[mythtv-users] Antenna amplifier
Yan Seiner
yan at seiner.com
Tue Aug 5 12:45:49 UTC 2008
Allen Edwards wrote:
> Yan Seiner wrote:
>
>> Brian Wood wrote:
>>
>>> Yan Seiner wrote:
>>>
>>>
>>>> More on the Olympics. NBC is broadcasting it. I never watch NBC. It
>>>> comes in with the weakest signal - my pcHDTV won't lock in on it. (Now
>>>> I find out.)
>>>>
>>>> So two alternatives:
>>>>
>>>> 1. Get up on the roof and fsck with the antennas to the great amusement
>>>> of my family and neighbors.
>>>>
>>>>
>>> Certainly the cheaper approach.
>>>
>>>
>>>
>>>> 2. Get a 2 way amplified splitter. About 9 to 12 DB should be plenty.
>>>> Any suggestions on model/brand/suitability?
>>>>
>>>>
>>> Depends, you may just be boosting the noise floor by 9 - 12 db.
>>>
>>> To do it properly you need to know where the xmtr is, what it's ERP and
>>> countour is, your antenna specs, your height, losses in your signal path
>>> etc. etc.
>>>
>>> An antenna in good condition, properly aimed and mounted is a good
>>> start. More basically - can your neighbors get a usable signal on NBC
>>> from an antenna? If not, you are not likely to do much better.
>>>
>>> I've read that capture cards require more signal than TV sets, but this
>>> doesn't make sense to me as the card makers are almost certainly using
>>> off-the-shelf tuners. If you can get +10dbmv. great, even zero should be
>>> watchable.
>>>
>>>
>> Well, here's what's really bizarre.
>>
>> I have two highly directional antennas at 90 degrees. They're far
>> enough apart where interference is not an issue. They go to an
>> unamplified splitter, there to an old Blonder-Tongue 6DB amp and 4 way
>> splitter, and then to the TV and the myth backend.
>>
>> The TV has a passive splitter that splits the signals to the analog and
>> digital antenna inputs. The TV shows a consistent signal strength
>> across all channels of about 60% (meaningless except that the signal
>> strength is approximately the same). Myth gets a straight run from the
>> B-T amp to a pcHDTV card. That card *also* shows a consistent signal
>> strength across all channels of about 60% - except NBC on channel 16
>> which comes in at a dismal 7 to 13%. Can anyone take a shot at
>> explaining this?
>>
>> Channel 16 is the closest station and has the strongest signal, so the
>> issue could be overfeeding, but I get dismal results with a straight run
>> to the pcHDTV with no splitters or amps....
>>
>> --Yan
>>
>>
>
> Let me see if I understand you correctly. You are combining the output
> of two antennas with a hybrid combiner (splitter). Then going to an amp
> that has 4 outputs, each of which has 6dB gain???. One of these outputs
> goes to a 2-way splitter that goes to the two TV inputs. Another of the
> outputs goes to the myth pcHDTV card.
>
> You have some unexplained behavior with your NBC station.
>
> Try disconnecting one of the antennas (the one without NBC) and see what
> happens to the signal strength of NBC relative to the other channels.
>
> You asked for an explanation. My guess is that you have a nasty notch
> in the passband of that station due to the two antennas and the TV set
> deals with it and the pcHDTV doesn't. This would be more likely if NBC
> is not directly down the throat of its main antenna but is a little off
> on the side lobe and the other antenna is picking up enough signal to
> mess up the equalizer in the pcHDTV. Just a guess which you should be
> able to verify by removing the second antenna.
>
> I tried combining two antennas and the results were terrible, similar to
> what you are describing.
>
>
This actually makes sense....
I think I'll get on the roof and realign the antennas as a first step.
The next step is to buy an HD HomeRun for Myth.
--Yan
--
o__
,>/'_ o__
(_)\(_) ,>/'_ o__
Yan Seiner (_)\(_) ,>/'_ o__
Personal Trainer (_)\(_) ,>/'_ o__
Professional Engineer (_)\(_) ,>/'_
Who says engineers have to be pencil necked geeks? (_)\(_)
"I worry about my child and the Internet all the time, even though she's too young to have logged on yet. Here's what I worry about. I worry that 10 or 15 years from now, she will come to me and say 'Daddy, where were you when they took freedom of the press away from the Internet?'"
--Mike Godwin, Electronic Frontier Foundation
More information about the mythtv-users
mailing list