[opendtv] Re: Charles Rhodes on SFNs
- From: "Manfredi, Albert E" <albert.e.manfredi@xxxxxxxxxx>
- To: "opendtv@xxxxxxxxxxxxx" <opendtv@xxxxxxxxxxxxx>
- Date: Fri, 25 Jun 2010 14:20:53 -0500
Craig Birkmaier wrote:
>> 1. Unless you deploy a Boston-to-Richmond regionwide SFN, you still
>> cannot reuse the same frequencies in these different markets. The
>> case today is that the same channels ARE used, in every other market
>> up the coast, using the intevening market as the interference zone.
>
> Not exactly. Many frequencies - especially VHF channels - need much
> wider protection, as in hundreds of miles.
Sorry Craig.
Things have changed some with the digital transition, because a lot of VHF
analog stations went and stayed in UHF. But when VHF was used extensively,
Richmond and Phildelphia shared VHF channels, Wash/Balt and NYC did as well.
For instance, Channel 12 is used in Richmond as was used in Philadelphia, and
the DC market was the interference zone. Channels 4, 7, 11, 13 were used in
DC/Balt and in NYC, and Phildelphia was the interfernece zone. (The Balt and
Wash towers are only about 30 miles apart, and the area between the two is
populated with people that commute to either city, so there isn't a lot of
opportunity to keep the two isolated.)
But now, after the transition ended, your point is even more off base.
Channel 42 is used in Richmond and in Annapolis MD.
Channel 7 is used in DC, and a low power Channel 7 transmitter also in
Phildelphia.
Channel 13 is used in Baltimore, and a low power Channel 13 in Philadelphia.
Channels 30, 32, and 42 are now used in DC/Annapolis and in Philadelphia.
Channel 39 is used in Richmond and in DC.
The above examples show that these UHF channels are satisfied to not have
continuous coverage between markets. For example, it would be difficult for
someone in Fredericksburg VA to receive Ch 39 from DC. Maybe with a good
directional antenna it's possible.
You won't do any better than that with single-market SFNs, Craig.
> With SFNs the potential for interference is much more limited and YES,
> you can checkerboard frequencies from market to market, which means
> that every market can have about half of the available channels, as I
> have noted for years.
What I have been trying to get across is that this *IS* how the frequencies are
assigned now.
I will concede that with very dense SFNs, the interference zones would be
reduced. For instance, Channel 39 from DC would be easier to receive in
Fredericksburg if the demarkation line were made a lot tighter. But that
requires the kind of dense mesh of low towers that Doug Lung mentioned, and by
the way you seemed to agree with his assessment when I pointed it out. None of
this "3 or 4 medium powered towers around the beltway" approach.
The European SFNs DO NOT employ such dense mesh topologies.
Bert
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