On 24 mayo, 05:06, John KD5YI wrote:
On 5/23/2011 5:10 PM, Wimpie wrote:



On 22 mayo, 20:04, 'Captain' Kirk
wrote:
I'm living in a wooded area and am trying to hit our club repeater
reliably. *It's cloudy now so I'm and getting a bit of ducting but I
have a lot of trees, mostly poplars, in the direct path. *I would have a
line of sight if not for the trees as I'm up enough in altitude. *I can
cut the trees, they're mine, but finding the right ones is difficult and
i don't want to waste the whole grove.

I go from keying the repeater with no intelligible signal to not being
able to hit it. *Today I actually have an S meter reading due to the
clouds. I am currently using a J-pole and will put up a Yagi soon but
wonder if NVIS would work on 2m? *I have only seen references to it
being applied in HF.

'Captain' Kirk DeHaan
N6SXR

Hello,

As you can see from the replies, we are in the speculation phase. If
you would like to receive more specialized feedback, you should
provide us with more details about the path, antenna height, nearby
obstacles, vegetation in between, etc (maybe some pictures).

As we are discussing 2 m wavelength, obstacles that may be optically
in the path may introduce less attenuation then expected, but
obstacles that are outside the optical path can still introduce
attenuation.

At 10m (33ft) from your antenna, the first Fresnel zone is about 9m
(30 ft) wide. In addition, the tree attenuation at these frequencies
is not that high. I think of 0.15 dB/m (I hope somebody can confirm
this). It can be less due to diffraction (bending) of the waves around
and over the trees.

I am almost sure, removing some poplar treetops at 10m from your
antenna or more will not change the situation from marginal to good
(because of the relative low attenuation).

Just to be curious, what type of poplar do you have at your site.

With kind regards,

Wim
PA3DJS
www.tetech.nl

According to his lat/lon numbers, he is 19 miles from the repeater and
its bearing is 185 degrees (ref true north) from him. *The repeater is
about 2000 feet above him (not including the tower height). *He is in a
valley that has little altitude variation until his signal reaches the
mountain.

This info is available from Google Earth using his numbers.

All of this leads me to think that something else is wrong. *I can hit a
repeater 20 miles from me with 5 Watts and its antenna is on a 300 ft
tower. My antenna (half wave end-fed dipole) is on a 20 ft mast.

I have tons of deciduous trees between me and the repeater but the
signal is always solid with no noise on it (I don't have an S-meter) and
I have never had a report of noise on my signal until I tried to carry
on a conversation with 200 mw output power.

Cheers,
John

Hello John,

With Google maps, results (distance and bearing) are similar (based on
the data given by Kirk).

If the trees south of his antenna are the problem (I am not
convinced), he needs to cut lots of them. They are about 150m from
his antenna, and at that distance first Fresnel zone width is about
30m (100ft).

It seems flat when looking to the activities in the valley. I hope
somebody can make a path profile and loss simulation to see what is
the real obstacle.

With kind regards,


Wim
PA3DJS