[mythtv-users] Antenna amplifier

Allen Edwards allen.edwards at oldpaloalto.com
Tue Aug 5 14:25:47 UTC 2008


Yan Seiner wrote:
> 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
> 
> 

When you get the HDHomeRun, you can put your secondary antenna in the 
pcHDTV input.  Only problem is that you need to figure out how to tell 
myth to assign certain channels to certain antennas, something I could 
not figure out before noticing that the channels were redundant anyway.

Not sure where you live, but here in the SF Peninsula area we have 9 
transmitting 54's channel on 9.3 and 54 transmitting 9's channel on 54.2 
or something.  Point is, I don't need to use that antenna pointing at 54 
for digital.

Allen



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