On 9/2/2010 1:08 PM, mm wrote:
On Thu, 02 Sep 2010 07:56:08 -0400, Jeff
wrote:

On 9/2/2010 2:59 AM, mm wrote:
On Wed, 1 Sep 2010 20:05:02 -0700 (PDT),
wrote:

snip

http://www.hdtvprimer.com/ANTENNAS/types.html

I have to take time to read this. It looks complicated.

I Googled a bit and that seemed about right. It does seem to cover a
lot for one page! I'll have to read it now myself!

It is, however, the first thing I've read that at all addresses what I
asked about elsewhere, about waves received by elements that bend and
go in the oppoosite directino, about the waves cancelling each other
out.

Well, actually they refer to this in a much different context, iiuc,
but I'm please that it says anything at all. I only have a little
bit of theory and a tiny bit of practice, and when I get an idea, I'm
glad to see it's not crazy.


Nonessential reading:
Question: How does the energy collected by the directors get to the
cable?
Answer: It is re-radiated to the driven element as normal radio
waves.

Question: Why don’t the re-radiated waves go backward or laterally?
Answer: Because all the directors cancel each other in those
directions.

Question: Why don’t these re-radiated waves prevent the diffraction
of incident waves inward toward the boom?
Answer: Because the phase of the re-radiated waves has been changed
by about 90 degrees, so they neither subtract nor add to the incident
waves.

Question: How did the director currents get changed by 90 degrees?
Short answer: The element lengths control this. The director
currents are shifted -90 degrees while the reflector current is
shifted +90 degrees.

Long answer: This graph shows how the current induced in a rod is
affected by the length of the rod. The phase changes quickly with a
small change in element


Those are some answers!
....

Ah, but it probably has an amplifier. It's much better to have a
strong signal from the antenna, than a weak signal that is amplified.
Amplifiers are recommended when there is a long distance from the
antenna to the tv. Of course maybe that used to be more true, because
the antenna would amplify the "noise" too. Now most noise is filtered
out in the process of digital detection. Maybe. I'm no techie.


That is my take also.

Note if you take the number of elements and do a rough gain
calculation, the numbers don't add up to all antenna gain. My rough
guess is about 8 dB or so.

Not sure what you mean here. Are you talking about the antenna the OP
brought up. It does have an amp after all.

Without the amp. Probably just a couple dB on VHF.

Jeff

If you're not talking about that, pelase explain a little.