The Sun is Back!

NASA and NOAA announced today that Solar Cycle 25 has now officially started...

https://wattsupwiththat.com/2020/09/15/solar-cycle-25-has-officially-begun/

“How quickly solar activity rises is an indicator on how strong the next solar cycle will be,” says Doug Biesecker of NOAA’s Space Weather Prediction Center, co-chair of the Solar Cycle 25 Prediction Panel. “Although we’ve seen a steady increase in sunspot activity this year, it is slow.”

Replacing the Telrex Tri-Bander

About three years ago, I noticed a stuttering of the heading needle of my Tailtwister rotor control box as I turned the yagis on my tower, and I initially figured it was just dirty contacts on the pot in the rotor.  Nope.   I wish it was that simple.

The tower is a 100 feet of phillystran-guyed Rohn 45G with a pair of multiband yagis on top.   The lower antenna is a Telrex 10/15/20 meter tribander (circa early 90's) on a 26' boom, and the upper antenna is a Force12 12/17/20 meter yagi.

When they were installed in about 2000, the tops of the oak and poplar trees were about 7 to 10' lower than the lowest antenna.    They grew enough over the years to just catch the longest elements on the Telrex....  This damaged the elements, and the resulting bends created a weak spot that eventually doomed several pieces of tubing.     The antenna persisted for many months after being damaged, but eventually succumbed to the wind vibration and resulting metal fatigue where the elements had been bent.

Is it dicey having a guyed tower in a wooded location?   Yes....but it was a risk I was willing to take given the alternatives in my situation.   My main concern over the years has been a tree falling on a guy wire, which would likely bring the tower down -- so I've had to be vigilant in removing any trees that look like they might fall in the wrong direction.   What I didn't do is keep a close eye on what was happening up top!

This TB6EM was the best made Yagi for HF that I've  used...and it'll be missed.  The enormous diameter double walled boom utilized through-the-boom elements.   It was beautiful and she performed extremely well for decades, despite being a trapped design -- which we know today is lossy, compared to other multi-monobander approaches.    I'm in the middle of tree pruning now and making plans for taking down what remains of the Telrex, and then, I'll be selecting a new 21st century model to replace it.   This is a lot of work, but it'll be worth it.

 

Update 4/14/2021:

This winter I was able to clear back a number of trees that were interfering with my turning radius of the yagi, and made sure I have a 30' wide path from the ground up to the top of the tower.  I've fabricated a trolley from aluminum (will have a separate post on this) which will run from the ground to the top on two cables.   This will be used to remove the TB6EM and replace.    After looking at many, many designs -- I'm leaning towards the OptiBeam Log Yagi design.

 

 

 

Weights for Tree Supported Wire Antennas

I'd been looking for a way to provide continuous tension on a wire antenna, like a doublet or a dipole, that is supported on one or both ends by a tree.   The idea is to run a line/rope from the end of the antenna, down through a pulley mounted high in the tree, and then to a weight hanging from the line; some people use springs to accomplish the same thing.   When the wind blows and the tree moves, the weight would move up and down, keeping more or less constant tension, thus keeping the antenna from snapping.  The ARRL Handbook and Antenna Book have had diagrams of doing stuff like this for decades...but finding a suitable weight can be an issue (besides getting the wire into the tree... that'll be another post...)

I've used a variety of things in the past including buckets full of dirt, cinder blocks, and even "no-weight" by just tying to the tree and hoping for the best, etc. but this time I wanted something that would minimize damage to the tree trunk should it swing into the tree and would be XYL friendly.     Below is what I've constructed from two feet of 2" and 3" PVC pipe, concrete, 12" of rebar, and a lag screw with a loop.

PVC-Concrete Antenna Weight

I mixed up the concrete in one of those plastic storage containers using a 60# bag of Sakrete High Strength mix (although any concrete should do) along with about 2 quarts of water.  After taping off one of the ends of the PVC with duct tape, I filled the pipe up with concrete and then inserted the rebar into the center, leaving about 2" sticking out.   (I had concrete leftover which I used for some driveway patching!)

Once it cured, my son welded the lag screws onto the end of the rebar.  Done.

I haven't weighed them yet, but it feels like about 10 lbs for the 2" pipe and maybe 20 for the 3".   Once I weigh them, I'll re-post my findings.   There's nothing magic about the length and size here, although bigger antennas are going to require more weight to prevent excessive sag.  And in my instance, the plan is to use a weight on just one end of the antenna.

73,

Rush, W4QA

Standard Wire Antenna Approach

2" PVC, Rebar, Lag Eye Bolt