Anyone using antennas for NVIS?
 

I have come to the conclusion the only antenna I am going to be able to use
is a ground mounted dipole or random wire. No antenna supports in the yard,
no fences, no attic. I tried a vertical "flagpole" but it is just too noisy.
Nothing but me and the yards of my two neighbours. I am able to run about
60 feet of 22 gauge green enameled wire along the length of the yards. I
have done extensive reading on NVIS propagation, but I'm curious if anyone
is actually using this method on 160, 80 or 40m.

Thanks,

Max

In rec.radio.amateur.antenna, you wrote:
have done extensive reading on NVIS propagation, but I'm curious if anyone
is actually using this method on 160, 80 or 40m.

I am using a 100 foot long wire about 6ft off the ground (basically a wire
tacked to a wooden fence). I am able to make contacts out to about 400
miles on 40m, but have not tried it on 160 or 80. Funny thing is that it
works really well on 6m (when the band is open) with contacts in the
1000+ mile range.


Alex / AB2RC

Max, VE3TMT wrote:
"I have come to the conclusion that the only antenna I am going to be
able to use is a ground mounted dipole or random wire."

Don`t expect much NVIS broadside to a dipole on the ground unless it`s
on deep dry sand.

For NVIS the ideal height over the effective earth reflector is about
1/4-wave. This is because the earth is 90-degrees away from the
radiator. This makes a round-trip for the signal of 180-degrees. This
added to the 180-degrees of phase inversion produced in reflection gives
a total of 360-degrees so that the reflected wave when it returns to the
radiator is back in-phase with the new emissions which are headed in the
same direction, that is toward the zenith (straight up).

Lowering the height of the radiator shifts the phase between the two
signal components from directly in-phase at 1/4-wave distance between
radiator and reflector sites to out-of-phase at zero distance between
their sites.

At zero height the radiator and earth behave as a lossy single-wire
transmission system where opposing polarities nullify radiation
broadside to the radiator.

Hope for effective radio communications using a near to the earth
antenna comes in the form of a Beverage antenna. I`ve used a Beverage
antenna very successfully for sky-wave tnans-Atlantic reception in
Portugal of WCBS in New York, and WWL in New Orleans.

The 1945 War Department book, "Electrical Communication Systems
Engineering" on page 317 says:
"Insulated wires of sufficient length laid on the ground, or better yet
on vegetation just above the ground, will provide ground-wave
transmission with vertical polarization in line with the direction of
the wire, that is, off either end of the wire, and for moderate
horizontal angles from this direction. Such low antennas have the
advantage of being easily concealed. A length of about 600/F feet (where
F is the frequency in megacycles), or somewhat longer, is suitable, if
the length is adjusted by trial to permit good transmitter loading. A
100-foot on-ground antenna attached to Radio Set SCR-536 (handie-talkie)
gives at least as good transmission in such directions as the whip
supplied with the set, and can be more easily concealed. Half-wave
on-ground antennas---can sometimes be used for short distance sky-wave
reception or transmission."

Stealth has a price to pay in efficiency when low height must be used.

Best regards, Richard Harrison, KB5WZI

hmmm, this stuff I have read on NVIS says 0.1 to 0.2 wavelengths. I can find
the source if anyone is interested (I am not at home right now). I am
certainly not arguing (I have no problem arguing, but this is one of many
subjects about which I have very little knowledge), Richard, just mentioning
a difference in what I have read.

Paul AB0SI


"Richard Harrison" wrote in message
...
Max, VE3TMT wrote:
"I have come to the conclusion that the only antenna I am going to be
able to use is a ground mounted dipole or random wire."

Don`t expect much NVIS broadside to a dipole on the ground unless it`s
on deep dry sand.

For NVIS the ideal height over the effective earth reflector is about
1/4-wave. This is because the earth is 90-degrees away from the
radiator. This makes a round-trip for the signal of 180-degrees. This
added to the 180-degrees of phase inversion produced in reflection gives
a total of 360-degrees so that the reflected wave when it returns to the
radiator is back in-phase with the new emissions which are headed in the
same direction, that is toward the zenith (straight up).

Lowering the height of the radiator shifts the phase between the two
signal components from directly in-phase at 1/4-wave distance between
radiator and reflector sites to out-of-phase at zero distance between
their sites.

At zero height the radiator and earth behave as a lossy single-wire
transmission system where opposing polarities nullify radiation
broadside to the radiator.

Hope for effective radio communications using a near to the earth
antenna comes in the form of a Beverage antenna. I`ve used a Beverage
antenna very successfully for sky-wave tnans-Atlantic reception in
Portugal of WCBS in New York, and WWL in New Orleans.

The 1945 War Department book, "Electrical Communication Systems
Engineering" on page 317 says:
"Insulated wires of sufficient length laid on the ground, or better yet
on vegetation just above the ground, will provide ground-wave
transmission with vertical polarization in line with the direction of
the wire, that is, off either end of the wire, and for moderate
horizontal angles from this direction. Such low antennas have the
advantage of being easily concealed. A length of about 600/F feet (where
F is the frequency in megacycles), or somewhat longer, is suitable, if
the length is adjusted by trial to permit good transmitter loading. A
100-foot on-ground antenna attached to Radio Set SCR-536 (handie-talkie)
gives at least as good transmission in such directions as the whip
supplied with the set, and can be more easily concealed. Half-wave
on-ground antennas---can sometimes be used for short distance sky-wave
reception or transmission."

Stealth has a price to pay in efficiency when low height must be used.

Best regards, Richard Harrison, KB5WZI

Max,
An antenna as you described would make a good wireless
'dog fence' on 160 meters, but that's about it, I'm afraid.
Just slightly 'better' on 80 meters, and on 40 meters, just
very slightly 'better' than that. It will become 'almost-
an-antenna' on bands higher than 40 meters where it's length
is more than just a fraction of a wave length, but don't expect
much performance, NVIS or not. That's for transmitting. On
the other hand, it'll make a very quiet recieving antenna for
bands where it's length is more than a small fraction of a
wave length.
From what you say (no supports of any kind for an antenna)
I think you are going to be 'hurting' for an HF antenna, other
than a vertical of some kind. Is there any way you could
attach a wire doublet of some length to the eaves or peak of
your roof? Doesn't necessarily have to be of any particular
lengths or symetrical shape Longer is better), although that
would peobably help. Any height is better than no height,
as you'll be finding out...
'Doc

VE3TMT wrote:
I have come to the conclusion the only antenna I am going to be able to use
is a ground mounted dipole or random wire. No antenna supports in the yard,
no fences, no attic. I tried a vertical "flagpole" but it is just too noisy.
Nothing but me and the yards of my two neighbours. I am able to run about
60 feet of 22 gauge green enameled wire along the length of the yards. I
have done extensive reading on NVIS propagation, but I'm curious if anyone
is actually using this method on 160, 80 or 40m.

Thanks,

Max

Can you not put a small pole at each end of the building and hang a doublet?

How about a loop or doublet on small stand offs attached to the eaves of the
building?

A pair of moble whips set up as a dipole on a pole somewhere?

A perusal of the ARRL Antenna Book for other ideas?

--
Jim Pennino

Remove -spam-sux to reply.

On Fri, 05 Dec 2003 16:44:04 GMT, "
wrote:

hmmm, this stuff I have read on NVIS says 0.1 to 0.2 wavelengths. I can find
the source if anyone is interested (I am not at home right now). I am
certainly not arguing (I have no problem arguing, but this is one of many
subjects about which I have very little knowledge), Richard, just mentioning
a difference in what I have read.

Paul AB0SI

Hi Paul,

The troops, during Desert Storm, achieved NVIS by laying the antenna
on the ground. I will add, that like Richard points out, it was sand.

Logic would suggest that an antenna very close to ground has no chance
of launching much energy tangential to the earth's surface (a direct
short), leaving what's left to go straight up and hazard a bounce from
above. If you raise that antenna to a quarter wave up, you simply
optimize the straight up radiation, but you also lose a lot of the
immediate ground loss that snubbed the tangential angles.

What few dipole users would admit (because they love to crow about not
having radials) is that if you add radials, you can further improve
your dipole performance up AND tangentially.

73's
Richard Clark, KB7QHC

wrote in message
...
VE3TMT wrote:
I have come to the conclusion the only antenna I am going to be able to
use
is a ground mounted dipole or random wire. No antenna supports in the
yard,
no fences, no attic. I tried a vertical "flagpole" but it is just too
noisy.
Nothing but me and the yards of my two neighbours. I am able to run
about
60 feet of 22 gauge green enameled wire along the length of the yards.
I
have done extensive reading on NVIS propagation, but I'm curious if
anyone
is actually using this method on 160, 80 or 40m.
Thanks,
Max

Can you not put a small pole at each end of the building and hang a
doublet?
How about a loop or doublet on small stand offs attached to the eaves of
the
building?
A pair of moble whips set up as a dipole on a pole somewhere?
A perusal of the ARRL Antenna Book for other ideas?
Jim Pennino

Number 28 is too small to be much use, and too fragile. Get some Electric
fence wire, which is 15 gage, and as you indicate a clear length of 60 Feet,
Run several strands spaced a few inches apart for that distance. It is not
too obvious, and could be described as a way to discourage birds, or
providing the birds a place to land, depending upon whom you are answering.
By adding a loading coil in a couple of the strands, and a few shorter
lengths to provide a wider band width, you can cobble together an all band
net...... or fence! I've done it, but I ran mine along the roof peak. The
HOA wouldn't like that!

Can you not put a small pole at each end of the building and hang a
doublet?

How about a loop or doublet on small stand offs attached to the eaves of
the
building?

A pair of moble whips set up as a dipole on a pole somewhere?

A perusal of the ARRL Antenna Book for other ideas?

--
Jim Pennino

I'm located on the ground level of a two level apartment. Balcony overhangs
my yard, which would be great to hang something off, but it is a strickly
"no antennas allowed period" building. I thought about a dipole using a
pair of hamsticks, but I would have to go out and change them to operate
different bands. And the height would not be great. If I stick anything
under the balcony above me it picks up too much electrical noise from the
building. There are wall supports at each end of the balcony, approx 50'
total length, but my feedline would be visible. My main intention is to get
something, anything hidden so I can spend the winter nights warm in the
shack. I am house hunting next year!!!

Max

On Fri, 05 Dec 2003 18:52:30 GMT, Richard Clark
wrote:



What few dipole users would admit (because they love to crow about not
having radials) is that if you add radials, you can further improve
your dipole performance up AND tangentially.

Where would I attach radials on a dipole?

Bob
k5qwg

73's
Richard Clark, KB7QHC