Transcript Document

Hearing Weak DX
on 80 & 160
Bill Tippett W4ZV
October 1, 2005
SEDCO – Ten-Tec Hamfest
7/17/2015
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Introduction
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“You can’t work ‘em if you
can’t hear ‘em!” ~The Old
Timer
K4RID – QRV 80m 1960
W0ZV – QRV 80m ‘80, 160m ‘84
80m DXCC 339 (need 4 more)
160m DXCC 317 (need 22 more)
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Weak Signals in Noise
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“Since you can’t increase the weak
signal, reduce the noise!” ~The OT
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1. Noise reduction (S/N issues)
2. Signal strength (propagation
issues)
3. Other (experience, practice)
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Noise Reduction
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Different types of noise:
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Atmospheric (lightning-induced)
Man-made (power lines, electric
fencers, FCC part 15 devices)
Precipitation static (rain, snow,
dust)
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Antenna Metrics
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Beamwidth – included angle for 3 db
gain reduction (azimuth or elevation)
RDF – W8JI definition based on Eznec
calculations of max forward gain versus
3D gain at all azimuths and elevations
DMF – ON4UN calculation based on
forward gain versus averaged F/R in rear
180 degrees (best F/R metric)
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Azimuth Example
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Elevation Example
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Where ’s the noise
coming from?
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Lightning Strikes
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Noise Reduction –
Forward Direction
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If the noise is from the same direction as
the signal, minimize forward beam width
to “slice through” the noise
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BSEF 8 el / 4el BS vert = ~25 deg. (but
not practical to cover 360 degrees)
Parallel 2wl Bev = 44 deg.
W8JI 8-circle vert = 55 deg.
Single 2wl Bev = 62 deg.
Single 1wl Bev = 78 deg.
4-square vert = 86 deg.
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…but, Optimize S/N
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If noise not exactly same direction,
use knowledge of geography and
antenna patterns.
Example: FT5XO’s bearing SE
and thunderstorm noise South.
Solution: ESE Beverage includes
FT5XO but attenuates noise.
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Noise Reduction – Rear
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Most wintertime DX not the same
direction as storm QRN…don’t need
narrow forward beamwidth.
Winter storms from Texas to Caribbean
are very common...thus need maximum
F/R performance toward EU (JA normally
not an issue).
ON4UN’s DMF is the most useful metric
for F/R performance.
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Directivity Merit Factor
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2X 2wl Beverages EF – 33.8 dB
2X 1wl Beverages EF – 30.1 dB
4-square – 24 dB
W8JI 8-circle – 22.6 dB
Conclusion: 1wl Beverage EF pair
extremely effective for Middle East,
Europe and Africa…not much more
space than single Beverage
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For City Dwellers…
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Acreage matters! So don’t set
unrealistic expectations.
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K9AY/Flag/Pennant/EWE arrays quite
effective but cannot compare to phased
Beverages or large vertical arrays.
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K2UO has ~225 DXCC on 160 from a
city lot so you can still have lots of fun!
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High-angle Antennas
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Sometimes high-angle antennas
are optimum. Most common at
your sunrise and sunset.
Beverages and vertical arrays are
all low-angle antennas, so consider
an inverted-V or dipole as a
complement. In this case use the
same antenna for both transmit
and receive.
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Inv-V vs 3el Vertical TOA
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Man-made Noise
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Noise audit (home, neighborhood, power
lines) and remove at the source (or
move!)
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SWL RX and whip or loop antenna
MFJ-852 (for power lines)
Tune 1710 kHz on your car radio
RX noise blankers work well for modern
electric fencers (but RX overload)
MFJ-1025 for local single-point noise
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Precipitation Static
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Verticals are bad
Beverages are good
Noise blankers sometimes work
Sometimes nothing works
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About That Weak Signal
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You can’t make it stronger but Mother
Nature can! Remember the 3 P’s --Propagation, Patience and Persistence.
Propagation – Know when the DX signal
may peak and watch azimuth changes.
Patience – Propagation may move
toward you. Don’t call if you can’t hear!
Persistence – Keep trying! JT1CO and
UK8DAN literally took seasons to work!
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Other Issues
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Practice listening to weak
signals. N2XE’s Beacon starts in
October; YR2TOP on 1810.5.
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Modern receiver sensitivity (MDS)
not a factor, but learn which
settings work best for your ears
(i.e. Pitch, Bandwidth, AGC, RF
Gain, NR, NB, Diversity, etc).
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Need more info?
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ON4UN’s Low-Band DXing 4th
edition (the only book you need)
W8JI.com (many pages of info)
Topband reflector archives
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Conclusion
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Low Bands are challenging but fun!
Great conditions are just ahead.
Good RX antennas are a must.
Nobody said it would be easy!
Get in there and have some fun!
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Beverage Kits - $10
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Transformer (50 or 75 ohm coax),
non-inductive termination &
instructions
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