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HF/MW/LW General Discussion - General discussion on monitoring the HF (High Frequency), MW (Medium Wave), and LW (Long Wave) spectrum (0.5 - 30 MHz)

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Old 03-11-2018, 1:42 PM
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Default Some interesting LF/VLF signals

Using a 192kHz soundcard with a long wire antenna connected to its left input channel, and using the SDR# software I screen capped this spectrum/spectrogram image. I have annotated it so that you can see what's showing in it.

Lots of signals are in here as you can see, most of which still unknown to me.

Of all the signals though, the one that's most interesting is the one that's not there, that should be. Where is the WWVB atomic-clock broadcast? It should be at exactly 60kHz, and is supposed to be so strong that even a tiny wristwatch with a receiver and internal antenna can receive it. The actual transmitter for WWVB is supposed to be so strong, that even though the 60kHz has a very long wavelength, even a tiny receiver antenna in a wristwatch is capable of receiving it. Certainly, my long wire antenna (which is 20 feet long) should have no problem picking up this signal.
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Old 03-11-2018, 1:47 PM
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It probably takes a loop antenna to hear WWVB and reject the local noise. I can hear it day or night on the loop, and nothing but noise on any of the wire antennas.
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Old 03-11-2018, 9:59 PM
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Originally Posted by zz0468 View Post
It probably takes a loop antenna to hear WWVB and reject the local noise. I can hear it day or night on the loop, and nothing but noise on any of the wire antennas.
Interesting. However, it should still appear as a tiny weak signal, with it looking like a vertical line on the spectrogram that's slightly brighter than the surroundings. But I see nothing at all. Did they recently turn off /decommission the WWVB transmitter?
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Old 03-11-2018, 10:03 PM
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On my Wellbrook loop and my 100' endfed, I've caught quite a few NDBs clear into Canada and out to Montana but I've never gotten WWVB on 60 nor those elusive LW foreign BCs.
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Old 03-11-2018, 10:14 PM
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You will not be picking up WWVB on a soundcard with 20ft of wire. The antenna to receiver impedance mismatch is probably horrific and loosing nearly all the signal. An active whip or loop might work if your in a very quiet area. Something you can do is find out what your noise floor is in the 60KHz region on your spectral display and you might need a noise floor 30 or 50dB lower to receive WWVB.

I've picked up WWVB in the past on my home made AMRAD active whip but my current location is too noisy.
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Old 03-11-2018, 11:31 PM
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Quote:
Originally Posted by prcguy View Post
You will not be picking up WWVB on a soundcard with 20ft of wire. The antenna to receiver impedance mismatch is probably horrific and loosing nearly all the signal. An active whip or loop might work if your in a very quiet area. Something you can do is find out what your noise floor is in the 60KHz region on your spectral display and you might need a noise floor 30 or 50dB lower to receive WWVB.

I've picked up WWVB in the past on my home made AMRAD active whip but my current location is too noisy.
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Im hearing WWVB every day with my Z1501D Clifton Labs active antenna.

My QTH, Beauharnois QC.

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Old 03-12-2018, 12:59 AM
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Interesting. However, it should still appear as a tiny weak signal, with it looking like a vertical line on the spectrogram that's slightly brighter than the surroundings.
Only if the signal to noise ratio is sufficient. Clearly, in your case, it is not, or you would be seeing it.

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Originally Posted by KE7IZL View Post
But I see nothing at all. Did they recently turn off /decommission the WWVB transmitter?
WWVB is on the air as normal. I can receive it any time, day or night, winter or summer. But I'm using much more than a sound card and a 20' piece of wire to do it.
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Old 03-12-2018, 3:23 AM
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Quote:
Originally Posted by zz0468 View Post
Only if the signal to noise ratio is sufficient. Clearly, in your case, it is not, or you would be seeing it.



WWVB is on the air as normal. I can receive it any time, day or night, winter or summer. But I'm using much more than a sound card and a 20' piece of wire to do it.

Considering that a tiny wrist-watch is too small to have all the electronics packet into it that my sound card has, and also doesn't have room for anything like a 20 foot antenna (more like a couple millimeters long), and yet it can automatically set itself with the WWVB signal, suggests that there's something really weird going on here. I can't imagine that there's a really powerful amplifier in a tiny watch. And also considering that at 60kHz, there is no way to make a practical transmitter antenna for it (quarter wave antenna for 60kHz is 1.25km long!). And the receiver antenna is even shorter, needing to be small enough to fit into a watch. Given these factors, I assumed they compensated for all these losses by simple using a massive output amplifier to feed the transmitter antenna, outputting a signal of well over 1 gigawatt into the antenna. So given this, the signal should be of decent strength in most parts of the US, meaning that a simple sound card with wide enough bandwidth (I'm using a 192kHz sample rate sound card, so I get a 96kHz bandwidth) with a long wire sticking into its line-in port, should be enough to easily receive WWVB. At least that's what I assumed.

Given that my assumption has turned out to be incorrect, it looks like I will need an amplifier that works at 60kHz. So antenna goes into the amplifier's input and the output of the amplifier goes into the sound card. However, there's 2 problems with that. First, if I did that I'd overdrive the input of the sound card's ADC (analog to digital converter) with the 60Hz AC powerline tone, which is by far the strongest signal in the entire VLF spectrum. Second, my sound card already has an amplifier on its input, as part of the sound card hardware itself, and in fact has a manually adjustable potentiometer to vary its gain (which by the way is set so that the 60Hz AC waveform, the strongest signal by far, takes up about 50% of the maximum range or its ADC, to avoid getting even close to overdriving it), so no need for separate amplifier hardware. You see, this isn't an internal PCI soundcard, or even a small cheap USB sound dongle I bought on eBay. This is a professional audio interface, with 24bit 192kHz ADC on the input and 24bit 192kHz DAC on the output. It is its own separate box that sits on my desk, and connects to my PC via a USB cable. It's about the size of a small portable ham radio transceiver, such as the ICom IC706. Certainly, it would seem that with 24bits of precision, it should have a VERY low noise floor, making it easy to see extremely weak signals.

In case you are curious what hardware I'm using, it's the Behringer U-Phoria UMC204HD. B&H Photo is selling them for $79.99.
https://www.bhphotovideo.com/c/produ...t_192_khz.html

Last edited by KE7IZL; 03-12-2018 at 3:29 AM..
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Old 03-12-2018, 3:58 AM
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As long as a signal is repeated consistently, the 'coherent signal detection' will be able to dig out the info below the noise. GPS receivers do it all the time on a tiny postage stamp antenna.
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Old 03-12-2018, 5:11 AM
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Anybody able to identify the other mystery signals? I'm particularly interested in the MSK (minimum shift keying) signal and the repeating downward sweeps that appear to have a sort of logarithmic look to the shape of the frequency sweep.
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Old 03-12-2018, 6:05 AM
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Can't help but say that you might have better luck if you replace the closest CFL's with incandescents, at least when you're on the radio. Halogens save a decent amount of energy and you mention you've got a CFL in your radio room. Putting in a Halogen might help. Just a thought.
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Old 03-12-2018, 7:20 AM
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Quote:
Originally Posted by KE7IZL View Post
Using a 192kHz soundcard with a long wire antenna connected to its left input channel, and using the SDR# software I screen capped this spectrum/spectrogram image. I have annotated it so that you can see what's showing in it.

Lots of signals are in here as you can see, most of which still unknown to me.

Of all the signals though, the one that's most interesting is the one that's not there, that should be. Where is the WWVB atomic-clock broadcast? It should be at exactly 60kHz, and is supposed to be so strong that even a tiny wristwatch with a receiver and internal antenna can receive it. The actual transmitter for WWVB is supposed to be so strong, that even though the 60kHz has a very long wavelength, even a tiny receiver antenna in a wristwatch is capable of receiving it. Certainly, my long wire antenna (which is 20 feet long) should have no problem picking up this signal.
There are some of us who "specialize" in looking at VLF and LF and can essentially identify everything we see down there. Your signal at 24.8 kHz is the USN station NLK at Jim Creek, WA. I can also see in you screen capture the USN station on 25.2 kHz in La Moure, ND. The downward sweep is definitely some sort of local interference as is all that crap from 40-70 kHz preventing you from seeing WWVB on 60 kHz. The peak above that in frequency is also interference. The best antenna you might try is a short active E-field probe for LF/VLF. These can be found cheap on eBay (mostly from Russia and the Ukraine) which you can experiment to get away from interference and house wiring. Good sensitive loops for a wide range of VLF/LF are expensive and I would recommend the other antennas first. some sellers on eBay include anton_ra0sms and transverters-store .
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Old 03-12-2018, 7:23 AM
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Quote:
Originally Posted by KE7IZL View Post
Anybody able to identify the other mystery signals? I'm particularly interested in the MSK (minimum shift keying) signal and the repeating downward sweeps that appear to have a sort of logarithmic look to the shape of the frequency sweep.
See my post, definitely some local interference. The only legit signal I could see in your display are the ones I see at 24.8 and 25.2 kHz.
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Old 03-12-2018, 7:40 AM
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Quote:
Originally Posted by VE2XWA View Post
Im hearing WWVB every day with my Z1501D Clifton Labs active antenna.

My QTH, Beauharnois QC.

Dan


Sent from my iPod touch using Tapatalk
For those interested, just a note that DX Engineering bought Clifton Labs and I do not think that antenna is currently availblbe.
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Old 03-12-2018, 1:24 PM
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Quote:
Originally Posted by dlwtrunked View Post
See my post, definitely some local interference. The only legit signal I could see in your display are the ones I see at 24.8 and 25.2 kHz.
I don't even see one at 25.2kHz

By the way, how do you know the 24.8 signal is USN? Do you have a decoder software that can decode this modulation? Any idea what baudrate it is?
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