Original post: There was a Sporadic-E opening today and I noted a constant carrier on 28.223 MHz. I noted this the previous day as well but it was stronger today. Just a constant carrier with no identification.
While I was waiting for it to ID, I thought I heard a very slight change in tone.
When I looked at the audio, sure enough it was changing frequency by about 4 Hz as can be seen above. This happened about 5 times a minute.
At the time, I was hearing lots of FT8 stations from France so I presume it was the F5SN beacon listed as 28.223 MHz? I sent an email to inquire but the question and answer got lost somewhere in Google Translate.
I did hear F5SN giving out its ID on the 29th of April so I'm not sure what happened to it.
Not exactly a QRSS (slow morse) signal but unusual all the same.
Update: 18th May 2020. I finally managed to discover thee identity of the mystery carrier on 28.223 MHz.
On the 18th of May, conditions on 28 MHz were really good and the mystery carrier on 28.223 MHz was nice and strong. This time however when I tuned around, I heard the F5BN/B beacon on CW just above the carrier. Not only that but I found an identical CW signal just below the carrier! One beacon, two signals.
Two CW signals with a big carrier in between.... I knew straight away that it had to be an AM signal!
Sure enough when I listened on AM and cut down the bandwidth, I could hear the CW ID on AM.
I took this spectrum of the signal while listening on CW...
What it shows is that the AM signal is being modulated by an 800 Hz tone and as a result, there are three signals... one CW signal 800 Hz above the carrier, the carrier itself and one CW signal 800 Hz below.
If you examine the timing carefully, you'll notice that the carrier frequency drops by about 4 Hz when the carrier is being modulated by the 800 Hz signal.
It's possible that the extra power output required then causes the supply voltage in the beacon to drop slightly resulting in a 4 Hz change in the frequency of the carrier.
As to why the F5SN/B beacon is on AM?? A curios case but it looks like problem solved.
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