Re: HUM_FORUM: Still gathering Information
- Thanks Tom,
I don't see those TWACS as you call them on the AC line. I guess that
technology has not made it to WV yet. I'm glad you recorded that
because now I know what they will look like. They still read the
meters here manually in this whole area. Yes the spikes are caused by
lightning, turning on and off switches, and equipment. If you want to
see some real junk, record a section of a new High Efficiency washing
machine. You talk about pulse modulation that is weird.
Yes I hear that raspy sound I guess its the TWACS you talked about. I
going to try and load that up in my spectrumlabs and watch it.
--- In email@example.com, Tom Becker <gtbecker@...> wrote:
> > ... The only item I am seeing and have for some time is the AC Line
> frequency of 60 Hertz, appears to be modulated and most of it
> The 60Hz signal itself cannot be directly modulated, but there are many
> signals that are carried on the AC line and are synchronized to it.
> Here is a spectrum (from Spectrum Lab) of a few minutes of mine, for
> example, detected with a VLF receiver. The top blue band is amplitude;
> the two black-background charts represent before (upper chart) and
> (lower) removal of the 60Hz components.
> Beyond the vertical spikes that are caused by lightning (the reason for
> the receiver), the lower chart clearly shows several line-borne
> signals. The strongest here is caused by a modulation scheme used to
> read electric meters, called TWACS. A few strong TWACS calls,
> originated at the substation that serves us about a mile away, are
> at the right end of this period, and the entire chart shows ghosts of
> more distant and weak TWACS signalling. Each ~5-second burst of TWACS
> carries about 32 bytes of data over several miles of distribution. As
> you suggest, TWACS - at least here - is most active at night, when
> meter on the local distribution network is read over 10 hours or so.
> Bursts of TWACS data also appear every 15 minutes throughout the day.
> You can listen, in fact, to my VLF receiver, in real time; you will
> TWACS if you listen long enough, and you can occasionally hear other
> line-borne signals, too. http://188.8.131.52/vlf9.m3u
> Despite being very common, TWACS surely is not a contributor to The Hum
> since it is so transient.