The N6TZ Antenna System
HAROLD E WILLIAMS
PO BOX 2726
CAMARILLO CA 93011
I live in on a small city lot that is 75 ft wide and 90 ft deep. My goal was an effective system with No Nonsense quick band change capability without large hardware in the sky. The result is a maximum use of a mini-beam called the Hex Beam and a very effective vertical which uses a shunt feed system on the tower. The city of Camarillo is easy on Hams, and only a $37 permit is needed for up to 75 feet tall in your back yard.
(Click on Photos to see Larger View)
The Street View
I have the Hex beam at 47 ft for 10, 12, 15, 17, 20 meters. The 20 meter element is at about 50 feet height. The beam is a commercial made Traffie Hex Beam...See www.hexbeam.com THIS IS THE BEST SMALL BEAM, IT RIVALS LARGE BEAMS !! I could not go higher because of guy angle limits that I determined. The city left the engineering up to me.
The whole tower with the beam is fed as a top-loaded shunt unipole vertical on 30, 40, 60, 75/80, and 160 meters. I have about two dozen or more ground radials of various lengths with a total amount of about 1200 - 1300 feet of # 14 wire in the ground. The radials were laid into the ground before the yard was re-done. A person could get away with less ground radials, but the bottom line is to use what is available.
View from the shunt feed
Since verticals are noisy on receive, I have a RECEIVE ONLY folded dipole made from TV ribbon 300 ohm line stapled onto the wooden fence going across the back yard. I use a tuner in the shack to peak the receive with the folded dipole on 40, 60, 75/80, and 160. The dipole is invisible as it is under the cap board. This receive dipole uses two RG-6 coaxes as a shielded balanced feed coming in thru underground conduit from the fence to the shack. The receive folded dipole improves sig-to-noise ratio up to 20-25 db on 160, 80, 60, 40 and less on 30. All Coax and control cables feed underground in pvc conduits to their various destinations.
As can been seen in the photos, the TRANSMIT shunt fed tower tuner is a complicated homebrew tuning box with a lot of relays and caps. This could be simplified if a person wanted to mount a commercial auto-tuner or a manual tuner in a weather proof box at the feed point. I am a broadcast engineer and had to build my own of course ! A year of effort seems to still be worth it, but next time I take on a project like this, will someone threaten me with the OM's Wouff Houng?
The Shunt Feed Tuning Box
Note the box is an old Collins broadcast isolation box for AM towers. The 4 inch copper ground strap ties the radial ground system to the tower and tuning box. The tower is fully grounded to the radial system as is the tuner box. Grounding is IMPORTANT for BOTH the tower AND the feed point tuning box. The tuning box sits about 15 feet away from the base of the tower.
The shunt feed wire goes from the tuning box to the top of the tower near the rotator and forms a tall steep triangle, often called a unipole design. A tracer wire comes down the tower from the top feed point and wraps around the tower two or three times and is tied to the ground point at the bottom of the tower; this makes the tower a more constant conducting element. There is no receive noise during wind gusts, so the tracer wire is doing a good job.
The shunt wire feed point was established along with the ground at the future final tuning box location. Then with a small plastic table at that exact location, the different configurations of tuning was "hammed-in" using a MFJ antenna scope (you know - the kind with built in signal generator) and an assortment of variable caps, coils, and clip leads. This was done for each band and the configurations drawn out and then worked over on paper until the simplest schematic was arrived at for the five band switching permanent system. After the final box was built in the garage using the arrived at configuration, it was amazing how repeatable the configurations and values were when I put it in place for final tuning. I got to know all the lizards that live and climb on the wooden fence during this time.
In the close up of the open box, the control matrix with diode steering to activate different components for different bands is in the very bottom. It is that white wad of wires in the bottom of the box. This allows the single toggle selection system.
I do not recommend building the final box outside "on location". It is a lot of work and time, and it will have problems. Extra time fabricating carefully inside on the work bench is worth it.
The tuner is toggle switch selection with no tweaking or fooling around for a band change. On 160, 80, and 40 there are two toggle switch positions on each band to cover the top and bottom halves of those wide bands.
Tuning Box Controls
The black box in the photo with LEDs and toggle switches is the control box in the shack. The control cable is like 10 or 12 wire cable, with a couple of pairs left over. I piped the 24 volt D.C. control voltage out there on the spare leads so I could use an alligator lead to turn on various relays during final tune-up. That little feature gave it real-world tuning up capabilities. I recorded all final tune-up info on paper, then built the diode steering/matrix jumpers and installed them to give me the needed switching.
The control box gives a selection for the following:
1. Top and bottom of 160 m
2. Top and Bottom of 75/80m (two switches on for lower 80)
3. The 60 m. band
4. The top and bottom of 40 m
5. 30 m.
When all switches are off, the default is the 80 meter long wire for short skip local use.
A picture of the whole tuner box (below) shows two antenna wires coming to the insulators on the tuning box, the one on the top is the tower shunt feed and the one on the bottom is the 65 foot random wire running across the yard at 15 foot height for 80 meter short skip within southern Calif. The vertical tower pattern is low angle radiation and does not give good short skip on 80 meters, thus the random wire. For the out of state 80 meter contacts and all other bands, the shunt fed tower is used. Remember, for a kilowatt there will be need of vacuum relays in many points of the configuration. Low impedance points can be switched with heavy power relays. The tuning box will easily handle 1.5 kW peak.
The Tuner Box mounted to Fence
The rotatable beam adds good top loading for the vertical. I modified the Hex Beam so that the reflectors were common to the mast/tower to enhance the top loading effect. More on this later in this document. Two pictures below show the mods to the Hex Beam. These mods did NOT change the characteristics of the Hex Beam. The wire is tying the center of the reflectors together as it goes down the PVC mast. It is then lugged to the base plate where another heavy braided wire goes around the rotator in the same bundle as the coax. The heavy braided wire then bonds to the bottom of the rotator at the tower. This is where the shunt feed wire begins it's run to the tuner box on the ground. Adding the reflector elements of the Hex Beam to the top loading of the vertical increases the effective electrical height of the vertical. This is important as operating on 160 with only a 50 foot tall vertical would be very difficult without lots of top loading.
Results - And I am not a DXer, just work them as they come along. The system has been in use for about 2 years.
A.) On 10 thru 20 meters, World-wide DXing, and I am very impressed with the Hex beam for a 5 band mini-beam.
B.) On 30 and 40 meters, it is a pile-up breaker. Looks like a 5/8 wave on 30 and about a 1/2 wave on 40.
C.) On 60 meters, It works very good as a 3/8 wave. We need CW on 60 meters.
D.) 75/80 meters, Very happy as I have Hawaii, most of North and South America and the Bahamas, Cuba, and Bermuda. Good SSB from California to the East coast of U.S. with 100 watts in the winter. With top loading, 80 looks like a 1/4 wave.
E.) On 160 meters, I have Hawaii, and most of North America, Alaska, Mexico. Fun on that band to break into nets and be given a good signal report.
VHF Antennas at the Site
Here are a couple of quick shots of the Pixel Magnetic Loop for wideband receive at N6TZ (Posted October, 2012)
Click on the photos for a larger image.
(Provided by Earthsignals.com)