Mobile DTV on the cheap

[wb4jfi]

On 1/16/2011 2:06 PM, Bob Bruhns wrote:
> I am still playing with a small VHF-UHF rotatable on an old lamp stand 
> in a back room in Herndon.  Before the switch I could get WBAL, but 
> since the switch, no.  I read that stations were running huge power on 
> digital before the switch, and they dropped way back afterward - like 
> 300 KW to 7 KW???   If so, that was bait and switch.
>
Not really bait & switch.  Many stations went back to their analog VHF 
channel assignments, so the power required to cover the same area on VHF 
can be much less than UHF.  W*USA and WJLA were two stations in DC that 
did, and I'm assuming WBAL went back to 11 as well.

> I was surprised that people were sold UHF-only antennas for digital.  
> I guess it was a matter of the blind (and the crooked) leading the 
> blind.  I am not sure which stations are on what RF bands and channels 
> these days.  I am not sure what would happen if two stations claimed 
> to be on virtual channel 15, maybe the box would ignore one of them, 
> because it tells me the virtual channel number.
>
Yep, many people were looking at the immediate issues, and not the 
long-run.  To be fair, not all stations made the decision to stay on the 
new DTV channel, or return to their analog channel right away.  But, it 
was known that many analog high-band VHFers (7-13) would return to their 
VHF channels.  I kept telling people that UHF-only antennas was very 
short-sighted... Here in Charleston, most/all stations stayed on their 
UHF channels, because they were a lot of low-band VHF analog stations 
(the big three anyway).

In a few markets, particularly smaller ones, some stations went back to 
their low-band VHF channel assignments (2-6) post-transition.  They just 
could not afford to keep those power-hungry UHF tubes fed.  With 
significant cable & satellite penetration, that helped them out.  An 
additional half-million dollar annual power bill, plus replacement tube 
costs wiped out any potential profit.  Too bad they could not recover 
the waste heat and resell it, at least that would have helped!

I don't think two different stations will have the same "virtual 
channel" assigned to them in the same market.  Maybe the same primary 
channel (such as 15.1 & 15.2).  If so, they are actually from the same 
transmission system, just two different program streams.  There are 
cases around the country where different network data streams are pumped 
out of the same transmitter, to appear as different sub-channels.  All 
this magic is done with something called "PSIP", which tells the 
receiver what program/data streams are assigned to what.  If two 
completely separate transmitters (obviously on two separate RF channels) 
announced they were the same channel, I'm not sure how the receiver 
would react.  Maybe Bill can tell us, since he was exposed to DTV much 
more recently than I was!

There are ways to find out what actual RF channel a stations is 
transmitting on, if that interests you.  I know you can go to the FCC 
database, or www.fccinfo.com, and a couple of tv antenna web sites.
Terry

> I do get many more channels with digital than I used to get with 
> analog, and the quality is fine as far as I am concerned - better than 
> NTSC was, although I'm using an old NTSC TV in composite mode with a 
> set-top box. (RF wasn't as good, and I think they forgot to add 
> pre-emphasis on the RF sound channel generator, too.)  I get some 
> breakup now and then, probably from aircraft landing at Dulles, but 
> I'll see how bad it really is when I put the antenna outside!  I have 
> never had cable, it costs too much.
>
>   Bob, WA3WDR
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