Ueli climbing the trees   

 

HAM  
Amateur Radio

KB9TTI    HB9TTI

The Beginning

 

Pulley attachmentThe idea of mounting the wire dipole antenna was to have the two outer ends attached to the upper part of trees conveniently located. Counter weightTo facilitate the access to the wires, I attached a pulley to the trunk and ran the rope from the end of the antenna over the pulley down the tree trunk and attached it to a tube filled with rocks. This way the antenna could stretch and the tree could move without tearing each other apart.   For the antenna wire, my choice after evaluating a large number of options, was unshielded #14 WG aircraft  (MIL) grade wire which is a tin-plated stranded copper wire with Tefzel insulation. Antenna feed and wire spacerWhen building my aircraft I found this wire and it's insulation to be extremely tough but good to handle.

To keep the wires spaced, I used Plexiglas rods with tie-wraps to attach the wire. This way I could slide the spacers along the wire when adjusting them at tuning. I am aware that at an altitude of 9000 ft,  the UV light would do it's job in damaging the integrity of some of the plastic. However, I was sure that I would eventually do some modifications.

Feed point for the three dipoleFeed coaxial cableThe feed point for the three dipoles is made of a solid square chunk of plastic, capable of taking the tension and load of the antenna construction and feeding coaxial cable. The ends of all the wires were sealed with the trusty glue gun and shrink tubing if necessary. The whole element was also suspended from a pulley to permit lowering.

As there is always a chance of lightning, not uncommon in the mountains, I built one of Rip's grounding contraptions. Grounding element before the antenna feed entered the houseWith the coaxial cable coming from the antenna I first coiled the cable to create an RF choke before attaching the feed to the grounding element [##2]. Of course I had part of the coax coming from the feed point radiating as part of the antenna before the choke took effect.

Dog house with grounding systemThe feed point of the antenna cable into the house is on the back side of the house, generally protected from the weather. The winds however, can come from all directions and it is not uncommon in winter to have the snow stacked up against the house. To avoid water entering the connectors or the cable ends I found a suitable little dog house, cut away the bottom and anchored it over the grounding rods. The front where the dog normally enters is closed off with a metal screen in order not to invite any wild mountain residents as a winter home and also to ground any lightning. The grounding rod and the screen is connected to a grounding wire leading away from the house into more moist soil and anchored to tree further rods driven into the ground.

Testing the antenna with Ripactual SWR Finally, it took me a few days to adjust the length of the various wires to resonate optimally on the amateur HF bands (before the antenna tuner). My guide and friend, Rip was a great help to suggest all those little details as only an old "Pro" would know and spot. 

##2  see ARRL Handbook, chapter 21 "Transmission Lines"
 

Response and suggestions are appreciated to  HB9TTI@Gmail.com

This page was serviced last on  12. July 2008