DTV issues

[Mark Casey]

Some of the issues with DTV. December 5, 2008.

Power--Most DTV stations are not at full power, so a comparison is hard to 
make. (WFSB in Hartford is at full power, 1,000,000 watts on CH 33.) Some 
stations are running less than 1%, with many less than 10%. But on the FCC's 
TV query, you can see where most stations are incrementaly raising power. 
Right now things are changing every day. It is a very interesting time in 
TV.

Multipath--Will probably greatly improve reception at some locations that 
had a slightly ghosty analog signal. However, some locations that had 
strong, but unwatchable, or nearly unwatchable analog signal may dissapear 
completely with DTV.

VHF high band (7-13) vs. UHF--Lower frequency signals still go over the 
horizon and over hills better than high frequency ones. This does not change 
for DTV. So, if the reciever is far from the TX site, and not on a hilltop, 
VHF might be the best. But, UHF channels get to operate at far higher power, 
so even with their lessened porpagation abilities, a channel 14 or 20 might 
be a good choice for a station owner to request. Overall, given the 
propagation and power factors, I'd say the best channels would be any of the 
VHF low band channels (7-13)  or the bottom of the UHF band (14-30). From my 
experience, after you get above around Channel 30, the ability of any signal 
top get over a hill is degraded that it really affects home reception 
severely. If you are line of sight--fine for higher channels, but with a 
hill or large building in the way ther are problems. Thes are not major 
problems in flat areas of the country, but are problems even with the 
smaller hills in the Boston area. I'm 12 miles from Ch 40 & 57 with a small 
hill in the way and, no matter how good of an antenna,  (couldn't) watch 
either of then but channel 59 in New Haven, at 50 miles,  is clear with no 
nearby hills in that direction.

Antenna size--Each element on VHF channel 7 is around 18" , for a total of 
36" for 2, at VHF channel 13 its' about 15" , for a total of around 30", at 
UHF channel 14, it's about 6" for a total of 12" , while at UHF channel 50 
is goes down to around 3 or 4" for maybe 8" across the 2 antenna element 
about. So it really depends on what type of antenna you have as to what's 
going to be recieved. There was some talk that one of the major antenna 
companies would be making a updated antenna sized for channel 7 to 50. Maybe 
they have already. That would make sense. Or, in order to cut down on space 
needed, maybe you can take the long low band channel 2-6 elements and cut 
them down to 18" or so. But, if space is not a consideration and you have an 
existing TV antenna that gives good performance on both VHF and UHF there is 
no real reason to change.

Class Power Limits--DTV power limits are 20% of Analog. But there is 
supposed to be an improvement factor in digital over analog that might make 
up for the lower power. Channel 7-13 DTV class limit is 63,200 watts. 
Channel 14-50 class limit is 1,000,000 watts.

Decoding--Reciever decoding quality varies greatly with these first and 
second generation dtv recievers and converters. Some will not decode a good 
signal, some sound but no audio. As the reciever chipsets get better, most 
of these problems should g away.

DTV Recievers--Are pretty good. I bought one flashdrive size unit for a 
laptop last year. On my friends' kitchen table in Ft. Lauderdale, Florida 
with a 14" portable antenna we got over 16 digital channels including 5 or 6 
out of market signals. For the limited set up we had and the DTV stations 
running mostly low power, it was pretty impressive reception. At my location 
, so far, every channel that had or has a decently watchable analog signal 
and has an operating digital station is recieved fine in digital. However, 
two of the snowy analog channels that have DTV channels are not always 
received on the digital side. But those DTV's are not at full power yet, so 
the jury is till out on those.

Who knows, maybe Ch 7-13 will do for digital what Ch 2-6 did for analog 
years ago, maybe not, or maybe it will be Ch 14-20 that will be the best. 
Or, probably, with cable and satellite in place, off air reception won't be 
a very big factor at all . We should see how it works out by next spring.

Mark Casey
K1MAP
near Springfield, Mass.


----- Original Message ----- 
From: "Larry Weil" <kc1ih@mac.com>
To: <boston-radio-interest@lists.BostonRadio.org>
Sent: Wednesday, December 03, 2008 2:33 PM
Subject: RE: CH 40 Analog was shut down Sun nite



> -----Original Message-----
> From: boston-radio-interest-bounces@tsornin.BostonRadio.org
> [mailto:boston-radio-interest-bounces@tsornin.BostonRadio.org]
>  On Behalf Of Jim Hall
> Sent: Wednesday, December 03, 2008 1:33 PM
> To: boston-radio-interest@lists.BostonRadio.org
> Subject: RE: CH 40 Analog was shut down Sun nite
>
> One of the problems I have encountered in helping people is
> that they don't
> understand that most of the stations are moving to the UHF
> band, even if
> their virtual channel number remains the same. So the old
> long pole rabbit
> ears won't work and you need an antenna with a good UHF element. I am
> wondering how my reception of WHDH-TV will be once they move
> from UHF back
> to VHF. I imagine I will have to extend the VHF poles on the
> antenna (which
> at the moment I have reduced to minimum).
>

Except that a lot of the stations will go back to VHF in February.  So you
really can't check things out until after the switchover to see what
channels are coming in, and to make appropriate adjustments.  For instance,
WHDH-DT is currently on Channel 42, but will return to actual channel 7 when
7 analog goes off the air.  But WLVI-DT will remain on actual channel 41.
but will be mapped to virtual channel 56.

Confusing?  Even those of us who work with this stuff every day are having
fun keeping it all straight.

Larry Weil
WHDH/WLVI Master Control