1. Antenna Take Off Angles
A Contester’s Perspective By
Gary C. Sutcliffe, W9XT
August 2018
Version 1.00 August 2018
Copyright ©2018 Gary C. Sutcliffe
This presentation can be used whole or in part without permission for non-profit or educational purposes. Attribution to the author is apprecieated.

2. What we will cover today
What affects antenna take off angles
Why antenna take off angles are important
What we can do about it
A high gain antenna is useless if it is pointed south and the station you want to work is east.
This is really a 3D problem and you also have to consider gain and nulls in the Z axis.

3. 3 Element 20M Yagi Patterns
40’ over flat terrain (average ground)
70’ over flat terrain (average ground)
The lobes are caused by signal reflected off ground adding/subtracting with elevated signal
Programs used in presentation EZNEC and HFTA are on CD in back of ARRL Antenna Book.
Beam pattern has lobes that vary with
Height above ground
Local terrain
Signals coming in at null angles will be many dB below optimum angle signals
Plots produced with EZNEC by W7EL
Antenna gain is great but take off angles can be more important!

4. 20M W9 to Europe Angles Plots produced by HFTA program by N6BV
Blue line is take off angle for 3 element Yagi at 40’
20M to Europe picked because 20 will be the best higher HF band for DX contests at sunspot min. Europe is a big population center with lots of multipliers
Note most openings are less than 20 degrees
This is the average probabilities over course of entire sunspot cycle. Predictions for Nov 2018 have 6 degrees as the most likely angle
There might be multiple angles in effect – could have 2X and 3X hops at same time
Plots produced by HFTA program by N6BV

5. Takeoff angles – W9 to DX
20 Meters – Probabilities are averaged across entire sunspot cycle
Europe
Africa
S. America
Longer paths will tend to concentrate at lower angles
Asia
Japan
Oceania

6. 20M to Europe from IL,IN, WI WI IL IN
This presentation was developed for the Society of Midwest Contesters for the 2018 SMC Fest.
This slide shows that there is a little change between the states most member resided in for 20M to Europe. IN
There is not a lot of difference between the different states which most SMC members live

7. 20M Antennas - W9 (WI) to Europe
Flat terrain, Wisconsin to Europe
Take off angle for entire solar cycle, lower take off angle will predominate in low part of sun spot cycle
You want to have high gain at the high probability angles.
You should run it with terrain analysis for your own QTH.
Other prediction program for expected conditions for 2018 CQWW CW had predominate 6 degree angle
Lower antennas have most gain at higher angles than we want
Higher antennas are better at low angles but have lobes with nulls at some angles
Local terrain will have a big effect on the antenna lobes.
Effect is based on wavelengths above ground, 10 & 15M will have more lobes at same height

8. A Really Good 20M Antenna System 5 el over 5 el over 5 el @ 200’-150’-100’
Stacks can increase gain and fill in the gaps
Sometimes a single antenna by itself is better than the stack

9. The solution! Thank you! Any Questions?
Put up a big tower and stack beams!
Thank you!
Any Questions?
K9CT 20M Array. K9CT Photo.

10. What about the rest of us?
What can we do?

11. What do we know? Most of us have maxed out our towers/beams
Low bands will be critical for next few years
Low take off angles will dominate for DX
Even low bands will go long and/or close early
We want to be loud in
High population and multiplier rich areas
Europe in DX contests
The coasts and Midwest in domestic contests
The SMC circle
Upgrading for 20M and above is probably not practical for most hams.
Note that any 10 and 15M openings will be on very low angle paths.
The rest of this presentation will concentrate low cost improvements for the low bands.

12. Verticals radiate equally poorly in all directions.
True or False?
Verticals radiate equally poorly in all directions.

13. But a poor radiator is better than a really bad one!
Mostly True!
But a poor radiator is better than a really bad one!
Actually the best answer is maybe.

14. The case for verticals and inverted L antennas on the low bands
If you only have dipoles, here is why you should look at putting up a vertical/inverted L

15. 40M W9-Europe with dipole
Dipoles are not very good for DX at typical city lot heights
Most of the paths are using angles that low dipoles have little or even negative gain vs. an isotrophic antenna.

16. 80M W9-Europe with Dipole Same heights but less WL above ground.
Low dipoles are less effective for DX on lower bands

17. 160M W9-Europe with Dipole
Lower angles are more dominant than on 80 & 40
Less confidence the takeoff angle is accurate on 160. Lower bands seem to follow a different set of rules.
Still it is a probably pretty good as an approximation.

18. 40M Vertical Over Real Ground
Max gain: 0 dBi
Best angle: 26°
3 dB points: 9°
53°
From EZNEC – a limited version is on the CD in the back of the ARRL Antenna Book
The 3 dB points are pretty wide. Max gain about 20 degrees lower than low dipole
Lower bands show a bit more gain and lower take off angles.

19. 40M Dipoles vs. Vertical to Europe
A vertical can be an improvement at lower angles compared to a low dipole.

20. 40M Dipoles vs. Vertical to Oceania
Similar results as to Europe, but the vertical should slightly outperform more often than dipole due to shift towards lower take off angles.

21. 80M Dipoles vs. Vertical to Europe
A vertical will outperform dipoles at lower heights most of the time.

22. 160M Dipoles vs. Vertical to Europe
Verticals outperform dipoles at typical heights on 160M

23. Vertical Antenna Conclusions
Verticals & Inverted Ls can be effective, especially on the lower bands.
Good ground/radial systems are important for high efficiency, but
On 80 & 160M there is a lot of difference between vert and low dipole performance. Even a vertical with a moderate radial system might still be an improvement over a low dipole.
Put in whatever radials you can – don’t let the perfect be the enemy of the good
Actual performance and comparison to a dipole will depend on local terrain

24. The Case for NVIS Antennas (Near Vertical Incidence Skywave)
We want to work more fellow SMC members & close in states
What we know
You want higher angles for close in stations (geometry)
Lower antennas have higher take off angles
As sunspots decline the lower bands will go long sooner
The Case for NVIS Antennas (Near Vertical Incidence Skywave)
NVIS is more commonly used for EMCOM and military use. Contesters could benefit from them.

25. 40M Dipoles at Various Heights
40’
Max gain °
E dB points 24° - 155°
27’
Max gain 7.6
3 dB points 33° - 146°
W9XT FD Dipole
Designed for coverage from close in to East Coast 8’
Max gain °
3 dB points 42° - 137°
W9XT NVIS FD Ant
About 4 dB over 40’ Dipole at 90°
Over average ground
Lower dipoles will direct more signal at higher angles.

26. Problems with Low Dipoles
Impedance drops as dipole is lowered
~12 ohms at 8’
Solution
Use a folded dipole with higher input impedance (~280 ohms)
Folded dipole impedance goes down to about 50 ohms at low height

27. NVIS Diagram More detailed info on NVIS Antenna at www.w9xt.com
Twin lead is shorted on ends.
One wire cut in middle to connect to coax.
A few ferrite beads near feed point act as an RF current choke.
The reflector wires are just a few feet longer than the dipole.
They are spaced about 2’ apart and are just laid on the ground
Fewer wires needed if the ground conductivity is good
More detailed info on NVIS Antenna at

28. W9XT FD Experience Been 40M CW FD specialist for over 30 years
Always trying new antennas to improve results
Current system: Vert w/2 raised radials, NVIS
Tried an NVIS dipole after a discussion at an ARES meeting
Effective for up to about 250 miles
Very quiet antenna – rejects signals from lower angles
Listening to W9CA circa 2012:
Vertical with elevated radials: not heard
S4 (just above noise level)
NVIS: S6
Not very good in 2018 FD - Why?
W9XT FD dipole is main antenna. It is designed to work the population concentration out to the East Coast
The vertical is used mainly at night for west coast.
The NVIS is used for close in stations
The station has a phasing network that allows me to feed one or two antennas at once and still show 50 ohms to rig
MUF for short distances on June 23, 2018 at 2345Z was about 6 MHz

29. MUF and Critical Frequency
Lower angles support higher frequencies because it has to be refracted less to return to earth and a longer period in the layer.
Vertical wave has to be refracted 190 degrees
For a given angle
There will be a maximum useable frequency (MUF) that will be refracted back to earth.
The lower the angle, the higher the MUF
fo, the Critical Frequency is the maximum frequency that will return a vertically launched signal
fo can be quite low!

30. Real Time Critical Frequency Info
This was the ionogram from Alpena MI during the August NAQP SSB contest a few days before the presentation was first given. Everyone complained about the poor conditions. This indicates
One reason we didn’t work a lot of other club members on 40 M
Alpena MI Ionogram
Note low MUF for short distances
Other factors are involved and can change over short distances. Use only as a general guideline.

31. Short Range MUF Chart Feb. 2018
Varies about 2:1 over the month.
Carl notes that this tracked well with days they needed to move to 160
Plot for 200 km path for Indiana 80M traffic net during Feb 2018
Curtesy of Carl Luetzelschwab, K9LA

32. NVIS Conclusions
NVIS antennas can be effective for short distances (SMC Circle!)
We are probably too far into sunspot minimum to be effective on 40M on a regular basis
An NVIS antenna for 80/75 could be useful
Overall, a dipole at moderate heights (30-60’) will be a more useful antenna, but the NVIS is a good second antenna for close in work.
If you only have verticals for the low bands, a low dipole or NVIS can be a big improvement for regional QSOs

33. Summary
Signals can arrive over a long range of angles depending on target location, band and solar conditions
We usually won’t know what the current angle is and there might be multiple angles in play at the same time
If we don’t match our antennas to the useful angles, our antennas will not be very effective.
It can be difficult (expensive) to match angles for the higher HF bands
Verticals and NVIS can be inexpensive upgrades for the low bands
Don’t let the perfect be the enemy with the good. Do the best you can putting up antennas and have fun!
“You can’t have too many antennas – unless they are so close that they interact and you really have one antenna with multiple feed points.”
Quote from the book “Radio Propagation and Science” by Eric Nichols, KL7AJ

34. Questions?
For real this time!

35. This presentation will be posted at www.w9xt.com
Acknowledgements
Carl Luetzelschwab, K9LA, for his help and suggestions
Craig Thompson, K9CT, 20M stack photo
This paper uses ionospheric data from the USAF NEXION Digisonde network. The NEXION Program Manager is Mark Leahy. (Alpena MI Ionograms)
This presentation will be posted at

36. Notes The following programs were used to generate plots:
HFTA by Dean Straw, N6BV
EZNEC by Roy Lewallen, W7EL
Both programs are on the CD in the back of the ARRL Antenna book (Paid EZNEC version used to prepare this presentation)