HFU HF Underground
Loggings => 10/11 meters => Topic started by: R4002 on March 21, 2017, 1430 UTC
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Hearing what almost sound like telemetry signals on 27255 kHz this morning. Data bursts roughly 10 kHz wide...varies from every 2 seconds to a 10-12 second wait between bursts. Nothing else on frequency this morning, and the 11 meter band is relatively quiet. Just the usual 27185 (Channel 19) and 27355 (Channel 35) AM voice traffic.
I've heard POCSAG mode paging on 27.255 (CB channel 23) before and I know it is used for various on-site telemetry system in addition to R/C purposes (with 26995, 27045, 27095, 27145 and 27195). I have also logged non-stop tone signals on 27255 (although this very well could have been CBers playing around).
FCC rules permit up to 25 watts carrier power on 27.255 MHz for telemetry, paging, etc...that means 100 watts PEP power in AM mode :D
Update:
Reference FCC Rules:
47 CFR 95.207 (FCC Rules Part 95 Section 207)
47 CFR 95.210 (FCC Rules Part 95 Section 210)
47 CFR 95.207 § 95.207 (R/C Rule 7) On what channels may I operate?
(1) The following channels may be used to operate any kind of device (any object or apparatus, except an R/C transmitter), including a model aircraft device (any small imitation of an aircraft) or a model surface craft device (any small imitation of a boat, car or vehicle for carrying people or objects, except aircraft): 26.995, 27.045, 27.095, 27.145, 27.195 and 27.255 MHz.
47 CFR 95.207b § 95.207b
(b) You must share the channels with other R/C stations. You must cooperate in the selection and use of the channels. You must share the Channel 27.255 MHz with stations in other radio services. There is no protection from interference on any of these channels.
47 CFR 95.207f § 95.207f
(f) Stations in the 26-27 MHz range are not afforded any protection from interference caused by the operation of industrial, scientific of medical devices. Such stations also operate on a shared basis with other stations in the Personal Radio Services.
47 CFR 95.210 § 95.210 (R/C Rule 10) How much power may I use?
47 CFR 95.210a § 95.210a
(a) Your R/C station transmitter power output must not exceed the following value under any conditions:
Channel: 27.255 MHz Transmitter power (carrier power) (watts) 25
Channel: 26.995-27.195 MHz Transmitter power (carrier power) (watts) 4
Channel: 72-76 MHz Transmitter power (carrier power) (watts) 0.75
Since the FCC regulations under 95.210 specifically state transmitter carrier power instead of peak envelope power, just like how the CB rules specify 4 watts maximum carrier power for 26.965-27.405 MHz, that means that peak envelope power (PEP) for 27.255 can legally be up 100 watts (just like PEP on the CB channels can legally be up to 16 watts).
This also means that you can transmit up to 4 watts carrier / 16 watts PEP on 26.995 MHz, 27.045 MHz, 27.095 MHz, 27.145 MHz and 27.195 MHz for R/C purposes. Interestingly enough, 27.255 MHz is included in the R/C services for telecommand and telemetry, which one could infer that the other 5 frequencies could be used for this purpose as well (with less maximum transmitter power than allowed on 27.255 MHz). 27.255 is also the only one out of the six available 26-27 MHz channels that is shared with a legal CB channel.
FWIW, this also translates to a maximum power (PEP) of 3 watts (0.75 watts carrier x4) on the 72.01 MHz to 72.99 MHz and 75.41-75.99 MHz bands.
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Very interesting, I was into monitoring these types of transmissions on 27255 many years ago. There was even a mailing list at one time dedicated to it.
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Very interesting, I was into monitoring these types of transmissions on 27255 many years ago. There was even a mailing list at one time dedicated to it.
Do you have any more info on that? I have been monitoring this frequency the past few months. Really interesting stuff.
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No, I think the mailing list basically died out.
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something i did many decades ago was record the RC data on one of those frequencies and play it back on a transmitter, i watched the kids RC car repeat the steps i recorded.
there was another that used telemetry for a wireless doorbell in a driveway, i made the neighbor go nuts looking out the window when no one was there.
car alarms with the pager, had alot of fun with those, cant imagine how many pagers i set off making people believe their car was being broken into lol.
then the radio shack paging systems, making the kids run home, lol.
even some baby room monitors mainly used 27.145Mhz FM, "hey, i got your baby!" lol.
these days, there is very little activity on those frequencies but back in the day, they were popular and very active and often times could be heard great distances when band conditions were great.
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something i did many decades ago was record the RC data on one of those frequencies and play it back on a transmitter, i watched the kids RC car repeat the steps i recorded.
there was another that used telemetry for a wireless doorbell in a driveway, i made the neighbor go nuts looking out the window when no one was there.
car alarms with the pager, had alot of fun with those, cant imagine how many pagers i set off making people believe their car was being broken into lol.
then the radio shack paging systems, making the kids run home, lol.
even some baby room monitors mainly used 27.145Mhz FM, "hey, i got your baby!" lol.
these days, there is very little activity on those frequencies but back in the day, they were popular and very active and often times could be heard great distances when band conditions were great.
You can still find lot's on 49 MHz. Of course that's not HF but I had a Lo Band handheld that I used to mess with baby monitors with. I did something similar to what you did with the doorbells too, was walking around with a handheld scanner in nearfield mode and found a Dakota Alert MURS sensor. Recorded the channel and CTCSS and would play jumpscare sounds through it at the middle of the night since the intercom receiver for that was a basically a handheld on all the time. You can also use transmit capable SDRs to mess with the garage doors and nowadays lots of wireless home alarm systems to set off the siren.
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One asshat used to activate the tornado sirens in town.
At 4am.
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49 MHz band (49.820 MHz to 49.900 MHz, no official standardized channels...) baby monitors, wireless mics, etc. are still newly made and sold in 2019. I’ve found 2-3 different monitors within 1 mile of me and that’s just driving around with a scanner.
https://youtu.be/gsgtZBfHRK4 (https://youtu.be/gsgtZBfHRK4)
and
https://youtu.be/6Q4iNFKAwN4 (https://youtu.be/6Q4iNFKAwN4)
https://www.hfunderground.com/wiki/index.php/Part_15#15.235_Operation_within_the_band_49.82-49.90_MHz (https://www.hfunderground.com/wiki/index.php/Part_15#15.235_Operation_within_the_band_49.82-49.90_MHz)