2003 Summer Tower Work


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In the summer of 2003 several antennas that were damaged over the winter had to be replaced.  I also took this time to replace some old antennas and reconfigure the stacks on 10m, 15m, and 20m.

Summary of work to be done:

  1. Replace whole 20m stack with new M2 antennas.
  2. Remove west antennas on 15m and replace 8 element 15m with 4 element.
  3. Remove broke 80m wire beam, replace with inverted V.
  4. Remove old 160m inverted V at 150’, put new one at 180’.
  5. Move 80m 4-square from 15m tower to 10m tower, improve radial system.
  6. Remove broke 6 element 10m and replace with 4 element.
  7. Move Ring rotor from 90’ 10m to 30’ 15m antenna.
Some of this may seem like downgrading capabilities, but actually most of it ends up with virtually the same arrangements with fewer maintenance headaches and hopefully better reliability in a cleaner setup.  Now on 10m, 15m, and 20m all the antennas in the stacks are the same, this should result in better power division and definitely makes the matching better.  Big headaches trying to keep the monster Telrex beams pointed the right way should be gone.  Also those big Telrex Yagis were not what they seemed, when I bought those I rand then through YO and optimized them… they were both really only long boom 5 elements with the other elements just acting as wind and weight balances.  The 4 element M2 Yagi that replaced the 6 element Telrex has almost the same performance at about 1/3 the weight and much smaller wind load.  Another improvement was to make all of the high band stacks the same.  This simplifies both the switching arrangements and operator training.  Now all of the stacks have 4 elements on top that rotate on a Yaesu rotor, then 4/4 fixed on Europe, then 4 elements on the bottom that rotate on a TIC Ring Rotor, and they all have a fixed south antenna.

The work started by removing the two 4 element 15m Yagis that were fixed to the west.  These never really did do anything special and were a constant maintenance headache as they were very old and one was also damaged by ice and wind over the winter.  These two were combined to build one decent one to replace the top 8 element Telrex.  On 6/8 a crew assembled to swap the 8 element Telrex with this new antenna.  A tram line was used to help remove the 8 element because of how heavy it was. 

Tram line anchored to old apple tree

Jeep ready to take the load (in 4wd low) note extra rope on roof so it doesn’t get run over. 

Pulley on way up to antenna.

wide view

Ground crew getting ready, note apple tree to left just beyond feed lines where tram is anchored. 

Going up! 

Tag lines ready.

wide view

Antenna free from mast.  It took a couple tries even with the tram wire to get the center two elements past the guy wires. 

On one of the elements I ended up taking the outer tubing section off to make it easier. 

Going down

And down. 

Almost down

Down and out.  

New one going up! 

The 4 element is so light that N1UR pulled it up instead of using the Jeep.

Almost up. 

close view

Attaching to tower.

wide view Ground crew:

W1TO (on 49mhz headset)

N1SR, not shown is a neighbor George Gruele driving the Jeep and KB2SAE behind camera.

Not pictured, but in mid June we got the south 3 element 20m Telrex down and the 4 element Telrex on the ring rotor down and replaced them with two of the M2 antennas.  It was too windy that day to do anything higher up the tower.

July 5th was a bit too windy to do the 6 element 20m job, but we did get the kinked boom Telrex at 105’ down and another M2 installed at 90’. 

Getting ready. 

Passing the new M2 on the ring going up. 

Rigging tag lines. 

Getting boom brace rigged. 

I used lots of extra rope on this one. 

Jeep and ground supervisor.

Off the tower, now you can see the kink. Note that the boom brace is still taut.

It had to come down a bit to get it around the guy wires. 

Clear of the guys on its way down. 

Going down.

Close up of rigging on ground.

Getting new M2 ready to go up.

Going up!

Almost there.

Had to tip it to get around guy wires.

Almost level.

Attached to tower. 

Finishing up feedline. 

After the IARU contest was over on 7/13 N1UR who operated 23 out of 24 hours of the contest and several others helped with the final antennas on 20m.  It was another breezy day, but better than the other attempts had been.  The first thing we did was to put up the

M2 at 120’.

Another view. Then we ran the ropes up to 150’ for the top one. 

Rigging up tag lines.

This one insisted on tilting backwards when I disconnected it.  This would have made it very hard to get over the top guy wires so I had to add another rope around the mounting plate to get it tipped back

Near level. 

I still had to take off the two middle element ends to get them over the top guy wires. 

Finally on its way down.

And down.  

And down. 

Telrex landed, M2 getting rigged to go up by W1TO and W1GQ. 

M2 taking off. 

I had them tip it to make it easier to get over the top guys, W1TO and N1UR on the tag lines, W1GQ and son on the antenna.  Not shown were KB1KE in the Jeep, George Gruele, and N1UR’s girlfriend Christine behind the camera. 

Going up! 

Getting close. 

Clamping to the mast. 

Getting rigging out of the way.  And so all the 20m antennas were finally on the tower.

Another trip up the 150’ tower on the weekend of 7/19-20 was made to attach the boom braces, fix the vhf antennas up on top, find the 20m-15m harmonic generator, tape down all the feedlines, move the south antenna to another leg to get it pointed south instead of southwest and finally the stack was done.  Also done that weekend were the removal of the old 160m V that was up there and installing the new 80m V.

Notes on the 20m-15m harmonic problem:

This has been a long standing problem here.  There was a problem on the tower that when you would transmit on 14000khz above a certain power level would create a harmonic on 21000khz, and also on 7000khz.  I figured out the mechanism last year as a pumped subharmonic oscillator, most likely some kind of rectification linked to something resonant on 40m... and when that went into oscillation when being pumped by 20m it made a 40m subharmonic which mixed with the 20m signal to make the 15m 3/2's 'harmonic'.  I was sure it was related to the 20m telrex on top since it uses a 1/2 wave balun and would have made the perfect source if the insulator was damaged. Another possible source was the 80m wire beam, or the old 160m V, either of which could have created that resonance if there was a bad insulator.

 

After removing the 20m telrex, the 80m wire beam, and 160m V the only things left were the vhf antennas which were above the top 20m beam.  So while I had someone at the radio to test I started disconnecting the vhf antennas.  When I disconnected one of them the noise stopped, put it back on and it restarted... I couldn't figure out why it would do it when the lower 20m antennas were used though because with the old antennas it only happened on the top one.  It turned out that the hardline for two of the vhf antennas is a plastic jacketed version, and at the top of the tower the shield was not connected to the tower... and there must be a spot where the insulation is worn through causing some arcing... and it must be a resonant length on 40m... and probably some other coincidences.  In any event, grounding the top of the hardline shield seemed to stop the problem.

To see how sub-harmonics can be generated with passive components see this experiment.


David Robbins, K1TTT K1TTT@arrl.net