¦ Article ¦ HF-antenna's ¦ Vertikal Dipole 10-40m ¦

Last review: 30-12-2003

 

Since we're heading to lower sunspotnumbers it was time to consider an antennaproject for the lower HF-bands. We all tend to start with a dipole which we usually can hangup in a decent way from 20 to maybe 30 meters. For 40 and 80 meters the dipole will have a length which becomes difficult to hang up fully horizontal . This is usually the length where some HAMS may come to the very painfull constatation that the lot or available space to play with antenna's should be much bigger (for an antenna freak, the lot should ALWAYS be bigger). Of course we can hangup the antenna in inverted vee, of course we can bend the ends, of course we can use techniques to shorten the dipole. This article and related physicall testing is ment to try to find an alternative for the horizontal dipole. Antenna efficiency, antenna pattern, used space and user satisfaction are taken into account.

 

STARTING POINT.

We will take an inverted V for 40 meters, an antenna which is widely known amoung HAM's as an allround antenna . Many know what to expect from a dipole, I will try to compare this allrounder theoretical and practical with a shorted VERTICAL dipole antenna which can be set from 10-40 meter.

 
Standing in the garden on 4 m². Antenne is placed 140 Cm above ground on an isolating tube.
 
   

DECISION MAKERS.

A well known item by DX-ers are elevation patterns. Due to many discussions about take-off angles, we might assume to easily that we need as much energy at as low as possible angles to work the DX. I believe you need the energy at the right angle at the right time and I don't expect an antenna which radiates straight up to be my main DX tool.

In FIG.1 we see several elevation patterns from wel known antenna's. Pink marked we see the elevation pattern from the inverted-V, which I modelled at a moderate hight of 1/4 Lambda. With this antenna we can see that a lot of the energy is goes upwards to the sky. This will make the antenna a champ for local contacts within the 800 km range. Even at this moderate height, this inverted VEE will need a 10 meter high support and a 20 meter long garden strip!

The black pattern gives the radiation from a short vertical dipole with capacitive HATS and coils for some center loading and exact tuning. At a 24° angle you can see that it gives as much energy as the inverted-V dipole. At lower angles there is little more and at the higher angles you will be below the dipole. Very interesting is to see how the place of the antenna is affecting the pattern, for worst case I assumed AVERAGE ground conductivity of 15 mS/m.

The blue pattern gives you an idea about performance if you can place this antenna in rich soil. I already started to glance after calculating those patterns.

And... if you're near salt water or go to an island expedition, there is absolutely no reason to do much effort in putting up horizontal antenna's, unless you can hang it as high as a wavelength.

 
 
   

The modelled inverted-V antenna is full size and will have a higher efficiency than a shortened horizontal dipole. If we consider a full size 1/4 wavelength vertical we need a 10 meter high radiator and enough radials for low angle radiaton and appropriate efficieny. I will not go into the theory on the amount of radials needed but even if you only use 4 of them you need a big square to install the vertical antenna for 40 meter (we didn't consider 80 meter yet !!). Some HAM's may not see the problem, but in a small country like Belgium a small lot of 800 square meter will be "average" for many HAMS, and of course our XYL don't want us to spoil the whole garden with wires hanging "around". Placing the dipole not horizontal but vertical with cancel the energy which goes upwards and provide low angle radiation depending on the conductivity-properties of the ground in the environment (several wavelengths around your antenna). If you're not in the desert you might have some advantages in using the dipole vertical. A full size vertical dipole for 40 meter will also be about 20 meter high, which might also be difficult to manage. Shortening the antenna will able us to accomodate the antenna. The most efficient way to load an antenna is top loading, if we load the antenna with coils we will have to deal with losses in the coil which can very fast turn into "heat radiators" intstead of radiators for our valuable RF-power. Instead of using the full size vertikal dipole or inductively loaded shorter dipole or monopole we can reduce the antenna size without loosing much gain by using capacitive HATS or a combination of both for lower bands. Hats are symmetrical arrays of wire at right angles to the dipole ends.It is the symmetry which results in radiation cancelling and hence does not yield significant horizontally polarized radiation. Non symmetry will not have much influence on the radiation, but will reduce the operation bandwith with a significant amount. The vertical dipole which we will test can be used with capacitive toploading from 10 to 20 meters, if you add some high-Q coils at the feedpoint you can use it on 30 and 40 meters too....BY SHORTEN THE ANTENNA THIS AMOUNT, WE WILL MAINLY LOOSE BANDWITH RATHER THAN GAIN.

 

BANDWITH CONSIDERATIONS.

The bandwith of an antenna is one of the important issues when we evaluate an antenna. I always assume operating bandwith to be 1.5:1 VSWR bandwith, higher VSWR values will require automatic or manual impedance matching.

On 10 and 15 meter there is only a small amount of shorting, so operating bandwith is wide enough to cover those larger bands.

On 20 meter we can easily cover 350 KHz with the shorting HATS.

30 and 40 meter do need the coils placed at the feedpoint, bandwith decreases to about 100 KHz due to the coils, but this isn't a problem on those bands. The Q-faktor increases and also the receive performance.

   
 
6 uH coils, 11Turns on 50 mm with 4mm² Cu wire. By increasing the winding spacing will increases the resonance frequency. Coil in the serves as B-match.
 

FROM 10 TO 40 METER.

Before we start with some construction details, lets look into the calculated patterns and SWR curves.

 
   
 
 
   
 
 
   
 
 
   
 
 
 
 
   

GAIN.

If we compare the patterns to, for example a shorted HORIZONTAL dipole we will be lower in gain but the pattern is omnidirectional and the energy is used where we might need it. Blue is the shorted Horizontal dipole, the black trace is the vertical dipole. <more patterns>

 
 
   

CONSTRUCTION DETAILS.

Below I propose a building schematic, some room is left for individual tuning to own preferences or to improve mechanical strenght. The antenna described is a testmodel and the prototype has been installed since last summer at the QTH of my antenna fellow Franki, ON5ZO, who has done some contest and DX testing after an initial testdrive by the author.

 
 

MORE CONSTRUCTION PICS...

 

 
 
One of the coils for tuning the antenna on 30Meter or 40 Meter. 11 turns of 4mm² isolated Cu wire will allow you to tune to 7 Mc. When you open the coil, you can bring the resonance to 10.125 Mc.

When adding coils, the impedance drops to about 20 Ohm. A Beta matching circuit is used for impedance-transformaion to 50 Ohm. A balun or coiled feedline will be needed to cancel return currents.

 
The assembled vertical dipole here shown in th 10 meter version.
With a M5 bold the drilled HAT sections are secured. Upper and lower HAT basic sections.
Balance checking, none of the ends touches ground ! Tapering for tuning and band change.
 
Half the hat with tapered sections. A completed hat for 876 grams.

B-MATCHING THE SHORT ANTENNA.

When shortening an antenna this amount, the GAIN will be lower, the bandwith smaller (higher Q),and feedpointimpedance lower. The unmatched feedpointimpedance is 14,91-J26,3 Ohms. The amount of reactance (-j26,3) will serve as capacity in our Beta matching network.

THE FORMULA'S FOR MATCHING NETWORK / Xc = -J23,3 / Rcoax = 50 Ohm / RYagi = 14,91.
 
XL = 32,59 WHICH CORRESPONDS TO A 0,73 uH COIL ON 7,025 MHz. COIL CAN BE SEEN IN ABOVE CONSTRUCTION PICTURES.
 
   
       

ON THE AIR.

After placing the antenna at my own QTH, near Gent, I asked my good friend ON5ZO, Franki, to do some real testing. As a dedicated DX-er and contester, ON5ZO used the antenna at his brand new QTH from march 2003.

In July 2003 I asked him about 40 Meter...

A61AR United Arab Emirates
VK2KM Australia
TA3/G3AB Turkey
UN4L Kazakhstan
TO5AA Martinique
D4B Cape Verde
3V8BB Tunisia
TA3DD Turkey
A61AJ United Arab Emirates
SU9NC Egypt
9K9X Kuwait
JY9QJ Jordan
UN7IKD Kazakhstan
W5AA/HP3 Panama
W2LNB United States
K3WU United States
PR7AR Brazil
VU3KJB India
JY9NX Jordan
UN7TS Kazakhstan
A61AR United Arab Emirates
UN2E Kazakhstan
4J6ZZ Azerbaijan
E21CJN Thailand
EX2M Kyrgyzstan
TK5EF Corsica
YB0DPO Indonesia
4K0CW Azerbaijan
9H3TM Malta
A61AR United Arab Emirates
JY9QJ Jordan
K5MA United States
KC1XX United States
N3AD United States
WA3AAN United States
WJ9B United States
K9MUG United States
KC1F United States
W1EBI United States
K2NG United States
AA3B United States
N3RD United States
UN9LW Kazakhstan
KB1EFS United States
N2NT United States
KT3Y United States
N2ED United States
PY2NY Brazil
K7SV United States
N9RV United States
K3CR United States
AY0F Argentina
UN7CZ Kazakhstan
K3DI United States
XM3AT Canada
WW2Y United States
VA3DX Canada
K1NA United States
N4CW/1 United States
W1FJ United States
K1PT United States
KD4D United States
K8GL United States
K4JA United States
W8KIC United States
W8LU United States
TA2ZF Turkey
VE3NE Canada
K1TTT United States
VY2ZM Canada
JA3YBK Japan
JA6OLZ Japan
4K0CW Azerbaijan
4Z5LY Israel
N4AF United States
W2AX United States
K3KO United States
4J6ZZ Azerbaijan
KQ3F United States
K3GHH United States
VE3KZ Canada
KE9I United States
VE9DX Canada
K5KG United States
K1UM United States
VE3DZ Canada
TA3DD Turkey
H2G Cyprus
VE3WO Canada
VE1ACU Canada
K9BGL United States
TI3M Costa Rica
W3RJ United States
K5ZD United States
K3EST United States
VE3RM Canada
KD2RD United States
N2GC United States
ZL6QH New Zealand
KU1CW/0 United States
W4PM United States
LU4FM Argentina
E21CJN Thailand
EX2A Kyrgyzstan
A45WD Oman
4L8A Georgia
HS0ZDZ Thailand
K2PS United States
K2UOP United State
...

ON5ZO Comment :

First of all, I want to thank Kurt ON4BAI for letting me use and test the prototype of his 40m vertical dipole. I just moved to this QTH, and even up to now there is a lot of work to be done, so there is not much time to install antennas. Kurt's offer was gladly accepted: no more worries about 40m.

Some statistics? I've been using the antenna for about 8 months now, during which I made about 1100 CW QSOs on 40m alone, yielding a total of 97 DXCCs on 40m. All with this antenna, from my QTH, with 100W.

How does it play? Well, I am very satisfied with this antenna. Previously (at another QTH) I used a delta loop and a quarter wave vertical with 50 radials on 40m. All of these have their benefits and drawbacks. The vertical was very noisy to listen to, and lawnmowers don't really like the radials in the lawn. But it was a good DX antenna. The delta loop was very good too, especially for DX. Much quieter than the quarter wave and it doesn't need radials. But you need a support that's high enough to support the apex. I also had the impression that the loop slightly favoured a direction, and was not really 'omnidirectional'.

Now, this vertical dipole combines the benefits of these two into one antenna. It is reasonably quiet to listen to, there are no radials, and I seem to work all CW DX I hear on 40m. It plays good in EU too, which is nice for contesting. So far, I have been working all that I could hear. NA, SA, AF, OC, JA's - all worked on a regular base. In SSB, I work EU in some local contests and always get good comments on the signal. I can even work K4JA on phone and have heard VK/ZL on phone - but don't bother to call those.

Mechanically, I have a bit of a weak prototype. The base is guyed in 4 directions, but the antenna is very flexible. We have had severe winds and strong gusts, and the antenna swings around, but never once did it bend, fall or fail. For a permanent version, slightly bigger tubing won't hurt, but this prototype survived so far.

Apart from it's electrical qualities, I think this antenna has some other benefits as well. It's easy to construct and assemble, does not require high towers or poles, not much guying, low profile.

Imagine 4 of these in a 4 square array.

Franki ON5ZO


 
   

SWR-measurements.

I tuned the antenna at my QTH for 40 meter CW. EZNEC 3.0 is accurate, but building the coils implements some tolerance. Therefore I tuned the antenna with the AEA-CIA HF ANALYZER. Although I could easily tune the antenna at my QTH, We found the antenna off-frequency after transport to the ON5ZO QTH. To be honest, we didn't do much effort to solve this trade off and Franki used the antenna with the autotuner from the TS-850SAT tranceiver.

 
   
 
 

CONCLUSIONS.

  • This project will provide you with a good antenna to work DX on 40 meter on a very limited footprint and even with limited mechanical skills you can build one yourself for an attractive budged.
  • We, ON5ZO and myself found a little frequency shift in function of the weather. This is a minus in which we will investigate to make it more stable.
  • It is a nice small antenna to put in the garden and if your partner or neighbour can't stand this type af antenna, your defenitely in the wrong HAM-environment.
  • The satisfaction is all yours if you work the ultimate DX with your homebrewed antenna-"construction".
 

SOURCES.

1/ARRL ON4UN Low-Band DXing Third edition.

2/ARRL Antenna book 17th edition

3/ARRL Simple and fun antennas for HAMS

4/W4RNL Website

5/EZNEC 3.0 from W7EL/ www.eznec.com

6/Hamcalc from VE3ERP.