Obnoxious audible tone to deter listening

[freqhopping]

Anybody ever heard of this?

I was at MotoGP race (motorcycle equivalent of Formula One) in Spain and was scanning for team radios. In the 450-470 range believe I may have found the freqs but there was an audible tone on them that quite successfully deterred me from trying to listen.

What sort of radios? Could this be filtered out some way by running the audio through some sort of filter?

However, I did find the radio feeds of the commentators, in Spanish, German, French and English. I had a close call hit or two and some other freqs but I don't know Spanish and couldn't ID them. I was really nice to be able to listen to the English commentators calling the race live, it's the guys who do the commentary for what is aired on SPEED.

 

[mkewman]

was it before or after the transmission, describe what it sounded like. was it a tone or some sort of digital noise. a garbled noise? a chirp?

 

[Jay911]

It didn't by chance sound like telemetry, did it?

I went to the Champ Car (er CCWS, whatever it's called this week) race in Edmonton, AB this past summer and there were DOZENS of channels that were saturated with this sound that I'm accustomed to hearing coming from oil wells and other such stuff as telemetry carrier signals. However, it had a DCS code, and very occasionally, another user could be heard (often down in the mud) with another DCS or CTCSS code.

I don't live in Edmonton so I don't know if this is a regular signal that just washes out the entire band in the area of the race circuit (airport grounds).. at the time, though, I was reasonably convinced that it was specific jamming to prevent people from listening to the event - especially considering that they declined to publish any freqs this year.

 

[k9rzz]

Was it low pitched? Perhaps the PL tone (Private Line). It seems that most FM radios have the audio filtered so you don't hear it ... my FT736R ham radio has a broad audio response and when I listen to the ham repeaters I can hear that PL and it's very annoying. Why you would hear the PL on your scanner whne normally you dont? ... got me, just thinking out loud.

 

[bna92]

If it was around 457 MHz, you might have been picking up the national railway's system. Did it come up on one or two frequencies, or on many frequencies? The railway's tone is about 1kHz, and pretty loud. What city are you in, by the way?

 

[mkewman]

Was it low pitched? Perhaps the PL tone (Private Line). It seems that most FM radios have the audio filtered so you don't hear it ... my FT736R ham radio has a broad audio response and when I listen to the ham repeaters I can hear that PL and it's very annoying. Why you would hear the PL on your scanner whne normally you dont? ... got me, just thinking out loud.

FYI: PL = subaudible. you're probably hearing some sort of interference or buzz. i don't know what you're hearing on the ham repeaters, but it taint a CTSS tone.

 

[freqhopping]

It was a steady tone that occurred throughout the transmissions. It was probably in the range of 5000-8000 Hz and was on several freqs. I was in Cheste, Spain (39 29' 22.39"N 0 37' 36.96"W ).

 

[bpckty1]

Could it have been a "pilot tone" similar to what I understand is used on the 220 MHz trunked systems?

 

[LordJ]

It could have been the Motorcycles engine noise...?

 

[loumaag]

I have heard such a thing passing through Wichita Falls, TX. There is some PS activity that has that going (I don't think we have it in the DB). A medium high pitched tone that overlays the transmission rendering listening very difficult and absolutely "headache producing". Since I only pass through WF I have not figured out what it might be, maybe someone from the area could help out.

It seems like I asked this question (about WF) previously but I don't' remember the answer. But in any case I think that what I heard there is what the OP heard at the race. Obviously the actual radios being used probably have a filter that removes the tone.

 

[n5usr]

FYI: PL = subaudible. you're probably hearing some sort of interference or buzz. i don't know what you're hearing on the ham repeaters, but it taint a CTSS tone.

Yes, you can hear the CTCSS tone on occasion. I've heard plenty of ham and even some commercial repeaters' tones. Usually it's just because the level of the generator is set too high, but I've run across some that did funky things - such as a local 220 machine, it doesn't transmit a PL tone but if you turn on PL when using the repeater, it actually amplifies the tone to the point others listening will usually comment on your bad power supply hum.

A PL tone is not actually subaudible, although they get commonly called that. The PL range is 67 to 250 Hz, while the human hearing range is down to 20 Hz at the low end. Better receivers will filter the PL range with a high-pass filter, so you don't hear it - or at least it's very quiet - but it can be especially noticeable if you use a good speaker with low-end response. (Wow, were the tones ever loud when I plugged my old scanner - which apparently filters nothing - into my car stereo! )

 

[902]

I don't know what your tone is for and won't guess since I haven't heard it. You can, however, use an outboard DSP device to filter all tones and only convey the voice to you. The ones I am aware of are not handheld devices, but may still suit your needs.

I have one of these that I use for VHF weak signal work:
http://www.mfjenterprises.com/products.php?prodid=MFJ-784B
See the automatic notch filter feature. I've hooked it up to a number of receivers and when it's on the scanner, it will even filter out paging tones completely.

 

[bna92]

I managed to find a recording of the train tone. I had forgotten about the data burst every few seconds... was it something like this?

 

[loumaag]

I managed to find a recording of the train tone. I had forgotten about the data burst every few seconds... was it something like this?

The one I encountered in WF was lower in tone and had no data bursts.

 

[902]

I managed to find a recording of the train tone. I had forgotten about the data burst every few seconds... was it something like this?

That's 2280 Hz (I used an audio spectrum analyzer). The data burst falls inside 1100 - 1800 Hz.

2280 Hz might be used for E&M signaling. It's probably triggering a carrier detect circuit when it disappears.

 

[freqhopping]

I managed to find a recording of the train tone. I had forgotten about the data burst every few seconds... was it something like this?

What I heard was higher. I haven't been able to find any tone files around 5k Hz just one that went from 1k to 10k. It was in the middle where it matched what I heard.

 

[902]

The one I encountered in WF was lower in tone and had no data bursts.

Do you remember what band it was on?

 

[loumaag]

Do you remember what band it was on?

Yes, UHF PS band. It came up again (while I was passing through last weekend) on one of the common UHF freqs I have programmed in the 396T in the truck. I really didn't notice which one, but disabled the system until I got out of range.

 

[902]

Only thing I could think of is maybe Decatur's MPT trunked system on 453 MHz. But they're far.

 

[loumaag]

Only thing I could think of is maybe Decatur's MPT trunked system on 453 MHz. But they're far.

No, I came up 287 from DFW and had to disable the system between Bowie & Henrietta and couldn't put it back on until way after Electra. There is speech on the frequency, but it sure is tough to take with the tone.