Here is the situation: have an inverted V for 80m and noise level is
S9.. Not good really....
I did the next logical step and tryied magnetic loop for 80, reciving
only, indoors. That antenna failed awfully.... Noise was S8 but I could
not hear stations that were 9+10 on inverted V. Did'nt matter how I
tryied to rotate the loop, all there was is noise. So, indoors is right
out..
All that is left is roof. And that makes my situation interesting. It
is a big house with new metal roof, electrically bounded. 10X60 metres,
17 metres hight, angled about 20 degrees. Big ground plane indeed. All
I could figure is to get some sort of antenna to the roof so the roof
would act as a shield from all the noise generated inside the house.
That antenna would be for receiving 80m, can be narrow band (50KHz
ok). NVIS pattern would be prefered.
So, I have huge ground plane, lots and lots of noise below it, and need
a receiving-only antenna.
What would you do in this situation? Loop, magnetic loop, dipole, short
beverage perhaps???
Any advice is welcome. Right now I cant even figure if that roof is
acting like a shield or a big noise-sucking antenna..

Andrus

I use 2 ham stick mobile antennas phased to produce a receive antenna on 80m
that works very well.
It has a response that is close to a reasonable sized beverage. They are
spaced 1/8 wavelength apart and feed 135 deg. out of phase with a coax
phasing line. I have a relay setup that lets me change the direction, in my
case north-east / south-west. The signal levels are down from the dipole I
use for transmit but the signal to noise level are much better. A signal
that would be S-9 with S-8 of noise on my dipole becomes S-6 to S-7 on the
verticals with no noise. It makes DXing on 80m fun. Details for the design
of the phasing system are in ON4UN's book on low band dxing. One of the
advantages of using mobile antennas is the mutual coupling is very low
between them. This greatly simplifies the setup. Note that this would be a
poor transmitting antenna do to the poor ground plane I have and mobile
whips are not a good antenna on 80m.


--
John Passaneau, W3JXP
Penn State University



"andy" wrote in message
oups.com...
Here is the situation: have an inverted V for 80m and noise level is
S9.. Not good really....
I did the next logical step and tryied magnetic loop for 80, reciving
only, indoors. That antenna failed awfully.... Noise was S8 but I could
not hear stations that were 9+10 on inverted V. Did'nt matter how I
tryied to rotate the loop, all there was is noise. So, indoors is right
out..
All that is left is roof. And that makes my situation interesting. It
is a big house with new metal roof, electrically bounded. 10X60 metres,
17 metres hight, angled about 20 degrees. Big ground plane indeed. All
I could figure is to get some sort of antenna to the roof so the roof
would act as a shield from all the noise generated inside the house.
That antenna would be for receiving 80m, can be narrow band (50KHz
ok). NVIS pattern would be prefered.
So, I have huge ground plane, lots and lots of noise below it, and need
a receiving-only antenna.
What would you do in this situation? Loop, magnetic loop, dipole, short
beverage perhaps???
Any advice is welcome. Right now I cant even figure if that roof is
acting like a shield or a big noise-sucking antenna..

Andrus

Andrus wrote:
"Any advice is welcome."

Andrus has a bonded metal roof 10x60 mtr which is 17 mtr high.

An automobile contains radio noise within its engine compartment by
using a metal cover. A roof does not completely cover and surround noise
sources within a house, but if it is effectively grounded at the
receiving frequency, the roof can help block transmission of noise into
an antenna mounted above it.

A dipole is balanced and slightly directional. This helps avoid noise
pick up. A balun at the antenna feedpoint helps keep the antenna
balanced and allows connection of coax to run through noisy areas
without pickup.

A low dipole over a reflective surface has a high-angle radiation
pattern, excellent for NVIS.

With an agile antenna tuner you may be able to hear and work stations
within several hundred miles.

Best regards, Richard Harrison, KB5WZI

andy wrote:
Here is the situation: have an inverted V for 80m and noise level is
S9.. Not good really....
Any advice is welcome. Right now I cant even figure if that roof is
acting like a shield or a big noise-sucking antenna..

If you can somehow get your inverted-V to a horizontal position
for testing, you might be plesantly surprised. At my QTH, going
from an inverted-V to a horizontal dipole at the same center
height lowered my noise level by 2 S-units on 40m.
--
73, Cecil http://www.qsl.net/w5dxp

A couple of antennas that work well at this qth...typical urban environment
with elevated power lines and assorted other racket.
Run a big horizontal loop around the place..feed with coax for recieve only
or twin lead plus transmatch for recieve/transmit. This is the one I am
currently using.
Previous antenna...which also works pretty good was a 100 ft bowtie doublet.
I used to run the doublet with vertical drops on the ends, but found that
any vertical drop on the ends of the antenna really picked up the racket. If
I left the vertical drops off the ends, I never did like the way the Johnson
Matchbox was coupling with the feedline...450 ohm...on 80 meters. I would up
with 10 ft end drops, then running a wire from the bottom of the end drops
back up to the feed point.
Tuned a lot better, broad banded and rejected noise pretty well.
"andy" wrote in message
oups.com...
Here is the situation: have an inverted V for 80m and noise level is
S9.. Not good really....
I did the next logical step and tryied magnetic loop for 80, reciving
only, indoors. That antenna failed awfully.... Noise was S8 but I could
not hear stations that were 9+10 on inverted V. Did'nt matter how I
tryied to rotate the loop, all there was is noise. So, indoors is right
out..
All that is left is roof. And that makes my situation interesting. It
is a big house with new metal roof, electrically bounded. 10X60 metres,
17 metres hight, angled about 20 degrees. Big ground plane indeed. All
I could figure is to get some sort of antenna to the roof so the roof
would act as a shield from all the noise generated inside the house.
That antenna would be for receiving 80m, can be narrow band (50KHz
ok). NVIS pattern would be prefered.
So, I have huge ground plane, lots and lots of noise below it, and need
a receiving-only antenna.
What would you do in this situation? Loop, magnetic loop, dipole, short
beverage perhaps???
Any advice is welcome. Right now I cant even figure if that roof is
acting like a shield or a big noise-sucking antenna..

Andrus

Denton wrote:
I used to run the doublet with vertical drops on the ends, but found that
any vertical drop on the ends of the antenna really picked up the racket.

Same as at my QTH. Anything vertical is noisier on receive.

If I left the vertical drops off the ends, I never did like the way the Johnson
Matchbox was coupling with the feedline...450 ohm...on 80 meters.

Because your feedline length was somewhere in the ballpark
of 1/4 wavelength and presented a very high impedance to
the Matchbox. Ladder-line feedline lengths for low-impedance
antennas need so be close to multiples of 1/2 wavelength,
a little over 100 feet on 80m. Unfortunately, a lot of
ladder-line-fed 80m dipoles and loops are closer to 1/4WL,
around 60 feet or so which may be worst case for limited range
tuners like Johnson Matchboxes and internal autotuners.
--
73, Cecil http://www.qsl.net/w5dxp

On 7 Nov 2005 04:04:09 -0800, "andy" wrote:

Here is the situation: have an inverted V for 80m and noise level is
S9.. Not good really....

Hi Andrus,

Put 1:1 BalUn at end of Coax transmission line as choke. This will
isolate local noise from line input. Also, does your transceiver
share a circuit (identified at the breaker) with a noisy appliance?
Change circuits (go to another outlet that is on a different breaker).
Do you have a good RF ground? This goes against much of the common
lore of dipoles being independent of ground. True, the antenna alone
requires no ground, but somewhere your rig is connected to it, and it
can be a very poor connection to a very poor RF ground. This is a
very common path for noise to enter your receiver.

73's
Richard Clark, KB7QHC

How about trying to locate the source of the noise? Is it in your
house or is it in the neighborhood? It could be something simple like
a streetlight buzzing a couple of blocks away. The power company
USUALLY pretty good about fixing those kinds of problems. Walk around
with a portable AM or shortwave radio and see if you can find the
offending pole or whatever. If the noise is in the house, like a
dimmer switch, or a tap on lamp, or an appliance, you can fix all that
easy enough too.
I'm also wondering about your rigs noise blanker. Most modern radios
have pretty darn good NB's. Its not a cure, but it should be
reasonably effective, unless the noise is a total monster. In that
case, all the more reason to find out where its coming from.

Good Luck K2TL

wrote:
How about trying to locate the source of the noise?

The source of noise at my QTH is the 33 ft. ground wire
running down the pole in my front yard from the giant
old-as-Methuselah capacitor mounted there. It generates
S7 noise on 40m. Maybe an RF choke would work?
--
73, Cecil http://www.qsl.net/w5dxp

Thanks fo sharing. That noise is surely not local: we have powerlines
and industry nearby, LAN in the roofspace, streetlights and so on. I
guess that I'll try a full-wave loop directly laying on the roof,
feedpoint will be low impedance but how low? 5, 1, 0.5 ohms?
Maybe I can transmit to it too if the currents are'nt too high? Is
there an antenna design that has high feedpoint impedance to start
with, so the impedance would be usable when antenna is layd directly to
the roof?

Andrus