• From: "John Willkie" <johnwillkie@xxxxxxxxxxxxx>
  • To: <opendtv@xxxxxxxxxxxxx>
  • Date: Thu, 18 Dec 2008 16:10:28 -0800



You can't just shunt transmitter output, or you will burn out the
transmitter's final power tube or transistor array in a flash  Some stations
- but not a whole lot - have dummy loads, which provide about the same
impedance as an antenna load, and stations with circulators (also somewhat
rare) or other rf switches can direct the output to their dummy load.


However, it's much simpler to unplug the input to the analog transmitter, in
which case the station will be transmitting "snow", or turning off the
transmitter, which means there is real snow.  Some transmitters will cause
transmission of "snow" in the absence of sync signals.   


Some can tell the difference in the quality of the snow when their
transmitter is off-air versus actively creating "snow."  In my experience,
the contrast range in the snow is significantly less and the "grain" is
bigger when the transmitter is "snowing."  It's the difference between white
noise and pinkish noise.


One can even detect the difference between an FM station that is off-air (no
sound) and one where the carrier is present, but no audio signal
(transmission noise only.)


John Willkie




De: opendtv-bounce@xxxxxxxxxxxxx [mailto:opendtv-bounce@xxxxxxxxxxxxx] En
nombre de dan.grimes@xxxxxxxx
Enviado el: Thursday, December 18, 2008 3:44 PM
Para: opendtv@xxxxxxxxxxxxx
Asunto: [opendtv] Re: STATEWIDE DTV TEST


Tom: "Was this one of those tests where the analog TV would display a

No, they actually shut the transmitter off, supposedly for 2 minutes at a
time and several times during the day for each station (every one of them).
Of course, I can't imagine them actually powering down the transmitter.  But
my mother-in-law said that her picture actually went to snow.  So perhaps
they shunted the power.   

My mother-in-law thought they were having problems and told my wife that the
TV stations kept breaking down.  And I even have the digital converters
hooked up to her TV.  But she still watches the analog.  She one of those
people that just has it on in the background so she must not have heard or
seen any messages before the test, if there was one. 

I, too, find myself still watching the analog and only turning on the
digital tuner to see what is on 10.3 (PBS Create) or 3.3 (Universal Sports).
Otherwise, I am lazy.  Truly, the digital won't be full time until they all
get turned off. 


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