Saturday, December 11, 2010

Dual-Band Inverted-L Antenna


Great day! I finally had an opportunity to transform my old inverted-L antenna using an article by Dennis Monticelli, AE6C from the QSO, July 1991 article ""A simple, effective dual-band inverted-L antenna" for 160 and 80 m. I found this article in the compendium ARRL's Wire Antenna Classics, pp. 7-13 to 7-16.

This variation uses a 3/8 wave-length wire....192 feet total for the radiator. This antenna is suspended (carefully) in a huge old oak tree out back. The distance from the shack is a total of 150 feet, so my first step was to upgrade coax to RG-213U. I preserved the existing two ~ 130 foot radials, and added two additional ~ 190 foot radials. About 70 feet of the radiating element is suspended vertically by the oak, and the remaining 120 feet sloops down to the back of my house an onto the balcony off our second floor. I had hoped to 'launch' a new wire over the house, but my son lost our sling-shot, and I had no suitable potato for the potato canon (life is difficult here :)

I had planned to hook up the antenna analyzer and evaluate resonance with and without the 100 to 400 pf capacitors placed in series with the feed line...as described in the original article. Well, it snowed last night, was cold, and the sun was setting fast (I'm whining). I hope to get to this done down the road.

A tuner and current choke sit at the base of the antenna, pictured above. Current choke is at top, MFJ remote auto-tuner turned on side in the middle, and a copper pipe terminal for the radials at bottom. Instead of home-brewing a matching system as described by AE6C in his 1991 article, I cheated by using the MFJ-927 remote auto-tuner at the base of the antenna. I also installed a DX Enginneering Feedline Current Choke. Hey, the antenna is precariously close the neighbors...I can't affort any type of feedline radiation / RF interference.

The new antenna tuned up nicely on 160, 80, and 40m. I was anxious to make a contact on 160. I was calling CQ for the SKCC weekend sprint. Richard, K2ZR was quick to answer my call and was patient with my ~12 wpm morse code. After the contact, I realized I hadn't increased my power above the 5 watt maximum for tuning!

So, new antenna, and the first contact on 160m was QRP to boot. A great day at N1Dn.

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