectively. So the blanker is reducing the peak RF, which in turn causes the AGC to pump more gently.

    What they're probably doing is running the blanker on the RF that's already been bandwidth-limited, just before the demodulator in the signal chain. What that buys you is a much lower bandwidth sample to process, basically a lot less data to look at. IMHO, there's enough CPU and/or FPGA horsepower available at this point to forgo that kind of savings. My software, which does full wideband blanking while doing a whole lot more as well, can run without problems on an old-dual core. Just barely, but it will run. You can't do anything else, though...

    I'm curious though what kind of noise blanking you use for the wideband signal. How does your blanker work?

    I take large samples of the baseband RF after it's been downsampled, examine it for spikes, and then remove them, while replacing the removed interval with a splined interpolation between the level just before the spike and the level just after the spike, using enough samples on both sides to set the spline curve up so the interpolation is somewhat sane. Then I pass the baseband RF block up the signal chain. You have control over the width and the depth of what is considered a spike. Once the spikes are removed, it is passed along to the demodulator, scope and spectrum/waterfall signal chains.

    You can also switch to the spectrum/waterfall being taken prior to the noise blanker; I did this mainly to demonstrate why you pretty much always want it after. 😊

    There are exceptions, to be sure — strong noise blanking on baseband RF can cause distortion in the wideband signal and leave you with some visual artifacts, but generally speaking, you do want it after the blanker.

    the noise remover doesn't help either.

    Yeah, so far, correlated noise removal tech — which is what Icom uses — is pretty sad. The more you remove, the worse the audio gets, and at least in the 7300, the quieter it gets, so I have to turn up the gain too. I went a different way in SdrDx, but it also has its drawbacks. I create a spectrum of the noise which, when it actually is noise, is generally pretty flat. I call this condition balanced. Then, when the spectrum becomes unbalanced, meaning that there is more on one side of it than the other, the implication is usually that there is audio in it where the audio frequencies are dominating. The balanced / unbalanced condition is used to modulate the audio gain, and it's really pretty good — no distortion at all — when there's actually audio. You have control over attack, decay, and depth of gain variation.

    However, when the signal is really just noise, it tends to pump now and then when the spectrum contains a stronger spike of one frequency or other. Makes for little noise pulses. Nothing's perfect, I guess. I've been thinking about using a correlated noise remover to generate the gate/nogate signal on a slightly (maybe 20ms) delayed audio stream so it can trigger ahead of the audio start, rather than using the correlated product as the audio. It's on my list to try. Might be pretty good.

    Being able to noise remove the waterfall though is a great feature!

    I just hate it when I don't have it. I am always looking at the waterfall and spectrum. There's only one direction I can point my beam or orient my wideband loop to reject all the crapola around here. When I'm looking off that way, everything is great. Any other direction... bah. Fortunately (or it would be fortunately if the sunspots weren't gone) that direction is right over the pole towards Europe. I guess it won't matter for the next 5-10 years... or longer. Europe is simply not reaching Montana. Not even the big SW blowtorches, much less some poor ham with 100 watts. Or even a kW.

    I do lots of signal processing specifically in the spectrum / waterfall chain designed to make the waterfall clearer, easier to read, etc. It's all switchable, of course... sometimes you just want to see what's there without any fooling with it. But the convenience of auto removal of lightning strikes (which would otherwise create great bands of noise in the waterfall), control over the amplitude of the noise floor separate from the amplitude of the signals... these kinds of visual amenities are really nice. Might be hard to imagine until you see them at work, but... nice. I should make some more Youtube videos, I guess.

    These are neat times for radios!

    Oh yeah. What's sad is this didn't happen before a lot of the SW stations went off the air and the solar minimum arrived like a ton of bricks.

    --
    Having cats is like having living art.
    That randomly throws up on the floor.

    • (Score: 2) by Knowledge Troll on Tuesday July 09 2019, @09:06PM (1 child)

      by Knowledge Troll (5948) on Tuesday July 09 2019, @09:06PM (#865152) Homepage Journal

      I take large samples of the baseband RF after it's been downsampled, examine it for spikes, and then remove them, while replacing the removed interval with a splined interpolation between the level just before the spike and the level just after the spike, using enough samples on both sides to set the spline curve up so the interpolation is somewhat sane.

      Damn that is very cool. I would love to try something like that as an audio soft clipper. it sounds like the performance would be really good for transients which are a frequent headache.

      Would you be interested in joining a chat system for a digital radio club? It's focused on getting fully qualified open source ham radio nerds together into one place in a way that's familiar for us. There's another guy there that does DSP professionally, a few competent programmers, and a couple power users / hobbiest programmers. It's a nice place to find people who have a clue to talk about topics exactly like your noise blanker. I know other people in there would go "that is really cool" and basically everyone in the club has big dreams of SDR. I can get you details outside of Soylent news if you like.

      • (Score: 2) by fyngyrz on Tuesday July 09 2019, @10:39PM

        by fyngyrz (6567) on Tuesday July 09 2019, @10:39PM (#865193) Journal

        Thanks for your kind words.

        You can contact me by going to section 39 [ourtimelines.com] on that page. Edit your subject accordingly.

        Might be fun to lurk a bit in your group. 😊

        --
        I had the house child-proofed. But they must
        have done it wrong. Kids still get in somehow.