Field Operation, IC 7000 and Buddipole at Champlain Lookout

It occurred to me while reading through the Buddipole information for the Triple ratio Switch Balun (TRSB) that I should be able to make a 20m vertical with a rigid loaded counterpoise.

This antenna configuration would

• have a lower take-off angle as compared to the flattop dipole
• would be directional to a degree
• would be easily rotatable as compared to a wire counterpoise
• would not need a standoff stake for a wire based counterpoise
• would operate very similar to a setup w/ a longer wire counterpoise
  

Modeling

I started with some simple modeling in 4NEC2.


The vertical arm is constructed with 3 dipole arms, 1 red coil, and 1 standard whip. Using more than 1 dipole arm helps make the antenna longer and more effective. The loaded counterpoise is built with a single dipole arm, a black coil and a standard whip.


The antenna is brought to resonance at the frequency 14.1MHz which is what I wanted with the following parameters and settings

Vertical

• Whip fully extended
• Red coil taped 9 turns from the whip end
• 3 standard dipole arms

Counterpoise

• Tilted down at 30degree angle
• Whip fully extended
• Black coil taped 12 turns from the whip end
• 1 standard dipole arms

In 4NEC2 I first assumed the red coil had an inductance of 28.2uH for all 42 turns. This is the value I have used in the past. However with this value, resonance was predicted at only 12MHz. Testing the antenna in the backyard confirmed that the antenna does resonate at 14.1MHz. I temporally centred the model at 14.1MHz by scaling the full coil inductance to 69% of the 28.2uH.


The predicted antenna pattern is as expected for a vertical w/ 1 counterpoise.

Putting it all to use.

Nearby to the city of Ottawa, is a federal park with some breathtaking lookouts. For a Ham operator this looks like very nice spots for an antenna, high up over the surrounding land.



The setup was simple and compact, 2 50AH Gelcells, IC7000, Laptop and the Buddipole



The above 2 pictures show the "picnic table shack" and the vertical. The counterpoise made with the standard whip, coil and arm is raised above the ground and this allows the antenna to be "pointed" and also there is no pesky wire counterpoise to string out.

Operation

There was 070 PSK contest going on and there was plenty to listen to. A big plus of this location is the excellent s1 noise level. Many US stations were on the air as expected but notable and very easily copied stations were from Uruguay, Brazil, Argentina, and a good selection of European stations including, Spain, France, England, and some Russian stations.

QSOs

Thanks to all who helped make this an interesting afternoon. I had some difficulties with the 7000 running a bit hot due to the hot sun. Also, at times there were a few stations who were answering my calls at the same time and I did my best to unravel these situations.

• Start Station Name Country QTH Distance (km)
• 21:34 IK4JQS Maurizio Italy Molinella 6,515.32
• 21:23 PD5DP Henk Netherlands Wolvega 5,681.14
• 21:16 W6DEI Peter USA Berkeley CA 3,893.00
• 21:05 K0WIU Bill USA Yankton, Sd 1,912.58
• 20:49 HA6ZB Gyuri Hungary Aldebro 6,836.85
• 19:53 N4MGA Don USA Rex, GA 1,512.57
• 19:40 N0EPW Simon USA 1,360.02

Thanks to IK4JQS and HA6ZB for the 6000km QSOs. and thanks for stopping by.

Adrien

Buddipole 4NEC2 Model Files

I have found a way to post my 4NEC2 Buddipole modeling files on line using Google Documents.

Eventually I will log many of my design files here for anyone to use.

4NEC2 is available at http://home.ict.nl/~arivoors/

Below is a list of the files I have created.

FILE AC_Vbud_40M_09_V01 40m Vertical, (longwhip, 4 dipole arms, red coil)
FILE AC_Vbud_40M_08_V01 40m Vertical, (longwhip, red coil, 4 dipole arms)

Detailed Files:

FILE AC_Vbud_40M_09_V01

Description, LongWhip with RedCoil and 4 Dipole Arms on VersaTee w/ TRSB set to 25ohms (2:1) and 1 8.6m Counterpoise.

This is a new configuration
a) attempting to generate a lower takeoff angle and more gain
b) 40m PSK31 frequency (7.07MHz)
c) Red coil was moved to below the arms and whip
d) Suggested by Ray (K7RFW)

1 fully extended Long Whip
4 22" Dipole Arms
1 RedCoil tapped turns from Bottom
1 Versatee
1 TRSB,(2:1) 25 ohms
1 8.6 (m) Counterpoise

Takeoff angle	30	degrees
Gain	0.0	dBi
SWR	1.6	into 25 ohms

Conclusion:
Moving the red coil to below the dipole arms, resulted in a modest loss of antenna gain from 0.6dBi to 0dBi, the take off angle remained the same at about 30degrees. The inductance needed to maintain the antenna at resonance (7.07MHz) was reduced from 15uH (18 turns form the bottom) to 10uH (25 turns from the bottom). Best case SWR was increased from 1.1 to 1.6 as the impedance of the antenna decreased from 22.5ohms to 15.6ohms.

Overall, I would take from this, that is it better to not have the coil placed adjacent to the feed point.

-------------------------------------------------------------------------------------

FILE AC_Vbud_40M_08_V01

Description, LongWhip with RedCoil and 4 Dipole Arms on Versatee w/ TRSB set to 25ohms (2:1) and 1 8.6m Counterpoise.

This is a new configuration
a) attempting to generate a lower takeoff angle and more gain
b) 40m PSK31 frequency (7.07MHz)

1 fully extended Long Whip
1 RedCoil tapped 18 turns from Bottom
4 22" Dipole Arms
1 Versatee
1 TRSB,(2:1) 25 ohms
1 8.6 (m) Counterpoise

Takeoff angle	30	degrees
Gain	0.63	dBi
SWR	1.11	into 25 ohms

-------------------------------------------------------------------------------------

Buddipole

I have been experimenting with using a Buddipole for portable operations. Details on the Buddipole can be found at this link.

One configuration that is interesting is the 40m vertical as described in the Buddipole document at this link. I have used this and it tunes up very nicely, but I was also interested in seeing if I could model this configuration and possible find another more efficient configuration using other components.

I loaded a copy of 4NEC2 and generated a few simple antennas, dipole, Inverted Vee, and a vertical.


Model 1: Basic 40m Vertical w/ 1 counterpoise

Setup is Versatee + Dipole Arm + Red Coil + Short Whip and 1 counterpoise. I use the TRSB at 1:1 setting.


Key parameters: With the help of Dave KI6AWR, I am using a 28.2uH for the red coil.



This prediction of this antenna can be made to resonate at 7.07MHz but the SWR of 3.4 is worse than I had observed in reality.


This configuration has the following predicted values

Resonant frequency: 7.07MHz
SWR: 3.45

Model 2: Extended 40m Vertical w/ 1 counterpoise

Setup is Versatee +Red Coil + Dipole Arm 1 + Dipole Arm 2 + Long Whip and 1 counterpoise.


In this configuration there the vertical is 1.4m longer due to the second dipole arm and the longer length of the long whip. Also the red coil has been placed at the bottom of the vertical. The counterpoise is unchanged, and the loading coil is tapped at 49% of its full value. (this returns the antenna to resonance at 7.07MHz.



There is expected to be 1.4dB more gain at the same takeoff angle of 50degrees.



It should be possible to use a long whip and both dipole arms to extend the vertical. A bit more gain is expected and the red coil is expected to be at to 49% (20 of 41 turns) to compensate for the longer antenna. The counterpoise length does not need to be adjusted.

End Notes:

a) I am unsure why the predicted SWRs are so high. I was expecting better than 2:1.