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Author Topic: What RTTY Station Is That on 4905 KHz?  (Read 8054 times)

cmradio

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What RTTY Station Is That on 4905 KHz?
« on: January 08, 2012, 0539 UTC »
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!

Offline Token

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Re: What RTTY Station Is That on 4905 KHz?
« Reply #1 on: January 08, 2012, 2015 UTC »
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!
T!
Mojave Desert, California USA

cmradio

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Re: What RTTY Station Is That on 4905 KHz?
« Reply #2 on: January 09, 2012, 0026 UTC »
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!

Offline Strange Beacons

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Re: What RTTY Station Is That on 4905 KHz?
« Reply #3 on: July 13, 2013, 1708 UTC »
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

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!

cmradio

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Re: What RTTY Station Is That on 4905 KHz?
« Reply #4 on: July 14, 2013, 0427 UTC »
Were you able to decode it? ???

Peace!

Offline Token

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Re: What RTTY Station Is That on 4905 KHz?
« Reply #5 on: July 14, 2013, 0520 UTC »
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!
T!
Mojave Desert, California USA

cmradio

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Re: What RTTY Station Is That on 4905 KHz?
« Reply #6 on: July 14, 2013, 2157 UTC »
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!

Offline BoomboxDX

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Re: What RTTY Station Is That on 4905 KHz?
« Reply #7 on: July 16, 2013, 0750 UTC »
When does this station operate?  I tuned in to 4905 khz. earlier tonight and there was nothing but static.
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The usual Realistic culprits on SW (and a Panasonic).

cmradio

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Re: What RTTY Station Is That on 4905 KHz?
« Reply #8 on: July 16, 2013, 0834 UTC »
It's on right now, but very noisy in those bands this week :-\

Peace!

Offline BoomboxDX

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Re: What RTTY Station Is That on 4905 KHz?
« Reply #9 on: July 23, 2013, 0925 UTC »
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.
An AM radio Boombox DXer.
+ GE SRIII, PR-D5 & TRF on MW.
The usual Realistic culprits on SW (and a Panasonic).

Offline Token

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Re: What RTTY Station Is That on 4905 KHz?
« Reply #10 on: July 25, 2013, 2052 UTC »
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!
T!
Mojave Desert, California USA

Offline Token

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Re: What RTTY Station Is That on 4905 KHz?
« Reply #11 on: July 26, 2013, 0326 UTC »
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!
T!
Mojave Desert, California USA

Offline ultravista

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Re: What RTTY Station Is That on 4905 KHz?
« Reply #12 on: April 21, 2018, 1451 UTC »
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.

Offline Josh

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Re: What RTTY Station Is That on 4905 KHz?
« Reply #13 on: April 21, 2018, 1724 UTC »
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/
Conveniently located near Vincennes Indiana.

Offline Token

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Re: What RTTY Station Is That on 4905 KHz?
« Reply #14 on: April 21, 2018, 1753 UTC »
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.
« Last Edit: April 21, 2018, 2157 UTC by Token »
T!
Mojave Desert, California USA