Building Yagis – Part 6 (SteppIR DB36 Completed)

Completed DB36 Yagi

Completed DB36 Yagi

We completed the assembly and testing of the first of our two SteppIR DB36 Yagi’s today. We installed the 80m dipole option on our antenna which provides a rotating dipole on 80m. This should work quite well at the 100+ ft height that our antenna will be installed at. The dipole runs parallel to the DB36’s boom and is attached to the element support trusses. The dipole uses the two end elements of the antenna as capacitance hats and a pair of loading coals to end-load the dipole. Its performance is just 0.8 dB below a full size dipole on 80m. It also functions as a 60m dipole.

80m Dipole Loading

80m Dipole Loading

The 80m dipole attaches to an antenna switch which is mounted on the DB36’s boom support truss. This devices enables the dipole to be switched in and out and matched to the feedline.

80m Dipole Switch

80m Dipole Switch

The single feedline to the antenna attaches to the switch and uses a pair of relays to connect the feedline to either the dipole or to the rest of the antenna depending upon which band is selected at the controller. The switch also contains a matching transformer and balun. A control cable runs from the switch to the main control cable connector box on the antenna. Note the knot in the control cable to keep it from being pulled out of the 80m dipole switch box.

Dipole Switch Internals

Dipole Switch Internals

The final option to be installed on the antenna was the 6m Passive Element Kit. This kit adds two passive director elements to make provide a total of 6 elements on the 6m band. This improves the antenna’s gain and F/B ratio on 6m to 12.8 dBi and 27 dB respectively making it an effective 6m antenna.

6m Passive Element

6m Passive Element

The final assembly step was to complete the wiring of the main control cable and connect the controller to the antenna. Shown here is the main control cable connected to the Connector Junction Box on the antenna. The other end of the 24 pin shielded control cable connects to a DB25 Splice Connector which is attached to SteppIR’s SDA100 Controller. Note the two cable ties attached to the main control cable just inside the box. The cable ties act as a  strain relief to prevent the heavy control cable from pulling on the associated connectors. Its is important to carefully verify all wiring before connecting and powering up the DB36’s controller. We used DMM to verify continuity and proper connection of the control cable wiring. SteppIR also provides a document for troubleshooting which contains a series of resistance and short checks to do on each of the controller connections to the elements. It is important to do these resistance and short checks before you connect the controller for the first time as mis-wiring of the control cable can damage the controller if it is not corrected prior to power up.

DB36 Connector Box

DB36 Connector Box

After completing all of the resistance checks, we powered up the antenna and connected a feedline from the antenna to an antenna analyzer to checkout the operation of the antenna on the ground. Before beginning the test, we enabled the 80m dipole and 6m passive element options in the controller. The next step is to run the calibration procedure on the antenna and then to individually run each of the elements out to its full length and check that each element motor is operating correctly and the associated element is fully extended. You can determine that an element is extended by gently shaking the element support tubes or sweep ends. If the element tape is extended, you will be able to hear it rattle inside the support tube.

With the elements checked out, we ran SWR test on each band. The antenna is only 4 ft off the ground at this point so the minimum SWR reading on each band occurs about 500 – 700 kHz below the frequency settings on the controller which is normal. Also, the SWR measures higher than normal due to the antenna’s proximity to the ground.

DB36 Test Setup

DB36 Test Setup

What you are looking for is a pronounced “dip” in the SWR reading indicating that the antenna is tuning to some sort of resonance. Shown below is the SWR measurement taken on 15m. In this case, the dip occurred at a frequency about 300 kHz below the setting on the controller. All bands should be checked including 80m/60m (the dipole), the WARC bands (30m, 17m and 12m) and 6m. It is also important that you switch between bands that are far apart and verify that the frequency of the SWR dip on a given band  is consistent when the antenna is moved to a different band and back again. Any significant inconsistency between multiple readings on a given band indicates unreliable operation of the antenna and needs to be investigated and corrected before the antenna goes on the tower. In our case, all of the tests and measurements checkout out fine.

DB36 Test SWR Measurement

DB36 Test SWR Measurement

The final step in the assembly of our DB36 was to attend to some details to ensure that the antenna is reliably on the tower. After carefully checking and making final adjustments on the boom and element support truss turnbuckles, we checked the  tightness of the turnbuckle jam nuts and safety wired the turnbuckles to ensure that they will not come loose over time.

Safety Wire on Turnbuckles

Safety Wire on Turnbuckles

We also added some addition coax seal where the control wires enter the element housings to ensure that this area is water tight. We did the same thing around the coax connectors on the Driven Element housing and the 80m dipole switch.

Control Cable Seal

Control Cable Seal

It is also a good idea to check that all bolts are tight including the screws that hold the element housings to their support plates. I also checked that all of the electrical tape joints were smooth and tight. The final step was to remove the main control cable from the connector box and to tape a couple of cable ties and a packet of connector protector grease inside the connector box to make it easier to install the control cable and lock the box connector box lid closed once the antenna is on the tower.

The next step in our project will be to rig our 2M and 70cm Yagis on a test mast and test them prior to installation on the tower.

– Fred (AB1OC)

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