Masts at 3B7C

We have now settled on the mast arrangements for our Yagi antennas at 3B7C.

On our previous DXpeditions we have used a combination of alloy masts at 40 ft (13m) high, and "push-up" telescopic masts at about 30ft (9m).  The "push-up" masts are relatively easy to erect, but are fairly fragile, and also are complex to rotate.

So for 3B7C we have decided to use only the 40ft alloy masts. These are made from two 20ft (6.5m) poles with a specially reinforced jointing sleeve to join them together. They are guyed at four levels with slip-rings, so that the Yagi antenna can easily be turned. A lever arm near the base of the mast allows effortless turning of the array.

We use what is often called a "gin-pole" approach to raising the masts. The mast is assembled with four point guying (guying stakes each 90 degrees around the base of the mast). The mast sits in a pivoted base (see below), in which also sits the "gin pole" at 90 degrees to the mast. Three sets of guys are made off on three of the ground stakes, and the fourth set is attached to the end of the gin-pole. Also attached to the end of the gin-pole is a pulley system, which allows the gin-pole to be pulled from near vertical down to horizontal. As it moves, so the mast moves into the vertical position.

The pivoted socket in which the mast sits has a locking pin, so that the yagi can be locked in a particular direction even in high winds.

The following diagram shows the gin-pole principle.

Using this method, we can get our yagis higher with very little effort.

Note: The above is simply an outline description of the system we use, and should not be used as a "how to do it" manual. For this, please refer to the various articles on the web and in antenna handbooks on raising tall masts.