HFU HF Underground
Loggings => Utility => Topic started by: cmradio on January 08, 2012, 0539 UTC
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Trying to ID a local (I don't have a decoder) RTTY ute that doesn't Google.
It's 18/7 groundwave (no QSB) near Vancouver. Not in the IC database, so it's not CG. No listings make me think CFB Esquimalt or Whidbey Island NAS. Could be Alaska somewhere, too (N-->S is really steady).
Too steady for California or Mexico and definately not the Chinese listings Google came up with.
Peace!
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Can you determine the shift of the FSK? This might help narrow the possibles.
But, I can tell you, I hear the Dixon CA, USN facility on that frequency just the way you are describing, and that is 500 kM away from me, it would be closer to 1000 kM for you I think.
T!
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Sounds like regular old 170Hz to me.
It's a rock steady S-5 regardless of time when it's on.... dunno, it may be in a perfect path from Cali ???
Thanks!
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I'm wondering if I may have recorded this same signal myself. I heard this last night from my home in Seattle, Washington:
http://youtu.be/d1xvcn1n_Rc (http://youtu.be/d1xvcn1n_Rc)
Sounds like regular old 170Hz to me.
It's a rock steady S-5 regardless of time when it's on.... dunno, it may be in a perfect path from Cali ???
Thanks!
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Were you able to decode it? ???
Peace!
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The FSK on 4905 kHz c/f is 850 Hz shift, and it is encrypted, also referred to as STANAG 4481 FSK. This is the signal in pcldltr's video. I strongly suspect it is US Navy on the west coast, I would say Dixon but I am not 100% sure Dixon is still active. It is heard at my location any hour of the day or night, and always strong.
T!
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Thanks Token!
I was able to install a little RTTY util, but it's fully manual and I couldn't decode it for the life of me.
Peace!
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When does this station operate? I tuned in to 4905 khz. earlier tonight and there was nothing but static.
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It's on right now, but very noisy in those bands this week :-\
Peace!
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I heard this 4905 khz RTTY station pounding in tonight around 0629 UTC, and it was also there during re-check of that frequency at 0700. Sounded like an S5 signal.
PS, I'm located in Washington state.
There's another one just as loud on 4985 khz., which I think I've heard more often. Not having a decoder, I've no idea who that one is.
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When does this station operate? I tuned in to 4905 khz. earlier tonight and there was nothing but static.
It operates off and on 24 hours a day. While it does not transmit constantly it does, generally, transmit for many minutes (guessing more than 20?) per hour. It is there on freq more often than not when I bother to look for it.
T!
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I heard this 4905 khz RTTY station pounding in tonight around 0629 UTC, and it was also there during re-check of that frequency at 0700. Sounded like an S5 signal.
PS, I'm located in Washington state.
There's another one just as loud on 4985 khz., which I think I've heard more often. Not having a decoder, I've no idea who that one is.
4985 is another 850 Hz shift FSK. It is the same kind of signal as on 4900. Even with a decoder youa re not going to figure out who it is (by decoding) as it is encrypted.
T!
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I too am able to tune 4905 khz in the AM from Las Vegas, NV. The signal is very strong.
Perhaps a dumb question but ... how do you know whether to tune USB or LSB for these types of data signals?
For example, it 'sounds' right at 4905 USB and LSB. I do not hear a difference.
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A lot of hf fsk is in usb mode anymore but not always, and can be considered irrelevant as most decoders can have their inputs set to inverted. Some decoders will even tell you if the sig is inverted and will compensate automatically.
When you come across 850/75 fsk it's almost always STANAG4481 mode in use by NATO, almost always a NATO navy, and will be kg84 encrypted. I ran a S4481 decoder on the youtube vid to see if any kg84 headers were apparent but the recording wasn't long enough.
https://en.wikipedia.org/wiki/KG-84
http://www.kd0cq.com/2013/07/sorcerer-decoder-download/
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I too am able to tune 4905 khz in the AM from Las Vegas, NV. The signal is very strong.
Perhaps a dumb question but ... how do you know whether to tune USB or LSB for these types of data signals?
For example, it 'sounds' right at 4905 USB and LSB. I do not hear a difference.
This signal will sound approximately the same in USB and LSB when tuned to 4905 kHz because 4905 kHz is the center frequency, not the tuned frequency.
The center of the FSK is 4905 kHz. However the FSK is 850 Hz shift. So each leg of the FSK, the space and the mark, are 425 Hz below and above the center frequency of 4905 kHz. So when tuned to 4905 kHz in USB you are hearing the Mark (on 4905.425 kHz), and when in LSB you are hearing the Space (on 4904.575 kHz). And heard alone the space and mark sound approximately the same to the ear.
So to tune this signal you must decide if you want to tune it in USB or in LSB. Most utilities and ham data are tuned in USB, however RTTY traditionally is tuned in LSB. Some RTTY, depending on the source, is in USB, other sources will be in LSB. It is acceptable to tune RTTY either way, USB or LSB, however you might have to click the "invert" button on your demodulator.
This is a military FSK encrypted signal (RTTY is FSK, this signal is specifically called "STANAG 4481 FSK"), and there is no one tuning offset that is correct in the civilian world to monitor it. There absolutely are standard tuning offsets for various civilian RTTY shifts, but this really does not fit those. In this case you might tune to 4903 kHz USB, that would put the space at 1575 Hz audio and the mark at 2425 Hz audio. If you are using a 2.4 kHz filter that might put mark outside or on the edge of your passband, and you might have to adjust this, maybe tune to 4903.5 kHz USB, putting the space at 1075 Hz audio and the mark at 1925 Hz audio.
T!
(edit) I see that while I was typing this Josh was responding, and said much the same.
(edit 2) I forgot to mention the source. This is probably US Navy, NPG Dixon, CA.
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Token - found the signal @ 4905 khz again this morning.
With my Yeasu FT-950, tuning while in CW mode seems best. The signal, as you described above, remains constant when switching from USB-CW to LSB-CW. It stays strong and 'centered' in HDSR.
With that said, is it logical to use CW mode for this?
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Token - found the signal @ 4905 khz again this morning.
With my Yeasu FT-950, tuning while in CW mode seems best. The signal, as you described above, remains constant when switching from USB-CW to LSB-CW. It stays strong and 'centered' in HDSR.
With that said, is it logical to use CW mode for this?
How you tune such signals is totally up to you. Particularly encrypted signals like this, since there is no correct or incorrect way based on how decoding must be done.
However, I would not use CW mode at all for these, I would use USB for this specific signal.
Why? Because the defined center frequency for this kind of signal (STANAG 4481 FSK) is 2000 Hz. That means there is a correct tuned frequency for the signal. If the center of the data is on 4905 kHz then tuning to 4903 kHz in USB mode will put the center of the data at 2000 Hz, or the space at 1575 Hz and the mark at 2425 Hz.
And yes, most military and utility modes are tuned in USB.
So for this signal it would go in my log book as 4903 kHz, USB mode, c/f (center frequency) 4905 kHz. But I would report it to people in chat as FSK on 4905 kHz c/f. Not confusing at all, is it? Also, tuning this way (4903 kHz USB mode) will allow you, without adjusting software from defaults, to use software to strip the KG-84 headers and confirm it is indeed STANAG 4481 FSK and encrypted. If, for some reason, the transmission was not encrypted it would also allow you to receive the text.
It is kind of like the question of WEFAX, do you report center freq? Or do you report tuned freq?
T!
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Thank you!
I am surprised that the little PA0RDT active mini whip can pickup so much here in Nevada. In the AM, I can tune at least 50+ APAC stations.
One day I'll put up another antenna to see what else I can get.
I am on a postage stamp sized lot in a tightly packed neighborhood. Do you have any 'wonder' antennas for HF RX - something that may outperform the mini whip?
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I am on a postage stamp sized lot in a tightly packed neighborhood. Do you have any 'wonder' antennas for HF RX - something that may outperform the mini whip?
Unfortunately, small space antennas are always a compromise.
I do, however, like loops when talking about antennas for small space, urban or higher noise, environments. While it may not outperform the mini-whip in all cases, a loop, something like the Pixel Pro or the Wellbrook 1530+, when mounted on a rotor will allow you to null offending local noise sources. Where the mini-whip is omni, the loops have a null in their pattern. If you tune to a signal and there is locally (in the house or neighborhood) generated noise on the same freq you can turn the loop to point the null at the noise source, often greatly improving reception of the desired signal.
Such a loop is more expensive and more complex (you need a rotor as well as the antenna) to set up, but in my opinion often very much worth it.
T!
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Don't forget the W6LVP loop. I'm not sure exactly how well it compares to the others, but it works well for me in my urban environment, and Larry Plummer (W6LVP) is terrific about service and answering any question you have. Just have to toss that out there.
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However, I would not use CW mode at all for these, I would use USB for this specific signal.
So why did I say this? In the past some radios did have CW/RTTY specific modes, often using the same switch position on the radio.
CW mode typically selects a narrower filter, CW being a narrow mode of operation. Such a narrow filter might very well clip out portions of the digital / image / data mode you are trying to receive. This is less an issue today with DSP radios and adjustable filters, but when radios used hardware filters (or modern radios with hardware filters) this was a potential problem.
Another issue is that CW mode introduces a frequency bias.
If a CW signal is on the frequency of 7500.000 kHz and you tune to it in USB or LSB, on 7500.000 kHz, then you will hear nothing (almost nothing), until you tune off frequency slightly. This is normal because in these modes the CW signal would be at "zero beat" when tuned to 7500.000 kHz, and so you hear no audio tones. To hear the tones you tune below the frequency in USB mode and tune above the frequency in LSB. The audio tones heard will be equal to the tuning offset.
So CW mode on a receiver intentionally introduces a frequency offset, often around 700 Hz. With such an offset when a signal is on 7500.000 kHz and you tune to 7500.000 kHz in receiver CW mode you hear the dots and dashes as 700 Hz tones (many newer receivers have adjustable CW offsets, so you can set this tone frequency to whatever you are comfortable with).
The problem is that using CW mode on the receiver this offset also is applied to any data signal you have. So now the audio will be the signal offset plus the CW offset.
Assuming your CW offset is 700 Hz if you tuned to the RTTY on 4905 kHz using CW-U and tuned to 4905.000 kHz, and you widened up the filter wide enough to get both Mark and Space the tones will be at 1125 Hz (700 Hz CW offset + 425 Hz from center) and 275 Hz (700 Hz CW offset - 425 Hz from center). Using CW-L mode will result in the same audio tones, but invert the relationship of the Space and Mark.
But STANAG-4481 FSK has a spec of space and mark at 1575 and 2425 Hz, so CW-U or CW-L clearly results in different values.
Better to just use USB (or LSB, as required) with such signals, for pretty much anything except Morse.
T!
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Here's some fsk logs from some time back;
04.005.00 850Hz 50Bd FSK 0412 11.12.16 CV-768/Rockwell 700B
05.340.00 850Hz 50Bd FSK 009Z 12.05.16
06.487.00 850Hz 75Bd FSK 0349Z 11.12 16 TST-4043/CV-768/Rockwell 700B/STANAG 4481
08.416.60 200Hz 100Bd SITOR 1358Z 11.14.13
08.471.60 200Hz 45Bd FSK 0300Z 04.05.14 WLO
08.471.60 200Hz 100Bd SITOR 0300Z 04.05.14 WLO
09.473.00 200Hz 100Bd SITOR 2048Z 11.13.16
10.153.00 850Hz 75Bd FSK 2226Z 11.15.16 CV-768/Rockwell 700B
11.685.50 850Hz 75Bd FSK 1837Z 11.17.13
12.012.50 850Hz 75Bd FSK 1834Z 11.17.13
12.117.50 850Hz 75Bd FSK 1834Z 11.17.13
12.603.40 200Hz 100Bd SITOR 2230 06.11.14 GREEK
13.869.50 850Hz 75Bd FSK 1739Z 11.17.13
14.928.50 850Hz 50Bd FSK 2107Z 11.11.16
15.598.50 850Hz 75Bd FSK 1736Z 11.17.13
16.122.50 850Hz 75Bd FSK 1733Z 11.17.13
16.267.00 850Hz 75Bd FSK 1733Z 11.17.13
16.806.60 200Hz 100Bd SITOR 1144Z 11.14.13
And my latest USN fsk sched;
USN HF FSK Network
NPN Barrigada Guam
8654 14887 15601 16015
Croughton UK
7477 9074 10286 11464
AFA/NSS Davidsonville Md
4005 4985 6487 6497 9830 10712 12015 13590 15959
NKW Diego Garcia BIOT
4550 8093 8547 8550 22471 22910
NPG Dixon Ca
4905 7597 8538 8694 9085 10320 10430 13870 16268
NAU Isabela PR
8676 7455 7711 10153 10895 11688 12120 16123
NPM Lualualei Ha
8676 9112 9960 14434 18558
NDT Totsuka Japan
5304 6358 10830 14375
NSY Sigonella Italy
5414 7420 9904 10974 18040 18411
Some channels have night/day ops qrg, example; Isabella 16123 day 10153 night.
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Token - thank you again.
Josh - how are you able to determine the location?
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Josh - how are you able to determine the location?
Some of the headings came from ITU and hobbyist df fixes, some from osint, some came from man on the ground sleuthing. Kinda like when I lived in West Omaha, anything that came out of the Elkhorn Communications Detachment was more than obvious.
http://www.offutt.af.mil/News/Features/Display/Article/312829/rural-communications-site-has-global-mission/
https://www.facebook.com/Det2Elkhorn/