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Author Topic: RTTY Beacon or transmissions on 27.551 USB  (Read 1244 times)

Offline PTR11EXP

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RTTY Beacon or transmissions on 27.551 USB
« on: October 07, 2021, 2355 UTC »
Hello. Lately I have been listening in SDR's from Central America and Bonaire to what seems like RTTY transmissions in 27.551 USB.
Does Anyone have information about it?
Enclosed a video that shows exactly what I listen to.


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Offline Teotwaki

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Re: RTTY Beacon or transmissions on 27.551 USB
« Reply #1 on: October 08, 2021, 0249 UTC »
I have a little info gleaned from the net for you. Because this signal is not a pirate beacon I will move the thread after replying.

Please do not post the same logging across multiple areas.


Mystery RTTY signals
Post by grafter » 09 Jul 2019, 08:25

I finally recorded a narrow band of signals I've been hearing for the last few years and wondered if the collective could shed any light on their origin. When propagation is towards Italy and Spain multiple RTTY beacons appear on 27.551 (USB). I've heard them on some of the European SDRs so appear to be authentic and distant but so far I have been unable to decode anything from them.

I'm aware of the continuous FSK wave buoy signals above 10M but these remain a mystery so any clues as to their origin or function would be very much appreciated.

Here's the video of this morning's reception.


Second Lead for you

Re: [UDXF] 26-28MHz FSK
 janJul 23   #286 
Hi Kurt

Interesting message!

I hear this FSK signal again today on frequency 27.551 usb , On Websdr from Italy "http://roma4.ddns.net/" you can also hear this FSK 27.551usb ,


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 Van: KD7JYK DM09
Verzonden: donderdag 22 juli 2021 20:43
Aan: vhfskip@groups.io
Onderwerp: Re: [vhfskip] [UDXF] 26-28MHz FSK

"I finally got a decent capture of the mystery FSK signal that appears
across the CB band when I have Es to Spain. I've uploaded a video and
the original IQ file in case anyone is able to suggest its purpose or
the type of transmission?"

Are you on the UDXF group, and did you get the Datawell telemetry links?
I also posted the following yesterday, but didn't see it bounce  back
to me through UDXF, did you see this, by any chance?  The post also had
some photos, and if this forum allows them, I can follow up with them in
a later post:

Initial UDXF post:

"I hear these mystery signals in Florida also, on multiple US CB
channels when conditions are right, and it appears to be something
different from the Datawell beacon.  The mystery data appears to be some
kind of query and response"
My response:
I enjoy hearing about such things.
I first saw "Class C" equipment in the 1980's, and began chasing it down
in the 1990's.  The service goes back to the 1950's, and from the 90's
onward, devices made to operate on the 27 MHz frequencies was in the
millions per year.  Most are very low powered, and can only be heard up
to a few hundred feet by design, but some frequencies, and equipment
allow up to 4 Watts output, and one frequency, 25 Watts output, both of
which can result in global coverage, but are generally heard in the
range of miles.
By the early 2000's, I began acquiring much of the equipment that
produces the different signals, and was able at one time to ID all but
perhaps two that could be heard regularly over the past forty years.  I
had a Yahoo Groups page up briefly with several hundred photographs of
equipment, and recordings, but as soon as they switched to "Neo", I lost
control of the group.  Yahoo was never able to make groups fully
functional before eliminating the groups entirely several years later.
The types of equipment is all over the board.  Remote controlled toys,
to computer accessories, irrigation controllers, to wireless card
readers, paging systems, alarm systems, hydrological, and meteorological
telemetry, medical equipment, remote control switches, garage door
openers, wireless modems, traffic light controllers, emergency pumps to
prevent flooding, even a device from the early 80's that measured the
chewing rate of reindeer.  Some equipment operates relatively rarely,
for example, lightning detection and alert systems.  Some send one-way
data bursts, some interrogate each other for status, others communicate
back and forth regularly.  Eventually, I was able to ID the make,
model, and application of much of the equipment, just by the sound of
the signal as heard over the air.  Over time, much of the equipment
moved to the 315, 433, and 900 MHz (eventually to 2.4, and 5.8 GHz) ISDM
bands, so for those that monitor ISDM bands, the swath of non-stop
signals you still hear, and resultant RF 'fog", was once focused on only
a few HF frequencies.
About fifteen years ago, when HF propagation conditions were "bad", I
was able to track down scores of signals, often to the source, see,
photograph, document, then acquire examples of the equipment, bits and
pieces, documentation, et cetera. When conditions are "good", signals
pour in from all over, making it difficult to find the source.  Was what
I heard regional, from another state, or country?  Tracking signals up
to tens of miles is somewhat easy, even across several valleys, mountain
ranges, and lakes, even to sources inside buildings, but some I had to
give up on, all indications suggesting their source was somewhere else
on the continent.
At one point, I found myself in competition with an odd, unknown at the
time, entity in acquiring some of the equipment, and prices began to
skyrocket.  I was eventually contacted by the CEO of a US based company,
and we exchanged stories.  I was trying to ID equipment, and prevent
much of it from being destroyed, he was trying to run a business.  As it
turns out, his company was acquiring as much equipment as possible from
one manufacturer, and pulling a single IC from the circuitry, as it was
no longer available, then disposing of the remains.  The IC was not
important to me.  We struck a deal.  He doesn't drive up the prices,
well beyond my price range, and in exchange, his techs ship everything
they can't use, to me.  Quite the deal for him, his acquisition costs
dropped, didn't have to pay electronics recycling fees, and everything
was shipped flat-rate from his end, so essentially free.  A few items
acquired here and there, increased exponentially.  A friend likened the
acquisition, and storage of Class C items as the ending scene in the
movie Raiders Of The Lost Ark, the warehouse filled with crates of
unique items.
As with many things, other aspects of life took priority, and although I
continue to acquire unique equipment as I come across it, the forum
dedicated to such equipment is long gone.  Receiving, and tracking
equipment installations have changed, I have not had HF equipment in
operation for such activities since ~2014, and until late last year, I
was interested in what appears to be a wideband radar signal covering
roughly 100 - 500 MHz simultaneously.  At times, I think of creating my
own webpage, far more extensive than what Yahoo allowed, and perhaps
spread out the information across other platforms, such as YouTube, and
In the US, the Class C frequencies are, in MHz:
Powers range from mW to 25 Watts in the US, depending on operating
Frequencies, and usage in other countries is comparable.  Many persons
disregard the frequencies as uninteresting, probably because almost all
modern references mention their application to remote controlled toys.
This can be compared to likening all radio activity, globally, as being
for music broadcasts, because some frequencies are used for that, too. I
suspect we all know better.  Radio controlled toys are one minuscule
aspect of what can be heard on these frequencies, and not too likely,
due to a range of tens to hundreds of feet.
What CAN be heard is roughly 3/4 of a century of devices up to thousands
of times more powerful, with antenna systems ranging from embedded, to
hand-held, to mobile, and some comparable to large broadcast facilities
on mountain tops.
I've had one system operating on 27.255 MHz for several years.  Listen
for a digital signal ~1.5 seconds long, repeating about every 8 seconds.
I'm unsure how much of such equipment is still in use, so what you
hear may be regional, or it may be something I operate.
Some aspects of the installation can be seen in the attached photos.  As
you can tell, what you see, may not be what you think, or expect.  For
reference, the height of the portion shown is roughly that of a 3-story


« Last Edit: October 08, 2021, 0252 UTC by Teotwaki »
NRD-525, Elecraft KX3 and Elecraft PX3 Spectrum Display
76' end fed long wire & 66' off-center fed dipole for 10/20/40 meters
Orange County, SoCal, The better half

Offline R4002

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Re: RTTY Beacon or transmissions on 27.551 USB
« Reply #2 on: October 08, 2021, 1314 UTC »
Datawell Waverider Buoys







I believe that's what I heard yesterday on 27.755 USB 27755 27.755 MHz USB - center frequency seemed closer to 27.756 MHz or 27.757 MHz.

I know the Datawell HF Link is 25.5 MHz to 35.5 MHz (standard coverage) or 35.5 MHz to 45 MHz band (special request).  The 25.500 MHz to 35.500 MHz band is almost certainly the more commonly used band.  25.5 MHz to 28 MHz and 29.7 MHz to 30 MHz are probably very heavily used for these types of transmissions.  Here's another good information page on it:


The Datawell documentation indicates a 50 km range over sea using the "HF data link" 25.5-35.5 MHz.  According to the documentation for the RX-D2 data receiver for the Datawell Buoys - the frequency for the HF link is crystal controlled and the crystal is included installed from the factory - FSK data link 81.92 bits/second BCH (63, 51) error correcting code.

Receiver bandwidth: 1.2 kHz IF bandwidth, 200 Hz detector bandwidth.

Transmitter technical specifications:

The buoy transmitter converts the combined digital data stream which contains the wave height
data, wave spectra, wave direction, seawater temperature etcetera into a high frequency (H.F.)

Technical details:
The HF output signal of the transmitter is FSK modulated with a rate of 81.92 bits per second in
a bandwidth of 200 Hz and a radiated power of 75 mW (19 dBm). The transmit frequency is
crystal controlled and between 25,5 and 35,5 MHz.   

Buoy transmit antenna
The transmit antenna is the interface between the buoy transmitter and the physical channel,
namely the atmosphere.
Technical details:
A vertically polarized quarter wavelength whip with a gain of 2 dBi is used as a transmitting
antenna for the Waverider- and Directional Waverider buoys, except for the DWR-G 0.4m.
The seawater around the buoy (or an other artificial ground plane) is an important part of the
antennas counterpoise and is therefore absolutely necessary for the buoy’s transmission system
in order to radiate its power efficiently. In other words, a buoy without a high conductance
groundplane such as normal soil2 will have a severely limited range.
The transmit antenna is of an omni directional type because the rotation of the buoy is
undetermined with respect to the receiving station.

"The RX-D2 is delivered with a factory-installed receiver crystal. This receiver crystal can be
exchanged to allow reception of other frequencies within the specified frequency range (see
chapter 6).
When the frequency of the receiver needs to be changed, the recommended procedure is to send
the RX-D2 back to Datawell for exchanging of the crystal and subsequent realignment of the
receiver. Please contact Datawell sales for more information."


With these band openings...I bet we'll be seeing a lot more of these types of data link transmissions.  There are a lot of different "Class C" data link, telecommand, telemetry, paging, pager and similar systems all over the 11 meter region. 

27.255 MHz is the big one in the USA.  There are a dozen or so known active frequencies in the 26 MHz region used in Europe, including 26.945 MHz, 26.950 MHz, 26.955 MHz, 26.960 MHz (plus 26.995 MHz, 27.045 MHz, 27.095 MHz, 27.145 MHz, 27.195 MHz and 27.255 MHz). 

26.150 MHz, 26.200 MHz, 26.250 MHz, 26.650 MHz, 26.665 MHz, 26.700 MHz (offset frequencies from 26.7 MHz including 26.695 MHz are popular), 26.850 MHz, 26.935 MHz and several other frequencies are used for on-site paging, including hospital paging services...much like 27.255 MHz is used in the USA.  POCSAG paging signals have been monitored all over the 11 meter band, including on weird offset frequencies like 27.007 MHz, 27.003 MHz, 27.000 MHz, etc. 

I have personally monitored POCSAG paging signals on 27.255 MHz in the USA. 

Here is a page with information on one of the telemetry systems that use 27.255 MHz with 10 watt transmitters:



I know that there are other devices manufactured by the same company that use 26.995 MHz instead of 27.255. 
« Last Edit: October 08, 2021, 1332 UTC by R4002 »
U.S. East Coast, various HF/VHF/UHF radios/transceivers/scanners/receivers - land mobile system operator - focus on VHF/UHF and 11m

Offline ~SIGINT~

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Re: RTTY Beacon or transmissions on 27.551 USB
« Reply #3 on: October 09, 2021, 0044 UTC »
I converted PTR11EXP's video to a wave file and tried to decode the signal but was unsuccessful. The mark and space is irregular and I had a hard time with the baud rate as the signal was wondering around. Difficult to get a good lock. I would have to build a continuous loop on 1 good segment to attempt any further analysis.