On 6/5/2011 10:59 AM, John S wrote:
On 6/4/2011 6:20 PM, Wimpie wrote:
On 4 jun, 23:26, John wrote:
On 5/24/2011 8:47 AM, Wimpie wrote:

Well, I have applied some numbers today and I am changing my mind that
the trees are not the problem.

If my numbers are correct: The repeater, 19 miles away, is 1900 feet
above his elevation. At that distance, the antenna will appear be about
240 feet lower than actual due to earth curvature. That makes the
antenna appear to be about 0.954 degrees above the horizon.

That is equivalent to 60 feet at 3600 feet. In other words, 60 foot
trees closer in will be completely in the way. The hurtful part of this
is that his antenna at 45 feet will have a lowest angle of radiation
(take-off angle) of .7 degrees, right into the near trees. The next lobe
above that is at 2.2 degrees. Between those two lobes is a null.

In short, I think his antenna is in a null. I think the only answer for
his present situation is to raise the antenna another 10 feet.

What do you think?

73,
John

Hello John,

This link:
http://www.tetech.nl/divers/Kirk_Repeater_USA_1.png
shows the path profiles with and without trees (from Radio Mobile,
VE2DBE). I will keep it there for some weeks.
I used 30m (98ft) high trees (so they are easy to see).

The trees cover some additional part of the first fresnel zone, but
the average canopy will be lower and the absorption loss is not that
high at 146 MHz.

So yes, there is influence from the trees, but not that much I think.
If you want to get some increase in signal, you need to remove lots of
them, and he don't want to do that. Note that the first trees are
160m away from his antenna (info from google earth, based on data
provided by Kirk).

With kind regards,


Wim
PA3DJS
www.tetech.nl


In that case, perhaps it is due to his antenna being at a height that
puts the target into a null. Along with low repeater output power, I
suppose that could cause it.

Thanks, Wim.

73,
John - KD5YI

Okay. I take that back. I just ran a simulation with EZNEC and it shows
twice as much uV available at the receiver than Radio Mobile, so my
conclusion is that a pattern null is not involved. I'm stumped.

73,
John