[mythtv-users] Understanding HD Antennas ( was HDHomeRun and jumpy video)

Brian Wood beww at beww.org
Wed Sep 26 20:32:12 UTC 2007

Drew Tomlinson wrote:
> On 9/15/2007 8:51 PM Brian Wood wrote:
>> Kevin Hulse wrote:
>>> On Sat, Sep 15, 2007 at 11:29:42AM -0600, Brian Wood wrote:
>>>> Michael T. Dean wrote:
>>>>> I tested the antenna balanced on a ladder in my front room and found it
>>>>> worked pretty well.  It worked significantly better in the attic
>>>>> (because it was higher).
>>>> The general rule is: twice the height, twice the signal.
>>> 	Now that's a handy bit of information... thx.
>> As was pointed out it's a "rule of thumb", not entirely accurate and
>> subject to a lot of possible factors that can change it, but it is more
>> or less correct most of the time.
> I had read somewhere that there are "heights" or "rows" (?) that provide 
> better reception than others.  In other words, if one mounts his antenna 
> in between the good reception "heights", lowering it into the next lower 
> good "height" will get better reception even though it's lower.  Is this 
> true and if so, how can one tell at what heights are optimum for mounting?

It is *theoretically* true, under some conditions (generally only found
on an antenna test range).

At the extreme, at microwave frequencies (over 3Ghz.), you can get
"fresnel zones" where this effect shows up clearly.

At TV frequencies, even UHF ones, with common TV antenna designs and
under real world conditions you can pretty safely ignore it.

TV antennas are designed to receive a very wide range of frequencies,
and the effects you speak of are very frequency-dependent. So, if you
found an "ideal" height for one channel it would almost certainly not be
ideal for other channels.

All broad-band TV antenna designs are a series of major compromises.

This is of interest to wave propagation and antena design experts, and
is not really of practical use to homeowners.


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