Anyone using antennas for NVIS?
VE3TMT
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
Alex Flinsch
> 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
Richard Harrison
"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
p.paulf...@comcast.net
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" <richard...@webtv.net> wrote in message
news:7481-3FD...@storefull-2315.public.lawson.webtv.net...
'Doc
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
ji...@specsol-spam-sux.com
> 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.
Richard Clark
>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
Roger Gt
<ji...@specsol-spam-sux.com> wrote in message
news:bqqjc4$gbb$1...@mail.specsol.com...
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!
MD
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
Bob Miller
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
VE3TMT
"'Doc" <w5...@cwis.net> wrote in message news:3FD0C6D6...@cwis.net...
> 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...
Hello Doc,
I am on the ground floor of a two level apartment building. No roof to get
at and no eaves. My unit itself has 3 floors counting the basement where
the shack is. I was running a vertical, about 25' hung from under the
balcony above me, totally invisible, except being so close to the building
itself, the noise levels on 40 and 20 made those bands useless. Also being
vertically polarized, it was causing RFI on the computer upstairs, and
probably the neighbours as well. I have no way of running anything
horizontal above the ground as this would involve climbing and hard to do
that without the neighbours noticing. I have a feeling the property managers
will be doing some work on the balconies in the spring anyway, so the
antenna would surely be noticed then. I think I am going to go for the
ground laid antenna and hope for the best. My other alternative is a 8' CB
whip with a flag on the top, which has been up before without any problems.
This antenna is however too short to load on 40 with the tuner.
Thanks for all the input guys, I will scratch my head some more, maybe I
will think of some way to hang something from the balcony.
Richard Harrison
"hmmm, this stuff I have read on NVIS says 0.1 to 0.2 wavelengths."
Yes, and I said 0,25 and explained how I arrived at that figure. So, I
went to page 3-11 of the 19th edition of the ARRL Antenna Book to look
at Fig 12.
Fig 12(A) is for 1/8-WL high and Fig 12(B) is for 1/4-WL high. Paul is
supported by Fig 12 because the 1/8-WL high antenna appears to have more
radiation toward the zenith than does the 1/4-WL high antenna.
I don`t know why, but would speculate it is due to closer coupling of
the radiator with the earth which gives the reflector (earth) more
energy to work with on the reflection. Maybe I`ll learn something from
this bum steer. I learn something nearly every day here and find this a
rewarding experience.
'Doc
If nothing else presents it's self, you might try a
'CCD' (Controled Capacitance Distribution antenna). The
biggest draw backs are that they are a wave length long
and use silver mica capacitors that are not cheap. But
it can be laid on the ground and they do work. There's
a pretty good writeup in one of the ARRL's Antenna
Compendium books, not sure which one. It wouldn't be my
first choice in your situation, but it is an alternative.
'Doc
p.paulf...@comcast.net
Interesting, thanks. This is one of the few places it seems where folks can
have a reasonable conversation without it quickly turning into a
name-calling contest. You idea of why a lower elevation works a bit better
sounds reasonable. I just remember the empirical fact. Sort of like a 5-year
old's reason for do anything --- b'cause!
Paul AB0SI
"Richard Harrison" <richard...@webtv.net> wrote in message
news:1272-3FD...@storefull-2318.public.lawson.webtv.net...
Crazy George
It appears you are overlooking the very useful possibility of using
different antennas for transmit and receive. If the computer RFI problem
can be addressed, then use the vertical for transmitting, and whatever is
quietest for receive.
--
Crazy George
Remove N O and S P A M imbedded in return address
"VE3TMT" <ve3...@rac.ca> wrote in message
news:Eu%zb.348$%i5.2...@news20.bellglobal.com...
VE3TMT
"'Doc" <w5...@cwis.net> wrote in message news:3FD0E556...@cwis.net...
Thanks Doc, I'll look into it. At this stage in the game I am open to any
suggestions!!
Richard Clark
<bxmi...@texas.netNOSPAM> wrote:
>On Fri, 05 Dec 2003 18:52:30 GMT, Richard Clark <kb7...@comcast.net>
>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?
>
Hi Bob,
Not to the dipole certainly; to the ground below the dipole. It is,
after all, the ground that presents the loss. The radials reduce that
loss as is their function.
For example, a 20M dipole one halfwave over a ground mat (1M grid
about 1 wavelength in XY dimension), shows a gain of 7dBi at 30°.
Take away that ground mat, it shows a gain of 6.5dBi at that same 30°.
Nothing remarkable in my book, but I have the ground mat anyway.
ji...@specsol-spam-sux.com
> Max
Unless you use an autotuner, just about anything you do will require
changing something to work multiple bands.
How about a collapsible pole with a pair of whips on the end hung off
your window/patio with clamps. Put it up after night falls and take it
down before morning.
A pain in the butt but extra motivation to go house hunting.
ka...@rahul.net
> My other alternative is a 8' CB
>whip with a flag on the top, which has been up before without any problems.
>This antenna is however too short to load on 40 with the tuner.
Interesting. How about mounting the whip on a small bike (for
extra height) and attaching an orange pennant to the top? Looks just
like the things some parents have their kids use for visibility when
riding near cars. Should questions arise about the feedline -- uh,
it's for theft-proofing?
KC1DI
HI all
In your Circumstance I would opt for a small transmitting loop.. that
you could set out when on the air and bring in when not.. Though the
small loop is very Hi-Q and has to be retuned every few KHZ. it would
be a good compromise for you as they work really well when mounted
vertically close to the ground. they offer all radiation angles from
0 to 90 degrees and will give you plenty of qso's .. give it some
thought and I bet you can even find ways to hid one.. in the yard.
73 , Dave KC1DI
P.S. a google search for small transmitting loop will return numerous
pages to explore on the topic.
bob
<ve3...@rac.ca> wrote:
We used an NVIS for Field Day this year, and it was a lot of fun. Good
for 40 and 80, and that's about it. Ours was built after the Jelenik
design (http://www1.vcars.org:8040/CARL/NVIS.html), with an SGC tuner
at the base.
73--
--
Namaste-
Mike Coslo
> On Fri, 05 Dec 2003 18:52:30 GMT, Richard Clark <kb7...@comcast.net>
> 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?
Just remove the bias plys and substitute the radials! 8^)
But seriously, they are set the same way as you would on a vertical, in
the ground. And Richard is right.
- Mike KB3EIA -
William F. Hagen
bicycle out in front of theapartment in the bike rack, with the very whip you
described with the triangle orange flag on the top to decieve the cops, and I
run coax from the house to the bike, running it up the kickstand, across the
frame to the 'flag' on the back. With it parked in the bike rack here at the
apartment complex with all the other kid's bikes, no-one seems to notice a
thing. I keep the power down on transmit just in case some kid just happens to
be getting his bike from the bike rack at the same time I am txing.
jkhh