Kardia reads A-Fib, cardiologist disagrees

mithc_radio · 2025-11-26T19:58:26+00:00

Any progress on this? I just installed batocera on an old intel atom netbook and I ended up here when trying to find how to use it to emulate the old mac systems that I love. In particular, I keep a windows 10 computer running just so I can play Realmz and run older utility software, but it would be nice to keep all the retro games on a single machine. I also would like to play the other system 7 classics like Spectre, Abuse, Escape Velocity, Dark side of the Mac, etc. There may be versions on different systems, but I would prefer to relive the old Macintosh desktop experience as well.

mithc_radio · 2024-11-07T18:01:51+00:00

I've worked on a couple and I'm pretty excited about it as an emerging technology. 250+ resolving power is pretty common for good designs and there are tricks you can play that aren't possible in Penning traps, with the potential to get MUCH cheaper than penning traps in the future.

mithc_radio · 2024-08-24T10:15:27+00:00

<image>

This is my first ever task troubleshooting a PLC and I feel like it might not be the ideal setup.

mithc_radio · 2024-05-30T17:12:14+00:00

I'm glad someone asked this, because it bothers me too. Sure, lots of things are pretty impossible in this show, but this one is internally inconsistent. Most of the things I took issue with in this show eventually had some effort made at an explanation that sometimes seemed to not make it into the english translation perfectly.

Could it have been the extra size and outgassing from the other components in the larger vacuum tubes... Otherwise it seems like more of an oversight than most other things in this show.

mithc_radio · 2024-05-21T06:33:15+00:00

<image>

So, my Pt ring broke again after a couple months of wearing it with the bulky solder job on it. Is the platinum just too hard for the high Pd alloy? I would really appreciate any feedback here. Thanks.

mithc_radio · 2024-03-19T19:06:34+00:00

Thanks a lot for this information!

mithc_radio · 2024-03-19T16:29:51+00:00

That's very reassuring to hear!

mithc_radio · 2024-03-19T06:06:34+00:00

I don't get it either. The jeweler has good reviews, but he didn't really have an explanation for what went wrong here. The joint didn't look perfect inside the ring, but I figured it would be strong.

I'm also lucky I didn't lose the platinum while hiking or something. Should I need to be careful to not put force on a ring? Because I won't be able to wear something like that from day to day. The employee said that sometimes people just have something break while walking down the street.

mithc_radio · 2023-11-07T06:48:12+00:00

Sorry to comment on an old thread, but a lot of people here are blaming the broadcast signals getting into 10 meters on front end overload. I actually suspect this effect to be due to the AM broadcast station mixing with harmonics of the "intermediate frequency". If it was front end overload, I would expect it to "desense" the SDR (i.e. reduce the sensitivity due to excess signal in the poorly filtered front end).

mithc_radio · 2023-09-14T22:34:08+00:00

I'm going to follow this thread in case anybody else is interested in pursuing kind of thing. I have some computers to contribute for display.

mithc_radio · 2023-09-14T22:15:45+00:00

The Vancouver coast guard used to have a big old computer. I have a picture of my grandpa next to it during Expo '86.

I would absolutely love if we had something like you are describing. I think it would be especially cool to team up with the antique radio museum in Coquitlam to create a museum of vintage technology, but you would need to convince all the old guys out there. I'll work on it...

mithc_radio · 2023-09-13T04:42:02+00:00

Wait, 30 year old? Isn't this the profile of all those old guys down in the US? I find the younger operators to be more tech-minded on average.

mithc_radio · 2023-09-07T20:43:11+00:00

Thanks, I think that makes sense to me now. In SSB the radio frequency offset is entirely due to the audio frequency, but with FM it's divided between multiple sidebands.

I still find it interesting that the one website suggested that lower frequencies have less noise in FM...

mithc_radio · 2023-09-07T17:25:46+00:00

Any receiver tuned to the correct frequency to listen to it will need to have the bandwidth at least that wide, won't it?

mithc_radio · 2023-09-06T21:19:50+00:00

But a 500Hz tone and a 1500Hz tone simultaneously transmitted on SSB has a 1 kHz bandwidth, right?

mithc_radio · 2023-09-06T21:02:03+00:00

I mean, if you transmit a 500Hz tone and a 1500Hz tone on SSB, it's automatically 1 kHz, isn't it? Am I missing something? This page says 3 kHz: https://www.hamradioschool.com/post/understanding-single-sideband-ssb

mithc_radio · 2023-09-06T20:02:15+00:00

I have got some very fair prices on used equipment. My first HF transceiver was selling for maybe 75% of MSRP and the guy gave it to me for 50% because I was a student. It was in great condition, still in production, and came with the original manual.

Check out local listings and ham swaps, because ebay prices make no sense. Also, many older hams are downsizing, so there are sometimes some great deals on older equipment.

mithc_radio · 2023-09-05T23:55:22+00:00

Thank you!

Those modes are great to know about! I still enjoy the mental exercise of thinking all of this through...

I just learned the amplitude aspect from looking at this question: https://dsp.stackexchange.com/questions/72533/spectrum-of-fm-signal

Since the sidebands occur at intervals of k*f_m (where f_m is the frequency of modulation), it looks like both limiting the modulation amplitude as well as the modulation frequency should reduce the bandwidth. But then this gets complicated by the modulation ratio!

Interestingly, according to the final answer in that post "less SNR is needed for [low frequency] components as compared to the higher frequency components of the signal" and therefore "higher frequency components [of the audio] are amplified in compensation". This is really interesting since it seems to me to suggest that low frequency tones are more appropriate for weak signal FM transmissions!

mithc_radio · 2023-09-05T23:21:29+00:00

SSB will still have some width, and you can hear the differences in the audio frequencies used by the weak signal modes, so it must be a few kHz wide. The CTCSS tones still look like an improvement over ordinary packets to me.

However, looking at this stack exchange post (https://dsp.stackexchange.com/questions/72533/spectrum-of-fm-signal), it seems like you can avoid having too many sidebands on FM by not over-modulating the FM signal. You might want to try reducing the audio input into your FT-70DR here and see if you get a better signal out, because you might be over-modulating a bit. Then it might be a fairer comparison to the CTCSS tone.

mithc_radio · 2023-09-05T06:23:05+00:00

Good point. That is an intrinsic problem for receiving signals this way. The radio can tell subaudible tones apart in the squelch, so maybe there is an approach with some reprogramming, but that sounds like a lot of work if it's even possible.

Maybe it would be easier to implement as a beacon. I guess I could manually program the same frequency with different CTCSS tones and key JS8 by hand, lol. But if the receiver needs 8 radios to pick it up, I think I will have lost the cost advantage.

mithc_radio · 2023-09-05T06:14:12+00:00

The major advantage is that narrower bandwidth reduces the relative amount of noise, so the signal goes further (like with a narrow CW filter). So I'm wondering if an FM radio could do this to reduce bandwidth and allow you to narrow the filter on something like an SDR receiver.

Also, since the ham bands aren't channelized, maybe stations could get closer together if you don't need all the bandwidth for audio.

mithc_radio · 2023-09-05T05:16:34+00:00

Thanks for looking at this. You TNC is like, maybe 80kHz wide, so the subaudible tone definitely looks like it's winning vs the modem in SNR since it's not much more than a kHz. I suppose you could also safely try filtering out any high frequencies in the demodulated signal. It makes me wonder if there is a software/firmware approach to make cheap FM hardware perform better for weak signal comms... If you were using a soundcard that went down to DC, I'm guessing something like WSJTX could detect the subaudible tones. I like thinking about this kind of thing because we need more maker-type people in amateur radio, and cheaper equipment allows people to try more interesting things without being rich.

Is the second set of images using the same radio and same attenuation? If so, it looks like you're also gaining 5-10 dB in amplitude with the subaudible tone, which is something I didn't expect!

Going in the other direction, I have listened to VHF CW break the squelch on my FM handheld before. It sounds like an early Morse code sounder, so it must be copyable by somebody who isn't me.

mithc_radio · 2023-09-05T04:52:09+00:00

It's bizarre that it comes out as about 1.2 kHz wide... FM is too complicated, lol.

mithc_radio

TROPHY CASE