Hi, thanks for your post. I'm curious about this. Could you post a couple pictures, I/Q plots I guess? I'll try tuning in with synchronous AM, never tried that mode. Very curious!
I have to agree with your listening as well, from here in Fort Collins, the worst sounding signal is by far the 10 MHz signal as you saw the splatter video I posted. They do fix it, after about a week or so of problems when it happens. The best sounding transmitters are 2.5;20;25 MHz. That is also why I took my 'master' recordings from 2.5 MHz! If anyone wants a sample of a different frequency I can do that, they are all ground wave here so SAM is not needed for me as you can imagine.
A few years ago, when we had a higher average MUF, I was frequently on 12m. Of course WWV at 25 Mhz is VERY close to the edge of that amateur band. Afternoons they would often have a BIG signal into FL, often S9+20, or more. One day I was tuning at the top of the 12m phone band segment and I heard a strange xmsn, a voice, on 24984 kHz, just above the band edge. It sounded familiar. I realized it was coming from WWV! It had a very weird sound, suppressed carrier (!) and DSB, on both USB and LSB. I wondered if there was more to it and also found the same phenomenon at 16 kHz above the fundamental, or 25016 kHz. The following links are audio clips. They start out listening on the fundamental freq, 25 MHz, then you will hear a "beep" as I flip to one of the spurious frequencies, where you will hear the fainter voice of the spurious signal. More beeps is more flipping to other sideband or to the other spur frequency, and then back to the fundamental. WWV 25 MHz clip 1 - https://vocaroo.com/i/s0jCjW2zTP9a WWV 25 MHz clip 2 - https://vocaroo.com/i/s0UxIPP9ViuC Note these spurs ONLY happened during the vocal "special announcements", like solar indices or sea WX, and NOT during the normal top of the minute time posts. Apparently the level of audio sent to the xmtr or some other parameter varies between those sources. I emailed WWV with a description and these clips to alert them of this incident. Eventually I received the following reply and confirmation. (I redacted the name of the responder to not create any trouble.) I don't hear WWV much on 25 MHz any more these days, so you may want to see if this is still occurring. 73, John, WØPV ------------------------------ wwv <wwv@nist.gov> Tue 12/8/2015 10:05 AM Hello Mr. Rech, Thank you for your report on the spurious emissions around the 25MHz. I was able to confirm your report of a modulated emission at 24.984 but found nothing at 25.946. I’m surprised you were able to receive it. The signal is 60 db down and is originating in a phase lock loop section of our modulator. I’ve backed off the modulation level on the special announcements so this may minimize the issue during those minutes but if conditions are right and you look closely I think you will find the spurious carrier still there and still modulated. I’m currently looking into a long term solution. Thanks for the report. Sincerely, XXXX XXXXX Technician, WWV From: John Rech [mailto:johnrech@hotmail.com] Sent: Sunday, December 06, 2015 1:19 PM To: wwv <wwv@nist.gov> Subject: 25 mhz - possible spurious adjacent channel emissions To Whom It May Concern, First, thank you very much for the QSL card I received for my signal report in February of this year. However, I want to report that today while listening in the 12m amateur band, I heard a very curious signal. It was a female voice coming from what appeared to be a double-sideband modulated (!) signal centered about on 24.984 mhz. The content of her message was solar index information, and looking at the time, I realized this could be the usual solar report broadcast by WWV. I tuned up to 25 mhz and could hear WWV with a very strong signal, peaking S9+2- db with QSB fading down to S8, on my Icom IC-781 and wire dipole at 30 ft AGL. The voice message interval had passed, and I did not hear any more spurious signals during normal time ticks or tones, nor during the on-the-minute male voice announcements. But, later, when there were more special broadcasts (sea states?) with a male announcer, I tuned and heard similar modulation artifacts, this time mostly above the primary 25 mhz frequency. These were not intelligible like the female announcement though, just distorted noises. I thought perhaps this was a fault in my receiver front end. After all, the IC-781 is an old gal now. So I switched to a FT-817 portable radio and waited for the next solar index announcement at 1918-19 UTC. To my astonishment, I heard the DSB modulated female voice distinctly on 24.984 and on 25.916 mhz! These signals were not strong, in my judgement at least minus 50-60db down from the primary carrier, but very clearly intelligible here. Anyway, this is NOT a complaint for me, but I thought it might be of interest to you. Best regards, John Rech - WØPV Bradenton Florida
You are not going to believe this, but I actually listen to the solar forecast 18 mins after the hour +16 kHz from center, basically the level of IMD the signal produces allows for the exact same signal to be heard and seen +- 16 kHz center. I thought about making a 1 min video showing the event but never did thinking that only a few people would care to see it or even understand what I as showing but I think it is really neat. Perhaps, I will whip this out and post that as well John. If you did not do so, check out the additional WWV videos I posted. You will love the Splatter one.
Classic! Nice work Tyler! Last year I made a cycling voyage to see the antenna farm at WWV. Loved it! Not least was the private hexbeam located literally just over the fence line...
Yes I know! I saw the HEX beam, when I was on site I saw that and shook my head!!! Great video clip, there are probably some people who have no idea what we keep talking about! What do you think runs my amp, "this sucker is electrical"!
Dimension 4 would certainly be good for setting off the internet. But this special event station WW0WWV is doing a Field Day type operation. See the photo album. So, despite cell phones, etc, they may not have a reliable direct connection to the web. However, they do have RADIOS and are in close proximity of a really strong NIST time standard transmitter . So I was expecting that in the SPIRIT of celebrating WWV they would have made provisions to decode their commemorative stations time signal off-the-air for setting their FT8 PC clocks. Like using this LINUX demod/decoder perhaps to set up a local NTP server for all the Windows PC's, or spending the 30 bucks for the F6CTE Clock program for Windows. If there are other WWV time signal decoders, I would like to learn about them.
Sure. Go to http://www.ka9q.net/wwv. You'll see a list of screen shots I made with the Kiwisdr at N6GN in Fort Collins. I grabbed IQ plots of all six HF transmitters. Look at 10 MHz; it looks like a banana! An AM signal should be a flat line exactly on the +I axis, with a dot in the middle of the +I axis for the unmodulated carrier. This one has so much phase modulation you can easily hear it in FM mode. It's no coincidence that the best-sounding transmitters are 2.5, 20 and 25 MHz. They're linear amplifiers. 5, 10 and 15 use high level audio plate modulation of a class-C final amplifier. Unfortunately, the linear transmitters only produce 2.5 kW; the high level ones produce 10 kW. I think this explains the difference. I need to brush up on my vacuum tube physics, but I think the change in plate voltage in a plate-modulated AM transmitter changes the electron density and distribution within the tube. This changes the plate/grid capacitance, which in turn changes the phase shift in the tube. There's really no other explanation since the low-level input to the transmitter is a continuous, unmodulated 5, 10 or 15 MHz sine wave. Anybody out there with SDR equipment and a plate-modulated (tube type) AM transmitter could test this, though I suspect these are distinct sets of people. Here in San Diego, 5 is pretty reliable at night and 10 during the day. Unfortunately, 2.5, 20 and 25 aren't as good; I can usually hear 2.5 at night but my old PV inverter produces a lot of RFI. (Yeah, it should shut down automatically at night but it's very old and the manufacturer never bothered with any firmware improvements.) I rarely hear 20 and 25 on what is probably sporadic E in the early evening. Synchronous AM detection provides several benefits. First, it avoids the distortion you hear on an AM detector when frequency-selective fading notches out the carrier. Second, you get a theoretical 3 dB SNR improvement because you're looking only at the signal in phase with the carrier; you ignore the in-quadrature phase that's noise only. (That's why an AM signal is a line on the +I axis.) This is how I discovered the distortion on WWV's transmitters. I've been working on my own SDR, including a synchronous AM mode, and noticed that their signals (especially 10 MHz) sounded noticeably more distorted in the synchronous mode than in the simple envelope mode. So I added a feature that put the I channel on the left earphone and Q on the right earphone. (I think this was once tried as an AM stereo technique.) On local broadcast stations I got the expected result: the audio was completely on the left channel; just noise and a very tiny amount of program audio on the right. On WWV the modulation seemed spread across the stereo image. Eventually I realized the problem was at WWV, not in my receiver. The audio distortion in synchronous AM mode is because it's designed to ignore signals in the Q channel, and because of the AM-to-PM conversion this resulted in a very nonlinear transfer curve when looking at only the I channel. Lots of harmonics on the audio tones and intermod between the 100 Hz subcarrier and those tones.
I would also be interested. I've used the free limited version of the Clock program. I think I once saw someone mention another app in another forum post about WWVB.
This is the GPS-based NTP server I have on my home network. It's a bit pricey, but it "just works". https://timemachinescorp.com/product/gps-time-server-tm1000a/
I just looked at all six HF frequencies again with N6GN's WebSDR. All are essentially the same as in my plots made several months ago. 10 MHz is the worst, as before.
You can also see this on the WWV Splatter Video quite clearly in the spectrum analyzer and waterfall I posted of the 10 MHz signal!
thanks so much for this... and the rest of your detailed, informative, excellent post. greatly appreciated.
