[Lowfer] OT: Growling audio on MWBC signals

Steve Ratzlaff steveratz at wildblue.net
Wed Dec 22 23:07:40 EST 2010


I've found several more with +/- 16 Hz sidebands tonight besides 1160 KSL. 
850 KOA, 1040 WHO, 1110 KFAB. And a bunch that it's not clear if the offset 
is on the dominant station, or just off-frequency stations. Some just have a 
+16, some a different - offset with a + offset, some +12 to +20; some -20 
to -10, etc. Very interesting!
73,
Steve
NE Oregon

----- Original Message ----- 
From: "C. Turner" <turner at ussc.com>
To: "Discussion of the Lowfer (US, European, &amp;UK) and MedFer bands" 
<lowfer at mailman.qth.net>
Sent: Wednesday, December 22, 2010 1:31 PM
Subject: [Lowfer] Growling audio on MWBC signals


> Slightly OT, but interesting nonetheless:
>
> Some weeks ago I happened to tune in our local 69 horsepower (formerly)
> "clear channel" AM radio station (1160 kHz - KSL) and upon listening to
> it in SSB mode using exalted carrier methods, I heard a rather obnoxious
> growling on the audio that disappeared when "normal" AM or synchronous
> AM techniques were employed.
>
> Upon inspecting the carrier, I noted that there was a pair of 16 Hz
> sidebands responsible for the "growling."  Curious, I asked the
> engineer, Randy, K7SL - who I happen to know - and here is an excerpt of
> his response:
>
> "16Hz is a low speed data stream used to send messages to warranty
> receivers.  These guys are battery operated 10 year lifetime receivers
> that attach themselves to things like Baby Cribs, Saws, etc.  These
> receivers set off alarms if a factory recall happens.  They then give
> details for the recalls.  The data also contains clock correction
> signals for home user clocks.  The clocks currently using WWVB don't get
> a good enough signal inside noisy environments and the 50kW signal from
> KSL and other Clear Channel stations cover the the US better.
>
> "Currently the signal ...  is just a test signal that repeats itself.
>  If [one] looks at night on other strong AM stations [you] will see
> similar signals. There are other uses for the signal, but I don't
> remember them right now.  All I know for sure is that it eats up a lot
> of transmitter power.  Of course any 1/2 db added to the modulation
> looks like it is stealing all the power when you look only at modulation
> levels around 95 to 100% (chuckle).
> 73,
>
> Clint
> KA7OEI/CT



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