ka9q

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ka9q
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  • Glenn, my configuration is too complicated to easily describe here, but I did try several simple experiments. First, I disconnected the GPS antenna from the KiwiSDR. The noise < 30-40 kHz actually went UP. (This connector comes from an HP GPS ant…
  • Hi Glenn, long time no hear! Wow, that's a really useful writeup that gives me a lot to chew on. I'd been off HF for a long time but returned to it in my retirement. Physics hasn't changed, but everything else has. There's been an explosion in digit…
  • Do you overlap windows? I'm a big fan of the Kaiser window for general purpose filtering, but I know that there are windows optimized specifically for spectral analysis (as opposed to filtering).
  • I can see how SMPS harmonics might be shaped by the driving circuit (eg, push-pull vs single ended) but it is indeed hard to understand why they should be so much louder at higher frequencies. Maybe stray capacitance in (or around) the toroidal indu…
  • Wow, that was fast! Thanks so much. I might be able to help with that FFT scalloping. Are you using a window ahead of the FFT?
  • How many threads or subprocesses does kiwid use? I use them heavily, mainly to take better advantage of ubiquitous multi-core CPUs but also to make bugs and memory leaks easier to isolate and contain. At the very least, a short-lived thread will cle…
  • I'm listening to your SDR now but I don't hear it, probably because it's too late (0108 UTC). In fact you have a remarkably quiet QTH compared to mine (San Diego CA DM12ju). But your description sounds remarkably like one source of QRM I'm working o…
  • If your goal is to check that the transmitter isn't splattering, why not just look directly at the modulated spectrum? Depending on the transmitter design, you could have more than 100% negative modulation and still not have splatter. One way is to…
  • Thanks much! A loop BW of 200 Hz does seem rather wide for AM on HF. If the loop gain or damping factor depend on signal strength, as they often do, it can also be upset by low frequency modulation components.
  • Yes, though the degree to which these internal DC-DC converters actually cause interference on HF depends on how much of that switching noise is conducted to the outside world. One of the biggest offenders in my shack is an external powered USB 3.0 …
  • Thanks for the details. It's just a fact of life that the closer a modulation/coding scheme gets to the theoretical limit, the more "brittle" it must become. That's why so many digital schemes either work perfectly or not at all. Even anal…
  • So what transmitting stations still exist in North America, even if they're not operating?
  • I concur with the suggestion to try another power supply. They can vary enormously in noise generation. I've been switching to Cat 7 ethernet cables where possible. Each pair is shielded, and the entire cable has an end-to-end shield that connects …
  • Wow, I thought all the transmitting stations had been demolished.
  • The most important factor is the choice of modulation; the higher order constellations (especially 64QAM) require a much higher SNR to decode. In my opinion, many DRM broadcasters are overly optimistic about 64QAM. I rarely decode even a 16QAM signa…
  • Are any LORAN-C signals still on the air anywhere in the world? I haven't heard one in over 10 years, since the US shut down its system in 2009 or so.
  • That's correct, my network is multi-homed on IPv6. The 2605:e000 prefix is Spectrum Cable, my ISP. The 2001:470 prefix is a free IPv6-in-IPv4 tunnel provided by Hurricane Electric. Multihoming is a pretty basic feature of IPv6, and every host is re…
  • Hi Glenn, long time no hear! jks, thanks for the pointer to the config file. I can probably suggest some other changes, but i want to verify them first. E.g., the US Coast Guard has shut down all of the DGPS reference stations -- not just the DGPS …
  • OK, I'm looking at my logs. The problem does indeed seem to be that local IPv6 addresses aren't recognized as local. Here's a sample log entry: Fri Jul 17 06:08:43 01:40:20.525 0123 [05] PWD isLocal_if_ip: FALSE IPv6 remote_ip 2605:e000:1c0e:43f7:d…
  • Actually, IPv6 doesn't depend on your ISP doing anything. It doesn't require you to have a router or even an Ethernet switch! That's what the link-local prefix fe80::/16 is for; every host is required to implement it so you will at least have local …
  • A server can't necessarily know the DNS name of the client talking to it. To do that it has to take the incoming IP address and perform a reverse DNS lookup, which often fails because people don't bother to maintain reverse records. Also, not every …
  • I'm more familiar with North Korean jamming signals (since they're so common, e.g., on 49 and 41m at night when I'm usually listening). From what I've seen of Cuban jamming, which seems different, it's designed to efficiently disrupt AM by concentra…
  • Note also that they're 50 Hz low (or they were about 8 hours ago when I last looked). I don't know how well the KiwiSDR DRM decoder tracks frequency errors, so I retuned manually. (Didn't help because the signal was just too poor). It's easy to fin…
  • What confused me is that I'd thought you do a right/secondary click by holding down the control key and doing an ordinary click. This seemed to work for most things, but not your program. Now I can calibrate frequency on the KiwiSDRs I run that don'…
  • Ah, so that's how you do it! I had it enabled and didn't know it. D'oh!
  • Wow, that was fast! Unfortunately I'm on a Mac where it's difficult or impossible to use the right menu, but that's my problem. I need to figure it out anyway. But thanks!
  • I have yet to decode Marti on 7345 here in San Diego but that's a combination of propagation, their schedule, and my location. Remember Shannon: channel capacity increases with power and bandwidth Narrower bandwidths put you at a definite disadvan…
  • I think the 9 kHz mode has more to do with the 9 kHz broadcast channel spacing in certain countries. In DRM robustness mode B (the most common on HF, as far as I can tell) the OFDM carrier spacing is 46.875 Hz. If the center (nominal) frequency is …
  • ha ha ha... :smile:
    in DRM Heard Comment by ka9q February 2020
  • "Update: after noting that they were running 9 KHz BW, I pulled the corners of the passband in a tad and got an SNR improvement." But does this actually help? I don't know the details of the DRM decoder implementation and how the displaye…
    in DRM Heard Comment by ka9q February 2020