[mythtv-users] HDHomerun signal strength required

[Roger Heflin]

backuppc at sundquist.imapmail.org wrote:
> On Fri, Feb 22, 2008, 7:33 AM, Brian wrote:
> 
>> Actually that situation almost guarantees things are not "OK". Unless
>> the antennas are spaced so that they are receiving the signal in phase
>> with each other, having identical lead lengths will not work well, and
>> will result in at least some phase cancellation.
>>
>> And if they are spaced for proper phasing on one channel, they will be
>> wrong for all others, since phasing depends on wavelength (frequency).
>> Stacked phased arrays are almost always single-channel affairs for
>> that reason.
> 
> ..and..
> 
> on Fri Feb 22, 2008, 8:16 AM, Craig wrote:
> 
>> I wonder if you could receive the south Buffalo transmitters through
>> the 'backside' of an antenna, like the CHannel Master 4221, and the
>> Grand Island and Toronto signals through the 'front'. These antennas
>> have a small lobe of reception off the back that may be quite
>> sufficient to pick up the 3 that are nearby to the south. Lots of
>> people in Toronto are using 4221's to receive Buffalo signals so the
>> reverse ought to work well for you. Diagram of the 4221 pickup
>> pattern is at:
>>
>> http://www.hdtvprimer.com/ANTENNAS/cm4221.html
>>
>> Mounting outdoors is obviously far superior to in the attic. Amping a
>> poor signal often results in a poor signal at higher levels. Combining
>> antennas works for some people but seems to be a black art with a ton
>> of little details that all have to be just right. Start with the
>> simplest solution and see if it is sufficient. Digital reception is
>> way easier than analog.
> 
> Hooboy, I got bigger issues than I thought.  Teaches me to take the free
> advice from the local Radio Shack (should have known better).
> 
> Right now, I've got two of these:
> 
> http://www.radioshack.com/product/index.jsp?productId=2103088&cp=2032057.2032187.2032189.2032205
> 
> I got those over the channelmasters because (a) could buy local and (b)
> the hdtvprimer pages indicated the channelmasters weren't too
> directional, so that I would have more of the possible interference
> problems.  I was under the impression that pointing two boom antennas
> in opposite directions would not lead to interferences, but I guess I
> was wrong.
> 
> My wife would probably kill me if I started going out buying more
> antennas at this point (although the 4221 and 4228 aren't too bad), so I
> would like to experiment more with the two U-75R's that I have now.
> 
> My house is ranch which means the attic is quite long.  If I separate
> the two laterally, will that help?  As you point out above, it doesn't
> make sense to try to calibrate the phasing since I am looking at
> channels ranging from 14 to 43.  Practically speaking, the maximum
> lateral spacing I could achieve would be on the order of 30 to 40 feet
> or so.  I'm not sure that would be enough to make it worth the effort.
> What do you think?  It also would put me closer to big evergreen trees
> at either end of the house.
> 
> I had previously discounted use of a preamp precisely for the issue you
> raise, that some of the channels are quite strong while others are
> quite weak.
> 
> I guess I'll be crawling around in my attic with my wireless laptop
> ssh-ed into my mythtv box checking signals and see what I can get just
> rotating the two antennae currently on the same mast.  If nothing
> works reliably, I may have to break down and try Craig's suggesion and
> put a 4221 or 4228 on the roof this summer and see if the back-side
> approach works.
> 
> Thanks again for the help.
> 

One thing that you can do, is test each antenna separately and note what
channels each gets and how strong it is, if both together are worse than
one single you know some canceling is going on.

Also, the trouble with the attic is there is enough metal reflectors on
the top of the roof to reflect things.

And also get the exact directions of the 2 sources that you have and make sure
to average the direction of each source and point each antenna at the
average direction with a compass.   Just being a few degrees off (around 5-10) 
with a highly directional antenna makes things a lot different.   Each of the 2 
locations with different stations I am pointing at have about a 10degree spread, 
so I pointed at the average of all of the stations,

It is also supposed to be possible to build a filter to filter out stations
from one antenna so that don't mess up the other antenna, though I have not
found exact instructions of how to do this.

                                 Roger