[opendtv] Re: Transition report

James Albro wrote:

> I don't think your specific case provides very much insight
> regarding the effectiveness of ATSC broadcasting on VHF-HI
> channels.
>
> As I understand it, you have two antennas, an Antennas Direct
> DB4 and a Radio Shack double bowtie over screen.

Yes on the Radio Shack, upstairs. I have two DB4s connected together
with a combiner, downstairs. And in the past, I checked VHF analog
reception often, to see how much signal and ghost I was getting. So I
know that the DB4 pair was doing okay for VHF, if not great. I also
compared it with the analog UHF signals I was getting, just to see if I
had a shot.

> Antennas Direct claims the DB4 has almost 14 dB gain for UHF
> channels.  They make no claim as to gain at high VHF.  Channel
> Master, which makes both 2-bay and 4-bay bowtie-over-screen
> antennas, says they are UHF only and lists the VHF-HI gain as
> "N/A".

The two makers design very much the same item. I recently read an
article about these, but where I don't remember, that claimed that even
in hi VHF, they met the FCC guildelines for gain. Something like 6 dB
gain in high VHF. But in any event, the Radio Shack upstairs provides
the valid check. It has real VHF-length rabbit ears. And these antennas
react precisely the same way to ABC7 and CBS9, and they also react the
same way to the two Baltimore VHF channels.

Side note: I also use the DB4 "antenna farm" for FM/IBOC radio. Even
lower freq than high VHF.

> For viewers who need to receive both UHF and high VHF channels
> they offer a Digital Advantage antenna, essentially a UHF corner
> antenna with gain that has a VHF dipole grafted on the back.
> The high VHF gain is only 2 dB at best and it's non-directional
> (as you would expect).  The addition of the VHF-HI dipole
> increases the antenna width to 47 inches, compared to their UHF
> bowtie-over-screen antennas that are only 25 inches wide.
>
> So what you have are antennas with elements that are too short
> for the high VHF band, that probably have negative gain at
> VHF-HI frequencies; which therefore don't work well (or at all)
> for receiving high VHF stations.  Why does the failure of these
> antennas to receive channels 7 and 9 for you indicate that the
> stations' power levels are too low?

Because, upstairs, ABC7 used to be one of the very easy ones to receive
when it was UHF, and it is now pixellating continuously. There is no
"not a VHF antenna" excuse with the Radio Shack antenna. It has real VHF
elements, fully extended. The simple truth is, ABC7 and CBS9, and NBC11
and CBS13 in Baltimore, have decided that moving back to VHF, and
reducing their power and signal margin rather dramatically, was a good
decision. It was not. They are finding out now.

Bert
 
 
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