Discussion:
Modulation and Digital Cable with Comcast
(too old to reply)
2005-03-11 20:18:16 UTC
Permalink
I have Comcast Digital Cable for my home. The box is a Motorola DCT-2000.
I also have a Channel Plus 5445 (4-channel modulator)

I am able to inject 4 channels into my home signal but I have a few
questions / problems.

Depending on what channel I inject to ( 77, 79, 81, 83), I lose some
of my digital channels. The channel displays something similar to ,
"signal unavailable should be available soon". If I disconnect my
modulator the channels appear fine. If I choose different channels to
inject to, I lose different digital channels.

How can I find which channels are available for creating modulated channels?
Also, I'm unclear on Low Pass Filters
The ChannelPlus Low Pass Filter LPF-750 passes CATV channels 2 to 116
Would this work? Does Comcast use any channels higher than 116?

thanks,
tom
weitrhino
2005-03-12 03:02:05 UTC
Permalink
Digital cable channels are compressed into a number of phase angles. This
allows for multiple digital channels to reside in the bandwidth a single
analog channel would use. When you introduce your modulator signal on a
frequency already in use for, say, 8 other digital channels, you
simultaneously introduce the problem you see.

The message displayed by the digital box is a default message designed to
show whenever the box cannot read the signal it's tuned to. Switching the
frequencies used will effect different channels.

So, how to find the 'open' bandwidth is the question. You could ask your
local company. Or you could tune to each digital channel and enter the box
diagnostic screen, probably option 3 for inband data, and see each frequency
being used. This would be a time consuming process. Better to ask the
local techs about it. Each system will vary.

Channel 116 corresponded to a 750mHz system. It's likely any channel above
550mHz is used for digital services including modems and VOD. Don't assume
that because you don't see a channel using a particular frequency that it is
not in use.

If you decide you must use a frequency already in cable use, a demodulator
should be used on that frequency before inserting your own signal. ($$$)

weitrhino
Post by
I have Comcast Digital Cable for my home. The box is a Motorola DCT-2000.
I also have a Channel Plus 5445 (4-channel modulator)
I am able to inject 4 channels into my home signal but I have a few
questions / problems.
Depending on what channel I inject to ( 77, 79, 81, 83), I lose some
of my digital channels. The channel displays something similar to ,
"signal unavailable should be available soon". If I disconnect my
modulator the channels appear fine. If I choose different channels to
inject to, I lose different digital channels.
How can I find which channels are available for creating modulated channels?
Also, I'm unclear on Low Pass Filters
The ChannelPlus Low Pass Filter LPF-750 passes CATV channels 2 to 116
Would this work? Does Comcast use any channels higher than 116?
thanks,
tom
t
2005-03-14 15:12:37 UTC
Permalink
I checked the diagnostics on my DCT2000 and also checked the digital
channels that I watch. It seems that of those channels, the highest
frequency used by my digital channels is 741mHz (mostly HBO channels).
If I use the LPF-750 would that leave the channels at the 741mHz
intact? or is 741 too close to 750 that it would eat those channels?
Post by weitrhino
Digital cable channels are compressed into a number of phase angles.
This
Post by weitrhino
allows for multiple digital channels to reside in the bandwidth a single
analog channel would use. When you introduce your modulator signal on a
frequency already in use for, say, 8 other digital channels, you
simultaneously introduce the problem you see.
The message displayed by the digital box is a default message
designed to
Post by weitrhino
show whenever the box cannot read the signal it's tuned to. Switching the
frequencies used will effect different channels.
So, how to find the 'open' bandwidth is the question. You could ask your
local company. Or you could tune to each digital channel and enter the box
diagnostic screen, probably option 3 for inband data, and see each frequency
being used. This would be a time consuming process. Better to ask the
local techs about it. Each system will vary.
Channel 116 corresponded to a 750mHz system. It's likely any channel above
550mHz is used for digital services including modems and VOD. Don't assume
that because you don't see a channel using a particular frequency that it is
not in use.
If you decide you must use a frequency already in cable use, a
demodulator
Post by weitrhino
should be used on that frequency before inserting your own signal.
($$$)
Post by weitrhino
weitrhino
Post by
I have Comcast Digital Cable for my home. The box is a Motorola
DCT-2000.
Post by weitrhino
Post by
I also have a Channel Plus 5445 (4-channel modulator)
I am able to inject 4 channels into my home signal but I have a few
questions / problems.
Depending on what channel I inject to ( 77, 79, 81, 83), I lose some
of my digital channels. The channel displays something similar to ,
"signal unavailable should be available soon". If I disconnect my
modulator the channels appear fine. If I choose different channels to
inject to, I lose different digital channels.
How can I find which channels are available for creating modulated
channels?
Post by
Also, I'm unclear on Low Pass Filters
The ChannelPlus Low Pass Filter LPF-750 passes CATV channels 2 to 116
Would this work? Does Comcast use any channels higher than 116?
thanks,
tom
Gary J Tait
2005-03-14 22:41:46 UTC
Permalink
Post by t
I checked the diagnostics on my DCT2000 and also checked the digital
channels that I watch. It seems that of those channels, the highest
frequency used by my digital channels is 741mHz (mostly HBO channels).
If I use the LPF-750 would that leave the channels at the 741mHz
intact? or is 741 too close to 750 that it would eat those channels?
The channels are 6 Mhz wide. IMO, you have plenty of room.
Post by t
Post by weitrhino
Digital cable channels are compressed into a number of phase angles.
This
Post by weitrhino
allows for multiple digital channels to reside in the bandwidth a
single
Post by weitrhino
analog channel would use. When you introduce your modulator signal
on a
Post by weitrhino
frequency already in use for, say, 8 other digital channels, you
simultaneously introduce the problem you see.
The message displayed by the digital box is a default message
designed to
Post by weitrhino
show whenever the box cannot read the signal it's tuned to. Switching
the
Post by weitrhino
frequencies used will effect different channels.
So, how to find the 'open' bandwidth is the question. You could ask
your
Post by weitrhino
local company. Or you could tune to each digital channel and enter
the box
Post by weitrhino
diagnostic screen, probably option 3 for inband data, and see each
frequency
Post by weitrhino
being used. This would be a time consuming process. Better to ask
the
Post by weitrhino
local techs about it. Each system will vary.
Channel 116 corresponded to a 750mHz system. It's likely any channel
above
Post by weitrhino
550mHz is used for digital services including modems and VOD. Don't
assume
Post by weitrhino
that because you don't see a channel using a particular frequency
that it is
Post by weitrhino
not in use.
If you decide you must use a frequency already in cable use, a
demodulator
Post by weitrhino
should be used on that frequency before inserting your own signal.
($$$)
Post by weitrhino
weitrhino
Post by
I have Comcast Digital Cable for my home. The box is a Motorola
DCT-2000.
Post by weitrhino
Post by
I also have a Channel Plus 5445 (4-channel modulator)
I am able to inject 4 channels into my home signal but I have a few
questions / problems.
Depending on what channel I inject to ( 77, 79, 81, 83), I lose
some
Post by weitrhino
Post by
of my digital channels. The channel displays something similar to
,
Post by weitrhino
Post by
"signal unavailable should be available soon". If I disconnect my
modulator the channels appear fine. If I choose different channels
to
Post by weitrhino
Post by
inject to, I lose different digital channels.
How can I find which channels are available for creating modulated
channels?
Post by
Also, I'm unclear on Low Pass Filters
The ChannelPlus Low Pass Filter LPF-750 passes CATV channels 2 to
116
Post by weitrhino
Post by
Would this work? Does Comcast use any channels higher than 116?
thanks,
tom
weitrhino
2005-03-15 05:56:10 UTC
Permalink
Post by t
I checked the diagnostics on my DCT2000 and also checked the digital
channels that I watch. It seems that of those channels, the highest
frequency used by my digital channels is 741mHz (mostly HBO channels).
If I use the LPF-750 would that leave the channels at the 741mHz
intact? or is 741 too close to 750 that it would eat those channels?
A well designed filter should not interfere at 741mHz. There may be
additional services above this, however. Perhaps Music Choice? If you
insert your modulator above 750 you should be in the clear. A few systems
do run to 860mHz, but mot many.

weitrhino

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