Interference on VHF Channels and WBBM-DT

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Tom...

Unfortunately, things are not as simple as they seem.

It's all about interference protection.

The FCC must protect full service stations... That means
you must observe co-channel (same channel) and adjacent channel
spacing for starters. This is not as simple as it sounds.

You cannot just drop a channel in and hope that it will work.

The channel allocation tables were generated by following the
basic rules of spacing and then going from there.

In the analog world you could not have two stations on adjacent
channels (in the same market) , e.g. 8 and 9, or 15 and 16,
or 31 and 32 for example.

BTW, 4 and 5 are not adjacent, 6 and 7 are not adjacent and 13 and 14
are not adjacent so they don't follow these rules!

Several of the requirements of the design of the digital system
were that you could have adjacent digitals and that you could have
digitals adjacent to analogs.

There are problems with some of the above scenarios, but these seem to
be caused by bad receiver design, and hopefully as we fully get into the

5th generation chip sets, these problems will go away.

If you want to take a serious look at the Chicago market, channel by
channel,
keep in mind that adjacent spacing is roughly 300kM for co-channel and 100kM
for adjacent.

This exercise would give you a very simple view of the headaches of the
channel allotment table.

When all is said and done, the digital core channels will be 2 - 51.

That means that channels 52 through 69 will go on the auction block.

Now, here is another problem!! What if a station has it's analog AND digital
channels OUTSIDE the core channels?? They can apply for a new digital
channel which is INSIDE the core!! BUT... they cannot move to the new
channel
until after the analog shutdown!!

This will require some stations to build a new transmission facility. Maybe
a new
tower or a new antenna or a new transmitter or some combination!!

Why are the low VHF channels being kept??

That's very simple: We are talking about a relatively large wavelength
compared
to channel 52 and up. Larger wavelength means bigger antennas for comparable
results!! The wireless people don't want to be dealing with BIG antennas!!!

Oh, and there is that IMPULSE noise problem too!!!


Don, W4WJ





----- HDTV Magazine Tips List -----

I need help
why are they FCC) keeping the Dig OTA in the 2-6
channel range? What did they FCC)
give up? in the bandwidth? I only see above Ch 55 +
going away.. where is all this bandwidth the FCC is
selling? sorry for a probably dumb question
TomV

--- [email protected]_ (mailto:[email protected]) wrote:

> ----- HDTV Magazine Tips List -----
>
> Unfortunately WBBM (analog Ch 2) did not get the
> luck of the draw on their
> digital
> channel. That was their assignment from the FCC
> table, channel 3. The
> reception
> problems with WBBM-DT have been ongoing since day
> one.
>
> As many people know, the low VHF channels, 2-6,
> suffer greatly from impulse
> noise.
>
> High VHF, channels 7-13, is a bit better off when it
> comes to this type of
> interference.
>
> Impulse noise to an analog signal might be some
> white dots here and there in
> the picture, or it might be more severe.
>
> Impulse noise to a digital signal can cause minor
> tiling or the blue screen
> of death or anything in between.
>
> What is impulse noise?
>
> How about we start with power line noise!! Bad
> lightning arrestors, loose
> hardware,
> leaky transformers, salt buildup on insulators etc
> etc etc...
>
> Florescent lights, neon signs, lawnmowers, elevator
> motors, fish tank
> thermostats,
> electric fences, door bell transformers light
> dimmers etc etc etc can all
> develop
> problems and saturate an area with RF trash!!
>
> WBBM-DT cannot move to another channel, until the
> analog cutoff.
> When will that be?? 1 JAN 2007?? 1 JAN 2009??
> That date
> has yet to be set.
>
> WBBM cannot increase power on their current channel.
>
> The other factor that is going against them is the
> fact that they are the
> only
> VHF digital in the Chicago market.
>
> So, for OTA in Chicago, you put up a small UHF
> antenna for everything but
> CBS, and then for CBS you need to put up a single
> channel Yagi (maybe aided
> with a low-noise GaAS FET preamp) and pray!! It
> doesn't help the average TV
> guy that a channel 3 yagi is very large in
> comparison to a UHF antenna.
>
> Impulse noise CANNOT BE FILTERED!! A channel 3
> bandpass
> filter might reduce the overall impulse noise a bit,
> but you still get the
> garbage
> on channel where the receiver is looking!!
>
> So, if you are in Chicagoland, it is going to be a
> long and bumpy ride for
> WBBM-DT.
>
>
> Don, W4WJ
>
>

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