Monitoring 121.500

[TRTech]

I am currently monitoring traffic on 121.500 NFM. It sounds like a continuous relay signal. There is a continues carrier and operator identifies as Western and LA Center. Signal is pretty strong from my location. Any thoughts on this one. I do have a FAA ATCSS within 20 miles of me and am guessing that may be where it is being repeated from. Not sure why they are repeating it though if it is the FAA.

 

[ecps92]

Please update your RR Profile to show, where you are....

I am currently monitoring traffic on 121.500 NFM. It sounds like a continuous relay signal. There is a continues carrier and operator identifies as Western and LA Center. Signal is pretty strong from my location. Any thoughts on this one. I do have a FAA ATCSS within 20 miles of me and am guessing that may be where it is being repeated from. Not sure why they are repeating it though if it is the FAA.

 

[K5MPH]

Is that not the (121.500 mhz) the International Air Distress VHF Guard Frequency.......

 

[TRTech]

I am in Cooperstown, ND and I am still listening to the carrier.

 

[TRTech]

My understanding is it is the National aeronautical distress channel.

 

[NDRADIONUT]

I dont hear it in fargo...

 

[NDRADIONUT]

It may be coming from the finley air force station...

 

[TRTech]

Still have the FM carrier but no traffic at this time. Thanks NDRADIONUT for the info on not hearing it in Fargo.

 

[TRTech]

That is my guess also on Finley FAA Site.. I have a retired FAA ET friend that I am going to run it by. See what his thoughts are.

 

[NDRADIONUT]

These freqs should be in use at finley if you dont have them running...

364.2000 c norad aicc pri
260.8000 c norad aicc sec
225.8000 c norad bigfoot
228.6000 c norad bigfoot
235.9000 c norad bigfoot
239.7000 c norad bigfoot
252.0000 c norad bigfoot
252.6000 c norad bigfoot
265.4000 c norad bigfoot
271.0000 c norad bigfoot
277.6000 c norad bigfoot
282.6000 c norad bigfoot
288.4000 c norad bigfoot
328.0000 c norad bigfoot
341.5000 c norad bigfoot
355.2000 c norad bigfoot
243.0000

 

[ecps92]

FM ??? The Freq is AM

Still have the FM carrier but no traffic at this time. Thanks NDRADIONUT for the info on not hearing it in Fargo.

 

[NDRADIONUT]

I thought is was p 25....

 

[bryan_herbert]

Switch to AM and check nearby freqs in 25 kHz steps (e.g. 121.450, 121,475, 121.525, 121.550)

 

[TRTech]

I am still monitoring the carrier. The center of the carrier is on 121.5. I tuned both sides with 5 khz steps and looks to be right on 121.500. Yes, the modulation is in narrow FM. Heard it first when receiver was in AM mode and was hard to understand. Turned it to NFM and audio was nice and clear. Guess I could get the IFR Marconi service monitor out but don't think it is necessary. May hook up the the Funcube ProPlus and do some more playing. If it keeps up I may have to drive to the FAA Site and check it out. Seems strange to be right on the Emergency Aeronautical Frequency. I have not heard any traffic on it for an hour or more. Just the carrier but it is still up.

 

[TRTech]

There have been no comments that I have heard from commercial airlines about the signal. I have two receivers go, one on 121.500 and the other scanner aircraft frequencies.

 

[jwt873]

I am still monitoring the carrier. The center of the carrier is on 121.5. I tuned both sides with 5 khz steps and looks to be right on 121.500. Yes, the modulation is in narrow FM.

Carriers have no modulation. They produce silence (or a large decrease in unsquelched receiver hiss) on AM and FM radios. You need a CW or SSB receiver (which produce a beat frequency in order to hear a carrier as a note).

If you are hearing a tone or speech when you select narrow FM then it most likely is FM.

It may be FM, but it's odd having an FM signal smack in the middle of the aeronautical band which is exclusively AM.

 

[ecps92]

Image from another bands ?
Do you get this on more than one Radio ?

I am still monitoring the carrier. The center of the carrier is on 121.5. I tuned both sides with 5 khz steps and looks to be right on 121.500. Yes, the modulation is in narrow FM. Heard it first when receiver was in AM mode and was hard to understand. Turned it to NFM and audio was nice and clear. Guess I could get the IFR Marconi service monitor out but don't think it is necessary. May hook up the the Funcube ProPlus and do some more playing. If it keeps up I may have to drive to the FAA Site and check it out. Seems strange to be right on the Emergency Aeronautical Frequency. I have not heard any traffic on it for an hour or more. Just the carrier but it is still up.

 

[TRTech]

Yes, I am using a Pro 2006 and a Pro 197. Both show the same thing. I am going to hook up my SDR receiver and do a little more checking. I was think about the image thing when I first heard it but seem like a normal signal other than it was FM. I am using two different antennas also. I monitor 121.5 all the time if I am home. It is in the aviation frequency bank in the Pro 2006. This is the first time I have come across this.

 

[krokus]

It may be FM, but it's odd having an FM signal smack in the middle of the aeronautical band which is exclusively AM.

My thought, too.

Have you tried monitoring any other aviation, or AM signals?

Sent via Tapatalk

 

[TRTech]

I just got my SDR receiver set up and tuned the signal. It was centered on 121.500. I tuned it with the spectrum display and showed 121.500. Checked it with upper and lower side band and the carrier was centered at that frequency. At 2.23 pm CDT the carrier disappeared. I can still see a very low level signal on the spectrum display but that is it. Whatever the remote transmitter was, maybe finals went or it was shut down. It sure has my curiosity up??? Thank all of you for your comments. Hope to get to the bottom of this one day.