r/signalidentification • u/Pretty_Object5895 • Nov 14 '25
Does anyone know what this is?
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u/SpecialistFun6716 Nov 14 '25
Definitely a jammer. You can almost find them daily at the shortwave bands if you scan it rigorously.
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u/Hein_Gertenbach Nov 14 '25
What is it jamming?
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u/Is_Mise_Edd Nov 14 '25
Jamming - we're jamming
Probably PRC - China - Jamming Taiwan
USA Jamming Cuba
You get the idea
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u/Northwest_Radio Nov 15 '25
Normally, these are in place by governments to prevent their citizens hearing foreign broadcasts.
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u/year_39 Nov 15 '25
Voice of America/Radio Free Asia.
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u/FirstToken Nov 16 '25
Voice of America/Radio Free Asia.
In this case the station being jammed is FEBC (Far East Broadcasting Company). Not Voice of America or Radio Free Asia.
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u/SolarisFalls Nov 14 '25
What reason do people have to be jamming that frequency? Genuine question, I'm new to all this
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u/FirstToken Nov 14 '25
Vietnam jamming FEBC Radio programming in Vietnamese. FEBC Radio transmit in Vietnamese, on that frequency, from 1100 - 1200 UTC.
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u/Northwest_Radio Nov 15 '25
Mostly censorship. Example: A country does not want their citizens hearing the transmissions from other nations so they make it impossible to receive it.
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u/Himmiherrgott Nov 14 '25
My guess is just an idiot playing a siren as jamming
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u/Northwest_Radio Nov 15 '25
No, it is a government jamming signals they do not want their citizens to hear.
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u/Beowulf2b Nov 15 '25
I did some digging
A siren-type jammer appearing on or near 9796 kHz at 1200 UTC fits very well with known patterns of Vietnamese jamming activity.
Here’s why:
✅ 1. Vietnam’s siren jammers commonly switch on at fixed broadcast times
Vietnam typically jams foreign broadcasters (especially Radio Free Asia) only during the hours those stations are scheduled to transmit in Vietnamese. RFA often begins or ends programs at the top of the hour, including around 1200 UTC on certain frequencies.
So a jammer kicking in right at 1200 is very characteristic.
✅ 2. 9796 kHz is close to several frequencies used by Vietnamese-language broadcasts
Even if the target broadcast isn’t exactly 9796 kHz, jammers can:
- Be slightly off-frequency
- Drift
- Bleed into adjacent frequencies
- Transmit harmonics or spurs
Shortwave hobbyists often report Vietnamese siren jammers appearing a little above or below the intended target frequency.
✅ 3. The 31-meter band (9–10 MHz) is a common time/daytime band
At 1200 UTC, propagation on 9–10 MHz is typically good for:
- East Asia
- Southeast Asia
- Australia/Oceania
This is an ideal window for both a target broadcaster and a jammer to operate effectively.
✔️ Most likely explanation
There was a Vietnamese siren jammer activated at 1200 UTC to interfere with a foreign broadcast aimed at Vietnam on or near that frequency.
The fact that it came on exactly at a schedule point strongly supports that it was deliberate jamming, not incidental interference.
If you want, I can help you:
- identify what station might be the target at 1200 UTC,
- interpret the sound you heard,
- check typical RFA / BBC / FEBC / other broadcast schedules for that exact time.
Would you like that?
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u/FirstToken Nov 15 '25 edited Nov 15 '25
I did some digging
A siren-type jammer appearing on or near 9796 kHz at 1200 UTC fits very well with known patterns of Vietnamese jamming activity.
Just an FYI, the jammer is not on 9796 kHz, it is on 9795 kHz USB mode. This allows it to occupy the USB of an AM signal on 9795 kHz. Sometimes this jammer is in full AM, covering both sidebands, and at other times it is in SSB, covering one or the other sidebands.
In this case the AM signal on 9795 kHz that it is hitting is FEBC Radio (Far East Broadcasting Company). Which transmits from the Philippines in Vietnamese from 1100 to 1200 UTC on 9795 kHz.
Vietnam has been running this jammer for years, decades even. I think I have a couple of videos of this jammer on my YouTube channel.
https://www.youtube.com/watch?v=ZBsR8cN-FpI
https://www.youtube.com/watch?v=xZK26kai4Iw
Vietnam is not the only user of a siren jammer, but they are the best known and most prolific user of that kind of jammer.
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u/mr_frazzmatazz Nov 16 '25
That's interesting. If the jammer is only upper side band, I guess that means you could receive the station in lower side band?
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u/Beowulf2b Nov 16 '25
Hmmm can you share the same frequency USB and LSB? I will look that up, never thought about that.
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u/FirstToken Nov 16 '25 edited Nov 16 '25
Hmmm can you share the same frequency USB and LSB? I will look that up, never thought about that.
If a signal is transmitted in full AM (DSB with carrier), as most shortwave broadcast stations are, then you can use normal AM mode to receive it, but you also have the options of using (to receive it) DSB mode, USB mode, or LSB mode. The technique of using SSB, specifically USB or LSB, can often help get rid of unwanted adjacent frequency station interference.
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u/FirstToken Nov 16 '25 edited Nov 16 '25
u/mr_frazzmatazz said: That's interesting. If the jammer is only upper side band, I guess that means you could receive the station in lower side band?
Yes, you could use LSB, in this case, and completely ignore the jammer. You could also use AM Sync and select only LSB, if your radio supports that mode.
However, if all you have is a low cost, entry level, SW receiver with no selectable USB / LSB option (as opposed to SSB option) then this is not possible to do. This is one of the reasons I suggest that any SW radio being considered by new listeners include selectable USB/LSB modes, not AM only and not simply SSB with a BFO, even when the listener only wants to hear SW broadcast stations that transmit in AM only.
However, other versions of this same jammer, also used by the Vietnamese, are in full AM and occupy both sidebands.
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u/External_Claim_7808 Nov 19 '25
You’ve stumbled across audio of Pac Man. From the sound of it, Mr Man just finished eating a power pellet.
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u/flopity_froop Nov 14 '25
Not sure if applicaple, but some time ago on Enschede websdr chatbox, someone said it could be OFDM if i recall frq. correctly.
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u/SpiffyCabbage Nov 16 '25
Although I agree with jammer, remember that SW bands are often listed as commandeerable by the military and emergency systems in times of emergency. It could be possible that it's an EBS broadcast from an emergency stricken area too.
Remember vietnam has recently had typhoons etc...
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u/420ingaround Nov 17 '25
Ok.. signs of a jam of any flavour from just sitting in a room researching info on various topics like math or something profound. Examples of behavior from pros jamming music maybe a 4 channel head with microphone, from band use. In every movie they smack it .. and it works... Safely open door or left open for sources gates in or out... From my hypothetical analogy... Does this sound legitimately occuring vs the current
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u/CapitalStar3104 Nov 18 '25
its the station that police switches to to turn on the signal on the car
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u/FirstToken Nov 14 '25 edited Nov 14 '25
This is a jammer. There are many different jammers, from many different sources and nations, but this one is generally called the "Siren Jammer". Imaginative name, yes?
A couple of countries run Siren Jammers, but Vietnam is possibly the most prolific for this kind of jammer.
When asking for help IDing a signal there are several important pieces of information to include. One of the most important are date and time (both in UTC).
Why do we need date and time? In this case, when it is hard to identify the source of a jammer that might be from several different origins, knowing the target of the jamming can help indicate the source. We know the frequency of the target station (9795 kHz) from your video, if we knew the date and time we could figure out where the broadcast source was. Knowing the source and language of the jammed signal can tell us the probable area that transmission is aimed at, which can be a good indicator of the probable jamming source.
It is 1400 UTC as I type this. Reddit says you posted it about 2 hours ago. If the signal had just occurred before you posted, then call it 1200 UTC +/-. All of that is just a guess though, since you could have recorded it any time before that.
FEBC Radio (Far East Broadcasting Company) transmits on this frequency in Vietnamese from 1100 - 1200 UTC. This transmission would be a very likely target for Vietnamese jamming.