short_vertical

New Shortened Vertical for 17-20-30-40 Meters
August 19, 2006

Last night I tested my latest antenna: a 4-band, 20' vertical half wave that uses two loading coils with taps. The results appear promising. On 20 meters I worked a Texas station. I was running 5 watts SSB and he used 800 watts. He had a rough copy on me, but there was much fading at 10 p.m. Later, on 40 I had a couple of nice CW chats to California and Louisiana from here in Colorado. The antenna was only 10 feet from the house and surrounded by tall trees - plus we have mountains on three sides not far away. Halfway through the evening it started to rain. I was sitting outside on a fabric-covered porch swing set up in the front yard and stayed (mostly) dry. I'd started at 10:00 in the evening and finally packed up around midnight after my last contact. It was getting chilly.

The antenna is only 30% of full size on 40 meters. It is a compromise, but I designed it specifically for an upcoming vacation to the mountain town of Crested Butte, Colorado at the end of this month. I will be staying in a 19-room lodge on the third floor with a walk-out balcony, so I wanted something very portable and hard to see. Everything is black: the pole, the antenna wire and I'll even painted the PVC support black. A 20-foot fishing pole will hold the antenna, and a PVC base will support it up against the hand railing. Because it is an electrical half wave, it needs no counterpoise or radials, something that would be difficult to set up on a tiny balcony.

Details follow each picture.

The antenna consists of three sections of wire and two coils. The outer two wires are 4' 4-5/8" long, and the inner wire is 10' 8-3/4". I used 22-ga. stranded wire for both the antenna and the coil windings. I began making coils out of stranded wire on the hunch that it would reduce some of the coil losses due to skin effect. After several shortened halfwaves and a logbook full of successful contacts, I discovered something called proximity efect that negates any benefits to using stranded wire in coils. Oh, well. I continued the tradition here anyway.

The coils are wound on 1-1/4" thin-wall (schedule-20?) pipe and are about 3-3/8" long. After winding the wire, I wrap everything in black electrical tape.
There are four taps on each coil. The lowest tap on the coil (from right-to-left) is for 17 meters, followed closely by the 20 meter tap. Finally, the 30 and 40 meter taps. The tap for 40 is actually one turn short of the full coil. I had intended to use the full coil centered around 7.040 MHz and use the tap for the novice CW portion of the band. During testing I discovered that the tap was a better fit, and the additional wrap tested out below 7.000 MHz.

Here are the windings for each band. The windings are based on a #22 stranded, insulated wire with an O.D. of 0.064" and approx. 15 turns per inch.
Band / total turns
17 m = 7.5 turns
20 m = 13.5 turns
30 m = 25.5 turns
40 m = 46.5 turns
Full coil = 47.5 turns (resonant below band edge - skip this turn)

Here is the PVC base I built for the high-mountain vacation and the top floor balcony. The back leg and support is in case the balcony has a solid railing with nothing to lash onto and it needs to be self-supporting. This photo was taken before I had painted it "midnight black." The antenna will be held up by a 20-foot fishing pole from Cabelas. The bottom of the pole will slide down on the PVC. Everything breaks down to 45" or less - the length of the fishing pole fully collapsed.

Here is the tuner I use for this and most of my half waves. It's on the bottom half of the page.

August 30, 2006 update: This weekend I made a few contacts on 40 from the top floor balcony of a mountain lodge.

Tonight I set the antenna up in my front yard here in Golden, Colorado. It was 10:00 p.m. and I only had time for one contact, so I talked to Ed, W7GVE in Arizona for almost 25 minutes. He was 589 and gave me a 569. Not bad for a seriously shortened antenna. Here are two shots taken in the dark.

What you don't see here are two huge trees on either side of the antenna. It's amazing any RF escapes from this small yard. The flash on my Canon G-2 really lights up the otherwise pitch-black night.

On the table you can see the FT-817, a SLA battery, headphones, a Palm Paddle, LED lamp and a UTC travel alarm clock. Above the table is the matching unit taped to the PVC support.
I've discovered a big advantage to CW. I can be outside late at night and not wake up the neighbors sleeping with all their windows open as I might using a microphone.

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