Were you imagining a horizontal yagi at 270 feet in the air? No way. It is actually a vertical yagi, meaning three 160m vertical antennas are in a line and spaced a typical distance apart for a yagi. Only the center vertical is driven and the other two verticals are a director and a reflector. The concept for this antenna came from an article in QST, W2FMI 20-Meter Vertical Beam, June, 1972, p 14, by Dr. Jerry Sevick. This is an autumn 2021 project with a goal of working the final 34 countries needed for 160 meter DXCC. Orientation is toward Europe.
The only vertical that didn’t already exist is the new reflector shown in the foreground. It is 50 feet tall. The tower with the beam on top is doing double duty. The beam is being used as a top hat for 160m. The tower becomes the 160m driven element thanks to Omega matching. Faintly visible in front of the tower is the director, which is a 43 ft. vertical with a top hat, resonated to 160m.
What distinguishes the yagi from a phased array is how it is driven. In a phased array all three verticals would be driven at certain phase angles and magnitudes with phasing cables and a phasing network. A phased array has more gain but is very complicated to implement. This yagi has only one driven element, no phasing cables, and is quite forgiving as to spacing. Yagi elements can be spaced for maximum gain or can be spaced for best front-to-back ratio. These yagi elements are spaced for gain using .2 wavelength. The reflector is resonated 5% lower in frequency than the driven element and the director is 5% higher. Center frequency is 1.840 MHz with a 2:1 bandwidth from 1.8 MHz to 1.885. The yagi will be ready for the winter 160m DX season.
A loading coil is housed in this enclosure at the base of the reflector. The coil is a roller inductor adjusted to resonate at 1744KHz, which is 5% lower than the driven element resonance of 1840 KHz.
At the base of the director (the other element) is an identical loading coil, resonated to a frequency 5% higher, or shorter, than the driven element. The director resonates at 1930KHz, shown below. SWR is irrelevant because it is not being connected to a feedline. It is connected directly to the radial ground screen.
In the pskreporter screen-shot below notice that the strongest reports (look at the “dB” numbers) are in a line to the northeast of the Colorado QTH which is very good news running barefoot at 100 watts.
Project 6 of 7 for October, 2020 – projects to keep sane during Covid-19 Lockdown
For the virtual Dayton Hamvention this year Contest University had some wonderful online presentations. One was especially interesting to someone who still has countries needed on 160, W3LPL – “Effective Low Band Receiving Antennas”. A video is still available on YouTube. Frank Donovan, W3LPL, listed receive antennas from the smallest to the largest along with ranking their effectiveness. The best of size, cost, and effectiveness looks like the 4 square high impedance active antenna. DXEngineering offers one in a bundle with all possible parts needed, DXE-RFS-SYS-4S. One is on order.
In Frank’s excellent presentation only one antenna performs better and that is twice as big and only has 1.5 dB Receiving Directivity Factor (RDF) improvement. The Hi-Z 4square appears to be the best bang for buck.
As of today grounds rods to mount the antennas have been made. A 1000′ roll of direct-bury CAT-5 cable is on hand to run power and control signals. A location has been selected about 500 feet north of the transmit antennas. A scheme to reduce the number of control wires so direction can be switched remotely has been invented. This receive antenna should coordinate nicely with the omega-matched tower transmit antenna upgrade this year.
One concern is how far apart to put the verticals for the best performance. The DXEngineering user guide says 135′ or one quarter-wave is optimum for 160. Other references says 80′ or 88′. An email was sent to Frank, W3LPL, to get the word from the master himself.
Hi Mark, Optimum 4-square spacing for 160M receive is 67 feet. Wider spacing produces higher signal levels but also higher side lobe levels.
Much more important is maximizing the spacing from resonant 160 metertransmitting verticals, towers more than 90 feet tall power lines andhomes or buildings that may contain RFI sources. I would try for at least one thousand foot spacing. Good luck!
Five hundred feet is do-able but 1000? Hmmm. We’ll see with a site visit tomorrow.
Cable was pulled from the shack to the 4-square site today which is 1000′ away. One thousand feet seems like no problem after today’s site visit. The site is very close to the Field Day site for 2019.
One cable is quad-shielded RG-6 and the other is direct burial CAT-5. One of the CAT-5 pairs will be used for direction control. The other three pairs will be grouped to provide power. Resistance of a single 24 gauge wire 1000′ long is 26 ohms at room temperature. Three wires grouped together will cut the resistance to about 9 ohms (8.77 to be exact). With 1 amp of current the voltage drop would be 9 volts (E=I X R). To provide 12 volts to a device the supply voltage will need to be 21 volts. Fortunately the battery voltage for the new inverter will be 24 volts. A linear buck converter (LM-317 voltage regulator) can be installed at the 4-square end and provide a regulated 12 volts. Per the instruction manual:
“The DXE-RFS-3 phasing unit uses and distributes the voltage to power the active antenna elements. For all four active elements, a nominal +12-15 Vdc at 250 mA current is required.“
At only 1/4 of an amp load the voltage drop would only be 1/4 as much or 2.25 volts. If a 13.35 supply was used the voltage at the 4-square would be 11 volts. That might work but might be unreliable. Using a 24 volt supply and a buck converter is a more reliable choice.
Today the ground rods were driven for mounting the verticals. They were measured out to be within 1″ accuracy, using the 67′ side lengths recommended by W3LPL. The sides are precisely east- west and north- south. That makes Europe at 45 degrees the default direction.
Status: 4-square arrived today (some assembly required). The Quad Shield RG-6 cable has been measured out as accurately as possible and cut to length at home for the delay lines.
Next the excellent quality Snap-N-Seal connectors provided by DXEngineering were crimped on.
Tomorrow the cables will be taken to the remote site and connected. The verticals will be installed on the ground rods.
Installed, here is one of the verticals:
This is the hub at the center of the four verticals. The three delay lines are coiled up and strapped to the post. The gray box on the far side contains the voltage regulator (buck converter). The black box in the foreground is the DXEngineering control box.
Inside the gray box is a LM317 voltage regulator or buck converter. It converts the 24 volts input to a 12 volt output. A LM317 is used instead of a LM2596 because the LM317 is linear technology (analog) and does not generate digital hash like the LM2596. This method was chosen to carry 12 volts over a 1000 feet of CAT5 to overcome it’s inherent cable loss. In the picture below the blue/white pair carries the BCD data to switch the relays that control the direction.
Testing to see if the design works in the field shows good results. The gold thing is a 50 ohm resistor which simulates the load of the relay controller. (E = I X R, E = .25A X 50 ohm, E = 12.5 volts).
With the weeds looking very much like vertical antennas a wide shot of the 4 square doesn’t show much. It blends in quite well.
Performance is extremely directional as expected. A station to the northeast that comes in S9 completely disappears when the relays are switched to null it out. Come on winter and 160 season. It will be fun to use this.
Next, FT8 signals on this antenna were compared to the same signals on the 160 meter transmit verticals. Signals are stronger on the transmit antennas but there is no way to null out unwanted signals. A preamp is under consideration to bring up the gain where it will be even with the transmit verticals. The loss in 1000 feet of RG6 may need to be compensated for.
Status: completed (but always looking for improvements). To try to get a little more gain on 160 the jumpers were put in place to peak the response on that band. Gain is still low but it is working as designed.
January, 2021 update: Performance is amazing. A YouTube demonstration should be produced. A preamp was added at the 4 square to overcome the loss in the 1000’ of coax.
An omega-matching system was added to the tower when it was on the ground in the hopes the tower could be made into a 160 meter vertical antenna. The concept was suggested by Bill, N0CU and illustrated in ON4UN’s Low Band-DXing, Fifth Edition on p 9-68.
PVC pipes were attached to the tower with stainless steel clamps and 8 ga aluminum wire was connected at the top.
Today was the first chance to see if could be tuned. Two large variable capacitors were mounted temporarily, one in parallel with the tower and the other in series with the feedline. It is held up by Velcro strips and connected with clip-leads.
The results were amazing with the capacitors set at half way on the first try. This is what it looks like on the RigExpert AA-55 antenna analyzer.
With a little tweaking the match could probably be made perfect. It is quite useable right now with no other adjustment. Upon re-reading some of the technical articles on gamma matching a tower some new (or missed) information came to light. The main point is the resistance of the match is determined solely by the gamma apparatus connection height and distance from the tower. Resistance cannot be changed by the matching unit. If this proves out we are stuck with 66.5 ohms.
Next the clip-leads were carefully removed without touching the capacitor settings. A Banggood tester was connected to the capacitors and readings were taken to determine a ballpark figure for required capacitance.
The Banggood shows one capacitor is 82pF and the other is 116pF. Capacitors to achieve these values but with higher voltage ratings will be obtained. Next step is to mount them more permanently in a NEMA box and attach the box to the tower. Getting ready for winter and the fabulous upcoming 160 meter DX season will be fun this year.
A new box with two variable capacitors is ready to be installed and adjusted. The capacitors are capable of handling a peak voltage of 3KV. That should be right on the edge of being ok.
Update 9/6/2020: New box with room for two 3KV variable capacitors has been installed and tuned up.
The results are below 2:1 swr but not down to 1:1 which was the goal, of course. Moving the gamma tap point location would probably be necessary but too much work to accomplish. One article mentioned moving the gamma wire closer or farther from the tower down at the matching unit level. That will be given a try later this month. Here is an analyzer view of the match. This was taken at the shack end of the coax.
The SWR of 1.27 is lower than we measured at the base of the tower due to the coax loss. At the tower the swr was slightly higher at 1.45 and the resistance was up to 72 ohms.