[mythtv-users] Semi-OT: OTA, Comcast business HSI and the single coax
meatwad2021 at gmail.com
Fri Jul 25 16:39:59 UTC 2008
Allen Edwards wrote:
> Justin The Cynical wrote:
>> Greetings. This is semi-off topic IMO, but not fully as I'm sure
>> someone on the list may have dealt with a similar situation.
>> I am currently set-up for OTA digital only and my current connection to
>> the world is via DSL.
>> I am switching to Comcast business for my pipe, and would like to make
>> use of a single coax for both.
>> I know that OTA and Comcast television do not mix over the same coax,
>> but what about just data? Is there a splitter or filter that I can get
>> to allow this to work, or am I going to have to run a new line just for
>> the data?
>> I am in Washington county, Oregon in the U.S. if that makes any difference.
> Cable modems use a normal TV channel for the data down and use
> frequencies below channel 2 (around 30 MHz if I remember correctly) for
> the return data. That is one reason the return data is slower.
> Obviously you can run another coax to your computer to bring in the data
> feed. I have more than a dozen coax cables running around my house. I
> just run them under the eves or along the bottom of the siding and drill
> a hole in the wall to get them in the house.
> Back to your question. If I had to combine the signals I would first
> put an amplifier on the antenna to keep the cable signals from going out
> over the antenna to the rest of the world.
Not a good idea. You would need an incredibly wide notch filter (or a
combination of low and high-pass filters re-combined) from just below
52MHz upward to 550MHz. Shortly (2009), the cablecos will begin removing
the analog allocations and replace them with digitally modulated content
(still 6MHz in width) but will eagerly begin to use those channels for
DOCSIS 3.0 which introduced channel bonding. Even prohibitively
expensive frequency agile filters would not solve the problem.
> If the cable company has
> filtered out all the TV channels you have not paid for, you should be
> able to just use a splitter to combine the signals at that point (after
> the amplifier). This assumes that the cable modem is at a frequency
> above all the OTA stations, and I think that is a good assumption. If
> there are still TV signals on the Coax, you would need to filter them
> out. I don't know where you would get such a filter, except perhaps
> through the cable company themselves. You should check the assumptions
> before trying it.
The simple cableco filters used are enough to deteriorate the signal,
not completely wipe it out. Once you overlay the standard OTA, the
amplified OTA signals mixed into the existing cable spectrum will more
than likely turn your inside wiring and the cableco's into unintentional
radiators of unpredictable spurious RF energy at various harmonics in
various strengths. Refer back to Brian Wood's example of unintentional
Anything that mucks up 108-137 or many chunks of 225-400 MHz will
endanger any private, commercial and military air operations in your
vicinity and earn you an unpleasant visit from the authorities such as
Brian's station did.
IF you can run a CAT-5/6 from the cableco's Point Of Entry to the
current location of the modem, simply install the modem at the POE and
use a switch at the desired location. Problem solved.
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