Thursday, June 23, 2011

Contest station VE6FI

Ve6fi Amateur Radio

160 Meter Antennas

This is a 160 meter antenna which is a shunt fed vertical. A 72 foot Trylon tower with a 6 element 15 meter mono bander mounted on the top is used as the radiating element. Information on this type of antenna was obtained from ON4UN Low Band DXing book. (Chapter 9-71). The electrical length is 92 degrees but it is reduced by 5 degrees because of the 6 element beam on the top.

The gamma match incorporates a #8 cable bolted to the tower at the 62 foot elevation. The distance of the cable from the tower is 12 inches. A 500 pico farad variable capacitor was put in series with the gamma rod (wire) to tune out the reactance. The capacitor and the distance of the wire from the tower were adjusted for minimum SWR. The amount of the capacitor required was 150 pfd.

The capacitor used was rated at 4.5 KV. With 150 pfd of capacity the Impedance at the capacitor terminals is 580 ohms. At 2 KW of power the peak voltage will be 1000 volts. Even with an SWR of 2.0 to 1, the voltage will not exceed the 4.5 KV rating.

The pictures shows an enclosure around the capacitor which will keep the insects and dust from accumulating between the capacitor plates.

We initially installed seven ground radials all .125 wavelengths long. They run on the ground and are made from #22 paired insulated wire. The ground bar is located in the pedestal located at the base of the gamma match for the loaded tower (vertical)

The transmission line length back to the radio room is about 300 feet. I used 3/4 inch CATV 75 cable for the transmission line. (Not too much loss there!)


160 meter Dipole

The dipole is a full sized dipole mounted around 120 feet between two towers and favors the north-south direction. This dipole is about 350 feet from the radio room and again 3/4 CATV foam cable is utilized.

At present we do not have too much for receiving antennas for 160 meters. What we have is a fair amount of intermod noise generated on the site. After that source is located and cleaned up we hope to install a K9AY loop and possibly a permanent Beverage antenna.

80 Meter Antennas

I built a phased array of four inline verticals for 80 meters. This is sometimes referred to a directional end fire array.

The verticals are almost 0.25 wavelengths high and are 0.25 wavelengths apart. Each self-supporting tower (vertical) has 48 radials, each 0.25 wavelengths long in a circular pattern around the base.

I modeled the array on the antenna modeling software called ‘Eznec’. Modeling allows one to see the antenna patterns one can obtain with different heights, spacing and radials. It is a lot easier to move elements in a model than it is to try moving them in the field.

This vertical phased array has a gain of 9.2 db dipole, a theoretical f/b of 39 (actual to date is 27db) and a take off angle of 18 degrees. The beamwidth in the direction aimed is 100 degrees. This vertical array is located approximately 600 feet from the radio room and is fed with 0.75 foam cable.

Matching - Matching these antenna means that you have to match the towers so that you have the correct amount of power going to the respective tower, and have the correct magnitude and phase of current into the base of each vertical. Instead of using lengths of coaxial cable for phasing and matching, I used L C components. I utilize the articles in Ham Radio magazine 1983 by K2BT and on line help from Greg W8WWV.

Some of my Learning’s:

One does not make the verticals exactly 0.25 electrical wavelengths long. You make them slightly shorter so that you can make the reactive portion equal to zero at the operating frequency. A quarter wave vertical has a theoretical impedance of 36 + j20 ohms and at resonance you want something theoretical like 36 + j0. In effect you make the vertical about 5 % shorter. This percentage depends on your average diameter of your vertical. W2PV discusses this in his book ‘Yagi Antenna Design’

The magnitude of currents into the base of the verticals follows the binomial theorem, which would be the ratio of 1 amp each if you have two verticals, 1,2,1 ratio if you have three verticals and 1,3,3,1 ratio if you have 4 verticals as in my case.

When verticals are 0.25 wavelengths apart one would think that you would phase them 90 degrees apart such as 0, -90, -180 and –270. I have found that the theoretical optimum for maximum gain and best front to back ratio is 0, -116, -232 and –348 degrees.

You cannot measure the driving impedance of a vertical – you have to calculate it. You can measure the self-impedance of a tower but make sure all the other towers are above ground when you do the measurement. Having another tower connected will throw off you measurements because of the mutual coupling. YOU HAVE to calculate the driving point impedance, which is the impedance your transmitter will see. The driving point impedance takes into account the currents in all other verticals.

Verticals are a low maintenance antenna and can be arrange to give you gain at low take off angles in different directions. The networks are in place and the remote switching is completed and now this 80 meter array is in use at VE6fi

40 meter Antennas

This is a 5 element home brew 40 meter beam at 125 feet. It has a 60 foot supported boom comprised of sections of eight inch square aluminum tower. This is an OWA (Optimized wideband antenna) based on the original OWA design by NW3Z. I did model this antenna and make the adjustments for operation on 40 meters. With this full size antenna array it is not a 'cut and try' effort; it is best if it works the first time.

This 40 meter beam will cover the complete 40 meter band with less than 1.2:1 SWR. The OWA feed is 50 ohms. You can tune this antenna on the sawhorses - well not quite as the elements sag six feet. You get a 50 ohm feed by bringing in the first director closer to the driven element.

The elements construction utilizes a 2.5 inch aluminum pipe at the center of the element and with pipe/tubing which gradually tapers down to 0.5 inch tubing at the tips. All material has a yield of 40KPSI. I utilized a spread sheet to calculate the strength of the elements at a given wind speed.

The actual antenna tuned to within 50 kHz of the modeled antenna on Eznec.

The antenna is rotated at 1/3 of an rpm by a home brew rotator mounted at the 110 foot level. A shock absorber/damper is used between the rotator and the mast to minimize the effects of any sudden stops and starts. Even at 1/3 rpm it will take this antenna 10 seconds to fully stop. It is fed with 7/8 inch and 1/2 inch foam heliax as the antenna is located some 400 feet from the building. It has been up for seven years and works well. As you can see in the picture the feed point is some twenty feet along the boom so it is not something you reach while standing on the tower. If something goes wrong with the feed then it is 'I walk the line' or is it 'I walk the boom'!

20 Meter Antennas

These four antennas are

mounted on a 150 ft tower

which has a 24 inch face.

The extra wires on this tower are for a wire log antenna

20 Meter 5 element Yagi at 150 ft.

This is a 20 meter homebrewed 5 element monoband yagi on a 46 foot boom. It has a integrated boom of three inch and two inch tubular aluminum.

This yagi is shown here ready to be raised to the 150 foot level on a 24 inch tower in 1996. It was put up by Denis and Evan themselves three days before the CQ WW contest. Things get done faster just before contests!

The rotator for this antenna is a large prop pitch rotator and it is designed to turn at 1/2 rpm. A shock absorber/damper is used between the prop pitch and the mast driving the antenna to remove any sudden stops and starts. The prop pitch motor is now a 100 volt DC motor with it's power source is located at the base of the tower. We usually park this antenna on Europe or on Japan.

20 Meter five element beam at 110 ft

It is a typical 5 element monobander on a 36 foot 3 inch diameter boom. The feed system is an OWA (Optimized Wide Array). From the picture you can see that the first director is close to the driven element. This brings the feed point up to 50 ohms. It is fed directly with 50 ohm coax and utilizes a coaxial wound balum.

This antenna is mounted at the 110 foot level and is pointed on the Caribbean. Both the 20 meter monobanders are on the same tower.

The 20 meter tower is located some 500 feet away from the building and is fed with 1/2 inch foam transmission line and switched at the base of the tower.

Another 5 element 20 Meter OWA Beam at 70 ft

This 20 meter was built and installed in 2005. It is on a 36 foot boom and the picture below shows how it side mounted on a 24 inch tower. The rotator used is an Alfa Spid, which has the feature where one can adjust the stop in the clockwise direction and the stop in the counterclockwise direction so that the boom does not contact the tower. The offsetting brackets are made off 2 X 2 X 3/16 inch galvanized steel. The Alfaspid is mounted on the bottom bracket and there is a wooden bearing on the top bracket. These Alfaspid rotators work in a reliable manner even in the cold weather.

This antenna is mounted at the 70 foot level of a 150 tower.

Log Periodic Antenna

This is one of the largest antennas that we have on site. It is a Telex Hygain LP 1001 model which covers a frequency range of 3.7 Mhz. to 30 Mhz. with an SWR of less than 2:1 This antenna is mounted on a 70 foot unsupported boom which is a triangular aluminum tower section 12 inches per side. The mast is a 12 inch pipe that attaches to a rotator at the base of the 100 foot tower.

I have modeled this antenna with Ezenec and it is equivalent to a 3 element Yagi on any particular frequency. The main advantage of the log antenna is that you do not have to switch antennas.

While we can use this antenna on 20 meters we usually use it as a second antenna for 40 meters during contests.

15 Meter Antennas

This is a home brew monobander for 15 meters. It is mounted on a 36 foot boom and the elements go through the boom. The elements are 1.5 inches in diameter and taper down to 5/8 of a inch. The beam is built along the lines of the W2PV antenna. It is physically symmetrical, is fed with a hairpin feed.

This antenna is mounted at the 70 foot level of a self supporting Trylon tower. It covers the band with an SWR of less than 1.7:1 It is fed with a 250 foot length of 7/8 foam transmission line. This picture was taken when it was loaded with frost.

10 Meter Antennas

This is a home brew 10 meter beam used at VE6FI. It uses a 36 boom of three inch aluminum tubing which is supported by a truss and utilizes the elements through the boom concept. The 10 meter beam utilizes the OWA (Optimized Wideband Antenna) concept by NW3Z. I did utilize the modeling program Eznec to modify the dimensions of a larger antennas to fit it on a 36 foot boom. The elements are 1.5 inch aluminum tubing tapering down to 1.0 inch diameter tubing at the ends.

This 10 meter beam will cover the complete 10 meter band with less than 1.5:1 SWR. The OWA feed is 50 ohms. You can tune this antenna on the sawhorses and get almost the same results when you put it in the air. You get a 50 ohm feed by bringing in the first director closer to the driven element. You minimize the reactance by adjusting the length of the driven element. All material has a yield of 40KPSI. I utilize a spread sheet to calculate the strength of the elements at a given wind speed.

The front to back ratio is good and the gain is great. In fact during a contest the front to back ratio is too good and it is difficult to hear someone calling on the back of the beam.

Above is the 4 element Stepper installed with the Alfa Spid rotator at the

base. It is used as a second antenna on 15 meters or 10 meters. Mighty nice


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