Cushcraft XM240 40 meter yagi is ready; need good wx
Spent some time in the past few days building my 40 meter antenna. Unfortunately, we’ve had some rain, so I finished the project in the mud. Although the Cushcraft XM240 Big Thunder is a small yagi for 40 meters it is a very large ham radio antenna by my standards.
The XM240 is a two element yagi with a 22 ft (6.7 m) boom and 43.5 ft (13.3 m) elements. The antenna weighs 55 lbs (25 kg)… for me, it’s a serious ham radio antenna.
This is how the finished antenna should look. You can just barely see the “capacity hats”.
A pair of capacity hats and loading coils are found in each element to electrically lengthen the element which keeps the size a bit more manageable for for typical ham radio operators who cannot install a full size yagi (with a bit of performance cost).
I do have a few minor complaints about the construction of the Cushcraft XM240:
- Some tolerances don’t quite match up. For example, there were times when I could not get the lengths exactly as documented - like when I needed to have a certain length between two pieces but the insulation around the loading coils prevented the length from being achieved.
- The hose-clamps that hold the element sections together don’t completely do the trick. I thought I had a clamp tightened all the way, then bumped the element tip and the length changed. I’ve seen that others add a bolt to lock (or pin) the antenna element sections together - I’ll do that as well.
- There was a couple of times where I had to get the drill out - either to slightly widen a hole for a bolt or to clean out a bolt hole that had black insulation in the way.
That said, it wasn’t that bad. The documentation was relatively good and I was able to single-handedly build the antenna without bloodshed. Some sections are reinforced quite well and look to be very sturdy.
I also used some NoAlOx between the element joints to help prevent corrosion and to make it a bit easier for the day when I need to disassemble this antenna.
Just for fun, I ran a piece of RG213 coax to the antenna and turned on 40m on my IC-746 - while the XM240 was still sitting on sawhorses. Sure enough, there was some activity on 40 meters. That’s a good sign. I’m hoping that this thing plays well when it’s at ~82 ft and about 10 ft above the 4 element SteppIR.
