Wednesday, April 16, 2025

Dipole Antenna Rebuild - Spring 2025

 Antenna Repair

After many years of hanging high in the air, my favorite antenna failed over the past winter.  My 40 / 80 meter trapped dipole became too far gone for my antenna tuner to make up the difference. 


40 Meter traps - weathered and cracked.


Finding the traps in such bad shape, I ran for my MFJ-259B and a few loops of wire to test them.  The oxidation and gunk from nearby trees, gave me a bit of hope, thinking that I might have had a bad connection.  This proved to be false, and the after testing the traps I found that one had gone bad.
Below is my quick and dirty test procedure to check the traps.

Trap sitting in loose coil connected to my antenna analyzer.


This one dipped at 7.26 Mhz and the second one failed.  


Anyone wanting more information, https://history.k4lrg.org/Projects/Repairing_Unadilla_Traps/index.html has some great information on these traps.

I estimate these have been in the air for 15 years.


These PVC traps are now up and have replaced the blue ones. 




Replacement traps being tested


These newer traps seem to be at the low end of the 7 Mhz band, where the one good blue one seemed to be at the upper end of the band, using this testing method.  Having these traps out of the antenna, without the rest of the wire antenna connected I expect the measurement to higher in frequency then when in circuit with the rest system.

Also, please enjoy the sun bleached blue jacuzzi cover that I chose to use a work bench... 

As a side note, it seems my wire has stretched by several feet over the years.  While on the roof, I found that I needed to cut about 10 inches off of the 40 meter section.  Whether this was from using different traps or the wire stretching I am not sure.  Stranded wire was used, because it was available and on hand.  

I also see the ends of the antenna that form the 80 meter section was old stranded bare copper wire.  I must have just modified what I had up at the time.  Everywhere else, I use soldered on lug connectors and have rebuilt the antenna as a whole using better methods.  

  

New trap measurement results


  This is the results of the testing of the replacement traps using my loosely coupled wire loop with the trap just sitting in the middle of the loop.