Topband: RE: skewed paths

[Milt Jensen]

Comments by Milt, N5IA, interspersed below.

----- Original Message -----
From: "Tom Rauch" <w8ji@akorn.net>
To: <Topband@contesting.com>; "Ford Peterson" <ford@cmgate.com>
Sent: Sunday, September 16, 2001 11:11 AM
Subject: Re: Topband: RE: skewed paths

Milt posted:
> > "The first couple of days of full operation on 160 Meters we knew the
> > signals were coming from the SSE but we were having problems copying
> > them on a two wavelength long Beverage oriented specifically in that
> > direction.  Reports via the pilot stations indicated our transmit
> > signal was being heard quite well."
Ford commented:
> > It seems to me that this is a perfect example of back scatter, where
> > the geometry of the skip along one path is impossible in reverse.
Tom commented:
> It is impossible to have any idea of what was going on because we
> have no idea how any of the antennas at that site actually work.
>
> How do we know the 2WL Beverage didn't have a lobe oriented into
> a major source of noise, while the dipole just luckily had a null
> towards that noise?  We don't, unless they had dozens of receiving
> antennas.
Milt replied:
Please see the description below of the 160 Meter antennas at XZ1N and XZ0A.

SNIP

Tom commented:
> Since we have no idea what the direction and angle of noise was at
> XZ, we can't possibly form any accurate opinion of what it means.
> All it means is they had better luck with the location of nulls on the
> dipole reducing noise than with the Beverage. Changing the
> beverage heading 20 degrees, or moving it 1000 feet, might had
> produced entirely different results.
Milt replied:
The only significant source of noise in any principal direction was the
mainland Myanmar city of Kawtaung, due north at a distance of 5 miles.

SNIP

> > Milt continues regarding a low dipole:
> >
> > "The proof is in the results because the high angle arrival signals
> > from the SSE skew path received by the low dipole accounted for
> > approximately 80% of the 400+ NA stations that were worked on 160
> > Meters from XZ0A."
> >
> > Again, I submit that this is consistant with what would be expected
> > from backscatter.
Ford commented:
> Unfortunately none of us have the faintest idea what the wave angle
> was. It is only a guess, based on no real evidence because nothing
> they had allowed wave angle measurements. Keep in mind the
> ONLY thing a better S/N ratio tells us is the antenna responds
> better in the direction of signal than in the direction of noise. We
> haven't any idea at all what that means so far as how the signal
> gets there, what polarization it is, or what wave angle it is.
Tom commented:
> It could be that the dipole had a null in the direction of noise 10dB
> deeper than the Beverage, and the signal direction gain was the
> same. It could mean almost anything.
Milt replied:
The ONLY significant source of noise at Thahtay Khun was Kawtaung, Myanmar,
5 miles away, broadside and in full view of the north side of the dipole.
The dipole was "noisier" than the Beverage to the SSE, the only other
antenna that could hear the skew path signals.  The Beverage was completely
shielded from view to Kawtaung, with Kawtaung off the left rear of the Bev.

Ford commented:
> > I'm no expert by a long shot but Milt's empirical evidence seems
> > consistant with the back scatter explanation.
Tom commented:
> Unfortunately it only means for them with the dominant noise
> source they had the dipole had a deeper null compared to
> response in the direction of the signal.
Milt replied:
I strongly suggest from the experience of a bit over three weeks of
building, changing, tweaking and using the low band receiving antennas at
XZ0A that there was NO null towards Kawtaung.  The response of the SSE
Beverage indicated that the signals were coming from that direction and the
low dipole responded to higher angle arrival signals from that direction.
--------------------------------------------------------------------------

For those that are interested, I can provide a Word Perfect document of all
the XZ0A  North American QSOs.

For those that have the availability of the Toshiba Image Expert
program I can provide an aerial photograph of Thahtay Khun Island with an
overlay showing the location of all the receive antennas and the 160 M
transmit antenna.

For those that have a broadband connection I can provide JPEG fotos of all
the receive antennas and transmit antenna setup at XZ0A as well as panoramic
views of the Andaman Sea, other islands, and both the Myanmar and Thai
mainlands as seen from the top of the 160 M Ground Plane..

Please make your requests direct to me.  XZ1N and XZ0A site statistics are
below.


Sites: XZ1N and XZ0A

Coordinates:XZ1N = 17N - 97E
                   XZ0A =  9N - 98E



XZ1N = River delta in capital city of Yangon.  Approximately 400' AMSL and
about 10 miles from the Andaman Sea to the south.  All north azimuths are
over land (Asian continent).  The EU path breaks out over water (Bay of
Bengal) at about 80 miles from Yangon.

XZ0A = Small island, Thahtay Khun, in the Andaman Sea about 5 miles south of
the southern most tip of mainland Myanmar (Burma) and 7 miles west of the
Thai mainland.  Located on the northern tip of the island 150' AMSL with
take off path over sea water from 250 degrees through north to 180 degrees.


Transmitting antennas:

XZ1N = 1/4 WL sloper off the north side of the hotel, attached 120' AGL to
the highest point on the elevator tower.  Sloping down at about 45 degrees
to 40' AGL above the top of a lower part of the hotel complex.  The feedline
was 150' of RG8X with the ground being the lightning rod ground grid of the
hotel.  Adjusted to 1:1 match at 1.825 by varying length and slope of the
wire.

XZ0A = Full sized 1/4 Ground Plane with insulated base at 40' AGL.  The
element was 90' of Thai made Rohn 25 type tower and 35' of aluminum tubing
stinger adjusted
to resonance.  Fed through 300' of RG8X and matched with toroidal
transformer to 1:1 at 1.835.  Twelve sloping radials 130' long and made of
#14 AWG insulated copper wire.  Slope was about 30 degrees down from
horizontal with the ends tied off to various trees and bushes.  The radials
were connected to the shield of the coax and the cold end of the toroidal
transformer.  No ground or ground rods.


Receiving antennas:

XZ1N = 4 Beverages 8-10' AGL, 1-2 WL long, terminated, unidirectional at
330, 0, 30, and 60 degrees.  Used 4' copper ground rods driven into wet
jungle soil.  One 1/2 WL dipole installed in dense jungle growth (Jungle
canopy 150' high) at 10' AGL, oriented broadside to the north/south.  Fed
directly with RG-6 coaxial cable.  Other Beverages were tried as well as two
EWEs.

XZ0A = 6 Beverages 8-10' AGL, 1-2 WL long, termianted, unidrectional at 0,
30, 70, 150, 225, and 225 degrees.  Used 6' copper ground rods driven into
damp, sandy and rocky soil.  One 1/2 WL dipole installed in the open across
a heliport at 20' AGL, oriented broadside north/south.  The west 30' end of
the dipole termianted into the jungle and the east 60' the same.  Fed
directly with RG-6 coaxial cable.  Other antennas were tried, including
Beverages in different locations and another dipole in another location.

73 de Milt, N5IA