Tower/Antenna System Design Details And Equipment Ordering


Now that we have back filled the guy anchors for our tower, they are ready to have the equalizer plates and guy wires attached. We are planning to use two sets of star guys on the tower – one set of 6 guys at 50’ and a second set at 95’ (5′ down from the top). Star guys use special brackets where the guys attach to the tower to connect two guy wires on each tower leg for a total of 6 at each level instead of the usual three. This prevents the tower from torque-ing when the rotators start and stop moving the large beams (we are using a pair of SteppIR DB36’s – full size 40m beams weighting about 165 lbs. each).

We also ordered a number of parts for the final tower over the last couple of days. Here is a rundown of the components and some links in case you are interested in what these components are:

The SteppIR antennas cover all bands 40m – 6m including the WARC bands. One of the DB36’s (the top one) will have an 80m dipole option which uses a wire running parallel to the beam (36’) plus the end elements of the antenna and a pair of loading coils to create a rotatable 80m dipole. This should be reasonably effective at the 105’ level where this antenna will be mounted. The ring rotator allows the lower beam to rotate around the tower and the Green Heron Controllers synchronize the upper Beam’s rotator with the lower ring to move both antennas in the array together. The Green Heron controllers also come with software which allows them to be operated over the internet which will allow me to use the station and move the beams while I am traveling via a PC and the Internet. The DX Engineering Broadband Matching system allows the two Beams to operate as an array increasing the overall gain of the system and improving the radiation patterns of the antennas. The Matching System and the two associated antennas can be used three ways – as an array in-phase, as an array out-of-phase and individually. This allows us to cover a much larger set of takeoff angles to optimize the performance of the system based upon the propagation conditions at any given time.

We chose Phillystran Guy material which is made of Kevlar and is non-conducting. This ensures that the guys wires will not be resonant on the HAM bands and upset the tune or interact with the antennas on the tower. The Phillystran will transition to normal steel guy wire near the ground for safety reasons. Rohn 55G tower is strong stuff and we chose it to maximize the antenna and wind loading capacity of the system. Check out the 55G Brochure via this link for details on the 55G tower kit and related hardware. Finally, the 21’ H.D. mast will allow us to add additional antennas for 2M and 70 cm above the top SteppIR beam in the future. The first 5’ of the mast goes inside the tower which leaves 16’ of mast to mount antennas on. This allows us to put an antenna as high as 115’. The mast is also climbable which should make for some exciting times (and pictures) sometime in the future.

We are also planning to add an 80m Delta Loop antenna and a 160m Inverted-L antenna to the tower. These antennas will be selectable at the tower via a DX Engineering Remote Antenna switch. The tower is located right next to our current SteppIR vertical antenna which has a large radial field under it (forty-eight 85′ radials). We need to move the Vertical antenna to a new location due to the tower but we can re-use the existing radial field to improve the performance of the 160m and 80m antennas on the tower. We plan to add a few 170′ radials to the field to improve its performance on 160m.

We are in the process of completing an HFTA and EZNEC modeling analysis of the complete antenna system to finalize the height of the two beams and the design of the 160m and 80m antennas. Look for a future post on this work. Right now it looks like the two beams will likely perform best when isntalled at 102′ and 60′.

– Fred (AB1OC)

Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out / Change )

Twitter picture

You are commenting using your Twitter account. Log Out / Change )

Facebook photo

You are commenting using your Facebook account. Log Out / Change )

Google+ photo

You are commenting using your Google+ account. Log Out / Change )

Connecting to %s