NVIS and VHF? (Update)
 

On Jun 2, 8:23*am, 'Captain' Kirk DeHaan
wrote:
Sal M. Onella said the following on 6/1/2011 10:37 PM:

snip

How much power are you putting out?

How well do you hear the repeater; are there times when it fades below
squelch while you're listening to other people?



My TM-721A is putting out 35 watts. *At least that is the spec. *The
repeater is always scratchy and barely readable. *I've only had one time
when it even showed up on the S meter. *That was low clouds so I assume
it was cloud bounce.

--
'Captain' Kirk DeHaan


You indicated that you're working other repeaters with ease. Blaming
the trees sounds right.

I think a 2m beam is the way to go. I've used one at Field Day for
ten or so years from south of San Diego and easily worked 100 miles
into Los Angeles, simplex, obviously. The improvement in performance
is dramatic with 15 dBi gain, compared to approx 2 dBi gain of an end-
fed dipole, your j-pole. My two beams were less than 50 dollars
apiece at ham swap meets. Mount with elements vertical.

I just did an experiment and, as I expected, a 10 dB increase in
signal strength took me from unreadable to Q5 copy with tolerable
background hiss. (I used switchable attenuators to set up the signal
test conditions and a distant repeater as the test signal.)

If the repeater is no worse than "barely readable," 10 dB should fix
you up.

By the way, the gain effect is not so great that you'd lose the other
repeaters, unless one just happened to hit a deep null by bad luck.

"Sal"

NVIS and VHF?
 

On 5/23/2011 5:53 PM, 'Captain' Kirk DeHaan wrote:

This is the repeater I am trying to access, 146.780, K7JEP. I have been
playing with Google Earth and getting coordinates so I can go over to my
neighbors property and stand on the ridge between our properties and see
if I can see the repeater and my house. Hopefully that will help me
locate the suspect trees.


Suspend a heavy object from a rope over level ground. If I have plugged
in the correct numbers, the repeater will be on a line drawn by the
shadow of the rope at 12:55. That is, the repeater will be directly
below the sun at that time.

Maybe you can get an idea of the path to the repeater that way.

73,
John

NVIS and VHF?
 

On 5/24/2011 8:47 AM, Wimpie wrote:
On 24 mayo, 05:06, John 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

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

NVIS and VHF?
 

On Sat, 04 Jun 2011 12:26:33 -0500, John S
wrote:

On 5/23/2011 5:53 PM, 'Captain' Kirk DeHaan wrote:

This is the repeater I am trying to access, 146.780, K7JEP. I have been
playing with Google Earth and getting coordinates so I can go over to my
neighbors property and stand on the ridge between our properties and see
if I can see the repeater and my house. Hopefully that will help me
locate the suspect trees.


Suspend a heavy object from a rope over level ground. If I have plugged
in the correct numbers, the repeater will be on a line drawn by the
shadow of the rope at 12:55. That is, the repeater will be directly
below the sun at that time.

Maybe you can get an idea of the path to the repeater that way.

73,
John

Clever trick, but methinks I have an easier way. I've sighted 1
degree beamwidth microwave dishes this way:

1. Place a road map on a flat surface[1]. If you can't find a road
map, print a Google Maps or equivalent road map on a piece of
paper[2].
2. Pound a nail or push pin into the map at your location.
3. Find a distant mountain, that's also visible. Pound a nail into
the map at its location and sight between the two nails to the distant
mountain.
4. Without moving the map, find the distant repeater location on the
map and pound in a 3rd nail or push pin.
5. Sight from the nail at your location, to the nail at the repeater
location. What you see is where it's located.


[1] Yes, the earth really is flat.
[2] When I didn't have a printed map handy, I've used my laptop LCD
screen and 3ea flat head screws.


--
Jeff Liebermann
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558

NVIS and VHF?
 

On 6/4/2011 5:31 PM, Jeff Liebermann wrote:
On Sat, 04 Jun 2011 12:26:33 -0500, John
wrote:

On 5/23/2011 5:53 PM, 'Captain' Kirk DeHaan wrote:

This is the repeater I am trying to access, 146.780, K7JEP. I have been
playing with Google Earth and getting coordinates so I can go over to my
neighbors property and stand on the ridge between our properties and see
if I can see the repeater and my house. Hopefully that will help me
locate the suspect trees.


Suspend a heavy object from a rope over level ground. If I have plugged
in the correct numbers, the repeater will be on a line drawn by the
shadow of the rope at 12:55. That is, the repeater will be directly
below the sun at that time.

Maybe you can get an idea of the path to the repeater that way.

73,
John

Clever trick, but methinks I have an easier way. I've sighted 1
degree beamwidth microwave dishes this way:

Easier than what I suggested? Actually, all he has to do is step outside
at 12:54 and look at the Sun's location. (I admit it is more accurate to
do this in the winter.)

1. Place a road map on a flat surface[1]. If you can't find a road
map, print a Google Maps or equivalent road map on a piece of
paper[2].
2. Pound a nail or push pin into the map at your location.
3. Find a distant mountain, that's also visible. Pound a nail into
the map at its location and sight between the two nails to the distant
mountain.
4. Without moving the map, find the distant repeater location on the
map and pound in a 3rd nail or push pin.
5. Sight from the nail at your location, to the nail at the repeater
location. What you see is where it's located.


[1] Yes, the earth really is flat.
[2] When I didn't have a printed map handy, I've used my laptop LCD
screen and 3ea flat head screws.

I am afraid I cannot tell whether items [1] and [2] are just screwing
with me or that you are sincere.

John

NVIS and VHF?
 

On 6/4/2011 5:39 PM, John S wrote:
On 6/4/2011 5:31 PM, Jeff Liebermann wrote:

By the way, Jeff, you have a great deal to offer the group by way of
your vast experience. If I have been disrespectful of that, then I
apologize.

73,
John

NVIS and VHF?
 

On 4 jun, 23:26, John S wrote:
On 5/24/2011 8:47 AM, Wimpie wrote:



On 24 mayo, 05:06, John *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

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

NVIS and VHF?
 

On Sat, 04 Jun 2011 17:39:03 -0500, John S
wrote:

Easier than what I suggested? Actually, all he has to do is step outside
at 12:54 and look at the Sun's location. (I admit it is more accurate to
do this in the winter.)

Well, your method only works at exactly 12:54PM, requires remembering
daylight savings time, requires dark glasses to avoid blindness, works
badly in fog, need to get it right the first time, and offers no way
to document the results. At 12:54PM, the sun is almost directly over
head with no point of reference, as you would have at the horizon.
Manually translating the sun's overhead direction, to azimuth at the
horizon, requires considerable guesswork. A plumb line might helpful.

Incidentally, trees are a very real problem with antenna sighting:
http://802.11junk.com/jeffl/pics/DBS/index.html
That's my view of the DirecTV bird at 101 degrees. The photos were
taken during the bi-annual solar outage, where the sun gets behind the
satellite belt.
http://en.wikipedia.org/wiki/Solar_outage
Note the branch shadows on the dish, which are blocking the signal.

[1] Yes, the earth really is flat.
[2] When I didn't have a printed map handy, I've used my laptop LCD
screen and 3ea flat head screws.

I am afraid I cannot tell whether items [1] and [2] are just screwing
with me or that you are sincere.

As far as this measurement is concerned, the earth is essentially flat
over fairly small areas. No spherical geometry required. Even the
United Nations has adopted the flat earth map for its flag.
http://upload.wikimedia.org/wikipedia/commons/2/2f/Flag_of_the_United_Nations.svg
Antarctica is a collection of icicles around the outer edge.

The 2nd item is for real. I was on top of a mountain, trying to aim a
dish without a map. I had Street Atlas USA v5 on my then ancient
Toshiblah 100CS laptop, which I used for my initial bearing. Other
than having a difficult time holding the laptop, problems viewing the
screen in the sunlight, and too short a base line, it worked.

By the way, Jeff, you have a great deal to offer the group by way of
your vast experience. If I have been disrespectful of that, then I
apologize.

Thanks and not a problem. You have a long way to go before such
comments become a problem.

--
Jeff Liebermann
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558

NVIS and VHF?
 

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

NVIS and VHF?
 

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