251.875 MHz (AM mode) frequency

scan_nepal

Member
Joined
Dec 17, 2007
Messages
67
Location
NEPAL
Came across what is most likely telephone conversation in this frequency. Heard both sides. However, even after the end of conversation, the transmission didn't stop. I heard keyboard sound along with one of the callers whispering. I am stumped what it could possibly be. Signal was loud and clear. I am in Nepal. Any ideas?
 

letarotor

Member
Premium Subscriber
Joined
Dec 19, 2002
Messages
941
Location
Arlington, TX
Wireless microphones. Did you try to listen in various modes like FM, FMN, wide FM, etc modes or just in AM? I thought I was receiving satellite communications last year and there were three different frequencies right in that same frequency range you're talking about I found active over a period of about a month. I researched the frequency (or really frequencies) and realized there are manufacturers that have wireless microphones in that frequency range and on those frequencies I was picking up traffic on. It took a little time to find what I was looking for but eventually I had the manufacturer of the microphone and other frequencies they used also. Now I don't remember who they were or what some of the other frequencies might have been.

In my case, it turned out to be a church that was practicing on Saturday nights for the songs and other presentations they were going to do on Sunday morning. It sounded like a youth director and maybe some younger people. He was real loud and clear and anybody close to him would come in a lot clearer. But some of the conversation I really couldn't hear because it was too far away from what I'm guessing was a lapel mic.

I don't recall hearing any DTMF tones. If you were unable to hear what was being said clearly, I guess it could be a WBFM phone patch? I used to hear a lot of those and they still occur but I don't think they can be tuned in quite as easily as they used to with LSB and USB. I've been able to tune in phone patches with AF1 and a lot of the NIGHTWATCH guys in years gone by. But I will occasionally hear one of the wideband carriers and I can hear the DTMF tones even though it sounds like the bandwidth on the AM signal is not wide enough for things to come through clearly. I'm not sure how they go about doing it nowadays but I think it's a lot more unusual to be able to tune in the traffic nowadays like we could do even 15 years ago.

Brian (COMMSCAN)
 

scan_nepal

Member
Joined
Dec 17, 2007
Messages
67
Location
NEPAL
Thanks for your feedback, Brian. Come to think about it, I don't know why I didn't bother to switch to other modes just by pressing one button! But it sounded so clear with both sides coming in broadcast-quality audio. I do have a log of one wireless mic frequency I monitored here during a conference in a hotel. It was 219.2 MHz and if I remember correctly it was in WFM mode.

Anyways, what surprised me was the lack of DTMF and hook off after the end of the conversation. It seemed like the transmitter simply stayed on even after the conversation ended. And the transmission disappeared after 1 minute or so. I have that frequency locked and loaded for possible reappearance soon.
 

letarotor

Member
Premium Subscriber
Joined
Dec 19, 2002
Messages
941
Location
Arlington, TX
Thanks for your feedback, Brian. Come to think about it, I don't know why I didn't bother to switch to other modes just by pressing one button! But it sounded so clear with both sides coming in broadcast-quality audio. I do have a log of one wireless mic frequency I monitored here during a conference in a hotel. It was 219.2 MHz and if I remember correctly it was in WFM mode.

Anyways, what surprised me was the lack of DTMF and hook off after the end of the conversation. It seemed like the transmitter simply stayed on even after the conversation ended. And the transmission disappeared after 1 minute or so. I have that frequency locked and loaded for possible reappearance soon.
It definitely sounds interesting and it has me wondering. If it was that clean and clear it probably was an AM mode transmission. I wonder if it could have been a satellite transmission that you received? I believe most of those are in a form of FM but they might also be in AM mode? And it sounds like you do have the experience with the WFM reception on the wireless microphones so that's good to hear. It definitely sounds interesting and now it has me wondering what it might be indeed. If you learn anymore, please update. And good luck confirming it also!

Brian (COMMSCAN)
 

scan_nepal

Member
Joined
Dec 17, 2007
Messages
67
Location
NEPAL
Update:

I did limit searching of the frequency range 250 MHz to 270 MHz and lo and behold, found another frequency. It is 259.075 MHz and like Brian mentioned, it was in FM mode. On AM mode, it was almost impossible to make out the audio. The signal strength was not as strong as original one and this is definitely a wireless microphone. The reason being someone with a pretty good voice is practice singing! No music means it is a karaoke program of some kind.

Anyways, this is an interesting discovery for me. Maybe I should build one ground plane antenna centered on 260 MHz for better reception!
 

letarotor

Member
Premium Subscriber
Joined
Dec 19, 2002
Messages
941
Location
Arlington, TX
Update:

I did limit searching of the frequency range 250 MHz to 270 MHz and lo and behold, found another frequency. It is 259.075 MHz and like Brian mentioned, it was in FM mode. On AM mode, it was almost impossible to make out the audio. The signal strength was not as strong as original one and this is definitely a wireless microphone. The reason being someone with a pretty good voice is practice singing! No music means it is a karaoke program of some kind.

Anyways, this is an interesting discovery for me. Maybe I should build one ground plane antenna centered on 260 MHz for better reception!

I'm glad you were able to confirm it. And now that you mention it, I do recall hearing somebody one time with a wireless guitar microphone somewhere in the military aviation band. They were trying to play some AC/DC music and of course Deep Purple's Smoke on the Water 😎 I think I may have also caught a karaoke machine in the past but I never did confirm that for sure. Good detective work!

Brian (COMMSCAN)
 
Top