unidentified station 27.6 MHz AM narrow

[Neckername]

I have been tuning in to short-wave for a while now and just started trying to decrypt digital signals like psk31. However, this signal is unlike any others I've heard. On the waterfal, it seems to have multiple carriers in one transmission (6 or 7 looking by eye). Then shortly after there are three very spaced out carriers. I have searched everywhere for information on this and cannot dig up anything other than that it is "possibly a weather fax".

 

[ka3jjz]

There is no 'decryption' necessary with a PSK31 signal. This is a well-known amateur radio digital mode, and there's tons of software that will decode it. It is actually illegal to encrypt such a signal, at least here in the US

See this article in our wiki for a summary of modes, frequencies and software for HF digital stuff...(links are always blue)

HF Digital Decoding - The RadioReference Wiki

Your 27600 khz signal could be any number of things, including a CB out of bander (yes, some are known to fool around in the digital world too). Having several carriers within the same frequency is a little odd, though, and not something a typical CBer would know how to do. Interesting catch.

I'm moving this to our data decoding forum to see if someone has some ideas. Mike

 

[Neckername]

Sorry about the misunderstanding. I should have also paid closer attention to where I was posting! I also need to mention that it is not AM narrow, just AM. I also hear replies now sometimes that sound like RTTY signals. Here is a download link to a .wav file sample I recorded. I hope this helps find out what it is! It is driving me nuts!

http://www.filedropper.com/276000khzam

 

[SCPD]

It's probably some control device. 27 Mhz is a common frequency for everything from garage door openers, remote sensors, R/C cars/planes, etc. It's probably FM mode.

 

[Neckername]

I found out it is a pager near the sdr's antenna that is overloading it. Is it possible to decode a pager?

 

[ka3jjz]

If indeed it is a pager - it's actually illegal to decode them, per federal law. However you likely couldn't do it with this signal; chances are that It's been too distorted to be actually decodeable. You would need to find out the actual frequency first...and with a little detective work in the FCC records (assuming here you are in the US) it might be possible to at least identify the offending signal without violating the law.

Mike

 

[DaveNF2G]

Two problems with Mike's answer.

1) It is not generally illegal to decode pagers in the United States. ECPA specifies paging signals originating from stations licensed in the Paging service.

2) There is an exemption in the law for steps needed to identify an interfering signal, however, it could be interpreted to apply only to a licensed party who is trying to identify interference with their own licensed transmissions.

 

[krokus]

I found out it is a pager near the sdr's antenna that is overloading it. Is it possible to decode a pager?

There are programs floating around, that will decode Flex. (Assuming it is a Flex signal.) They do require a discriminator tap, or the equivalent signal from an SDR.

Sent via Tapatalk

 

[ka3jjz]

And you would need to know the original frequency - I kinda doubt the 27 Mhz signal would be decodeable with the mode-induced distortion

Mike

 

[Token]

Another point to consider….the OP stated “I found out it is a pager near the sdr’s antenna that is overloading it. Is it possible to decode a pager?”

The OP does not state where the SDR is, but this sounds an awful lot like a description of the University of Twente, Netherlands, wideband SDR setup. There is a pager located close to the SDR antenna, the pager is on something like 26950 kHz (not sure of the exact frequency, but close to that), and it sends images up and down the covered spectrum.

So, assuming the SDR is located in the Netherlands and is being accessed via the web, and the pager signals in question originate in the Netherlands, the question becomes, do US laws apply?

T!

 

[ka3jjz]

I highly doubt that US law would influence something like this in Holland...assuming that your guess is correct.

Unless the University moves the antenna (and I think it's an active antenna, somewhat like the North Country), I'm afraid not much can be done about it. Fortunately it's in the part of the HF spectrum where neither utilities nor broadcasting uses very much if at all

Mike

 

[DaveNF2G]

Evidently "SDR" has two different meanings. I took the OP's comment to mean that the transmitter was close to his software defined receiver. I don't know what University of Twente's SDR is.

 

[Token]

No Dave, it is the same meaning, Software Defined Radio, remember a number of SDRs are remote accessed via the web, for example I have remote users on one or the other of the remote SDRs I host almost all the time. There is a wide band Web based SDR at the University of Twente, Netherlands ( websdr.ewi.utwente.nl:8901/ ). It is an SDR that can host multiple users at one time, there used to be a limit of 256 users but that was upped recently, and I have seen over 290 active users at one time on the single SDR.

Because of exposure on certain web sites and online articles about Short Wave radio and particularly “mystery” stations like the Russian Buzzer, this is also a point of entry into the hobby for many folks. Lots of first time ever SW listeners drop in there regularly. So the site ends up generating a lot of basic questions by new users. And as I said, it has a close placed pager that generates dozens of questions daily in the chat there, the description here sounds very much like what is seen on the Twente.

T!

 

[DaveNF2G]

Ahhh. Now I understand. I thought it was some kind of special radio system operated by the University. Thanks for clearing that up.

 

[Neckername]

well I believe my sample I uploaded disappeared from the file sharing site. You can go here to the SDR http://websdr.ewi.utwente.nl:8901/ and tune to 27,600 kHz AM. Every now and then you will hear another transmission with it as well. It is not a repetitive computer or anything either. Responses vary in length, tones, and other stuff as well.

 

[Neckername]

Well there are 3 different sounds coming from this transmission. Two main ones, the first one in the general sequence I found when tuning in is mini call that sounds like this Swedish POCSAG Minicall - Signal Identification Wiki. That minicall is ALWAYS followed by a response that just sounds like a long mono-tone hum. However, the third sound is never consistent. The third sound almost always happens in the middle of that hum, and sounds like this POCSAG - Signal Identification Wiki

 

[Token]

well I believe my sample I uploaded disappeared from the file sharing site. You can go here to the SDR http://websdr.ewi.utwente.nl:8901/ and tune to 27,600 kHz AM. Every now and then you will hear another transmission with it as well. It is not a repetitive computer or anything either. Responses vary in length, tones, and other stuff as well.

This data, location, in this case the Twente SDR, was missing from your first few posts, and if you read the responses you will find it led to some confusion.

On Twente there are three main freqs for pagers, 26950, 27600, and 27750 kHz. There are also the many, many, images of the 26950 kHz freq that I mentioned in my response.

The mode used by the pager data on all of these frequencies is FM, not AM.

I have never really messed with pager data, not had any real desire to read it, but the pagers there do NOT sound like either POCSAG or FLEX to me (based on recordings of POCSAG on the web). Specifically the preamble sounds different.

There is a software called PDW that can be used to demood POCSAG and FLEX pager signals. You might try using that to confirm that what is heard on Twente is not POCSAG.

T!

 

[DaveNF2G]

It could be Golay, which is relatively uncommon in the USA but used more elsewhere.