RadioReference on Facebook   RadioReference on Twitter   RadioReference Blog
 

Go Back   The RadioReference.com Forums > U.S. Regional Radio Discussion Forums > California Radio Discussion Forum > San Diego Metro Area Discussion

San Diego Metro Area Discussion Local area specific discussion for San Diego and Imperial Counties.

Reply
 
LinkBack Thread Tools Search this Thread Display Modes
  #1 (permalink)  
Old 08-01-2011, 12:43 AM
Member
  Premium Subscriber
Premium Subscriber
 
Join Date: Apr 2011
Posts: 233
Default The curious sound of 864.0500 (SD City TRS)

LCN #522 at 864.050 MHz on the San Diego City TRS has a sound unlike the other frequencies.

In the background of every call assigned to this channel there is a strong whistling/warbling signal. I've heard it on my Uniden, and on Mot radios as well.

I thought it might be interference, but there is a predictable 'data' sound to the whistle that changes near the end of the call. I could be fooling myself.

The sound is not subtle, and the same radios on different channels don't exhibit it.

Any ideas what this is from?
Reply With Quote
Sponsored links
  #2 (permalink)  
Old 08-01-2011, 10:41 PM
Member
  Premium Subscriber
Premium Subscriber
 
Join Date: Apr 2011
Posts: 233
Default

Hmm.. I should probably just start by asking: "Does anyone else hear this?"

If not, it's something about my locale or listening equipment.
Reply With Quote
  #3 (permalink)  
Old 08-02-2011, 9:56 AM
inigo88's Avatar
California DB Admin
  RadioReference Database Admininstrator
Database Admin
 
Join Date: Oct 2004
Location: Kern County, CA
Posts: 1,568
Default

I monitored it last night and it sounded the same as all the other voice frequencies, so it may be local interference.
Reply With Quote
  #4 (permalink)  
Old 08-02-2011, 1:46 PM
Member
  Premium Subscriber
Premium Subscriber
 
Join Date: Apr 2011
Posts: 233
Default

Good info! Thanks inigo88.. I'll do more sniffing around. I'm starting to think the 'data' sound comes from the subaudible tones at the end of the voice transmission somehow mixing with my local interference.
Reply With Quote
  #5 (permalink)  
Old 08-03-2011, 10:18 PM
WayneH's Avatar
Moderator
  RadioReference Database Admininstrator
Database Admin
 
Join Date: Dec 2000
Location: Sitting in an airport somewhere
Posts: 8,408
Default

There's always subaudible data ("lowspeed") during a trunked analog call in this situation. If it disappears the call will drop. Then there's the specific disconnect tone/word at the end.
__________________
-Wayne
PM's are permitted by contact list only. Please use direct email: wayne_h at radioreference dot com
Got an admin question? -> Forum Rules & Guidelines
Please follow the forum rules and contact a moderator directly, not via a thread.
Reply With Quote
Sponsored links
  #6 (permalink)  
Old 08-03-2011, 10:45 PM
Member
  Premium Subscriber
Premium Subscriber
 
Join Date: Apr 2011
Posts: 233
Default

I did some exploring and found that this whistle is somehow caused by an NVidia graphics card, even a hundred feet away. It's entirely local.

My guess is that the graphics card is putting out a CW at close to this frequency, and it 'beats' with the signal in such a way as to make the subaudible data audible. You can see that RF is voodoo to me, and this is clearly outside my ken, but at least I know the source.
Reply With Quote
  #7 (permalink)  
Old 11-26-2011, 11:08 PM
Member
  Premium Subscriber
Premium Subscriber
 
Join Date: Apr 2011
Posts: 233
Default

I like threads that come to closure, so I thought I'd correct my own misinformation here.

I borrowed a fine Anritsu spectrum analyzer and went hunting for the source and nature of this signal a bit more. I was wrong to blame the NVidia card.. the source of my particular spur is (with certainty), a Plantronics Audio 630M USB conferencing headset. This little bugger has a small ferrite choke near the USB connector, but puts out an incredibly strong unmodulated (22 Hz wide) signal that starts around 910MHz at power-up and drifts down to 864.053400 MHz as it warms up. It's temperature dependent.

I read about -40dBm off just a Radio Shack scanner antenna.

Disabling the (Windows) device driver does not stop the signal.

Just goes to show, you never know what gadget brings in a hidden splinter for radio listening.
Reply With Quote
Reply

Thread Tools Search this Thread
Search this Thread:

Advanced Search
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are On
Pingbacks are On
Refbacks are On



All times are GMT -5. The time now is 7:10 AM.


Powered by vBulletin® Version 3.8.2
Copyright ©2000 - 2014, vBulletin Solutions, Inc.
All information here is Copyright 2012 by RadioReference.com LLC and Lindsay C. Blanton III.Ad Management by RedTyger
Copyright 2011 by RadioReference.com LLC Privacy Policy  |  Terms and Conditions