A New “Random Wire” Antenna Goes up the Maple Tree in the Backyard

It was time to repair the damage from the big “Halloween storm” at the onset of winter (cf.: https://thewakesileave.wordpress.com/2015/10/31/a-spooky-sight/) and restore a wire antenna in the branches of the maple tree in the backyard.

First the “single set of elevated counterpoise cables”: this is made of 12.5 metres of six-wire, non-insulated telephone cable, with interruptions of several inches at the end of every 1/4-wavelength distance (calculated around mid-band) for the following bands 10m, 15m, 17m, 20m and 40m. The 1/4 WL wire for the 80m band was made by connecting the full length of the cable (12.5m) with the distal portion of the cable used for 10m band (7.5m) for a total folded length of 20 metres. This multi-wire cable is deployed horizontally at about 1 meter from the ground around the inside of two of the sides of the wooden fence that encloses the yard.

Then 58 feet were cut from a piece of 14 AWG insulated wire (labelled: “LL90458 S CSA AWG 14 CU T90 NYLON OR TWN75 600 VOLTS FT1”). The tip to be at the top was made into a 1-2 inch closed loop with the wire soldered back onto it after making a small gap in the sheath. Then the soldered area was sealed with shrinking tube and epoxy cement. This loop was used to attach the rope holding the wire up.

The old “EZ Hang” (http://www.ezhang.com) was put to use and a fishing line was shot through the branches of the maple, making sure that the yellow lead weight would not fall on any of the neighbouring backyards. The weight was then removed and a silky and strong yarn was attached to the end of the fishing line and pulled back through the tree branches. When the junction reached down, a thin and stealth rope was attached followed by the top of the 58-foot antenna cable. This length was determined for practicality, given the height of the trees, but 58 feet is also a measure recommended by Jack VE3EED (SK) (http://www.hamuniverse.com/randomwireantennalengths.html) and Mike AB3AP (http://udel.edu/~mm/ham/randomWire/) for “random” wires. The whole was then threaded through the tree. The final arrangement was a long and slightly twisted “C” with the tip of the antenna a few feet below the point at which the wire is held up by a fork in the top branches of the maple tree.

This antenna connects to a 2-foot piece of RG-58 coax that leads directly to the Elecraft T1 tuner operated remote. A second piece of RG-58 coax (15-foot long) connects the tuner to the sensor unit of the WII Elecraft SWR/Wattmeter, and from it, a 3-foot coax connects to the transceiver (the ICOM 703+, or on occasions, the Elecraft KX3 or even the KX1). The internal ATU of the 703 is bypassed. The tuning cycles in the T1 are triggered with microphone PTT in FM mode, or with the straight key in CW mode. The T1 is grounded to copper pipe used as ground for the house.

The short coax connecting the T1 to the antenna goes through the external wall of the house, inside a small PVC pipe. On the outside a little outdoor waterproof box harbours the banana connectors from getting wet in rain or snow. This does not appear too conspicuous because at that same corner the wall is pierced with the electric cables and the ducts of the air conditioner, and higher up is the air intake of the furnace. All wires reaching the waterproof box are shaped with a dripping loop to avoid water from reaching into the connector.

A 4:1 unun (RU LDG 4:1) is then connected to the short coax. Here are SWR and Impedance curves for HF frequencies between 3 and 30 MHz as determined with the aid of a mini-VNA antenna analyzer. The measurements were made  with an without the 4:1 unun. These would be the SWR and impedances “seen” by the remote Elecraft T1 tuner. Although very slight changes are introduced by the unun on the SWR curve, the effect on that of the impedance is very large (the range in Ohms of the graph with the unun is ~1/5 of that of the graph without it).

58 Ft Antenna 2

The short piece of RG-58 between the antenna and the unun does not seem to cause much hindrance to the RF in any band. However, it would have been better to place the unun and remote tuner outside the wall and eliminate altogether the short coax. Nevertheless, there are advantages in keeping the T1 tuner inside the house: it is protected from sun, rain, snow and cold temperatures and it is easier to operate remote as its lights can be seen and its clicks heard.

This is at best a compromise antenna: it is not really vertical as it partially folds back on itself, it has a single set of “L-shaped” 1/4 wave length counterpoise cables, the tuner t is not independently grounded and there is a short 50 Ohm coax connecting the wires to the tuner. However, in practice it has demonstrated to be a reasonable QRP multiband HF antenna. It is also not meant to be a permanently connected antenna and no lightning arrestor has been installed. In fact, the antenna is most of the time disconnected from the short coax and the low end of the wire is brought back to the base of the tree. Needless to say, it is never connected when an electric storm is a possibility. Also, so far, there have not been reports of any RF in the house or in neighbouring homes…

 

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